JP2016171556A5 - - Google Patents

Description

Sound equipment

The present invention relates to an acoustic device composed of a speaker and an electric circuit for driving the speaker, and relates to so-called bass reproduction technology for reproducing lower sound with a relatively small speaker unit and an enclosure.

The current general audio device is connected to a speaker system including a speaker unit elastically supporting a diaphragm directly connected to an electromagnetic drive on a frame and an enclosure to which the speaker unit is attached, and an electromagnetic drive of the speaker unit It consists of an electric drive circuit.

FIG. 1 shows a sealed enclosure 2 having a housing 201 and an internal space 202, a diaphragm 102 elastically supported by a frame 102 and an elastic support system (not shown) in the frame, and an electromagnetic drive for oscillating the diaphragm. FIG. 2 is a mechanical system equivalent circuit showing mechanical resonance in the low range of the speaker system 1 to which the speaker unit 1 including the driving device 103 is attached.

In FIG. 2, Fo, Mo, Co, Ro are mechanical equivalent elements of the speaker unit, Fo is the driving force of the electromagnetic drive, Mo is the equivalent mechanical mass of the vibration system including the diaphragm, and Co is the equivalent mechanical stiffness , Ro are equivalent mechanical resistances and Ce is equivalent mechanical stiffness of the enclosure interior space.

Although this mechanical equivalent circuit constitutes a series resonance circuit of Mo, Co and Ce, Ce in FIG. 2 becomes infinite in free space not attached to the enclosure, and the resonance frequency in that case is Mo and Co In general, it is called the lowest resonance frequency fo specific to the speaker unit. The strength of the resonance is restricted by Ro and is generally called Qo. If Ro is large, the resonance strength Qo is small, and if Ro is small, Qo is large.

Here, when the speaker unit is attached to the closed enclosure as shown in FIG. 1, since Ce is finite, if Cs is a series composite stiffness of Co and Ce, then Cs becomes smaller than Co, so its resonance frequency is fs Then fs is higher than fo.

By the way, this equivalent circuit shows that the vibration plate vibrates more in the frequency range centered on the resonance frequency than in the driving force Fo due to the resonance phenomenon. FIG. 3 shows the relationship between the low frequency resonance and the sound pressure, which is generally called frequency-sound pressure characteristic (f characteristic).

In FIG. 3, (a) is the characteristic when there is resonance, and the conventional speaker system utilizes the above-mentioned resonance, and the electromagnetic drive device of the speaker unit at a constant voltage with respect to frequency by the power amplifier with sufficiently low output impedance. Is designed and manufactured so that the sound pressure for each frequency is almost constant. Therefore, the lowest frequency that can be reproduced by the above-mentioned system is limited to the low resonance frequency fs, and at lower frequencies, the sound pressure suddenly decreases as the frequency decreases.

Fig. 3 (b) shows the characteristics without the above-mentioned resonance, and theoretically the sound pressure drops gently at 6 dB / oct from the frequency fh determined by the aperture of the speaker to a lower frequency, It is known to be. The larger the aperture of the speaker unit, the higher the fh.

Such a relationship holds when the space including the tympanic membrane and the diaphragm of the speaker unit is sufficiently large, ie, when listening to music in a room, and such space is extremely small, such as headphones and earphones. The case does not hold and is excluded from the subject matter of the present invention.

Based on the above principle, the inventor suppressed the resonance of the bass region of the speaker by mechanical means using a breathable acoustic resistance material, and determined the frequency-sound pressure characteristics in the bass region of the speaker system. As shown in Fig. 3 (b), it was considered that the electric drive circuit system could compensate for the sound pressure of the insufficient bass. (Patent Document 1, Patent Document 2)

Japanese Patent Application No. 2004-102435 Japanese Patent Application No. 2005-244036

FIG. 4 shows the configuration of the electric drive circuit system, and FIG. 5 shows the relationship of the frequency characteristics. In FIG. 4, 3 is an electric signal source of sound to be reproduced, 4 is a frequency correction circuit, 5 is a power amplifier, 1 is a speaker unit, and the output of the power amplifier 5 is connected to the electromagnetic drive device of the speaker unit 1.

The characteristic of the frequency correction circuit 4 of FIG. 4 is, as shown by the frequency characteristic of the frequency correction circuit of FIG. 5, from the frequency fh shown in FIG. 3 (b) to the frequency f lower than the lowest resonance frequency fo of the speaker unit. It is supposed to rise at 6 dB / oct. Such characteristics can be easily realized by combining the electric circuit elements C and R and an appropriate buffer amplifier, and are also commonly called an equalizer.

Since the characteristic of the frequency correction circuit 4 is in a relationship reverse to the characteristic shown in (b) of FIG. 3, when the speaker system of the characteristic of (b) in FIG. 3 is driven by such an electric circuit, The frequency-sound pressure characteristic can be reproduced to a frequency lower than the lowest resonance frequency fo specific to the speaker unit as shown in FIG.

It is self-evident that this makes it possible to reproduce even lower-frequency sounds than the speaker unit's inherent fo, even with a relatively small aperture speaker unit or small enclosure. That is, since the larger the aperture diameter and the smaller the diameter of the ordinary speaker unit is, the lower the maximum frequency that can be reproduced is limited depending on the aperture of the speaker unit, but the effect of the lowest resonance frequency fo is eliminated or It is because it will be released from the limit if it can be restricted.

The enclosure also has a function of raising the lowest resonance frequency, so it is obvious that the enclosure should be enlarged if it is intended to reproduce sufficient bass, and if the resonance itself can be suppressed, it is compact without regard to the resonance frequency. It is possible to

In order to realize that, in the above-mentioned inventor's patent application, the resonance of the mechanically low band is basically divided between the diaphragm of the speaker unit and the main space inside the enclosure by a breathable acoustic resistance material. To suppress. As the air-permeable acoustic resistance material, the density of the air-permeable urethane foam, and fibrous materials such as cotton and glass wool can be used with high density.

The use of such an acoustic resistance material is equivalent to the insertion of a new equivalent mechanical resistance between Ro and Ce in the equivalent circuit of FIG. The degree of resonance Qo due to the combination is reduced, and the frequency-sound pressure characteristic of the system can be made close to the characteristic of FIG.

Based on such a theory, the inventor devised a speaker system as shown in FIG. In the speaker system of FIG. 6, the speaker unit 1 is attached to the cylindrical enclosure 6 and the main space 602 in the enclosure and the diaphragm 101 of the speaker unit are partitioned by the air-permeable acoustic resistance material 8 in the vicinity of the diaphragm 101 Inside the main space 602, the sound absorbing material 9 is appropriately disposed at an appropriate density, more specifically, one obtained by cutting urethane foam into pieces of 1 to several centimeters square, cotton, glass wool, etc. continuously at an appropriate density. It is The end farthest from the speaker unit is an open end 603 in contact with the space including the tympanic membrane and the diaphragm.

Here, to explain the functions of the acoustic resistance material 8 and the sound absorbing material 9, the purpose of the acoustic resistance material 8 is mainly to suppress the mechanical resonance of the bass region due to the interaction between the speaker unit and the main space inside the enclosure, The purpose of the sound absorbing material 9 is mainly to mute the sound leaked from the back surface of the diaphragm 101 through the acoustic resistance material 8, but also contributes to the suppression of the above-mentioned mechanical resonance in the low frequency range.

More specifically, the suppression of the resonance by the acoustic resistance material 8 is a flow suppression using the viscosity of air by the restriction of the ventilation cross-sectional area from the diaphragm 101 to the main space 602. Therefore, the density of the acoustically resistant material 8 is more important than the volume, and it is necessary to arrange the acoustically resistant material 8 without forming a gap between the diaphragm 101 and the main space 602. Specifically, a soft fibrous sound absorbing material such as breathable urethane foam or cotton is used in a compressed state.

On the other hand, the purpose of the sound absorbing material 9 is to muffling, and generally a fibrous material such as urethane foam or glass wool is used, but the volume as a whole and the thickness through which air vibration passes are sufficient to muffle sufficiently to low frequencies. And the density may be lower than that of the aforementioned acoustically resistant material 8.

The sound absorption coefficient of such a sound absorbing material is generally close to 1 at about 300 Hz or more and to about 0.1 or less at low frequencies of about 100 Hz or less. It is considered that the sound absorption effect of the sound absorbing material is caused by the conversion sublimation from the acoustic energy to the thermal energy due to the vibration friction of the substances, and the friction frequency per hour is high at high frequencies but the friction frequency is low at low frequencies. It is considered to be due to low.

In FIG. 6, the enclosure has a long cylindrical shape, because the sound absorption coefficient of this sound absorbing material is very small at a low frequency of about 100 Hz or less, so the thickness of the sound absorbing material from the diaphragm 101 to the opening end 603 is secured and low This is to allow sufficient absorption of sound energy of frequency.

The mechanical equivalent circuit of the low frequency range of such a system is shown in FIG. In the figure, Rt is the equivalent mechanical resistance of the acoustic resistance material 8, Ct is the equivalent mechanical stiffness of the space between the diaphragm 101 and the acoustic resistance material 8, Ce1, Re1, Ce2, Re2, ... Ren is the main space inside the enclosure 6. The equivalent mechanical stiffness and the equivalent mechanical resistance are simulated by sequentially arranging the sound absorbing material 9 at an appropriate density at 602. C∞ is the equivalent mechanical stiffness of the space including the diaphragm and tympanic membrane, which is sufficiently larger than other Co, Ct, and Cen.

The characteristics of the mechanical resonance in the low-pitch range of such a system depend on the equivalent mechanical resistance Ro, Rt, Re1 to Ren, and the combined equivalent mechanical stiffness of Co and Ct, Ce1 to Cen, C .. Is considered to be continuously dispersed in the frequency range determined by the series stiffness of Co and C∞ at the lowest and Co and Ct at the highest, and the forms of the continuously dispersed resonance peaks are Rt, Re1 to Ren and Ct. , Ce1 to Cen are considered to be related to the individual size

However, the volume of Ct is considered to be about 0.5 liter if the distance from the diaphragm to the acoustic resistance material 8 is 3 cm when the speaker unit has a diameter of, for example, 16 cm, and the speaker unit fo Assuming that it is 40 Hz, the series resonance frequency of Mo, Co and Ct can be estimated to be 400 Hz or more if separately simulated.

On the other hand, as mentioned above, the sound resistant substance 8 is a breathable urethane foam, a cloth material such as cloth or cotton and is the same as a general sound absorbing material, and its sound absorption coefficient is 1 if it is 300 Hz or more. The resonance energy is considered to be sufficiently suppressed by the fact that it covers nearly the entire surface of the rear surface of the diaphragm close to it.

Therefore, in the equivalent circuit of FIG. 7 in the speaker system as shown in FIG. 6, the influence of Ct can be neglected, and only Ce1, Ce2,... Cen and CC should be considered. In that case, since the acoustic resistance Ro + Rt + Re1 +... + Ren entering between Co and C∞ is larger than the acoustic resistance Ro + Rt entering between Co and Ce1, the strength of resonance is within the continuously dispersed resonance peaks, The resonance of the frequency determined by the series stiffness of Co and Ce1 appears strongly.

The meaning of the open end 603 in the enclosure shown in FIG. 6 will be described. When the open end 603 is closed, C∞ becomes zero in the equivalent circuit of mechanical resonance shown in FIG. 7 and the high frequency resonance determined by Co and Ce1 in the above-mentioned continuous resonance peaks becomes stronger, and The presence of the open end 603 takes account of that, since it is thought that the low frequency resonance determined by the series stiffness of C 欠 け is lost and the diaphragm amplitude at the low frequency is restricted.

If the acoustic resistance of the acoustic resistance material 8 is made as large as possible, while the equivalent mechanical resistance of the sound absorbing material 9 is as small as negligible, and the length of the tube 6 is infinite, the resonance is at its limit It is considered that the frequency-sound pressure characteristics close to the ideal (b) in Fig. 3 can be obtained by suppressing the energy of the sound until the sound reaches the space where the tympanic membrane contacts and is suppressed. Since not only the size of the speaker unit but also the enclosure is to be compact, the length of the tube is preferably limited and as short as possible, and practically it is considered to be several tens cm to about 1 m.

The inventor devised and prototyped a speaker system having a structure as shown in FIG. 8 after the speaker system shown in FIG. The speaker system shown in FIG. 8 is designed to further miniaturize the basic concept shown in FIG. In the speaker system of FIG. 8, the speaker unit 1 is attached to the enclosure 10, and the enclosure is configured to have tapered spaces 1001 to 1003 by internally bending from the unit 1 side to the opening end 1004 from the unit 1 to the space in contact with the tympanic membrane. The air gap between the diaphragm 101 of the speaker unit 1 and the main space 1001 inside the enclosure is divided by the air-permeable acoustic resistance material 8, and the sound absorbing material 9 is arranged in the spaces 1001 to 1003.

Although the arrangement density of the sound absorbing material 9 is basically the same, the length of the passage from the diaphragm 101 to the space in contact with the tympanic membrane is secured as a space obtained by bending the inside of the enclosure and toward the opening end 1004 of the enclosure The space is tapered, and the density of the sound absorbing material 9 is higher than that of FIG. 6, that is, the equivalent mechanical resistance is increased to absorb and eliminate the sound leaking to the external space.

In the prototype of the one shown in FIG. 8, the speaker unit 1 uses a 16 cm aperture and a 40 Hz fo, and the enclosure 10 is about 20 cm on a side of a hexahedron, and an enclosure for a 16 cm aperture speaker considering bass reproduction. As an exceptionally small one.

Such a speaker system was driven by an electric drive circuit as shown in FIG. 4, that is, a circuit including a frequency correction circuit 4 and a power amplifier 5 having a constant frequency to voltage gain.

However, such an acoustic device has caused two problems. The first problem was explained that the speaker unit of 16 cm in diameter was used in the trial production of the speaker system shown in FIG. 8, but when using a smaller speaker unit having a diameter of about 10 cm or less, the reproduced sound pressure at low frequency In this method, which depends only on the vibration of the diaphragm, the area of the diaphragm is too small to provide sufficient sound pressure in a frequency range lower than the fo of the speaker unit.

Here, it will be described that sufficient sound pressure can not be output at a frequency lower than fo when using a small speaker unit in such a speaker system. Originally, the speaker unit has the maximum swingable amplitude of its diaphragm, and the diaphragm amplitude is considered to be maximum at the lowest resonance frequency fo when driven with a constant voltage with respect to the frequency, so a frequency higher than fo If the sound pressure of the speaker unit is uniform, it can be said that the maximum sound pressure that can be output by the speaker unit is restricted by the sound pressure that can be output at the fo frequency. Based on the maximum sound pressure, the application of the speaker unit, for example, the usage such that the distance from the speaker unit to the ear is about 1 m is assumed. Based on such usage, if it is attempted to reproduce a frequency lower than fo by the amplitude of the diaphragm alone with the same sound pressure as the frequency of fo, the necessary amplitude of the diaphragm exceeds the amplitude that is possible at the frequency of fo And it is impossible.

Though sound pressure can be secured if the amplitude is increased even if the diaphragm area is small considering the simplicity, the maximum amplitude is small with the diaphragm area in a realistic small speaker.

Next, the second problem is that when the loudspeaker system of FIG. 8 is driven by the correction characteristic of the electric drive circuit of FIG. 4, that is, the frequency correction circuit of FIG. Sound pressure peaks occur at unintended frequencies at the expected resonance, specifically 150 Hz, and it is sufficient to lower the start frequency of correction (fh above) to avoid the sound pressure peaks Sound pressure can not be obtained.

This will be described with reference to FIGS. 9 and 10. FIG. 9 shows the case where the frequency correction characteristic fh has almost the same relationship as the one close to the ideal described in FIG. 5, and a peak of sound pressure is formed at the frequency fp as shown in FIG. ing. This is considered to be the influence of the series stiffness of Co and Ce1 in FIG. 7 described above. In the speaker system described above with reference to FIG. 8, the frequency of fp was about 150 Hz.

FIG. 10 shows the characteristic when the frequency of fh is shifted to fh 'close to fp so that the peak of the sound pressure does not appear, and although the peak of the sound pressure near fp is smaller, this time is as shown in (HA) The sound pressure drops by one step at a frequency lower than the frequency fp.

Therefore, the present invention inhibits the interference between the sound on the back side of the diaphragm and the sound on the front side of the speaker unit including the diaphragm elastically supported by the frame and the electromagnetic drive device for driving the diaphragm in amplitude. A frequency correction circuit which is attached to the enclosure and includes means for suppressing mechanical resonance in the low frequency range due to the speaker unit and the internal space of the enclosure, and compensates for the lack of low frequency due to suppression of mechanical resonance in the low frequency range in the electric drive circuit. It is an object of the present invention to obtain sufficient sound pressure by using a speaker unit or an enclosure with a relatively small aperture rather than reproducing a desired bass only with the diaphragm amplitude in the acoustic device provided with the. Another object is to obtain more uniform frequency-sound pressure characteristics.

According to a first aspect of the present invention, there is provided a speaker unit comprising a diaphragm elastically supported by a frame and an electromagnetic drive device for driving the diaphragm in a vibrating manner and having a mechanical resonance inherent to a bass range An acoustic device comprising an enclosure mounted with the speaker unit to block interference between the sound on the back side and the sound on the front side of the diaphragm of the speaker unit and the electric drive circuit connected to the electromagnetic drive device of the speaker unit; The apparatus includes: a suppression unit for mechanical resonance of the speaker unit; and a frequency-sound pressure correction circuit for compensating for the lack of sound pressure in the low range suppressed by the suppression unit for mechanical resonance in the electric drive circuit. The correction characteristic is that the gain is limited so that the diaphragm amplitude does not exceed the amplitude at the predetermined frequency at frequencies lower than the predetermined frequency. There are provided a sound device, characterized in that the sound pressure of a frequency lower than a predetermined frequency of missing and to compensate in the enclosure of the resonant means thereby.

In the second aspect of the present invention, the mechanical resonance suppressing means includes the back surface of the diaphragm of the speaker unit and an opening at a predetermined distance from the back surface of the diaphragm. The air-conditioning and sound-absorbing material is disposed between the diaphragm and the opening in a small space where vibration is transmitted to the main space inside the enclosure. Provided an acoustic device.

According to a third aspect of the present invention, the resonance means of the enclosure for compensating for the sound pressure below the predetermined frequency which is insufficient is a combination of equivalent mechanical stiffness provided separately from the equivalent mechanical stiffness of the main space of the enclosure. The acoustic device according to claim 1 or claim 2 is provided.

Therefore, according to claim 1, under the desired use environment of the acoustic device, the mechanical resonance of the diaphragm of the speaker unit is suppressed, and the sound pressure shortage of the bass thereby electrically corrected. Low-frequency bass that exceeds the maximum amplitude of the diaphragm when generating the required sound pressure only by the amplitude of the diaphragm compensates for the sound pressure by the resonance means of the enclosure, so the diameter of the speaker unit is, for example, Even with a compact one having a size of 10 cm or less, it is possible to obtain a bass of sufficient sound pressure at a low frequency which can not be considered conventionally under a desired use environment.

According to the second aspect, the means for suppressing the machine resonance that can be used in the invention of the first aspect can be provided easily and inexpensively.

According to the third aspect of the present invention, the resonance means of the enclosure applicable in the first or second aspect can be provided, and in particular, a compact one can be provided.

Schematic of a speaker system with a conventional enclosed enclosure Diagram of mechanical equivalent circuit of low frequency mechanical resonance of the speaker system shown in FIG. 1 Explanatory view of frequency-sound pressure characteristics of the speaker system shown in FIG. 1 Diagram of the electric drive circuit used for the speaker system of the frequency-sound pressure characteristic of (b) of FIG. 3 Explanatory drawing of the frequency-sound pressure characteristic at the time of driving the speaker system of the frequency-sound pressure characteristic of FIG. 3 (b) using the electric drive circuit of FIG. A diagram of an example of a speaker system for obtaining the characteristics of FIG. 3 (b) Mechanical equivalent circuit of low frequency mechanical resonance of the speaker system shown in FIG. 6 A diagram of a realistic speaker system prototyped based on Figure 6 First diagram illustrating frequency-sound pressure characteristics when the speaker system shown in FIG. 8 is driven by the electric drive circuit of FIG. 4 The 2nd figure explaining the frequency-sound pressure characteristic at the time of driving the speaker system shown in FIG. 8 by the electric drive circuit of FIG. The figure which shows the speaker system and electric drive circuit which used the 1st Example of the audio equipment by this invention. Diagram showing the relationship between sound pressure characteristics and frequency correction characteristics of an acoustic device using the first embodiment The figure which shows the frequency-sound pressure characteristic measured without using the frequency correction circuit of the speaker system shown to (a) of FIG. The figure which shows the relationship between the sound pressure characteristic at the time of using the frequency correction circuit different from FIG. 12, and a frequency correction characteristic FIG. 15 shows an example of a frequency correction circuit for obtaining the frequency correction characteristic shown in FIG. The figure which shows the frequency correction circuit different from FIG. 15 A diagram of an example showing the relationship between sound pressure characteristics and frequency correction characteristics when the frequency correction circuit shown in FIG. 16 is used The figure which shows the speaker system using 2nd Example of the audio equipment by this invention. The figure which shows the frequency-sound pressure characteristic which driven and measured the speaker system shown in FIG. 14 by the electric drive circuit which does not have a frequency correction circuit. The figure which shows the speaker system using 3rd Example of the audio equipment by this invention Figure showing another speaker system using the third embodiment of the acoustic device according to the invention of the present invention Figure showing an electric drive circuit of a fourth embodiment of an acoustic device according to the invention of the present application Example of basic circuit used for the band attenuation filter of the electric drive circuit of FIG. 18 The figure which shows the speaker system using 5th Example of the audio equipment by this invention. Low frequency mechanical resonance mechanical equivalent circuit of a speaker system using the fifth embodiment shown in FIG. The figure which shows the frequency-sound pressure characteristic which driven and measured the speaker system shown in FIG. 20 by the electric drive circuit which does not have a frequency correction circuit. The figure which shows the speaker system using 6th Example of the audio equipment by this invention The figure which shows the frequency-sound pressure characteristic which used and measured combining the speaker system using the 2nd Example of this invention, and the electric drive circuit shown in the 4th Example, without using a frequency correction circuit.

A speaker system using the first embodiment of the present invention is shown in FIG. The enclosure 12 of the speaker system shown in (a) of FIG. 11 is basically of a bass reflex type constituted by an internal main space 1201 and a duct 1202.

The general bass reflex type enclosure sets the resonance frequency of the main space 1201 and the duct 1202 to about 70% of the resonance frequency of the speaker unit 11 and the main space 1201. This is a speaker unit in the case where the sound pressure of frequencies higher than the resonance frequency is flattened by the resonance of the speaker unit 11 and the main space 1201, and the sound pressure of a lower frequency is compensated by the resonance of the bass reflex duct and the main space. This is a general standard for flattening the frequency-sound pressure characteristic as a whole without generating a valley of sound pressure between the resonance frequency by the main space 1201 and the resonance frequency by the main space 1201 and the resonance frequency by the bass reflex duct.

Therefore, in the case of such a single-stage bass reflex type enclosure, even if the size of the main space is made sufficiently large and the resonance frequency of the speaker unit and the main space approaches the frequency of the fo resonance of the speaker unit, the fo frequency The sound pressure can only be secured up to about 70% of the frequency of In addition, the enclosure can not be made small because the size of the main space must be taken sufficiently large as a precondition.

There is also a double bass reflex system as a technology that enables further reproduction of the low tone range. This is a two-stage bass reflex resonance, and if the first stage and second stage resonances are set well, it is possible to reproduce frequencies up to about 50% of the fo resonance unique to the speaker unit. It is said that there is.

In contrast to such a general bass reflex box, the bass reflex enclosure used in the speaker system of the present invention shown in FIG. 11 uses a loudspeaker unit having a diameter of 8 cm and an fo of about 125 Hz in the actual example produced. The size of the main space 1201 is about 1.5 liters so that the resonance frequency of the unit and the main space is about 160 Hz to 200 Hz.

Also, the resonance frequency of the main space 1201 and the bass reflex duct is about 50 Hz, and it is as low as 40% in contrast to the fo frequency of the speaker unit, and the concept is different from the conventional general one-stage bass reflex type enclosure.

Such a speaker system is driven by an electric drive circuit as shown in FIG. 11 (b). The circuit shown in FIG. 11B is obtained by adding so-called MFB (motional feedback) to the circuit shown in FIG. 4 and detects the movement of the diaphragm of the speaker unit 11 with 14 sensors and converts it into a voltage signal Then, the voltage signal is added to the original reproduction signal by the addition circuit shown at 13. If the signal phase of the sensor to be added is selected and the gain is adjusted with a circuit not shown, excessive movement of the diaphragm with respect to the electric signal to be reproduced, that is, excessive vibration due to resonance is suppressed. Function.

The frequency sound pressure characteristics of the acoustic system shown in FIG. 11 will be described with reference to FIG. In the frequency-sound pressure characteristic of FIG. 12, the characteristic represented by (b) is the frequency when the speaker system of (a) of FIG. 11 is driven by a general electric drive circuit without the frequency correction circuit in FIG. Sound pressure characteristics, fp is the center frequency of the resonance peak due to the main space 1201 of the speaker unit 11 and the enclosure 12 and fp was about 160 Hz in the above-mentioned actual prototype example. It shows frequency-sound pressure characteristics.

FIG. 12 (e) shows the sound pressure of the resonance peak of the center frequency fd by the main space 1201 and the duct 1202 of the enclosure 12 shown in FIG. 11 (a), and the speaker unit 11 vibrates including the component of the frequency fd. When it does, it resonates and generates larger sound pressure.

Such a speaker system is driven by an electric drive circuit shown in FIG. The frequency correction circuit 4 shown in (b) of FIG. 11 performs sound pressure correction shown by the characteristics of the frequency correction circuit of FIG. The characteristic of the frequency correction circuit is configured to increase the gain at 6 dB / oct from frequency fh to fl ', where fl' is a reasonable frequency considering the fo and amplitude of the speaker unit. Specifically, based on the lowest resonance frequency fo specific to the speaker unit to be used, it is selected in the range of about 50% to about 200%.

The reason that the basic of fl 'is fo is based on the premise that the maximum amplitude of the diaphragm in the speaker unit is possible at the frequency of fo as described above, and it is most appropriate from the above theory which is the basis of the present invention it is conceivable that.

If fl 'is set to 50% of the fo frequency, the correction characteristic of the frequency correction circuit is 6 dB / oct, so if it is vibrated to the maximum amplitude of the diaphragm in the speaker unit at the frequency of fl', The amplitude of the possible diaphragm at the fo frequency is 1/2 of the maximum amplitude, but if the distance between the speaker unit and the ear is 1/2 of the reference usage environment, that is, such a usage environment It is practically acceptable if set.

Conversely, when fl 'is set to 200% of the fo frequency, the diaphragm amplitude at a frequency twice the fo frequency can be made the maximum amplitude of the diaphragm that can be used by the speaker unit, so the above-mentioned reference operating environment A sound pressure that can withstand practically can be obtained even at a distance twice that of

Also, another reason for setting the range of about 50% to about 200% of fo as fl 'is that the relationship between the lowest resonance frequency fo and the maximum amplitude of the possible diaphragm may differ depending on the speaker unit used. It is because it is assumed. The resonance frequency fd of the bass reflex duct is also adjusted by the frequency setting of fl '.

In an actual prototype, fl 'is 125 Hz which is the same as the fo frequency. When the sound pressure is corrected by such a frequency correction circuit, the speaker system of (a) of FIG. 11 reproduces at the same sound pressure as middle and high sound up to the frequency fl ′ as in (f) of the frequency-sound pressure characteristic of FIG. Although this is possible, frequencies lower than fl 'are insufficient in sound pressure. (Ho ') is the sound pressure due to the resonance of the main space 1201 and the duct 1202 of the enclosure 12 of (a) of FIG. 11 and compensates for the sound pressure of a frequency lower than that of fl' described above.

Here, if the relationship between the frequency that can be reproduced with the same sound pressure as middle-high tone and the resonance frequency of the bass reflex duct in the diaphragm of the speaker unit is compared with the case of the conventional bass reflex type enclosure and the present invention, When the conventional bass reflex type enclosure is configured on the basis of the speaker unit 11 of the prototype example of (a) and the main space 1201 of the enclosure 12, the resonance frequency of the speaker unit 11 and the main space 1201 is about 160 Hz as described above Therefore, the resonant frequency of bass reflex duct could not be significantly lower than 112 Hz which is 70% of 160 Hz. This is due to the resonance of the speaker unit and the main space, the sound pressure decreases sharply at frequencies below 160 Hz, and if the duct with a resonant frequency extremely lower than 112 Hz is combined, between the resonant frequency of the duct and the resonance at 160 Hz This is because valleys of sound pressure occur.

On the other hand, according to the present invention, even if the resonance frequency of the main space 1201 and the duct 1202 is selected to 50 Hz, which is about 30% of the resonance frequency 160 Hz of the speaker unit 11 and the main space 1201, as in the prototype example Pressure characteristics can be made uniform. In the embodiment shown in FIG. 11, first, the resonance of the speaker unit 11 and the main space 1201 is suppressed by the MFB, and the sound pressure is made uniform by the frequency correction circuit to a frequency fl ′ lower than the resonance. Second, since the attenuation of the sound pressure at frequencies lower than fl 'is theoretically as slow as 6 dB / oct, the resonant frequency fd of the duct is set to 50 Hz with fl' set to 125 Hz as described above. Even if, it is because it is hard to produce a valley between fd and fl '.

Note that the sound pressure due to bass reflex resonance without a frequency correction circuit can only obtain a low sound pressure along with the reproduced sound pressure (lo) of the bass due to the diaphragm amplitude of the speaker unit without resonance as shown in FIG. Although the frequency correction does not work, the sound pressure increases as in (E ').

The sound of the first embodiment of FIG. 11 was manufactured using the 8 cm aperture speaker unit as described above, and the volume of the main space of the bass reflex enclosure was 1.5 liters, and the resonance frequency of the bass reflex duct and the main space was 50 Hz. The system was able to reproduce sufficiently low sound pressure of 50 Hz, and it was verified that such a small speaker system could reproduce a low frequency which has not been achieved before.

By the way, if a double bass reflex type enclosure is designed using a speaker unit of the same diameter, the inner volume of the enclosure is 5 to 6 liters including the duct and space, and it can be imagined that the reproducible bass frequency is still 60 to 70 Hz.

In the above, the frequency correction circuit 4 has been described as having the same gain at frequencies lower than fl 'as shown in FIG. According to it, theoretically, at frequencies lower than fl ', the sound pressure generated from the diaphragm of the speaker decreases at a slope of -6 dB / oct toward lower frequencies starting from frequency fl'. Based on the idea of compensating for the lack of sound pressure at low frequencies by the resonance of the enclosure and flattening the frequency characteristics.

However, depending on the sound pressure at the maximum amplitude at the frequency of fl ', depending on the sound source to be reproduced, there are cases where additional sound pressure is required at frequencies lower than fl'. For example, it is a sound source that emphasizes the sound of a bass drum or a large-sized Japanese drum. In that case, the sound pressure level felt by people as a whole music is at a frequency of fl 'or higher, ie, the midrange, so when the desired sound pressure is set in the midrange, the bass drum and the large-sized Japanese drum as described above The amplitude of the diaphragm of the speaker may exceed the maximum amplitude at fl 'in the time domain where the heart beats.

Assuming such a case, the characteristic of the frequency correction circuit 4 is set so that the gain is decreased from the frequency lower than fl '' to a lower frequency as shown in FIG. It is also possible to configure to compensate. The frequency of fl "is set to a frequency equal to or lower than that of fl ', but when a frequency higher than fl' is set, fl" in FIG. , And fl 'of FIG. 12 are the same as when they are set to fl "of FIG.

An example of the frequency correction circuit for obtaining the correction characteristic of FIG. 14 is shown in FIG. The figure shows a combination of filter a and filter b by CR element and buffer amplifier, but the filer a and filter b may be changed places, and CR may be combined in the NF loop of the buffer amplifier. . In such a configuration, since the diaphragm amplitude of the diaphragm of the speaker unit at the resonance frequency fd of the enclosure is smaller than that of FIG. 12 by (f) in FIG. 14, the frequency-sound pressure characteristics should be flattened. Assuming that, the resonance strength of the enclosure needs to be strongly adjusted at that resonance frequency. In addition, it is also necessary to adjust the resonance frequency according to the occurrence of valleys of the frequency-sound pressure characteristics. Such adjustment is possible in the case of a bass reflex box by adjusting the opening area and length of the duct.

As another method, there is a method in which the frequency correction circuit is configured as shown in FIG. The filter 1 to the filter 3 are, for example, a band elimination filter (BEF) as shown in FIG. 23, in which the center frequency and the amount of attenuation are changed to several types, and the diaphragm amplitude of the speaker unit is unique depending on the sound source It is switched so as not to exceed the maximum amplitude. 0 When SW is switched from s0 to s3 in the circuit shown in FIG. 16, the correction characteristic is less than fl 'at s0 and the gain is the same, and at s1 to s3, the gain is in the center frequency and frequency band set by each filter It is supposed to decrease. Normally, SW is set to s0, and in the case of a sound source such as the bass drum described above or a large-sized Japanese drum, it is switched to s1 to s3 as needed, and the diaphragm of the speaker unit at a specific frequency is not impaired Suppress the amplitude of

Yet another way is simpler: s1-s3 switch s0 and s1 as a single filter only. Alternatively, it is free to omit s0 and always connect to s1 so as to reduce the gain in a specific frequency band in advance. In the experiment, for a sound source whose frequency is about 30 Hz to 70 Hz lower than fl 'and about 6 dB higher than the sound pressure of fl' or more, gain at 50 Hz using a band attenuation filter with a center frequency of 50 Hz Sound pressure of about 30Hz-70Hz decreases when it is set to -6dB, musicability is not impaired, the maximum amplitude of the diaphragm of the speaker unit can be suppressed, and the result is that the maximum sound pressure is high and the balance as the whole music is good The FIG. 17 is a diagram showing the relationship between the frequency correction characteristic and the sound pressure characteristic in that case. Although FIG. 17 shows the case where the resonance center frequency fd of the bass reflex duct is 50 Hz and the center frequency of the band attenuation filter is also 50 Hz, the center frequency of fd and the band attenuation filter may be shifted. Furthermore, it is also free to use one such as the filter a of FIG. 15 for any or all of the filters 1 to 3 shown in FIG.

In the above, gain reduction in ultra-low frequency band such as 20 Hz or less in amplifier etc. is neglected in obtaining characteristics of frequency correction circuit, but such gain reduction is caused by using capacitor or output transformer for amplifier especially input / output circuit This is a general characteristic of the vacuum tube amplifier and the like, and it is possible to utilize the gain reduction characteristic of the low band of the amplifier in obtaining the gain reduction characteristic of fl ′ ′ or less shown in FIG.

As described above, the characteristics of the frequency correction circuit can make the gain equal to or lower than the frequency fl ', or lower than the gain of fl' in a part or almost the entire frequency range lower than fl '. It is. The basic idea of the present patent is an audio device comprising a speaker unit having mechanical resonance specific to a low frequency range, an enclosure to which the speaker unit is attached, and an electric drive circuit connected to an electromagnetic drive device of the speaker unit. Means for suppressing mechanical resonance of the unit and the electric drive circuit are provided with a frequency-sound pressure correction circuit that compensates for the lack of sound pressure in the bass region, and the correction characteristics of the frequency-sound pressure correction circuit The amplitude of the diaphragm of the speaker unit is set so that it does not exceed the maximum value inherent to the speaker unit at a desired sound pressure taking into account the distance, the size of the space, the required maximum sound pressure, etc. The following sound pressure is to be compensated by the resonance means of the enclosure.

In the frequency correction characteristic of FIG. 12, the gain at fl 'represents the characteristic as linearity for convenience, and therefore, is indicated as completely the same frequency as fl' in fl '. When the frequency correction circuit as shown in FIG. 4 is configured by the CR element, the gain is -3 dB at the maximum value at the frequency fl ', but is ignored in the description.

Next, the function of the MFB shown in (b) of FIG. 11 will be described with reference to FIG. In FIG. 11 (b), when there is no addition circuit of 14 sensors and 13 and only the frequency correction circuit is in the electric drive circuit, the center frequency fp as shown by dotted line with respect to (c) of frequency-sound pressure characteristics. A resonance peak appears. On the other hand, when 14 sensors and 13 addition circuits are added to constitute an MFB, excessive vibration of the diaphragm due to the resonance of the center frequency fp with respect to the source signal of the signal source 3 is detected by the sensor 14 and sourced by the 13 adders. It acts as a filter that cancels out the signal and attenuates the excess vibration due to the resonance from the source signal, just like the resonance suppression characteristic by the MFB in FIG. As a result, it is possible to obtain a sound pressure characteristic that is uniform with respect to the frequency by suppressing the resonance peak of the dotted line shown in the frequency-sound pressure characteristic.

A further advantage of the acoustic system using the MFB according to FIG. 11 b as resonance suppression means is that the distortion based on the nonlinearity of the input and output of the diaphragm amplitude of the speaker unit is also improved. That is, it is well known that the amplitude of the diaphragm of the speaker unit itself is improved even if it is not proportional to the voltage output from the electromagnetic drive.

Although the embodiment shown in FIGS. 11 to 17 has been described as an example using MFB as the resonance suppressing means, an embodiment using another method will be described next. FIG. 18 is a view showing a speaker system using a second embodiment of the present invention. In the figure, 11 and 12 are the same as (a) of FIG. In FIG. 18, 15 is an air-permeable acoustic resistance material and is disposed on the back side of the diaphragm 1101 of the speaker unit 11 so as to partition it from the main space 1201. This functions as a resonance suppression means of the diaphragm as well as 8 in FIG. 6 and FIG.

Here, when the frequency-sound pressure characteristic was measured using the air-permeable acoustic resistance material 15, it becomes as shown in FIG. 19, and compared with the characteristics of FIG. It can be seen that the acoustic resistance material 15 functions as a resonance suppression means because the height of

In an acoustic system in which such a speaker system is driven by the electric drive circuit shown in FIG. 4 and fl in FIG. 9 is set to a frequency such as fl 'in FIG. Although the resonance peak (d ') described in 9 remains, it is improved over that shown in FIG. 13, and the resonance is suppressed using a small speaker unit, and the sound pressure shortage of the bass due to the suppression is suppressed by the frequency correction circuit. In the sound system to be corrected, the sound pressure shortage of the bass due to the shortage of the diaphragm amplitude can be compensated by the resonance by the enclosure to obtain a larger sound pressure.

In the bass reflex type enclosure shown in FIG. 14, in order to bring out the resonance by the bass reflex duct sufficiently, the air vibration due to the vibration of the diaphragm of the speaker unit must be sufficiently transmitted to the main space in the enclosure. When a general sound absorbing material is used, the sound absorption coefficient is very low at a frequency of 100 Hz or less as described above, and in the actually tried feel the compressed urethane foam which is generally air-permeable as an acoustic resistance substance The vibration of the diaphragm was transmitted to the main space through the acoustic resistance material.

In addition to the method according to FIG. 18, it is possible to use a mechanical resonator as the resonance suppression means. FIG. 20 shows a speaker system using the Holm Hertz resonator 16 according to the third embodiment. In FIG. 20, 11 and 12 are the same as in FIG. 11 (a). In the figure, the resonator 16 includes a space 1602 and an opening cylinder 1601, and the opening of the opening cylinder 1601 is in contact with the main space 1201 of the enclosure 12.

The resonance frequency of the Holm Hertz resonator 16 is determined by the volume of the space 1602, the opening area of the opening cylinder 1601 and the length of the cylinder, but in the case of the above-mentioned trial manufacture, the resonance frequency fp by the speaker unit 11 and the main space 1201 is about 160 Hz. By making the resonance frequency of the Holm Hertz resonator 16 approximately the same as fp, the resonator 16 can absorb the resonance energy in the main space 1201 to suppress the resonance.

According to trial calculations, if the volume of the space 1602 is about 1 liter, the opening area of the opening cylinder 1601 is 1.9 cm ² , and the length is 2 cm, the resonance frequency can be about 160 Hz. The strength of resonance of the resonator is adjusted by arranging the sound absorbing material in the volume of the space 1602, the opening area and length of the opening cylinder 1601, the space 1602 and the opening cylinder 1601, providing an acoustic resistance in the opening of the opening cylinder, etc. It shall be. The electric drive circuit similar to that of the speaker system of FIG. 18 is used for such a speaker system, and the frequency-sound pressure characteristic in that case is the resonance suppression characteristic by MFB in FIG. Will be replaced by

The resonance cylinder 1601 of the Holm Hertz resonator 16 has the same effect as a diaphragm having a mass and elastically supported around the periphery.

In another method using a mechanical resonator, a method as shown in FIG. 21 can also be considered. In FIG. 21, reference numeral 17 denotes a resonator installed in the main space 1201. A weight 1701 is attached to the free end side of the elastic plate 1702, and a base end is fixed to a base 1703. The resonance frequency is determined by the elasticity of the diaphragm 1702 and the mass of the weight 1701. If the resonance frequency is adjusted to the above fp by using a plastic plate with high elasticity and large mechanical loss as the diaphragm, air in the main space 1201 It resonates with vibration and absorbs resonance energy in the main space.

The resonance suppression means may be a band attenuation filter provided in the electric drive circuit. FIG. 22 shows an electric drive circuit used in the fourth embodiment of the present invention, in which 18 band attenuation filters (BEF: band elimination filter) are added to the electric drive circuit shown in FIG. Specific circuit examples of the 18 band attenuation filters (BEF) are shown in (a) and (b) of FIG. FIG. 23 (a) shows a series resonant circuit of L and C, which utilizes the characteristic that the impedance is minimized at the resonance frequency, and FIG. 23 (b) shows a circuit generally called a T notch filter. Frequency-gain characteristics similar to resonance suppression characteristics by MFB can be obtained. In recent years, such characteristics can be easily obtained by digital technology (computer and software).

Therefore, if the center frequency of the filter is set to be the same as fp in FIG. 12, an acoustic system similar to that of FIG. 11 can be configured by using it in combination with the speaker system of FIG.

Although the mechanical resonators shown in FIGS. 20 and 21 and the band attenuation filter shown in FIG. 22 have been described as single ones, the attenuation bandwidth can be broadened by combining a plurality of resonators whose resonance frequency is shifted near fp. Good.

FIG. 24 is a view showing a speaker system using mechanical resonance suppressing means according to the fifth embodiment of the present invention. The enclosure 19 of the speaker system shown in FIG. 24 is basically the same bass reflex type enclosure as 12 shown in FIG. 18, resonates in the main space 1901 and the duct 1902, and the resonance frequency is the same as in the second embodiment shown in FIG. It is intended to compensate for the low frequency sound pressure.

The difference between FIG. 24 and FIG. 18 is that the speaker system shown in FIG. 18 directly arranges the speaker unit 11 and the breathable acoustic resistance material 15 in the main space 1201, while the embodiment of FIG. The vibration of the air generated by the vibration of the diaphragm 1101 of the speaker unit 11 disposed in the small space 21 covered by the enclosure 19 and the wall 20 propagates to the main space 1901 through the opening 2101 of the small space 21 and the small space Inside, the sound resistance material 22 having air permeability on the back side of the diaphragm 1101, and the sound absorbing material 24 on the side of the sound resistance material 22 and the opening 2101 are disposed. In the trial production, the enclosure shown in FIG. 11 was modified, so the main space 1201 of the enclosure in FIG. 11 had a volume of 1.5 liters, but in the embodiment of FIG. The volume of the two-liter main space 1901 is about 1.3 liters including the volume of the wall portion 20.

A space 23 between the acoustic resistance material 22 and the sound absorbing material 24 may be filled with a suitable sound absorbing material, and in some cases, may be filled with the same material as the sound absorbing material 24. Furthermore, the components from the acoustic resistance material 22 to the sound absorbing material 24 may be integrally formed of the same material.

Here, the purpose of the acoustic resistance material 22 is to brake the diaphragm by limiting the air flow rate due to the vibration of the diaphragm 1101, and more specifically, by using the viscosity of air by limiting the ventilation area. In order to limit the air flow rate per hour, in the trial production, we used compressed urethane foam, cotton cloth, etc. as mentioned above. With such a material, not only damping of the diaphragm but also sound absorption effect can be expected.

The purpose of the sound absorbing material 24 is to absorb sound, and specifically, as in the case of the acoustic resistance material 22, a fibrous material, air-permeable urethane foam, or the like can be used. With such a configuration, a further resonance suppressing effect can be obtained with respect to the second embodiment shown in FIG. FIG. 25 is a mechanical equivalent circuit of mechanical resonance of the bass region of the speaker system shown in FIG. 24, and FIG. 26 is a frequency-sound pressure characteristic of the speaker system shown in FIG. is there.

In the mechanical equivalent circuit shown in FIG. 25, Rt 1 represents the equivalent mechanical resistance of the acoustic resistance material 22, and Rt 2 represents the equivalent mechanical resistance of the sound absorbing material 24. Ct1 is the stiffness of the space between the diaphragm 1101 and the acoustic resistance material 22, Res and Ces are the equivalent mechanical resistance between the acoustic resistance material 22 and the sound absorbing material 24 and the equivalent mechanical stiffness. Cem is the stiffness of the main space 1901 in the enclosure 19, and Md is the equivalent mechanical mass of air in the duct 1902.

Here, the resonance of the speaker unit 11 and the space in the enclosure 19 will be described with reference to FIG. First, the lowest frequency resonance occurs in a series circuit of the equivalent mechanical mass Mo of the speaker unit 11, the equivalent mechanical stiffness Co and the equivalent mechanical stiffness Cem of the main space 1901 of the enclosure 19, and the volume of the main space 1901 shown in FIG. As described above, if it is about 1.3 liters, the resonance frequency is about 160 Hz.

The next lower frequency resonance occurs in the series circuit of the equivalent mechanical mass Mo of the speaker unit 11, the equivalent mechanical stiffness Co and the equivalent mechanical stiffness Ces of the small space 20, and the volume of the small space 21 shown in FIG. If it is 2 liters, the resonance frequency is 300 Hz or more. The highest frequency resonance occurs in a series circuit of equivalent mechanical mass Mo of speaker unit 11, equivalent mechanical stiffness Co, and equivalent mechanical stiffness Ct1 in the space between diaphragm 1101 and acoustic resistance material 22, and Ct1 is the volume of small space 21. The resonance frequency is 500 Hz or more because the frequency is further smaller.

Here, the acoustic resistance material 22 is made of breathable urethane foam or fibrous cloth as described above, and the sound absorbing material 24 is also the same. Here, common to such materials, these materials are generally used as a sound absorbing material as described above, and the sound absorption coefficient is higher as the frequency is higher and lower as the frequency is lower. It is close to 0.1 or less at about 100 Hz or more, and between 0.1 and 1 at about 100 to 300 Hz. The thicker the sound absorbing material, the higher the sound absorption coefficient.

Therefore, as described above, the resonance due to the space between the diaphragm 1101 and the first acoustic resistance material 22 has a frequency of 300 Hz to 500 Hz, but most of the acoustic energy due to the resonance is absorbed by the sound absorption characteristics of the acoustic resistance material 22 Resonance is suppressed. Further, since the frequency of the resonance due to the small space 21 is also about 300 Hz, most of the acoustic energy due to the resonance is absorbed by the sound absorption characteristics of the acoustic resistance material 22 and the sound absorbing material 24, and the resonance is suppressed.

Finally, the resonance with the main space 1901 is about 160 Hz, and the sound absorption coefficient of the acoustic resistance material 22 and the sound absorbing material 24 is in a frequency range of 0.1 to 1. However, by sufficiently securing a distance from the opening 2101 in the direction of the diaphragm 1101, that is, by securing the thickness of the sound absorbing material through which air vibration passes, acoustic energy of 160 Hz can be absorbed and resonance can be suppressed.

On the other hand, although the resonance occurring in the mutual relationship between the speaker unit 11 and the main space 1901 fills the main space 1901 with acoustic energy, the acoustic energy is the main space 1901 of the inner wall surface of the enclosure constituting the main space 1901 and the wall portion 20 Although it tries to propagate as uniform pressure per unit area according to the area of the side surface and the opening 2101, only the area of the opening 2101 can propagate in the direction of the diaphragm 1101, and the others are reflected by the wall, and the next moment Then, the same thing is repeated, and the energy acting on the diaphragm 1101 from the main space 1901 side is appropriately limited as compared with the case of FIG. 18 without the wall portion 20 and the opening 2101, and the resonance suppression effect can be further enhanced. The energy that can not be transmitted from the opening 2101 to the diaphragm 1101 attenuates in the main space 1901 over time.

As described above, in the speaker system using the resonance suppressing means of the fifth embodiment shown in FIG. 24, the sound absorption in the mutual relation that causes the resonance between the diaphragm 1101 and the main space 1901 compared to that shown in FIG. The resonance suppressing effect can be enhanced by the action of the sound absorbing material between the material 24 and the sound absorbing material 24 and the acoustic resistance material 22, and the opening 2101 and the wall portion 20.

In addition, the area of the sound absorbing material 24 exposed to the main space 1901 is limited to the portion of the opening 2101, and thus hardly affects the strength of the bass reflex resonance of the main space 1901 and the duct 1902.

The frequency-sound pressure characteristics of the speaker system shown in FIG. 24 are shown in FIG. 26. The frequency-sound pressure characteristics of the speaker system with only the acoustic resistance material 15 shown in FIG. It is understood that it is done.

In FIG. 24, the small space 21 is constituted by the enclosure 19 and the wall portion 20 integrated with the enclosure 19. However, the wall portion may be, for example, a resin molded product as one component different from the enclosure or the speaker unit. It may be configured such that the entire back surface of the speaker unit is covered with the component. That is, the small space may be configured to be surrounded only by the component. In addition, the sound absorption coefficients of the acoustic resistance material 22 and the sound absorbing material 24 at the frequency of resonance occurring due to the volume of the space between the speaker unit 11 and the diaphragm 1101 of the speaker unit and the acoustic resistance material 22, ie the equivalent mechanical stiffness Ct1. 1 and the volume of the speaker unit 11 and the volume of the main space 1901 of the enclosure, that is, the equivalent mechanical stiffness Cem. If the relation that the sound absorption coefficient of the sound resistance material 22 and the sound absorbing material 24 is less than or equal to 0.1 at the frequency of resonance occurring due to the relation between the main space 1901 and the duct 1902 holds, the sound resistance used The volume of each space and each resonant frequency are It can be adjusted from the value of the predicate.

Although the above has been described individually as the first to fifth embodiments according to the difference in resonance suppression means using the acoustic system of the present invention, the resonance suppression means of the first to fifth embodiments are two or more. It may be used in combination of two or more. FIG. 27 first covers the back side of the diaphragm 1101 of the speaker unit 11 with a breathable acoustic resistance material 15 as a resonance suppressing means, and further, the Holm Hertz resonator 16 has its opening tube 1601 as the main space 1201 of the enclosure 12. It is provided in contact with the The electric drive circuit combined with this speaker system uses the thing of the structure of FIG. 4, and what set only fl like fl 'of FIG. 12 is used.

Further, as the speaker system, one having the configuration of FIG. 18 may be used, and an electric drive circuit using the MFB shown in FIG. 11B may be combined. Further, an electric drive circuit to which BEF shown in FIG. 22 is added may be combined. FIG. 28 shows frequency-sound pressure characteristics when the speaker system of FIG. 18 and the band-limited attenuation filter (BEF) shown in FIG. 22 are used in combination. In this example, the band attenuation filter is a combination of two filters with center frequencies of 125 Hz and 250 Hz. When the resonance suppression effect is insufficient by one means, a more sufficient effect can be achieved by combining with other means.

Furthermore, although the above description was described using one-stage bass reflex resonance as the enclosure method of the embodiment of the present invention, the diaphragm amplitude of the speaker unit is about 50% to 200% based on the lowest resonance frequency unique to the speaker unit. By the characteristic and basic idea of the frequency-sound pressure characteristics described in FIG. 12 of not increasing at frequencies lower than the range of, thereby making it possible to compensate the insufficient low sound pressure by the mechanical resonance of the enclosure. For example, it is obvious that the mechanical resonance of the enclosure, that is, the resonance of (e) of FIG. 12 may be a method other than the one-stage bass reflex resonance described above.

The double bass reflex type enables regeneration of even lower frequencies, and similar to the bass reflex type, the same effect is obtained with the drone cone type utilizing resonance due to the equivalent mechanical stiffness of the main space in the enclosure separately from the equivalent mechanical stiffness. can get. In these methods, the main space directly acting on the speaker unit is a substantially enclosed space of the equivalent mechanical stiffness Cem shown in FIG. 25, and mechanical resonance due to the speaker unit and the main space appears strongly, so the first to fifth embodiments are effective. Works. Further, the characteristic of (e) of FIG. 12 can be obtained sufficiently except the aspect that the external dimensions become large even in a system called a resonance tube or TQWT as another system or a system using a horn.

The effects of the present invention will be described again. In the speaker system based on the utilization of the mechanical resonance of the low frequency band of the conventional speaker unit, the speaker system and the space inside the enclosure can reproduce the low frequency resonance frequency. Even if the lower limit of the frequency is limited and the lower frequency range is compensated by the resonance of the enclosure, a low frequency of about 50 Hz is sufficient for a small speaker unit with a minimum resonance frequency, for example, a diameter of 8 cm or less. It was difficult to regenerate with pressure, and the enclosure was inevitably required to be large.

In addition, in an acoustic system in which the mechanical resonance in the low range of the speaker unit is suppressed and the lack of bass thereby is electrically corrected, the lower resonance frequency of the speaker unit can be released to lower frequency reproduction. However, with a small diameter speaker unit of about 10 cm or less, sufficient sound pressure could not be generated due to the restriction of the amplitude of the diaphragm at frequencies lower than the lowest resonance frequency of the speaker unit.

In the present invention, on the other hand, the mechanical resonance of the bass region of the speaker unit is suppressed to electrically correct the shortage of the bass thereby, and the amplitude correction of the electrical diaphragm is performed at the desired sound pressure of the speaker unit. Since the sound pressure of the low range is compensated by the resonance of the enclosure without exceeding the maximum amplitude of the diaphragm, it is possible to reproduce low frequencies not restricted by the lowest resonance frequency of the speaker, Sound pressure is also secured sufficiently. Furthermore, if the method of an enclosure is chosen, the size can also be made small.

Furthermore, by combining and using the means for suppressing resonance of different types of bass regions, the suppression effect of the resonance can be made sufficient, and the peak of the sound pressure due to the influence of the resonance can be eliminated to realize flattening of the frequency characteristics.

The present invention can be applied to a stereo device, a TV device, a PC audio device, a subwoofer system, etc. that reproduces high-quality sound without making the presence of an audio device appear in a burden in size.

1 ... speaker unit 101 ... diaphragm 102 ... frame 103 ... electromagnetic drive 2 ... sealed enclosure 201 ... housing 202 ... internal space 3 ... signal source 4 ... Frequency correction circuit 5 ... Power amplifier 6 ... Enclosure 601 ... Case 602 ... Internal space 603 ... Opening 8 ... Breathable acoustic resistance material 9 ... Venting Acoustic Resistive Material 10 · · · Enclosure 1001 · · · Main space 1002 · · · bending space 1003 · · · bending space 1004 · · · open end 11 · · · speaker unit 1101 · · · diaphragm 12 · · · Bass reflex type enclosure 1201 · · · Main space 1202 · · · Bus reflex duct 13 · · · Addition circuit 14 · · · Sir 15 ··· Air-permeable acoustic resistance material 16 ··· Holm Hertz resonator 1601 ··· Open cylinder 1602 ··· Space 17 ····························································································································································· Weight portion 1702 ··· plate portion 1703 ··· · · · 18 · · · Band attenuation filter (BEF)
19 enclosure 1901 main space 1902 duct 20 wall forming a small space 21 small space 2101 small space opening 22 acoustic resistance material 23.・ Sound absorbing material 24 ・ ・ ・ Sound absorbing material

Claims (3)

A speaker unit comprising a diaphragm elastically supported by a frame and an electromagnetic drive device for driving the diaphragm in oscillation and having mechanical resonance specific to a low frequency range, and the speaker unit attached to the diaphragm of the speaker unit Means for suppressing mechanical resonance of the speaker unit, and an acoustic device comprising an enclosure for blocking the interference between the sound on the back side of the speaker and the sound on the front side and an electric drive circuit connected to the electromagnetic drive of the speaker unit The drive circuit includes a frequency-sound pressure correction circuit that compensates for the lack of sound pressure due to the amplitude reduction of the diaphragm suppressed by the mechanical resonance suppression means, and the correction characteristic of the frequency-sound pressure correction circuit is a predetermined frequency At lower frequencies, the gain is limited so that the diaphragm amplitude does not exceed the amplitude at the given frequency, and Acoustic device being characterized in that as supplement in the resonant means of the sound pressure of a frequency lower than a predetermined frequency enclosure insufficient Ri. The means for suppressing mechanical resonance includes a back surface of the diaphragm of the speaker unit and an opening for setting a predetermined distance from the back surface of the diaphragm, and air vibration due to the vibration of the diaphragm only through the opening is inside the enclosure 2. An acoustic device according to claim 1, wherein an air-permeable and sound-absorbing acoustic resistance material is disposed between the diaphragm and the opening in a small space which is made to propagate to the main space of. The resonance means of the enclosure that compensates for the sound pressure below the predetermined frequency that is lacking is a combination of equivalent mechanical stiffness separately provided in the main space of the enclosure and an equivalent mechanical mass provided separately. Sound equipment.