JPH01319792A - Electronic musical instrument - Google Patents

Abstract

PURPOSE:To improve low-frequency regeneration characteristics by incorporating two speaker systems with resonance boards similar to a bass-reflex speaker system and a driving means for canceling air reaction from a electroacoustic transducer and a Helmholtz resonator to a vibrator, and shifting the resonance frequency of the resonator mutually. CONSTITUTION:A keyboard 3, speaker fitting bases 5a and 5b for two left and right channels which have speaker units 4a and 4b, sound sources which are not shown in a figure, and amplifiers for speaker driving are mounted on a shelf plate 1 constituting the electronic musical instrument. Further, opening part 6a and 6b are bored in the shelf plate 1 and a boxy body 7 which constitutes a cavity part and a resonance port part is provided below the opening parts. This box body 7 is sectioned into two by an intermediate plate 10 so as to match the left and right speaker systems, thereby constituting cavity part of the Helmholtz resonator which differs in resonance frequency from said space parts and space parts of the fitting bases 5a and 5b. Further, the bottom plate 8 of the box body 7 is provided with tube resonance preventing means 12a and 12b such as felt and distribute radiation sound from the speaker units 4a and 4b.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electronic musical instrument equipped with a built-in sound system for generating musical tones, and more particularly, to miniaturization of the sound system and frequency characteristics, particularly low frequency reproduction. Concerning electronic musical instruments with improved characteristics.

[Prior Art] In electronic musical instruments, design, frequency characteristics, operability, etc. are all important factors.

Regarding frequency characteristics, for example, 881! The lowest note (AO) of a type piano is 27.5 Hz, and the frequency of the fundamental wave of a bass drum in automatic rhythm performance is about 30 Hz.

Even if the fundamental wave itself is not reproduced, the audible level of these ultra-low tones is corrected if the harmonics are reproduced, so there is no problem in monitoring normal performances. However, for example, in the case of a bass drum, if the fundamental wave of approximately 30H2 is emitted even slightly, and the overtones of 50 to 60Hz are sufficiently emitted, it will be felt as a deep bass that shakes the body, whereas the lowest There is a big difference in sound quality, as if you use a sound system with a reproduction frequency of about 70 Hz or higher, you will end up with a light "bong, bong" sound.

Many of the recent electronic musical instruments use PCM sound sources as sound sources, and if the input to the sound system is reproduced as is, the sound quality is extremely high. In order to reproduce this high-quality musical tone, it is desired that the sound system built into an electronic musical instrument has high fidelity. The reproduction characteristics of a sound system are largely determined by the reproduction characteristics of the speaker system.

By the way, conventionally, the sound system built into an electronic musical instrument consists of a sealed type or phase inversion type (bass reflex type) speaker system and a power amplifier with an output impedance of essentially 00, which drives the speaker system at a constant voltage. Ta. In this case, the lowest reproduction frequency of the speaker system is mainly determined by the volume of the box (cabinet) and the characteristics (fo, Qo, etc.) of the speaker unit being used. In other words, with conventional electronic musical instruments, if you want to reproduce even lower frequency sounds, you need a box with a larger volume, which limits your design freedom, and depending on the arrangement, it can interfere with performance. This had the disadvantage of causing operational problems. FIG. 14 shows the appearance of an electronic musical instrument with a design in which the back frame 21 and the box body 7 are integrated. In the figure, 9a and 9b are bass reflex ports (resonance ports).

[Problems to be Solved by the Invention] The present invention has been made in view of the problems with the conventional electronic musical instruments. It is an object of the present invention to provide an electronic musical instrument that can be downsized without impairing the design flexibility and operability, or that can improve low frequency reproduction characteristics without increasing the size of the box.

[Means for Solving the Problems] The electronic musical instrument of the present invention has, as a sound system, an electroacoustic transducer disposed on the outer wall surface of a box with a resonance port constituting a Helmholtz resonator. A speaker system 2 with a resonance port, which is similar in shape to a bass reflex speaker system, drives the Helmholtz resonator on the inner surface of the vibrating body, and directly radiates sound on the outer surface.
and drive means for driving the transducer to cancel the atmospheric reaction from the Helmholtz resonator to the vibrating body;
The resonant frequencies of the Helmholtz resonators of each speaker system in the set are shifted from each other.

[Operation] In the present invention, the speaker system is of the type having a Helmholtz resonator, similar to a bass reflex speaker system. Therefore, sound is radiated directly from the vibrating body of the electroacoustic transducer and also from the Helmholtz resonator driven by this vibrating body, and the frequency characteristics of the output sound pressure of this speaker system are determined by these electroacoustic transducers. The direct radiated sound from the vibrating body of the device and the resonant sound from the resonator are combined, and the resonance sound is lower than that of a closed speaker system that emits only the directly radiated sound. It is possible to improve the range characteristics.

In this invention, the driving means for the electroacoustic transducer drives the transducer so as to cancel the atmospheric reaction from the resonator side when the Helmholtz resonator is driven. Such driving means include a negative impedance generation circuit that generates a negative impedance component (Zo) equally sparingly in the output impedance, and a motional signal corresponding to the movement of the vibrating body that is detected by some method and sent to the input side. A known circuit such as a motional feedback (MFB) circuit that provides negative feedback can be applied.

In this way, if the electroacoustic transducer is driven so as to cancel out the reaction to the vibrating body, for example, if the atmospheric reaction is completely canceled, this transducer will eliminate the atmospheric reaction from the resonator side, that is, the box side. The vehicle will be driven in a so-called dead state, with sufficient braking and unaffected by this. Therefore, the frequency characteristics of the directly radiated sound are not affected by the volume of the space behind the transducer, and the volume of the box should be small as long as it does not cause any inconvenience as a cavity for the Helmholtz resonator and as a container for the transducer. be able to. Also, from the perspective of the Helmholtz resonator, driving the transducer in such a way as to cancel out the atmospheric reaction from the resonator when driving the first unit means that the vibrating body of the transducer is not driven from the resonator side. In other words, it has become an isometric wall that cannot be used, that is, a part of the inner wall of the resonator. Therefore, the Q value of the Helmholtz resonator is not affected by the characteristics of the converter, and a sufficiently high Q value can be ensured even if the resonance frequency of the resonance port and the box body is lowered. This results in
Even if the cabinet is made smaller, the Helmholtz resonator can generate deep bass (resonance) at a sufficient level.

That is, according to a sound system that combines the speaker system with a resonance port of the present invention and a driving means that drives the transducer of this speaker system so as to cancel the atmospheric reaction from the resonator side when the Helmholtz resonator is driven. Compared to a conventional bass reflex speaker system driven at a constant voltage, the volume of the box can be made smaller, and by forming the resonance port into an elongated shape and setting the resonance frequency of the resonator low, it is possible to produce even lower tones. Playback becomes possible.

However, in order to reproduce even lower frequencies, if the resonant frequency of the Helmholtz resonator is set low and the Q value is set high,
This causes waviness in the playback frequency characteristics. This waviness can be corrected by increasing or decreasing the human input signal voltage, especially by boosting the low sound pressure part. However, the sound system of an electronic musical instrument must be considered with a continuous rating to take into account the continuous pressing of keys, and requires several times the capacity of a normal audio amplifier, which is considered with an instantaneous or intermittent rating. do. Therefore, it is difficult to make this a larger capacity for correcting (boosting) the waviness.

On the other hand, in a low frequency range of several tens of Hz or less, the wavelength is several meters or more, so the sound image is not very clear, and the position of the sound source does not matter much.

Therefore, in the present invention, two sets of speaker systems are used, and the resonant frequencies of the Helmholtz resonators of each system are made to differ from each other.

In this way, the two Helmholtz resonators complement each other in the sound pressure characteristics obtained by combining the sounds radiated from the two speaker systems, and the undulation is reduced.

As a result, the amount of boost by the drive means is reduced, and the maximum output of the drive means can be reduced.

[Effects] As described above, according to the present invention, the box body of the speaker unit can be made smaller without impairing the reproduction low-frequency characteristics, and the operability and design freedom of the electronic musical instrument can be improved.
It becomes possible to improve reproduction low-frequency characteristics without increasing the size of the box.

In addition, since the low frequency range is shared by two sets of speaker systems, each speaker system can be operated with higher efficiency, and the capacity of the drive means can be reduced or suppressed from increasing.・.

[Example] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows the appearance of an electronic musical instrument according to an embodiment of the present invention. This electronic musical instrument has a Helmholtz resonator as the speaker system that makes up the sound system, similar to a conventional bass reflex speaker system, and uses a speaker system with a resonance port that is similar in shape to this bass reflex speaker system. It is something. However, the volume of the cavity of the Helmholtz resonator is reduced to a few degrees Celsius and 8i end compared to the 2.30 ft of the conventional bass reflex type, and the resonance port is made elongated so that the resonant frequency of the resonator is equal to that of the bass reflex type, or It is set to a lower frequency of 50 to 60 Hz.

FIG. 2 is a sectional view taken along line A-A in FIG. 1, and FIG. 3 is a perspective view with a part of the exterior removed. In FIGS. 1 to 3, a shelf board 1 is held at a predetermined height by two vertically provided legs 2a and 2b, and a keyboard 3 is placed on top of this shelf board 1.
, speaker mounting bases 5a and 5b for the two left and right channels to which the speaker units 4a and 4b are attached, and an electric circuit including a sound source and an amplifier for driving the speakers of each channel (
(not shown) is installed. Further, the shelf board 1 is provided with openings 6a and 6b, and a box body 7 that forms a cavity and a resonance port between the shelf board 1 and the shelf board 1 is disposed below the shelf board 1. ing.

As shown in FIGS. 4(a) and 4(b), this box body 7 has frontage port portions 9a and 9b provided on the bottom plate 8, and is further partitioned internally by an intermediate plate 10 and partition plates 1fa to 1lid. . When the box body 7 is attached to the shelf board 1 and the upper part is closed, the opening port portions 9a, 9b and the portions separated by the partition plates 11a to lid communicating therewith are used as resonance port portions of the Helmholtz resonator. form. Also, the space excluding this resonance port portion is this box body 7.
is a part that forms a cavity when it is attached to the shelf board 1 and its upper part is closed, and is divided into two by the intermediate board 10 for each of the left and right speaker systems. When this electronic musical instrument is completed, these spaces communicate with the spaces formed on the rear sides of the speaker units of the left and right speaker mounting bases 5a and 5b through the openings 6a and 6b, respectively, and connect these boxes. Space of body 7 and speaker mounting base 5
A Helmholtz resonator cavity is formed by the spaces a and 5b. Here, by attaching the intermediate plate 8 slightly to the right in the figure, the cavity volume for the left channel speaker system is approximately 5.5 degrees Celsius, and the cavity volume for the right channel speaker system is approximately 4.5 degrees Celsius. It is being distributed. Further, the resonance frequencies of the left and right Helmholtz resonators are set to 50 Hz and 60 Hz, which are different frequencies. The resonant frequency f of such a Helmholtz resonator. P is the sound velocity, C1, where the cross-sectional area of the resonance port is S, the length of the resonance port is l, and the volume of the cavity is V, then fop=c (S/JZV)''/2π...
1).

Felts 12a and 12b are attached to the bottom plate 8 of the box body 7. In this embodiment, the box body 7 has a thickness equal to the width.
/10 or less, the space has a strong character as a pipe, and if the entire wall surrounding this space remains a rigid body such as wood, plastic, or metal, the width of the space can be reduced to 1 /2.1.・・・・・・Produces tube resonance with wavelength. Here, the tube resonance is prevented by pasting felts 12a and 12b. As such tube resonance prevention means, the felt 12a,
Instead of 12b, other breathable and acoustically resistant materials can also be used, such as sponges, non-woven and woven fabrics, etc. Furthermore, a material having flexibility and viscoelasticity, such as rubber, may be used. Due to its flexibility, such a flexible viscoelastic material exhibits a pressure-relieving effect that is substantially equivalent to the breathability of the felt, etc., and due to its viscoelasticity, it acts as a resistance that consumes energy when deflected. .

This box body 7 has triangular prism-shaped reinforcing members 13a to 1 at several locations.
It is reinforced by attaching 3F.

Referring to FIGS. 1 to 3, this electronic musical instrument has a front panel 1
A speaker unit 4a, which is provided with a group of slit-shaped openings 15a and 15b in the speaker unit 4, and is arranged diagonally inside the speaker unit 4a.
The direct radiated sound of 4b is transmitted through the aperture groups 15a and 15b, respectively.
is released to the outside via the This eliminates the need to provide the opening for directly emitting sound on the top plate 16, and it is possible to place musical scores, ornaments, and other objects on the top plate 16 without worrying about sound quality.

A frame 21 for reinforcing the structure consisting of the fence plate 1, legs 2a, 2b, etc. is provided between the legs 2a and 2b on the lower side of the box 7.

FIG. 5 is a diagram for explaining the basic configuration of an acoustic device (sound system) built into the electronic musical instrument of FIG. 1. This audio device includes the aforementioned resonance ported speaker system and an amplifier that drives this speaker system. The configuration of the speaker system in its installed state is shown in FIGS. 1 to 4.

The speaker system 40 shown in FIG. 5 has a hole made in the front of a cabinet (box body) 7 and an electrodynamic electroacoustic transducer (speaker unit) 4 (4a, 4b) having a diaphragm 41 attached thereto. Opening port part 9 (9a,
Sound path 1 opening to the outside of the cabinet 7 through 9b)
A resonant port 18 having a resonant port 1 is provided.
8 and cabinet 7 form a Helmholtz resonator. In this Helmholtz resonator, an air resonance phenomenon occurs due to the air spring of the cabinet 7, which is a closed air conditioner, and the air mass in the sound path 17 of the resonance port 18. This resonant frequency fOP is determined by the above equation (1) as fop=c(s/ILv)""/2π.

In FIG. 5, the drive circuit 50 includes an f-characteristic correction circuit 51, a negative impedance circuit 52, and the like. The negative impedance circuit 52 includes an amplifier circuit 53, a resistor Rs, and a feedback circuit 54.

In this negative impedance circuit 52, the output of the amplifier circuit 53 with a gain of A is applied to the speaker unit 4 of the speaker system as a load.

Then, the current IL flowing through the speaker unit 4 is detected by a load current detection resistor R8, and is positively fed back to the amplifier circuit 52 via a feedback circuit 54 with a transfer gain β. In this way, the output impedance ZO of the drive circuit 50 is Ro = Rs (1-Aβ)...
- Required as (2). From this equation, if Aβ>1, Ro becomes an open stable negative resistance.

FIG. 6 shows the speaker system portion of FIG. 5 replaced with an electrical equivalent circuit. The parallel resonant circuit Z1 in FIG. 6 is due to the equivalent motional impedance generated by the movement of the unit vibration system consisting of the diaphragm 41 etc. of the speaker unit 4, where ro is the equivalent resistance of the vibration system, and SO is the vibration system's equivalent resistance. The equivalent stiffness, mo, indicates the equivalent mass of the vibration system. In addition, the series resonant circuit Z2
is due to the equivalent motional impedance of the Helmholtz resonator composed of a resonant port and a cavity, rC is the equivalent resistance of the cavity, SC is the equivalent stiffness of the cavity, rp is the equivalent resistance of the resonant port, and mp is The equivalent mass of the resonant port is shown. In addition, A in the figure is a force coefficient, and if the speaker unit 4 is an electrodynamic direct radiation speaker, then B is the 61 density in the magnetic gap, and AV is the total length of the voice coil conductor. BJ! , becomes.

Furthermore, Zv in the figure is the internal impedance (non-motional impedance) of the speaker unit 4, and when the speaker unit 4 is an electrodynamic direct radiation speaker, it is mainly the resistance Rv of the voice coil and includes a small amount of inductance. There is.

Next, the operation of the acoustic device having the configuration shown in FIGS. 5 and 6 will be explained.

When a drive signal is given to the speaker unit 4 from the drive circuit 50 having a negative impedance drive function, the unit 4 electromechanically converts this signal to move the diaphragm 41 back and forth (the fifth
It drives reciprocatingly (left and right in the figure). The diaphragm 41 converts this reciprocating motion into mechanical sound. Here, since the drive circuit 50 has a negative impedance drive function, the internal impedance of the unit 4 is isometrically reduced (ideally disabled).
has been done. Therefore, the unit 4 includes the drive circuit 50
The diaphragm 41 is driven in faithful response to the drive signal input to the diaphragm 41, and drive energy is independently applied to the Helmholtz resonator constituted by the resonance port 18 and the cabinet 7. At this time, the front side of the diaphragm 41 (right side in FIG.
The left side in the figure) constitutes a resonator drive section for driving a Helmholtz resonator consisting of a cabinet 7 and a resonance port 18.

Therefore, sound is directly radiated from the diaphragm 41 as shown by arrow a in FIG. 5, and the air inside the cabinet 7 is resonated, so that
Sound with sufficient sound pressure is resonantly radiated from the resonance radiating section (opening port section 9 of the resonance port 18). Then, by adjusting the air equivalent mass in the resonance port 18 in the Helmholtz resonator, this resonance frequency f is adjusted. P is the Helmholtz resonance frequency f, which is a standard setting value for a conventional bass reflex speaker system. p-f oc/ 1 gun (however, f
oe is set lower than the resonance frequency of the speaker unit 4 when it is installed in a bass reflex type cabinet, and the Q value is set to an appropriate level by adjusting the equivalent resistance of the resonance port 18. By further increasing or decreasing the input signal level as appropriate, it is possible to obtain the frequency characteristic of the sound pressure as shown by the solid line in FIG. 7, for example.

In Figure 7, the two-dot chain line shows the impedance characteristics of a conventional closed speaker system and the output sound pressure frequency characteristics when it is driven at a constant voltage, and the dashed line shows the impedance characteristics and output sound pressure frequency characteristics of a conventional bass reflex speaker system. Indicates frequency characteristics.

Hereinafter, the operation when driving a speaker system using a Helmholtz resonator with negative impedance will be explained in more detail.

FIG. 8 shows the electricity in the negative impedance circuit 52 and subsequent parts when Zv −Zo = 0 in FIG. This is the equivalent circuit. Here, the equivalent resistance r of the resonant port 18 and the cavity. .

rp is converted into a series resistance, and the coefficients attached to the values of each element are omitted.

The following is clear from this equivalent circuit.

First, the parallel resonant circuit Zl based on the equivalent motional impedance of the speaker unit 4 is short-circuited at both ends with zero impedance in terms of alternating current. Therefore, this parallel resonant circuit ZI has a Q value of 0, and is essentially no longer a resonant circuit. That is, in this speaker unit 4, the concept of the lowest resonant frequency that existed when the speaker unit 4 was simply attached to a Helmholtz resonator no longer exists.

Hereinafter, when we refer to the amount equivalent to the lowest resonant frequency f0 of the speaker unit 4, we are only temporarily referring to the above-mentioned concept, which has been essentially invalidated. In this way, as a result of the unit resonance system (parallel resonance circuit) Zl becoming substantially no longer a resonance circuit, the only resonance system in this acoustic device is the port resonance system (series resonance circuit) Z2 due to the equivalent motional impedance of the Helmholtz resonator. It becomes.

In addition, as a result of the vibration system being substantially no longer a resonant circuit, the speaker unit 4 responds linearly to the human power drive signal in real time, faithfully converts the human electric signal E0 into electromechanical signals without any transient response, and This will displace the diaphragm 41. In other words, it is in a complete braking state (so-called speaker dead state). In this state, the output sound pressure frequency characteristic of this speaker near the value corresponding to the lowest resonance frequency fO is 6 dB/oct. On the other hand, the characteristic of normal voltage drive state is 12 dB/
oct.

On the other hand, the series resonant circuit Z2 based on the equivalent motional impedance of the Helmholtz resonator is connected to the drive signal source Eo.
Since it is connected with zero impedance to the parallel resonant circuit Z, there is no longer an interdependent relationship between the parallel resonant circuit Z1 and the series resonant circuit Z2, and the parallel resonant circuit Z1 and the series resonant circuit Z2 coexist independently. Therefore, the volume of the cabinet 7 (inversely proportional to se) and the shape and dimensions of the resonance port 18 (proportional to mp) do not affect the direct radiation characteristics of the speaker unit 4, and the dimensions of the Helmholtz resonator also do not affect the direct radiation characteristics of the speaker unit 4. The frequency and Q value are also not affected by the equivalent motional impedance of the speaker unit 4. That is, the characteristic value (f or, Q op) of the Helmholtz resonator and the characteristic value (f OC+Qoc) of the speaker unit 4 can be set independently. Furthermore, the series resistance of the series resonant circuit Z2 is only rc+rP, and these are usually sufficiently small values, so the series resonant circuit Z2
That is, the Q value of the Helmholtz Ime 2% meter can be set sufficiently high.

From another perspective, the unit vibration system is no longer effectively a resonant system, so it is displaced according to the human power of the drive signal,
It is substantially unaffected by external forces, especially atmospheric reactions due to the equivalent stiffness Sc of the cabinet 7. Therefore, the diaphragm 41 of the speaker unit 4 becomes a wall when viewed from the cabinet side, and the existence of the speaker unit 4 when viewed from the Helmholtz resonator is nullified. Therefore, the resonant frequency for the Helmholtz resonator (hereinafter referred to as port resonant frequency) and the Q value do not depend on the non-motional impedance of the speaker unit 4.
Even when setting the frequency to such a value that the value becomes very small, the Q value can be maintained at a sufficiently large value. Also,
The port resonance system Z2 can be called a virtual speaker that emits sound completely independently of the unit vibration system Z1. Although this virtual speaker is realized with a small diameter corresponding to the port diameter, in terms of its bass reproduction ability, it corresponds to an extremely large diameter speaker as a real speaker.

Comparing the above with a conventional method in which a conventional bass reflex speaker system is driven at a constant voltage by an ordinary power amplifier, in this conventional method, as is well known, multiple resonance systems including a unit vibration system Z1 and a port resonance system Z2 are used. Moreover, the resonant frequency and Q value of each resonant system were closely dependent on each other. For example, if the port is made longer or thinner (m p becomes larger) in order to lower the resonance frequency of port resonance system Z2, the Q value will become higher in unit vibration system Z, and lower in port resonance system Z2. , when the volume of the cabinet is reduced (Sc becomes larger), even if the resonant frequency of the port resonant system Z2 is kept constant by making the port longer or thinner, the Q value and resonant frequency of the unit vibration system Z, became high, and the Q value became even lower in port resonance system Z2. In other words, the output sound pressure frequency characteristics of a speaker system are closely related to the characteristics of the speaker unit, the volume of the cabinet, and the dimensions of the ports.
Matching these requires sophisticated design technology, and it was generally considered impossible to downsize the cabinet (system) without impairing the output sound pressure frequency characteristics, especially the low-frequency characteristics. Furthermore, the relationship between the frequency in a band lower than the resonant frequency fOP in the port resonance system Z2 and the resonant acoustic radiation ability is 12 dB/o with respect to the decrease in frequency from the perspective of the sound pressure level.
If c is reduced at a certain rate and the resonant frequency is set extremely low relative to the basic concept of a bass reflex speaker system, it becomes extremely difficult to correct for increases or decreases in the human signal level. Furthermore, there is no way to correct the increase in Q value near the resonance point and the deterioration in sound quality due to phase characteristics.

Since the drive circuit of this embodiment drives the speaker system using Helmholtz resonance with negative impedance as described above, the characteristics and dimensions of the unit vibration system and port resonance system of the system can be set independently, and Even if the resonant frequency of the port resonance system is set low, the Q value and bass reproduction ability can be maintained high, and the resonator driving ability of the unit vibration system is also strong (6dB/o
c t ), the advantage is that the undulations in the frequency characteristics can be corrected by increasing or decreasing the human signal level by the f-characteristic correction circuit 51, for example, by increasing or decreasing the level of normal sound quality adjustment. A cabinet can be made smaller and a speaker system can be made smaller without deteriorating sound quality. In addition, according to the drive circuit of this embodiment, the resonance frequency and Q value of each resonance system can be set relatively freely, so the sound quality of an existing speaker system can be improved compared to the conventional constant voltage drive. Alternatively, it is possible to easily expand and drive the odd playback band, especially the bass side.

In addition, in the above description, only the case where Zv Zo=O was explained, but in this example, if -20<0, ZV -20>O may be satisfied, and in this case, the unit vibration system and the port resonance system The characteristic values and the like will be values between the case of the above Zv Zo=O and the case of the conventional constant voltage drive method depending on the value of the impedance ZV-ZO.

Therefore, by actively utilizing this property, for example, instead of adjusting the Q value of a port resonance system by adjusting the port diameter or inserting a mechanical Q damper such as glass wool or felt into the cabinet. , by adjusting the negative impedance -20.

FIGS. 9(a), 9(b), and 9(c) are diagrams simulating the electrical characteristics of a fifth tooth acoustic device using the resonance ported speaker system and drive circuit 50. FIG. Here, the nominal impedance of speaker unit 4 is 8Ω.
, the AC input voltage e of the negative impedance generating circuit 52 of the drive circuit 50 is IV, and the output impedance -20 is -7.
Ω.

In FIG. 9(a), the solid line a represents the impedance ZL of the speaker system with a resonance port, the broken line represents the impedance due to the equivalent inductance A2/So of the speaker unit 4, and the broken line C represents the equivalent capacitance m of the speaker unit 4. / Impedance due to A2, dashed line d is impedance due to equivalent inductance A2/S of cabinet 7, broken line e is impedance due to equivalent capacitance m p / A' of cabinet 7, -
A dashed dotted line f indicates each frequency characteristic of the impedance of the unit resonance system Z1. In the figure, the resonant frequency of the unit resonant system is approximately 35 Hz, which is the intersection of the broken line S and the broken line C, and the resonant frequency of the port resonance system is approximately 40 Hz, which is the intersection of the broken line d and the broken line e.

In FIG. 9(b), the solid line g is the output terminal voltage of the negative impedance generating circuit 52, the broken line is the output sound pressure characteristic of the resonant radiation sound from the port resonance system, and the broken line i is the direct radiation from the unit resonance system. Acoustic output sound pressure characteristics and solid line j
is a composite of the broken line 1 and the broken line i, and shows the overall output sound pressure characteristics of the speaker system. The output terminal voltage (2) is determined by the following formula: V=Zbe/(zL+-Zo) (3). Therefore, if -20 and ZL are the pure resistances -Ro (=-7Ω) and RL, respectively, the voltage V is V=8V when RL=8Ω, and V=4.5V when R+ and =9Ω.
,... and so on.

FIG. 9(C) shows that the f-characteristic correction circuit 51 of the drive circuit 50 increases or decreases the input terminal e of the negative impedance generation circuit 52 according to the frequency, and corrects the output voltage of the circuit 52 as indicated by the solid line g°. By this, 50 as shown by the solid line J°
This shows that flat output sound pressure characteristics can be obtained above Hz. In the figure, the broken line shows the output power (W) characteristic of the amplifier 53 (that is, the negative impedance generating circuit 52) when flattening the output sound pressure characteristic.

In the electronic musical instrument shown in FIG. 1, the port resonance frequencies of the speaker systems in the left and right two-channel audio equipment are set to 50 Hz and 60 Hz, which are different from each other. In this way, the overall frequency response of the left and right speaker systems is such that the output sound pressure characteristic from the right speaker system, which is flat at 60 Hz or higher, is complemented by the sound pressure characteristic that has a peak at 50 Hz from the resonance port of the left speaker. With this shape, the -like reproduction band can be extended to the low frequency side. Of course, by appropriately setting the characteristics of the f-characteristic correction circuit 51, the low frequency side of the uniform playback band can be adjusted to 50Hz only for the right channel.
Although it is possible to extend it to
As shown by the broken line k in c), it is necessary to increase the output power of the amplifier 53 near the port resonance frequency. Looking at the figure, in order to extend the low frequency side of the −-like reproduction frequency by 10 Hz, an amplifier 53 whose output power is 6 dB (4 times) larger is required. In particular, in electronic musical instruments, the size of the amplifier 53 needs to be considered in terms of continuous rating, considering the case where keys are held down continuously.If the normal output is the same, it is necessary to consider the size of the amplifier 53 in terms of intermittent or instantaneous maximum output. A power amplifier with several times the output is required compared to an audio amplifier that only requires a power amplifier. Increasing the output even further in order to flatten the frequency characteristics is extremely burdensome in terms of circuit design. Therefore, in this embodiment, the left side port resonance frequency is set to 50Hz, which is 10Hz lower than the right side, and this 50Hz
The output sound pressure having a frequency around Hz is mainly radiated from the resonance port of the left speaker system to reduce the burden on the right drive circuit 50. Similarly, sound around 60 Hz is mainly radiated from the resonance port of the right speaker system, thereby reducing the burden on the left driver circuit 50.

In the low frequency range of several tens of Hz or less, the wavelength is several meters or more, so the directivity of the sound is weak, and it hardly matters whether the sound is radiated from the left or right channel. In other words, in the low frequency region, even if sounds with different sound pressures are emitted from the left and right sides as described above, problems such as localization of sound images hardly occur.

In this example, as a result of extending the output sound pressure characteristics of the acoustic device to lower frequencies, the low-pitched piano sound and the like became rather muffled and different from the actual tone. Therefore, here, the sound quality is adjusted by reducing or removing the fundamental wave component in the sound source.

FIG. 10 shows the basic configuration of a negative impedance generating circuit 52 for driving the camera with negative impedance.

The circuit shown in the figure applies the output of an amplifier 53 with a gain of A to a load ZL by a speaker system. And this load ZL
A feedback circuit 54 with a transfer gain β detects the current flowing in the
It is positively fed back to the amplifier circuit 53 via. In this way, the output impedance Z0 of the circuit is Zo = Zs (1-A β) ・−・・−
... It is obtained as (4). From this equation (4), A
If β>1, Zo becomes an open stable negative impedance. Here, Zs is the impedance of a sensor that detects current.

Therefore, in the circuit shown in FIG. 10, by appropriately selecting the type of impedance Z5, a desired negative impedance component can be included in the output impedance. For example, the current ■, the impedance ZS
When detecting by the voltage across the impedance Z
If , is the resistance R8, the negative impedance component becomes a negative resistance component, which is an inductance, then becomes a negative inductance component, and if the capacitance CS becomes a negative capacitance. Further, an integrator is used in the feedback circuit 54, and the inductance L5 as the impedance ZS is
By integrating and detecting the voltage across the capacitance C8, the negative impedance component can be made into a negative resistance component. Furthermore, using a differentiator in the feedback circuit 54, the voltage across the capacitance C8 as the impedance Z3 is differentiated and detected. However, the negative impedance component becomes a negative to resistance component.

As the current detection sensor, in addition to these impedance elements R5, L, Cs, etc., it is also possible to use a current probe such as C, T, or a Hall element.

A concrete example corresponding to such a circuit is, for example,
-51771 etc.

Furthermore, it is also possible to perform current detection on the non-grounded side of the speaker unit 4. A specific example of such a circuit is shown in, for example, Japanese Patent Publication No. 54-33704. 11th
The figure is an example of BTL connection, and it is easy to apply it to the circuit of FIG. 10. 56 in FIG. 11 is an inverting circuit.

FIG. 12 shows a specific circuit example of an amplifier including a negative resistance component in its output impedance.

The output impedance Zo in the amplifier shown in FIG. 12 is as follows: Zo = Rs (I Rb / Ra ) = 0.2
2 (1-30/1..6) = -3.9 (Ω).

[Modifications of Embodiments] Note that the present invention is not limited to the embodiments described above, and can be implemented with appropriate modifications.

For example, the driving circuit may be one that drives the vibrating body so as to cancel out the reaction from the surroundings when driving the resonator, and may be used in addition to the negative impedance generating circuit.
A so-called MFB circuit as disclosed in Japanese Patent No. 31156 can be used.

Furthermore, by giving the output impedance a frequency characteristic, the Qo can be improved. YaQ. It improves the degree of freedom in setting parameters such as P, characteristics, especially resonance frequency f. It is also possible to adjust the output sound pressure characteristics near C and fOP, and to suppress an increase in distortion rate due to nonlinearity of the voice coil inductance component in high frequencies.

Furthermore, the tube resonance sound may be removed by outputting the output of the resonance port through a mechanical acoustic filter. In this case, as shown in FIG. 13(a), one filter is used for the left and right channels. By sharing the so-called 3
A D (three dimension) system may be configured. In addition, in this case, the left and right resonance ports 18a
By making the lengths of and 18b different, it is also possible to make the frequencies of port resonance different on the left and right sides. The mechanical filter may be of any type, band-pass, band-eliminate, or low-pass, as long as it passes port resonance sound and blocks tube resonance sound, and its structure does not matter. ) or (C) can be used. FIG. 13(b) shows an opening 91 provided in the box 7c, which acts as a low-pass filter that passes only frequencies lower than the tube resonance sound.

FIG. 13(b) shows a case in which a passive vibrating body 92 such as a drone cone is provided on the box body 7c, which acts as a band pass filter that passes only the band including the port resonance sound.

The resonance ports 18a, 18b may be housed inside the box body 7a, 7b, or 7c with the capacity shown in FIG. 4 or 5, in which case the entire system can be configured more compactly.

[Brief explanation of the drawing]

1 is a perspective view showing the external appearance of an electronic musical instrument according to an embodiment of the present invention; FIG. 2 is a sectional view taken along line A-A in FIG. 1; and FIG. 4(a) and 4(b) are top and right side views of the box body in FIG. 1, and FIG. 5 shows the basic configuration of the electronic musical instrument in FIG. 1. 6 is an electrical equivalent circuit diagram of the acoustic devices shown in FIGS. 1 and 5, and FIG. 7 is a frequency characteristic of the sound pressure of the sound emitted from the acoustic devices shown in FIGS. 1 and 5. 8 is an equivalent circuit diagram when Zv Zo=0 in FIG. Figures 10 and 11 are basic circuit diagrams of circuits that generate negative impedance, Figure 12 is a specific circuit diagram of negative resistance drive, and Figures 13 (a), (b), and (c) are , a configuration diagram of a 3D system according to another embodiment of the present invention,
FIG. 14 is a perspective view showing the external appearance of an electronic musical instrument incorporating an acoustic device that drives a conventional bass reflex speaker system at a constant voltage. 1: Shelf board, 3: Keyboard, 4a, 4b speaker unit, 5a, 5b: Speaker mounting stand, 7: Cabinet (box body), 12a, 12b: Felt, 18: Resonance port, 4]: Cutting plate , 50: Drive circuit, 52: Negative impedance generation circuit.

Claims (1)

[Claims] (1) An electronic musical instrument comprising a keyboard, a sound source that generates a musical sound signal based on key press operations on the keyboard, and two sound systems that convert the musical sound signal into sound and radiate the sound system, are arranged on a box body and a resonance port constituting a Helmholtz resonator, respectively, and on the outer wall of the box body, drive the Helmholtz resonator on one side of the vibrating body, and directly radiate sound from the other side. an electroacoustic transducer that drives the transducer so as to cancel an atmospheric reaction from the Helmholtz resonator to the vibrating body, and the resonant frequency of the Helmholtz resonator corresponds to two sets of sounds. An electronic musical instrument characterized by different systems.