JP2001519637A - Improved low frequency converter enclosure - Google Patents

Abstract

(57) [Abstract] The acoustic transducer enclosure (10) is acoustically coupled to the electro-acoustic transducer (70) to allow all emitted sound to pass through the acoustic lever (80). Hold the lever (80).

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION The present invention relates to improving the efficiency of acoustic transducer enclosure procedures and methods.

Description of the Prior Art The design of transducer enclosures for acoustic loudspeaker reproduction is a highly developed science. The past technology of their design dates back nearly 100 years and there have already been many recent advances in this area. The basic design methodology is described in Novak's “Performance of Enc.
losure for Low Resonance High Compliance Loudspeakers), Thiele's "Loudspeakers in Vented Boxes" Part I and
II, Small's "Vented-Box Loudspeakers System"
Systems), Part I, II, III and IV, and the classic study of Geddes's “An introduction to Bandpass Loudspeakers Enclosures”. All of these papers are Audio Engineering So
ciety, found in a selection of loudspeakers available from New York and New York. The references incorporated in those studies cover most of the latest state of the art in the design of commercial loudspeaker enclosures.

[0003] A recent trend has been toward the bandpass version of the encircling stem from the desire to produce more power with less energy, ie, with improved efficiency. By tuning a single or multiple resonant acoustic systems, the loading provided to the loudspeakers can be increased with a corresponding increase in efficiency. According to the rule of thumb of these designs, the narrower the bandwidth of the frequency band pass device, the higher the acoustic gain and the greater the efficiency. It is stated that high efficiency, low bandwidth or low efficiency, high bandwidth limitations sometimes require that the effective bandwidth result for a frequency bandpass loudspeaker system be kept constant. This is not strictly mathematically accurate, but in practice it is.

[0004] It is highly desirable to increase the acoustic load applied to the loudspeakers, but without having to correspondingly reduce the frequency bandwidth of the final system.

[0005] Another new attempt to increase the radiation efficiency was made by the 1981 "U-Haloud speaker.
(Woofer Loudspeaker), patent No. 4,301,332 by Dusanek's inventor. In this patent, the "inner and outer passive speaker cones" are such that the rear of the loudspeaker is such that the outer radiation cone is larger than the inner cone.
Attached to. An example of this patent is shown in FIG. A mechanical amplification of the vibrations of the loudspeaker cone is created as a result. The inventor claims thereby "the combination of lower frequency response and higher efficiency from a small outer box". Although the frequency response of the device may be low, the design cannot increase the efficiency of the frequency passband. This is because the larger cone movement of the passive radiator will increase sound emission only within a very narrow range of frequencies around the box resonance. Below this resonance, the forward and backward radiation cancel each other (as in any port enclosure) and what is the difference in radiation efficiency that might otherwise have been caused by mechanical amplification. It will also make no gain. Above resonance, the passive radiator will be disconnected from the loudspeaker, and the frequency passband efficiency of the device must maintain that of the direct radiator. At resonance, the increase in efficiency is evident, and this improved efficiency can only be exploited by tuning the box lower than in the other case. Dusanek did not realize that all of the radiated sound had to pass through a two-cone mechanical amplifier to be truly efficient. This design has never been commercialized.

[0006] Other forms of mechanical advantage have also been tried. Niewendijk et al. (1985), in US Pat. No. 4,547,631, disclosed the use of an older voice coil and a mechanical arm acting as a lever between a sieve. The ideal is to create a large volume displacement of the radiating surface from very little movement of the voice coil or other drive motor. The disadvantage of this design is that it is very complicated to design and manufacture, and there is a major question of reliability. This design was never commercialized.

[0007] A similar (identical?) Design to that of Dusanek is described by Clarke in Patent 4,076,097, "Augmented Passive Loudspeaker System."
-Radiator Loudspeaker System) "(1979). In this invention, too, the two cone units are mounted at the rear of the freely radiating drive, but the sound energy is directed to the connection between the cones of the two passive radiators. An example of this patent is shown in FIG. The inventor states that this new design provides improved responsiveness over standard passive radiator designs because the net compliance of the passive radiator can be controlled by adding a second box. Complain about what you do. This "improvement" is of little importance since any effect of passive radiator compliance will occur below resonance where the sound power is negligible. In fact,
The compliance of the passive radiator is not very important and its control is of little importance. This design was never commercialized.

In the direction of achieving pure acoustics of frequency bandpass devices, there are several patents for a number of duct and enclosure shapes, all aiming for improved efficiency. Each of these methods of achieving sound suffers from the tradeoff between efficiency and frequency bandwidth described above. While some are very effective in terms of power and structure, it would still be desirable to improve their design without reducing the frequency bandwidth and in a manner that is easier to assemble.

SUMMARY OF THE INVENTION The present invention provides a novel use of "acoustic levers". An acoustic lever is a mechanical device composed of two rigid surfaces that are rigidly joined together and held flexibly so that they can vibrate along a single line. I have. The two surfaces have protrusions on a plane perpendicular to the axis of vibration, with an area called the driven or radiating surface. Acoustic levers can consist of two standard loudspeaker cones with an outer retaining elastic part. The two cones, placed vertex-to-vertex, are glued together and mounted in the enclosure by gluing the outer ends of the retaining resilient portions. In this way, the two cones will oscillate freely along their common axis. This device is referred to as acoustic for the purposes of this document. By this definition, Dusanek and Clarke have used acoustic levers in their invention, but in a completely different structure than described here.

When the acoustic lever is acoustically joined to the electro-acoustic transducer by a method of passing all emitted sound through the acoustic lever, ie, by passing acoustically continuously, then the result is The resulting device allows the radiated volume velocity of the transducer to be increased many times through the operating frequency bandpass of the device. As a result, the efficiency of the combination of transducer enclosures is significantly increased when compared to the same transducer without leverage.

The novel transducer enclosure can also be assembled using two acoustic levers, each located on each side of the electro-acoustic transducer, the electro-acoustic transducer having a radiant of this design. The sound output will be further enhanced. This one could be replaced with a standard duct or passive radiator device to provide more flexibility in the design.

The acoustic lever design will also reduce the distortion radiated from the transducer.

Description of the Preferred Embodiment A preferred embodiment of the enclosing box of the present invention is shown in FIGS. The outer enclosure 10 has at least three internal chambers, an acoustic lever chamber 20, an acoustic lever-electro-acoustic transducer coupling chamber 30, and a tightly sealed enclosure by an electro-acoustic transducer partition 50 and an internal lever transducer partition 60. It is divided into an electroacoustic transducer rear chamber 40. The outer box and inner partition are of standard construction. Since the standard configuration of the electro-acoustic transducer 70 is firmly attached to the partition 50, there is only negligible airflow between the chambers 40 and 70.

Acoustic levers 80 are mounted with their radiating surfaces 8l along their flexible frame 82, they are mounted on one of the outer walls of the enclosure 10 without gaps,
Further, the driven surface 85 is attached to the partition 60 along the flexible frame 86 without any gap. The two flexible frames 82 and 86 work simultaneously to achieve a single acoustic lever compliance.

Referring to FIG. 4, transducer 70 is energized by connecting its motor through wire 95 to an amplifier (not shown). In this manner, acoustic energy from the transducer is introduced into the chamber 30. The sound pressure resulting from this acoustic energy acts on the driven surface 85 facing the transducer. This action causes the lever 80 to be displaced by a value approximately equal to the ratio of the radiating surface of the transducer to the driven surface acoustically multiplied by the displacement of the cone of the transducer. That is, Xd is the surface Ad
X1 = (Ad / A1) Xd where X1 is the displacement of the driven surface with X1 being a sound having the surface A1.

Since the acoustic lever moves integrally, the displacement of the radiation surface of the acoustic lever also becomes X1. The emission surface A2 faces the outer fluid medium. The volume (area multiplied by the amount of displacement) V2 of the air displaced by the acoustic lever emission surface is: V2 = A2 / X1 = A2 (Ad / A1) Xd = (A2 / A1) Ad / Xd = (A
2 / A1) Vd. Here, Vd is the volume of air displaced by the transducer. If the radiating surface is wider than the driven surface, the volume velocity of the air radiated by the acoustic lever will increase to the ratio of its radiating surface to the driven surface of the acoustic lever, rather than that of the transducer. This conversion of radiation volume velocity is very similar to the function of a transformer in electrical terms or leverage in mechanical terms. Therefore it is the name of sound.

As an example of the above relationship, consider an acoustic lever consisting of two cones, where the driven side is 2
It is assumed that the surface is assumed to be 00 square centimeters, and the emission side is assumed to be 400 square centimeters. From the above equation, it can be seen that the displacement of the emitted air volume is twice the displacement of the air volume of the cone of the electroacoustic transducer. This means that the volume velocity of the radiated air is also twice the volume velocity of the air radiated from the electro-acoustic transducer, and the sound pressure level (SPL) generated by this sound emission is an acoustic lever. Means that it increases to about 6 dB.

The relations derived above do not apply to all frequencies. At frequencies higher than the resonance frequency defined by the volume of the chamber 30 and the acoustic mass of the lever 80, the amplification effect will disappear and the emitted sound will decrease. This roll-off can be made steeper, if desired, by making the connection between the radiating surface and the driven surface of the leverage 80 flexible rather than rigid. The volume of the chamber 30 and / or the acoustic mass of the lever 80 can be determined from the relationship and the desired high operating frequency.

The chamber 20 acts acoustically to reduce this compliance. The acoustic compliance of the chamber 20 adds (in parallel) to the acoustic lever compliance to form a single massed compliance for this component. In most designs, this compliance is assumed to be high enough that the compliance created by the acoustic lever and the resonance caused by its physical mass is well below the operating frequency bandwidth of the desired device. . This can always be done by increasing the volume of the chamber 20, and by increasing the acoustic mass of the acoustic lever 80, and / or by increasing the acoustic lever compliance. In fact, if the bulk of the compliance is not small compared to the combined compliance of the transducer 70 and the chamber 40, the bulk of the acoustic lever will have little effect on the performance of the device. If the compliance of the chunk of acoustic levers is not of sufficient magnitude, this will result in the device being out of tune and reducing its overall efficiency, mainly at low frequencies. This detuning can be partially compensated for by changing the adjustments of the other components of the device.

The apparent acoustic compliance physically applied by the chamber 20 results in the standard acoustic compliance of this volume of air, but is affected by the acoustic lever as the difference between the estimated areas of the surfaces 81 and 85. This is because the acoustic levers move in opposite directions with respect to the volume between them.

The above equation for the net gain at the acoustically radiated volume velocity gives an infinite increase in gain by increasing the ratio of the acoustic lever surface, that is, the ratio of its driven surface to the acoustic lever slope. Predict that you can. The above description of lump acoustic lever compliance indicates that there is a practical upper limit on amplification. The apparent acoustic compliance of the chamber 20 and the acoustic leverage will both decrease when attempting to increase the acoustic gain by increasing the ratio of the acoustic leverage. The bulk of the lump acoustic lever eventually becomes very small, limiting the effective gain at a faster rate than increasing the gain by increasing the ratio of the acoustic leverage.

Good results have been obtained with acoustic levers whose radiating surface is somewhat wider than the radiating surface of the transducer and whose driven surface is somewhat narrower than the driven surface of the transducer. A radiating surface approximately 1.4 times the radiating surface of the transducer and a driven surface approximately 0.7 times the driven surface of the converter provide a theoretical increase in volume velocity of 2 and a radiated pressure of 6 dB. Generate improvement. The result of these structural parameters is that the sound has a face that is not very different from that of the electro-acoustic transducer, facilitating easy configuration and producing a stunning 6 dB increased output.

Referring now in detail to FIG. 5, the chart shown therein illustrates the theoretical improvement in emitted pressure expected from the present invention. This figure shows a typical frequency bandpass tuning of the fourth order variation with a Q of about 0.7 (as described in the inventor's paper "Overview of Bandpass Loudspeaker Devices") (lower side). And the encircling device using acoustic levers (upper curve). The transducer and the enclosed volume in this figure are kept constant. The particular design of the acoustic lever shown in FIG. 5 is such that when the transducer 70 is placed in the chamber 40, the acoustic mass of the lever 80 and the volume of the chamber 30 are adjusted to resonate at the resonant frequency of the transducer 70. It operates in a frequency bandpass mode. The acoustic mass of the lever is 1.414 of the acoustic mass of the transducer.
Make it double. This adjustment is the same as that described in the inventor's article above, except that a lump of acoustic lever was ignored here. This is valid as long as the compliance is not too small, as described above. The acoustic mass of an acoustic lever is its moving mass divided by its radiation area.

In general, all the designs described in the inventor's paper "Frequency Bandpass" are applicable here, and through the use of acoustic levers opposed to the "ports" described in that paper. A substantial improvement in output can be obtained. This is true so long as the compliance of the acoustic leverage is not too small as described above.

Referring now in detail to FIG. 6, the perspective view shown therein emphasizes another aspect of the present invention. The enclosure 100 of the two acoustic lever devices is provided by an internal acoustic lever partition 140 and an electro-acoustic transducer partition 50 by a front acoustic lever-electroacoustic transducer coupling chamber 11.
0, rear acoustic lever-electroacoustic transducer coupling chamber 120 and acoustic lever chamber
It is divided into 30. Forward acoustic lever 150 is applied to transducer 7 through chamber 110.
0 to the front part. Rear acoustic lever 160 is coupled to the rear portion of transducer 70 through chamber 120. An acoustic lever isolation partition 145 may be required in chamber 130 to prevent interference between levers 150 and 160. The partition is not shown in this perspective view, but is shown in the cross-sectional view of FIG. In this way, the radiation output can be further increased using both radiation sides of the converter 70.

Determining the exact volume of the chambers 110 and 120 and the exact acoustic mass of the levers 160 and 150 is based on the sixth-order asymmetry described in the inventor's paper, "Introduction to Frequency Bandpass Enclosure Design." This is done along a line similar to the design of the frequency band pass enclosure. This is also true, as mentioned above, as long as the compliance of the lumps is not too small.

In some cases, it is undesirable to use two acoustic levers due to phase interference effects. The problem is to use an acoustic duct 170, especially a hollow tube of standard construction, sometimes used in a "ported" loudspeaker enclosure, such as the acoustic mass during low frequency box resonance tuning. Can be avoided. When this is done, an improved frequency passband effect can be obtained without reducing the low frequency output that would result from phase interference when using two acoustic levers. This structure is shown in FIG.

In any of the designs disclosed herein, an effective acoustic lever may be comprised of three or more acoustic levers. In this case, the sum of the individual acoustic masses of the levers is one effective acoustic mass used in the design. These multiple levers facilitate other structures and guiding responses for the device, and also reflect the freedom in other designs.

It should be noted that in the present invention, the fluid medium acting between the transducer and the acoustic bar can be any fluid material including air, gas or liquid. In some cases, using a liquid as the binding medium is advantageous because of its incompressible nature. This allows for a much wider device frequency bandwidth than would be possible with a compressible medium such as air. This feature is useful, for example, in devices where two or more transducers cannot be used due to space constraints. Examples of such devices are hearing aid converters and earphone converters.

A further feature of the present invention is to reduce acoustic distortion of the device. It is a well-known effect of nonlinear distortion in transducers that the diaphragm exhibits a static displacement due to the asymmetric nonlinearity, thereby moving the cone to a region of higher nonlinearity. This quiescent force is countered by the stiffness of the device seen at the transducer at zero frequency. In a transducer device that uses air as the acoustic mass, such as a port, the stiffness of the device at frequency 0 is simply the stiffness of the transducer diaphragm support. When an acoustic lever is used, the frequency 0 stiffness against static forces is sufficiently high for acoustic leverage. Thus, the diaphragm is less displaced from the quiescent force and the net distortion of the device is reduced.

[0031] Other novel and unique modifications to the above will be apparent to those skilled in the art.

The present invention is as described in the claims.

[Brief description of the drawings]

FIG. 1 is a diagram of a preferred embodiment of Dubenek's prior art.

FIG. 2 is a diagram of a preferred embodiment of Clarke's prior art.

FIG. 3 is a perspective view of a novel enclosure using one acoustic lever.

FIG. 4 is a cross-sectional view of the converter enclosure seen from the direction of 4-4 in FIG.

FIG. 5 is a comparison of the frequency response of a standard frequency bandpass enclosure design with a new design incorporating acoustic levers.

FIG. 6 is a perspective view of a novel enclosure design incorporating two acoustic levers.

FIG. 7 is a cross-sectional view of the converter enclosure as viewed from 7-7 in FIG.

FIG. 8 is a cross-sectional view of a transducer enclosure with a front chamber (low frequency tuned) acoustic mass performed by a duct.

[Explanation of symbols]

 Reference Signs List 10 apparatus enclosure 20 acoustic lever chamber 25 acoustic lever-electroacoustic transducer coupling chamber 40 electroacoustic transducer rear chamber volume 50 electroacoustic transducer partition 60 internal acoustic lever partition 70 electroacoustic transducer 80 acoustic lever 81 acoustic lever emission surface 82 Acoustic lever radiating surface flexible support 85 Acoustic lever driven surface 86 Acoustic lever driven surface flexible support 95 Electroacoustic transducer biasing wire 100 Two acoustic lever enclosures 110 Front acoustic lever-electroacoustic transducer coupling chamber 120 Back acoustic lever Electroacoustic transducer coupling chamber 130 acoustic lever chamber 140 internal acoustic lever partition 150 forward acoustic lever 160 rear acoustic lever 170 acoustic duct

Claims (11)

[Claims] 1. An enclosure containing an acoustic transducer, comprising: an outer rigid framework having at least two internal baffles partitioning the interior into at least three chambers; and an active mount attached to one of said internal baffles. An enclosure comprising: a passive acoustic transducer; and a passive acoustic lever coupled between at least one of the internal baffles and the outside of the enclosure. 2. The enclosure of claim 1, wherein the enclosure includes two internal baffles that partition an internal enclosed space into three internal chambers, wherein the acoustic transducer is mounted on one of the internal baffles; Further, the passive acoustic lever is an enclosure coupled between the inner baffle and the outside of the enclosure. 3. The enclosure of claim 2 wherein said acoustic lever is mounted such that only one side of said acoustic lever assigns a common chamber to said acoustic transducer. 4. The enclosure of claim 2, wherein said acoustic lever is mounted such that both sides of said acoustic lever assign a common chamber to said acoustic transducer. 5. An enclosure containing an acoustic transducer, an outer rigid framework including at least two internal baffles partitioning the interior into at least three internal chambers, and a sound mounted on one of said internal baffles. An enclosure comprising: a transducer; and at least two passive acoustic lever means mounted between the inner baffle and the outer side of the enclosure. 6. The enclosure of claim 5, wherein the passive acoustic lever has only one of the surfaces of the lever shared by the interior chamber containing the acoustic transducer. 7. The enclosure of claim 6, further comprising an internal baffle between said chambers containing said acoustic lever. 8. The enclosure according to claim 5, wherein said passive acoustic lever has both surfaces of said lever common to said interior chamber containing said acoustic transducer. 9. The enclosure of claim 1, further comprising a port including a passive diaphragm or an acoustic duct attached to said partition between said internal chambers. 10. The enclosure of claim 1, further comprising a port including a passive diaphragm or acoustic duct mounted between said interior chamber and an exterior of said enclosure. 11. The enclosure of claim 10, further comprising a port including a passive diaphragm or an acoustic duct attached to said partition between said internal chambers.