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Herman von HELMHOLTZ

Resonator


















http://en.wikipedia.org/wiki/Helmholtz_resonance

Helmholtz Resonance

A brass, spherical Helmholtz resonator based on Helmholtz's original design, from around 1890-1900.


Helmholtz resonance is the phenomenon of air resonance in a cavity. The name comes from a device created in the 1850s by Hermann von Helmholtz to show the height of the various tones. An example of Helmholtz resonance is the sound created when one blows across the top of an empty bottle.

Qualitative Explanation

When air is forced into a cavity, the pressure inside increases. Once the external force that forces the air into the cavity disappears, the higher-pressure air inside will flow out. However, this surge of air flowing out will tend to over-compensate, due to the inertia of the air in the neck, and the cavity will be left at a pressure slightly lower than the outside, causing air to be drawn back in. This process repeats with the magnitude of the pressure changes decreasing each time.

This effect is akin to that of a bungee-jumper bouncing on the end of a bungee rope, or a mass attached to a spring. Air trapped in the chamber acts as a spring. Changes in the dimensions of the chamber adjust the properties of the spring: a larger chamber would make for a weaker spring, and vice-versa.

The air in the port (the neck of the chamber) is the mass. Since it is in motion, it possesses some momentum. A longer port would make for a larger mass, and vice-versa. The diameter of the port is related to the mass of air and the volume of the chamber. A port that is too small in area for the chamber volume will "choke" the flow while one that is too large in area for the chamber volume tends to reduce the momentum of the air in the port.

Quantitative explanation

It can be shown[1] that the resonant angular frequency is given by:

\omega_{H} = \sqrt{\gamma\frac{A^2}{m} \frac{P_0}{V_0}} (rad/s) ,


where:

* ? (gamma) is the adiabatic index or ratio of specific heats. This value is usually 1.4 for air and diatomic gases.
* A is the cross-sectional area of the neck
* m is the mass in the neck
* P0 is the static pressure in the cavity
* V0 is the static volume of the cavity

For cylindrical or rectangular necks, we have

A = \frac{V_n}{L} ,


where:

* L is the length of the neck
* Vn is the volume of air in the neck

thus:

\omega_{H} = \sqrt{\gamma\frac{A}{m} \frac{V_n}{L} \frac{P_0}{V_0}}



By the definition of density: \frac{V_n}{m} = \frac{1}{\rho} , thus:

\omega_{H} = \sqrt{\gamma\frac{P_0}{\rho} \frac{A}{V_0 L}},

and

f_H = \frac{\omega_H}{2\pi} ,



where:

* fH is the resonant frequency (Hz)

The speed of sound in a gas is given by:

v = \sqrt{\gamma\frac{P_0}{\rho}} ,

thus, the frequency of the resonance is:

f_{H} = \frac{v}{2\pi}\sqrt{\frac{A}{V_0L}}



The length of the neck appears in the denominator because the inertia of the air in the neck is proportional to the length. The volume of the cavity appears in the denominator because the spring constant of the air in the cavity is inversely proportional to its volume. The area of the neck matters for two reasons. Increasing the area of the neck increases the inertia of the air proportionately, but also decreases the velocity at which the air rushes in and out.

Depending on the exact shape of the hole, the relative thickness of the sheet with respect to the size of the hole and the size of the cavity, this formula can have limitations. More sophisticated formula can still be derived analytically, with similar physical explanations (although some differences matter). See for example the book of F.Mechels [2]. Furthermore, if the mean flow over the resonator is high (Mach number above 0.3 typically), some corrections must be accounted for.

Applications

Helmholtz resonance finds application in internal combustion engines (see airbox), subwoofers and acoustics. In stringed instruments, such as the guitar and violin, the resonance curve of the instrument has the Helmholtz resonance as one of its peaks, along with other peaks coming from resonances of the vibration of the wood. An ocarina is essentially a Helmholtz resonator where the area of the neck can be easily varied to produce different tones. The West African djembe has a relatively small neck area, giving it a deep bass tone. The djembe may have been used in West African drumming as long as 3,000 years ago, making it much older than our knowledge of the physics involved.

Helmholtz resonators are used in architectural acoustics to reduce undesirable low frequency sounds (standing waves etc.) by building a resonator tuned to the problem frequency thereby eliminating it.

Helmholtz resonators are also used to build acoustic liners, which aim at reducing the noise of aircraft engines for example. These acoustic liners are made of two components:

* a simple sheet of metal (or another material), perforated with little holes that can be regularly spaced or irregularly spaced, called resistive sheet,

* a series of so-called honeycomb cavities (holes with a honeycomb shape, but in fact only their volume matters).

Such acoustic liners are used in most today's aircraft engines. The perforated sheet is usually visible from inside or outside the airplane; the honeycomb is just under it. The thickness of the perforated sheet is of importance, as shown above. Sometimes, there are two layers of liners; they are then called "2-DOF liners", by opposition to the "single DOF liners" (DOF meaning Degree Of Freedom).

This effect could also be used to reduce drag on aircraft by 40%.[3]



http://physics.kenyon.edu/EarlyApparatus/Rudolf_Koenig_Apparatus/Helmholtz_Resonator/Helmholtz_Resonator.html



Patents

Novel Helmholtz Resonator

CN101435356

Abstract -- The invention relates to a novel Helmholtz resonator which is arranged on an automobile exhaust pipe. The resonator comprises a resonance box and a tuning pipe, wherein the resonance box is spanned on the exhaust pipe which passes through the resonance box, and the tuning pipe is arranged on the exhaust pipe in the box and is positioned wholly inside the resonance box. Compared with the prior art, the resonator has the advantages of low resonance frequency and great noise reduction. The resonator is suitable for the low frequency noise abatement for an automobile exhaust system.     



SILENCER OF INTERNAL COMBUSTION ENGINE  
JP2009036185

Abstract
-- PROBLEM TO BE SOLVED: To provide a silencer of an internal combustion engine capable of suppressing the intake and exhaust noise of a plurality of frequencies by one resonator. ; SOLUTION: In the silencer of the internal combustion engine including a hollow part for facilitating a sound attenuation function by resonance wherein a space communicating with the inside of an intake and exhaust pipe of the internal combustion engine is formed, a volume variable means for enabling a volume in the hollow part to be variable is provided. The volume variable means varies the volume by a throttle opening or engine negative pressure. A resonator switch means for switching a side branch type resonator and a Helmholtz type resonator is provided. ; COPYRIGHT:



RESONATOR                                                                             
JP2008309050

Abstract -- PROBLEM TO BE SOLVED: To reduce the cost of a resonator by making a main-volume chamber and a sub-volume chamber communicate to an intake air duct via a neck part. ; SOLUTION: The resonator 1 includes a resonator body part 11 provided with the main-volume chamber 12 communicating to the intake air duct 4 via the neck part 10, and a long and narrow sub-volume chamber 13 directly connected to the main-volume chamber 12, and has a function of a Helmholtz type resonator of which resonance frequency is determined according to volume of the resonator body part 11 which is sum of volume of the main-volume chamber 12 and volume of the sub-volume chamber 13, and a function of a side branch type resonator of which resonance frequency is determined according to length along a longitudinal direction of the sub-volume chamber 13 together. Consequently, the resonator 1 can get two resonance frequencies without complicating a structure of the resonator body part 11, and can reduce manufacturing cost in general.



Infrasonic Helmholtz resonator  
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Abstract
-- An infrasonic Helmholtz resonator capable of producing clean sinusoidal frequencies in the range of 6-14 Hz is described.



High intensity infrasonic tunable resonant acoustic test cell  
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Abstract -- An apparatus and method are provided for high intensity acoustic test cells that employ the Helmholtz resonator principle, incorporating at least one moderately-sized volume or test cell that is tunable to a given infrasonic to low-sonic frequency and generates sound of high intensity with very pure sinusoidal waveforms in this test cell or volume, by varying the geometry of a port which is connected to the test volume and open to either atmosphere or a second or input volume and by introducing to the test volume or the input volume a driving acoustic signal at the given tuned frequency. The apparatus and method are used for testing or performing experiments on materials, structures, devices, products, biological entities or humans at high acoustic intensities and frequencies in the low-sonic to infrasonic ranges.     
 


ACOUSTIC MATERIAL       
JP2006337886
 
Abstract of JP 2006337886  (A)
PROBLEM TO BE SOLVED: To provide an acoustic material which has excellent sound absorbing performance, can be made thinner than before, and is suitably used for, specially, an air-conditioning duct of an automobile. ; SOLUTION: The acoustic material is made of a fiber body or foamed body laminated on a surface of a base material and has a Helmholtz resonator structure comprising a void space 23 recessed in the acoustic material from a laminated surface 21 of the base material and a through hole 24 formed to reach the void space from the opposite surface from the laminated surface. When the volume V1 of the void space portion, the volume V2 of the through hole portion, and the volume V3 of the remaining portion of the acoustic material are so related that V1/(V1+V2+V3)=0.2 to 0.6, the acoustic material has excellent sound absorbing performance and can be made thinner than before.



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VOLUMETER       
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Mechanically coupled helmholtz resonators for broadband acoustic attenuation       
US6069840

Vehicle wheel       
EP0936083

RECIPROCATING COMPRESSOR       
JP2000179458

RECIPROCATING COMPRESSOR       
JP2000161220

RECIPROCATING COMPRESSOR       
JP2000161219

RECIPROCATING COMPRESSOR       
JP2000161218

RECIPROCATING COMPRESSOR       
JP2000161216

PULSATION DAMPING DEVICE       
JP11201367

VACUUM CLEANER AND SUCTION PORT BODY THEREFOR       
JP2000126098

Sound-absorbing plate        
DE19841975

Combustion engine with EGR device, especially diesel engine       
EP0911510

Air induction device for IC engine has Helmholtz resonator        
DE19833326

Device for directed noise attenuation in a turbomachine       
EP0974788

Variably tuned helmholtz resonator with linear response controller       
EP0894970

Noise absorption device for a centrifuge motor-fan unit in an automobile air conditioning system       
FR2780454

Integrated resonator and filter apparatus       
US6048386

PASSIVE RADIATOR       
JP11346395

Combined air cleaner-resonator       
EP0896148

Noise attenuator for an induction system or an exhaust system       
US6009705

INTEGRATED DUCT AND RESONATOR
WO9849440

HORN LOADED MICROPHONE WITH HELMHOLTZ RESONATOR ATTENUATOR       
WO9851122

STRUCTURE OF SOUND ABSORBING MATERIAL       
JP11259076

INTAKE DEVICE FOR INTERNAL COMBUSTION ENGINE       
JP10227261

PROCESS FOR REFINING THE MICROSTRUCTURE OF METALS       
WO9830346

Vehicle interior noise level suppression       
DE19755751

Motor air intake silencer       
DE19754840

TELEPHONE HANDSET       
JP10229435

EXHAUST MUFFLER FOR VEHICLE       
JP11062547

RESONATOR       
JP11044266

Noise determination method for road or railway       
DE19726608

COGGED BELT DRIVE OF INTERNAL COMBUSTION ENGINE MECHANISMS       
RU2131524

DIFFERENTIAL MICROPHONE ASSEMBLY WITH PASSIVE SUPPRESSION OF RESONANCES       
CA2205722

REFRIGERATOR       
JP10306972

AIR INTAKE SYSTEM FOR AN INTERNAL COMBUSTION ENGINE       
WO9742408

Refining microstructure of metals continuously cast by Hot Top technique       
FR2761624

Wheel tyre and road noise reducer       
DE19710029

SOUND ABSORBING DEVICE AND SOUND ABSORBING STRUCTURE FOR ROOM       
JP10227084

Refining microstructure of metals continuously cast by Hot Top       
FR2758101

Tunable acoustic system       
US5930371

Valve for an air flow channel       
EP0800030

LINING       
JP9175436

Resonator       
EP0778399

Sound absorption structure       
US5783780

Sound absorbing wheel-housing cover       
EP0769422

Tyre/road noise reduction arrangement       
EP0769421

Device for damping thermo-acoustic vibrations in combustion chamber of gas turbine       
DE19640980

Sound absorber element for absorber plates         
DE19640087

SOUND REPRODUCTION DEVICE       
JP10075494

Acoustic alarm employing a resonant cavity arrangement       
GB2316784

Sound absorptive hollow core structural panel       
US6021612

STANDING WAVE SPACER FOR INTERNAL COMBUSTION ENGINE       
JP10008990

POLYGON SCANNER       
JP9311286

LINT HANDLING SYSTEM       
CA2174460

HELMHOLTZ RESONATOR LOUDSPEAKER       
WO9631106

SILENCER       
JP9212176

Adjustable silencer for air intake of vehicular combustion engine       
FR2743848

SOUND ABSORBER       
JP9198051

Arrangement for reducing tire/road noise       
US5839761

MAGNETIC TAG EXECUTING ACOUSTIC OR MAGNETIC INQUIRY       
JP8249431

System for absorption of air noise       
DE19533623

SOUND ABSORBING MATERIAL       
JP9062267

TELEVISION RECEIVER       
JP8322095

Assembly for reducing tyre/road surface noise.       
EP0680866

DAMPING DEVICE FOR THERMO-ACOUSTIC VIBRATION IN COMBUSTION CHAMBER       
JP7293885

Engine enclosure air inlet/discharge sound attenuator       
US5625172

Sound absorber for motor vehicles       
US5681072

HELMHOLTZ HYDRAULIC PRESSURE PULSATION FILTER OF GAS SEALED TYPE       
JP8240202

GAS-TURBINE ENGINE AFTERBURNER       
RU2117806

Apparatus for acoustic noise reduction         
US5508477

Sound absorption system for automobile       
DE4446080

Structure of rear window shelf portion to partition vehicular passenger compartment...
US5498050

PRODUCTION OF SOUND ABSORBING MATERIAL       
JP8166787

Dynamics free low emissions gas turbine combustor       
US5644918

Vehicle with IC engine       
DE4435296

Method and composite resonator for tuning an engine air induction system       
US5572966

INTAKE STRUCTURE OF ENGINE       
JP8093583

ADAPTIVE MANIFOLD TUNING       
WO9511373

Rotary throat cutoff device and method for reducing centrifugal fan noise.       
EP0638728

RESONATOR TYPE SOUND-ABSORBING BODY AND SOUND-ABSORBING CEILING       
JP8013642

Vibration-insulating panel element       
US5473125

MULTIBLADE BLOWER       
JP7332284

Sound-proofed swimming pool       
FR2718479

SILENCER FOR ATTENUATING DISCHARGE NOISES...
WO9419596   
          
Quantitative determination of air present in refrigerant sample        
US5524477  

RESONATOR       
JP7208287

VOLUMETER       
JP7190834

PISTON POWER MACHINE OR WORKING MACHINE       
JP6213072

HAND-HELD APPARATUS RADIATING SOUND       
JP6223215

GAS TURBINE COMBUSTION DEVICE       
JP7139738

SOUND FIELD ADJUSTING DEVICE       
JP7160268

COMBUSTION CHAMBER OF GAS TURBINE       
JP6221563

SPEAKER SYSTEM       
JP6205491

SILENCER DEVICE FOR COMBUSTION ENGINE       
JP6202673

VOLUMENOMETER       
JP7083730

VOLUMENOMETER       
JP7083729

VOLUMENOMETER       
JP7083728

VOLUMENOMETER       
JP7083727

Silencer arrangement for combustion engines.       
EP0589516

Exhaust gas system of an internal combustion engine       
DE4330129

Sound absorption method for motor vehicles.       
EP0586831

SECONDARY BURNER       
JP6094227

SPEAKER SYSTEM       
JP7015783

Air intake device for an internal combustion engine.       
EP0569714

A refrigeration compressor.       
EP0561383

Piston-type engine with valve cover
DE4305281

Covering element.       
EP0584442

Sandwich construction panel for acoustic insulation       
FR2700179

Noise-attenuating internal combustion engine air intake system       
US5424494

Sound-absorbing housing cladding for machine        
DE4241515

Piezoelectric sound sources       
US5386479

Low frequency sound generation system for use in vehicular passenger compartments       
US5394478

SOUND VOLUME CONTROLLER FOR PIANO       
JP6149232

Device for determining the volume of objects using a chamber with two resonators
US5385069

Earplug and hearing devices formed in-situ       
US5333622

SPEAKER EQUIPMENT       
JP6038290

Acoustic muffler for high volume fluid flow utilizing Heimholtz resonators    
US5276291

Musical instrument incorporating a Helmholtz resonator       
US5248846

Gas turbine combustor.       
EP0576717

RECIPROCATING TYPE ELECTRIC RAZOR       
JP6000261

Self-supporting wall with sound absorbing properties.       
EP0518305

Guard-rail with sound absorbing properties.       
EP0518304

CALIBRATION OF SEISMIC STREAMERS IN A HELMHOLZ RESONATOR       
US5210718

AIR SUCTION DEVICE FOR INTERNAL COMBUSTION ENGINES       
DE4215416

EXTENDED FREQUENCY RANGE HELMHOLTZ RESONATORS       
WO9321625

NOISE REDUCTION DEVICE       
JP5195746

Sound attenuator for low frequencies, in particular for air ducts in paper mills.       
EP0495763

SOUND ABSORBING BODY       
JP5158484

CVD FILM FORMING DEVICE       
JP5117860

Silencer arrangement for internal combustion engines.       
EP0481450

NOISE REDUCTION DEVICE       
JP5059927

No title available       
JP5294230

SILENCER FOR FAN OF HOVERCRAFT(R)       
JP5016795

ACTIVE MUFFLING DEVICE       
JP4350314

SPEAKER SYSTEM       
JP4336795

Loudspeaker system.       
EP0456416

SOUND ABSORBING PANEL       
CA2040076

Exhaust system for small planing boat       
US5234364

Method and means to adjust sound characteristics of club head upon impact with golf ball       
US5064197

ACTIVE TYPE PULSATION PRESSURE ABSORBER       
JP6026448

HELMHOLTZ RESONANCE TYPE WIDE BAND TRANSMITTER-RECEIVER       
JP4278798

ROTARY TYPE ENCLOSED COMPRESSOR       
JP4265490

Tubewave damper probe for seismic applications       
US5171943

SPEAKER UNIT       
JP4369996

METHOD AND DEVICE FOR REGENERATING SOOTY SMOKE FILTER IN DIESEL ENGINE       
JP3242413

ROTARY COMPRESSOR       
JP4159490

INTERNAL SIDEBRANCH RESONATOR       
US5162621

INTAKE PIPE WITH INTAKE RESONATOR       
JP4109071

METHOD AND APPARATUS FOR MONITORING AND CONTROLLING A HEAT GENERATOR       
CA2020832

QUASI-OPTICAL GYROTRON HAVING A YOKE STRUCTURE...
US5134341

Quasi-optical gyrotron       
US5052003

LASER PRINTER DEVICE       
JP4000469

EXHAUST DEVICE FOR SMALL SPEEDBOAT       
JP3295791

PULSE COMBUSTION APPARATUS       
CA2013491

DIRECT RADIATION TYPE SPEAKER       
JP3201796

Fan silencer apparatus       
GB2237323

VARIABLE TENSION TRANSDUCER       
JP2123900

Acoustic apparatus.       
EP0361445

VOLUMETER       
JP3108614

Acoustic apparatus       
US4987601

ELECTRIC ACOUSTIC UNIT CONVERTER       
JP2075299

NOISE-SUPPRESSING DEVICE       
JP2161134

Keyboard instrument.       
EP0347775

IC engine exhaust system - incorporates Helmholtz resonator
DE3916429

GAS LASER       
JP2285686

GAS LASER DEVICE       
JP2281676

GAS LASER DEVICE       
JP2270384

Arrangement for diminishing the noise level within a motor car.       
EP0342353

Acoustic apparatus       
US5004066

Acoustic apparatus.       
EP0336303

Acoustic Apparatus.       
EP0334238

Method and apparatus of expanding acoustic reproduction range.       
EP0334217

Acoustic apparatus       
US5012890

Passive structural and aerodynamic control of compressor surge       
US5199856

Damping device for air transmitted and rigid-body sound vibrations.       
EP0337077

INTAKE DEVICE FOR ENGINE       
JP2176113

METHOD AND APPARATUS FOR MONITORING AND CONTROLLING A HEAT GENERATOR
WO8906771

Sound insulation panel for preset frequency bands       
IT1225514

Compressor noise attenuation using branch type resonator       
US4927342  

ACOUSTIC DEVICE       
JP2113697  

MEASURING APPARATUS OF INTERNAL VOLUME       
JP2064418  

ELECTRIC/ELECTRONIC MUSICAL INSTRUMENT       
JP2041098  

ELECTRIC/ELECTRONIC MUSICAL INSTRUMENT       
JP2041097  

PORTABLE ELECTRIC MUSICAL INSTRUMENT       
JP2029795  

PORTABLE MUSICAL INSTRUMENT       
JP2029794  

AUTOMATIC WASHER       
JP2026598  

ELECTRONIC MUSICAL INSTRUMENT       
JP1319792  

ELECTRONIC MUSICAL INSTRUMENT       
JP1319791  

ELECTRONIC MUSICAL INSTRUMENT       
JP1319790  

ACOUSTIC EQUIPMENT       
JP1254098  

ACOUSTIC EQUIPMENT       
JP1254097  

ACOUSTIC EQUIPMENT       
JP1241297  

ACOUSTIC EQUIPMENT       
JP1241296  

MAGNETIC RESONANCE IMAGING DEVICE       
JP1201247  

VOLUMETER       
JP1184417  

ACOUSTIC DEVICE       
JP1302998  

ACOUSTIC DEVICE       
JP1302997  

BODY RESONANCE INSTRUMENT       
JP1144099  

VOLUME MEASURING INSTRUMENT       
JP1118722  

PRINTER       
JP63239076  

A silencing ventilating device
EP0265000            

Method and apparatus for nonintrusively determining mach number       
US4829813  

VOLUMETER       
JP63298013  

Acoustic inspection method
EP0242060  

Sound attenuating box       
US4787473  

VOLUMETER       
JP63113315  

VOLUMETER       
JP63044127  

Method of mounting a piezoelectric helmholtz transducer on a printed circuit board       
US4630342  

ACOUSTIC DISPLACEMENT METER       
JP62070705  

Measure for reducing the sound emitted from railway rails       
DE3532765  

SILENCER DEVICE FOR INTERNAL COMBUSTION ENGINE       
JP62038815  

FLUID DRIVING APPARATUS       
JP61265396  

Heating boiler       
DE3517859  

Exhaust system for outboard motors       
US4897060  

SILENCER DEVICE OF ADAPTABLE TYPE       
JP61129414  

Infra-sonic intensification of glow bed       
SE456524

Method and apparatus for acoustically measuring the volume of an object       
US4640130  

Sound probe       
DE3439546  

SOUND ABSORPTIVE STRUCTURAL BLOCK WITH SEQUENCED CAVITIES       
CA1214396  

Exhaust system for outboard motors       
US4607723  

INTERNAL COMBUSTION PISTON ENGINE USING AIR CHAMBER IN PISTON  
CA1242121  

SPEAKER DEVICE       
JP61020490  

Broadband matching network       
US4644505  

Low noise hand-held hairdryer       
US4596921  

Sound-absorbing building element       
DE3412432  

Sound attenuating ventilating box
NL8304487  

Burner for the processes of the autogenous welding technique
DE3329937  

PULSER BURNER       
JP60038514  

PULSATING COMBUSTION APPARATUS       
JP60033408  

GASEOUS COMPONENT DETECTOR       
JP59212761  

General purpose modular acoustic signal generator       
US4602245  
          
PIEZOELECTRIC TYPE LOW FREQUENCY TRANSDUCER       
JP59190795  

Method and apparatus for low frequency active attenuation       
US4527282  

APPARATUS FOR DETECTING GAS TEMPERATURE       
JP59160730  

Gas pressure regulator       
GB2136095  

BAR FOR A POWER CHAIN SAW       
CA1173330  

Passive acoustic absorber device also absorbing low frequencies       
FR2540912  

Vehicle roof liner.       
EP0079253  

INFRARED RAY DETECTOR       
JP59054950  

Low frequency muffler       
US4501341  

SOUND SUPPRESSOR LINER       
CA1160850  

CYLINDER BLOCK OF INTERNAL-COMBUSTION ENGINE       
JP58107839  

Directional microphone with high frequency selective acoustic lens       
US4401859  

Perforate tube muffler       
US4371053  

Electro-acoustic transducer       
US4379212  

Piezo-electric ringing transducer.       
EP0025955  

COMPACT EXHAUST SILENCER FOR DIESEL LOCOMOTIVES       
CA1138780  

Two stroke cycle engine with sustained power stroke       
US4370959  

Mufflers for percussive pneumatic machines       
US4294330  

ELECTRONIC AUDIO SIGNALLING DEVICE FOR TELEPHONES       
CA1138137  

SOUND-ATTENUATING MUFFLER FOR EXHAUST GASES       
CA1123749 




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