Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
  • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
  • H04R1/28—Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means
  • H04R1/2807—Enclosures comprising vibrating or resonating arrangements
  • H04R1/2838—Enclosures comprising vibrating or resonating arrangements of the bandpass type
  • H04R1/2842—Enclosures comprising vibrating or resonating arrangements of the bandpass type for loudspeaker transducers

Definitions

• the present invention relates to acoustical transducer enclosure methodologies and ways to improve their efficiency.
• Transducer enclosure design for audio loudspeaker reproduction is a highly evolved science.
• the art of these designs goes back nearly one hundred years and yet there have been numerous recent advances in this art.
• the basic design methodologies are well described in the classical works of Novak "Performance of Enclosures for Low Resonance High Compliance Loudspeakers", Thiele “Loudspeakers in Vented Boxes” Parts I and II, Small “Vented-Box Loudspeaker Systems” Parts I, II, III, and IV, and Geddes "An Introduction to Bandpass Loudspeaker Enclosures". All of these articles can be found in the Loudspeaker Anthology series available from the Audio Engineering Society, New York, NY. A combined reference to these works would encompass most of the current state-of-the-art in commercial loudspeaker enclosure design.
• the frequency response of the system may be lower, but the efficiency in the passband cannot be increased with this design. This is because the larger cone motion of the passive radiator will increase the sound radiation only in a very narrow range of frequencies around box resonance. Below this resonance the front and rear radiation will cancel one another (as in any ported enclosure) defeating any gains in radiation efficiency that might otherwise have been produced by a mechanical amplifier. Above resonance a passive radiator becomes decoupled from the loudspeaker and the pass band efficiency of the system must remain that of the direct radiator. At resonance an increase in efficiency will be evident and this improved efficiency can be utilized only by tuning the box lower than otherwise would be the case. Dusanek failed to realize that to be truly effective all of the radiating sound must be directed through the dual cone mechanical amplifier. This design has never seen commercial implementation.
• An acoustic lever is a mechanical device constructed of two rigid surfaces rigidly coupled together and compliantly supported so as to allow motion along a line. The two surfaces have projections onto a plane perpendicular to the axis of motion with areas denoted as the driven area or the radiating area.
• An acoustic lever can be constructed from two standard loudspeaker cones with their attached outside supporting compliances. Placed apex to apex the two cones are glued together and mounted in an enclosure by gluing the supporting compliance at its outside edge. In this way the two cones will be free to move along their common axis.
• This device will be called an acoustic lever for purposes of this document.
• both Dusanek and Clarke used acoustic levers in their inventions, although in completely different configurations than those described herein.
• an acoustic lever When an acoustic lever is acoustically coupled to an electro-acoustic transducer in a manner which forces all radiated sound go through the acoustic lever, i.e. acoustically in series, then the resulting system can be made to cause a many-fold increase in the radiated volume velocity of the transducer, throughout the operating pass band of the system. This results in a significant increase in the efficiency of the transducer enclosure combination when compared to the same transducer used without the lever.
• a novel transducer enclosure can also be assembled by utilizing two acoustic levers, one on each side of the electro-acoustic transducer which will further enhance the radiated sound output of this design.
• One of the levers can be replaced by a standard duct or passive radiator system for even more design flexibility.
• FIGURE 1 shows a drawing of the preferred embodiment of the prior art of Dubenek
• FIGURE 2 shows a drawing of the preferred embodiment of the prior art of Clarke
• FIGURE 3 is a perspective view of the novel enclosure utilizing a single acoustic lever
• FIGURE 4 is a cross sectional view of the transducer enclosure shown in FIG. 3 as taken in the direction of 4 - 4 thereof;
• FIGURE 5 shows a frequency response comparison of a standard bandpass enclosure design and the novel design incorporating an acoustic lever
• FIGURE 6 shows a perspective view of the novel enclosure design which incorporates two acoustic levers
• FIGURE 7 shows a cross sectional view of the transducer enclosure shown in FIG 6 as taken in the direction of 7 - 7 thereof; and
• FIGURE 8 shows a cross sectional view of a transducer enclosure with the front chamber (lower frequency tuning) acoustical mass implemented with a duct.
• An external enclosure 10 is subdivided into at least three internal chambers; an acoustic lever chamber 20, an acoustic lever to electro-acoustic transducer coupling chamber 30 and a rigid closed electro-acoustic transducer rear chamber
• electro-acoustic transducer partition 50 by electro-acoustic transducer partition 50 and an interior acoustic lever partition 60.
• the enclosure and the internal partitions are of standard construction.
• An electro-acoustic transducer 70 of standard construction, is securely attached to partition 50 and sealed so that negligible air flow exists between chamber 40 and chamber 70.
• An acoustic lever 80 is mounted such that it has its radiating surface 81 along with its compliant surround 82 are sealingly mounted in one exterior wall of enclosure 10 and its driven surface 85 along with its compliant surround 86 are sealingly mounted on partition 60.
• the two compliant surrounds, 82 and 86 will act together to create a single acoustic lever compliance.
• transducer 70 is energized by connecting its motor to an amplifier (not shown) via wires 95. In this manner acoustic energy from the transducer is introduced into chamber 30. The sound pressure that results from this acoustic energy acts on the driven area of the lever 85, which faces the transducer. Lever 80 will be displaced by this action in an amount that is substantially equal to the ratio of the transducer radiating area to the driven area of the acoustic lever multiplied by the transducers cone displacement. That is, if X ⁇ j is the displacement of a transducer having area Ad and Xi is the displacement of the driven surface of an acoustic lever having area A then:
• An acoustic lever moves as a unit and thus the displacement of the radiating area of the acoustic lever is also x- ⁇ .
• the radiating area, A 2 faces the exterior fluid medium.
• the volume of air displaced (displacement times area) by the radiating area of the acoustic lever, V 2 will be:
• V d is the volume of air displaced by the transducer. If the radiating area is greater than the driven area then the volume velocity of air radiated by the acoustic lever will be greater than that of the transducer by the ratio of the acoustic levers radiating area to its driven area. This transformation of radiating 5 volume velocity is very similar to the function of a transformer in electrical terms or a lever in mechanical terms. Hence the name acoustic lever.
• the driven side is constructed with a projected area of 200 cm 2 and the radiating side is constructed with a projected area of 400 cm 2 .
• the radiated volume displacement will be twice that of the electro-acoustic transducers cone displacement.
• the radiated volume velocity will also be twice that of the electro-acoustic transducer and that the Sound Pressure Level (SPL) resulting from this sound radiation will be increased by approximately 6 dB as a result of the presence of 5 the acoustic lever.
• SPL Sound Pressure Level
• Chamber 20 will act so as to decrease the compliance of the acoustic lever.
• the acoustic compliance of chamber 20 will add (in parallel) to the acoustic lever compliance to form a single lumped compliance for this component. In most designs this compliance is assumed to be high enough so that the resonance created by the lumped compliance of the acoustic lever and its physical mass is well below the operating bandwidth of the desired system. This can always be made to be the case by making the volume of chamber 20 larger, the acoustic mass of lever 80 larger and/or by increasing the acoustic lever compliance. In practice the lumped acoustic lever will not effect the system performance to a large extent unless this lumped compliance becomes small compared to the combined compliance of transducer 70 and chamber 40.
• the result will be a de-tuning of the system, lowering its overall efficiency, primarily at the lower frequencies.
• This de-tuning can, to a certain extent, be compensated for by changes in the tuning of the other components of the system.
• the apparent acoustic compliance added by chamber 20 will be the normal acoustic compliance of this volume of air but acted upon by the acoustic lever as the difference in the projected areas of surfaces 81 and 85, since the two surfaces of the acoustic lever move in opposite directions relative to the volume between them.
• the above equation for the net gain in acoustically radiated volume velocity predicts that the gain can be increased indefinitely by increasing acoustic lever surface ratio, the ratio of the driven area of the acoustic lever to its radiating area.
• the above discussion regarding the lumped acoustic lever compliance indicates that there will be a practical upper limit to this amplification.
• the apparent acoustic compliance of chamber 20 and the acoustic lever compliance will both decrease as one attempts to increase the acoustical gain by increasing the acoustic lever surface ratio.
• the lumped acoustic lever compliance will eventually become so small as to limit the effective gain at a rate faster than the gain is increased by increasing acoustic lever surface ratio.
• FIG. 5 a chart is illustrated which shows the theoretical improvement in radiated pressure that is to be expected from my invention.
• This figure compares a standard bandpass tuning of the fourth order variety with a Q of about .7 (as described in my paper "An Introduction to Bandpass Loudspeaker Systems")(lower curve) with an enclosure system utilizing an acoustic lever (upper curve).
• the transducer and enclosure volumes in this figure have been held constant.
• the specific design of the acoustic lever shown in FIG. 5 operates in a bandpass mode wherein the acoustic mass of lever 80 and the volume of the chamber 30 are adjusted so as to resonant at the resonance frequency of transducer 70 when placed in chamber 40.
• the acoustic mass of the lever is made to be 1.414 times the acoustic mass of the transducer. This alignment is identical to that discussed in my paper above except that here the lumped acoustical lever has been ignored. This is valid so long as this compliance is not too small, as described above.
• the acoustic mass of the acoustic lever is its moving mass divided by its radiating area.
• Dual acoustic lever system enclosure 100 is partitioned into front acoustic lever to electro-acoustic transducer coupling chamber 110, rear acoustic lever to electro-acoustic transducer coupling chamber 120 and acoustic lever chamber 130 by interior acoustic lever partition 140 and electro-acoustic transducer partition 50.
• Front acoustic lever 150 is coupled to the front of transducer 70 through chamber 110.
• Rear acoustic lever 160 is coupled to the rear of transducer 70 through chamber 120.
• An acoustic lever separating partition 145 in chamber 130 may be required to avoid interference between levers 150 and 160. This partition is not shown in the perspective view but is shown in the cross sectional view of FIG. 7. In this manner both radiating sides of transducer 70 can be utilized for an even greater increase in radiated output.
• the effective acoustic lever can be made up of several acoustic levers. In this case the sum of the acoustic masses of the individual levers would yield a single effective acoustic mass to be used in the design. These multiple levers would facilitate alternative constructions and polar responses for the system and reflect yet another design degree of freedom.
• the fluid medium acting between the transducer and the acoustic lever can be any fluid substance including air, a gas or a liquid.
• the use of liquid as the coupling medium will be advantageous due to its incompressible nature. This would allow for a much wider bandwidth of the device than would otherwise be possible if a more compressible fluid, such as air, were used.
• This feature would be useful, for example, in an application where it is impractical to use more than a single transducer because of space issues. Examples of this type of application are hearing aid transducers and earphone transducers. It is a further feature of my invention that the acoustic distortion of the system would be lowered. It is a well known effect of nonlinear distortion in transducers that a non-symmetric noniinearity will cause the diaphragm to exhibit a static displacement, thus moving the cone into regions of even higher non- linearity. This static force is opposed by the system stiffness seen by the transducer at zero frequency.
• the zero frequency stiffness of the system is simply that of the transducer diaphragm support.
• the zero frequency stiffness opposing the static force is substantially higher due to the stiffness of the acoustic lever.
• the diaphragm will not displace as much from the static force and the net distortion of the system will be lowered.

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• Health & Medical Sciences (AREA)
• Otolaryngology (AREA)
• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Details Of Audible-Bandwidth Transducers (AREA)
• Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)
• Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)

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• 1998
  • 1998-10-01 EP EP98950880A patent/EP1033061A1/de not_active Withdrawn
  • 1998-10-01 JP JP2000515410A patent/JP2001519637A/ja not_active Withdrawn
  • 1998-10-01 WO PCT/US1998/020817 patent/WO1999018755A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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