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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.

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Page 1 of 25Helmholtz Resonators

06.01.2010http://www.rexresearch.com/helmholtz/helmholtzresonators.htm


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Helmholtz resonance is the phenomenon of air resonance in a cavity. The name comes from a device created in the 1850s byHermann von Helmholtz to show the height of the various tones. An example of Helmholtz resonance is the sound created whenone 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 cavitydisappears, the higher-pressure air inside will flow out. However, this surge of air flowing out will tend to over-compensate, dueto 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 bedrawn 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 trappedin the chamber acts as a spring. Changes in the dimensions of the chamber adjust the properties of the spring: a larger chamberwould 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 portwould make for a larger mass, and vice-versa. The diameter of the port is related to the mass of air and the volume of thechamber. 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 thechamber 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:




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\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. Thevolume of the cavity appears in the denominator because the spring constant of the air in the cavity is inversely proportional toits volume. The area of the neck matters for two reasons. Increasing the area of the neck increases the inertia of the airproportionately, 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 ofthe cavity, this formula can have limitations. More sophisticated formula can still be derived analytically, with similar physicalexplanations (although some differences matter). See for example the book of F.Mechels [2]. Furthermore, if the mean flowover 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 resonatorwhere the area of the neck can be easily varied to produce different tones. The West African djembe has a relatively small neckarea, giving it a deep bass tone. The djembe may have been used in West African drumming as long as 3,000 years ago, makingit 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.) bybuilding 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 theairplane; 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 meaningDegree 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 ResonatorCN101435356




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

SILENCER OF INTERNAL COMBUSTION ENGINEJP2009036185

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

RESONATORJP2008309050

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 bodypart 11 provided with the main-volume chamber 12 communicating to the intake air duct 4 via the neck part 10, and a long andnarrow sub-volume chamber 13 directly connected to the main-volume chamber 12, and has a function of a Helmholtz typeresonator of which resonance frequency is determined according to volume of the resonator body part 11 which is sum ofvolume of the main-volume chamber 12 and volume of the sub-volume chamber 13, and a function of a side branch typeresonator of which resonance frequency is determined according to length along a longitudinal direction of the sub-volumechamber 13 together. Consequently, the resonator 1 can get two resonance frequencies without complicating a structure of theresonator body part 11, and can reduce manufacturing cost in general.

Infrasonic Helmholtz resonatorUS6665413

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

High intensity infrasonic tunable resonant acoustic test cellUS2002085723

Abstract -- An apparatus and method are provided for high intensity acoustic test cells that employ the Helmholtz resonatorprinciple, incorporating at least one moderately-sized volume or test cell that is tunable to a given infrasonic to low-sonicfrequency and generates sound of high intensity with very pure sinusoidal waveforms in this test cell or volume, by varying thegeometry of a port which is connected to the test volume and open to either atmosphere or a second or input volume and byintroducing to the test volume or the input volume a driving acoustic signal at the given tuned frequency. The apparatus andmethod 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 MATERIALJP2006337886

Abstract ofJP 2006337886 (A)PROBLEM TO BE SOLVED: To provide an acoustic material which has excellent sound absorbing performance, can be madethinner than before, and is suitably used for, specially, an air-conditioning duct of an automobile. ; SOLUTION: The acousticmaterial is made of a fiber body or foamed body laminated on a surface of a base material and has a Helmholtz resonatorstructure comprising a void space 23 recessed in the acoustic material from a laminated surface 21 of the base material and athrough hole 24 formed to reach the void space from the opposite surface from the laminated surface. When the volume V1 ofthe void space portion, the volume V2 of the through hole portion, and the volume V3 of the remaining portion of the acousticmaterial 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.

BARRIER SYSTEM




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WO2009108071

Process for the preparation of nanocrystalline hydrotalcite compoundsGB2457771

Vibration damper for damping hydraulic vibration of hydraulic oil in pressure lineDE102009004705

Pressure sensing device adapted to corrosive or explosive atmospheres and with means to filter disturbance frequencies

GB2456865

Resonator device for e.g. non supercharged internal combustion engineFR2926608

INLINE HELMHOLTZ TYPE RESONATORKR20090047083

Handheld electronic device having hidden sound openings offset from an audio sourceEP2081400

Hydraulic system for actuation of clutch of motor vehicleDE102008062336

Hydraulic system for motor vehicleDE102008060584

COOLING DEVICE AND ELECTRONIC DEVICE COMPRISING SUCH A COOLING DEVICEUS2009168343

LITHOGRAPHIC APPARATUS HAVING ACOUSTIC RESONATORUS2009161085

Microphone for audio source trackingCN101449593

Novel Helmholtz resonatorCN101435356

EXHAUST DEVICE FOR STRADDLE-TYPE VEHICLE AND STRADDLE-TYPE VEHICLEUS2009139796

MICROREACTOR DEVICEJP2009090265

Noise attenuation device for a centrifugal compressor discharge or suction nozzleEP2063130

MEASUREMENT OF SOUND SPEED OF DOWNHOLE FLUID BY HELMHOLTZ RESONATORWO2009055197

Method and device for achieving better heat transfer when using pulse heatersUS2009084036

SILENCER OF INTERNAL COMBUSTION ENGINEJP2009036185

Supply gas cooling circuit for overheating turbo-compressor of motor vehicleFR2921123

Acoustic liner for gas turbine engine manufactured by an additive fabrication processGB2452476

HANDHELD ELECTRONIC DEVICE HAVING OFFSET SOUND OPENINGSSG149882

MOTORCYCLE AIRBOX WITH HELMHOLTZ RESONATORJP2009013980

HERMETIC COMPRESSORUS2009022605

RESONATOR




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JP2008309050

TURBINE ENGINE FUEL INJECTOR WITH HELMHOLTZ RESONATORWO2008153736

Recess lower cross member for motor vehicle, has Helmholtz resonatorFR2917044

Cross head for dashboard of motor vehicle, has acoustic resonator

FR2917055

Apparatus for delivery of pressurised gasCN101291703

Novel Helmholtz resonatorCN201125766

Earphone with acoustical filterCN201114712

Adjustable helmholtz resonatorCN101230818

COMPRESSOR SOUND SUPPRESSION

US2008260547

INTAKE NOISE MUFFLING DEVICE AND MUFFLING METHODJP2008223745

RECORDING APPARATUSJP2008213310

PNEUMATIC TIREJP2008213596

RESONATOR WITH INTERNAL SUPPLEMENTAL NOISE ATTENUATION DEVICEUS2008236937

ACOUSTIC FLOW STRAIGHTENER FOR TURBOJET ENGINE FAN CASING

US2008236137

HELMHOLTZ RESONATORWO2008116870

Porous acoustic material for Helmholtz resonatorFR2914479

Flowmeter using tube wavesGB2447691

System for Damping Thermo-Acoustic Instability in a Combustor Device for a Gas TurbineUS2008216481

PNEUMATIC TIREEP1964691

PNEUMATIC TIREWO2008102780

Device for reducing pulsation in a variable displacement compressorUS2008199329

Combustion chamber for gas turbine engineEP1962018

THERMAL EXCITATION TYPE SOUND WAVE GENERATORJP2008167252

Piezo-Hydraulic Linear Actuator For Vibration ControlUS2008191397

Silencer for an exhaust systemEP1959106




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SPEECH COMMUNICATION DEVICEJP2008135864

Assessing Porous Media Properties by Downhole MRI and Acoustic LoggingGB2445085

INTAKE ASSEMBLY HAVING HELMHOLTZ RESONATORSUS2008135010

VEHICULAR SOUND-PROOF STRUCTUREJP2008114697

Device for attenuating cavity noise in a tire and wheel assemblyEP1932689

ELECTRONIC DEVICE AND SOUND PROOFING METHOD FOR THE SAMEJP2008090931

Combustion Control for a Gas TurbineGB2443838

Helmholtz resonator type marine signalUS7360499

Combustion chamber for a gas turbine engineUS2008087019

Exhaust silencer for automotive vehiclesEP1908930

NOISE SUPPRESSOR, ELECTRONIC APPARATUS AND CONTROL METHODJP2008058389

Vacuum cleaner equipped with a noise-attenuation deviceEP1905334

Thermoacoustic DeviceUS2008060364

Gas turbine helicopter engine with reduced sound emissions due to acoustic treatment of a jet pumpEP1902948

METHOD FOR CLEANING OF SPENT GASES...RU2361094

Resonator device at junction of combustor and combustion chamberUS2008041058

A SILENCER, A MARINE VESSEL AND A METHOD OF SILENCING A MARINE EXHAUSTWO2008012501

Combustion chamber for gas turbine of power plant systemDE102005062284

CENTRAL BODY OF TURBOJET NOZZLEJP2007292064

INSULATION DEVICE FOR STEERINGJP2007290432

CENTRAL BODY FOR A TURBOJET EXHAUST CHANNEL, TURBOJETUS2007272477





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Handheld electronic device having hidden sound openings offset from an audio sourceUS2007252810

Noise reduction of rotary mowers using an acoustical helmholtz resonator arrayUS2007234699

Sound absorbing device forFR2899537

Flushing system for a vacuum toilet bowl, especially in an aircraft, has a Helmholtz resonatorDE102006014011

A GOLF CLUB DRIVER HEAD HAVING HELMHOLTZ RESONATORKR20070078374

Combustion chamberDE102006007711

A GOLF CLUB DRIVER HEAD HAVING HELMHOLTZ RESONATORWO2007086676

AIR SUPPLY REGISTERJP2007139223

Acoustic resonator e.g. Helmholtz resonator, for use in motor vehicleFR2895714

Low-noise cabinet type air conditionerCN2893501

SilencerEP1785602

Resonator performance by local reduction of component thicknessUS2007102235

Heating device e.g. oil-heated heating device, has helmholtz-resonatorDE102005052881

Cannula handle and storage systemUS2007093755

SPEAKER SYSTEMJP2007060099

Resonating device for combustion chamberEP1775515

CANNULA HANDLE AND STORAGE SYSTEMWO2007038433

Motor vehicle engine with Exhaust Gas Recirculation ... Helmholtz resonatorFR2891015

MUFFLER FOR ELECTRONIC EQUIPMENT...JP2007047560

Exhaust system with external Helmholtz resonator and associated methodUS2007051556

Fuel injection device for internal combustion engine of motor vehicle...FR2890415

FLUID VOLUME DETECTING DEVICEJP2007017320

INTAKE DEVICEJP2007016652

Handheld electronic device having offset sound openingsUS2007025582

Silencer for use in exhaust system of motor vehicle, has helmholtz chamber and resonator pipe...




9/25

DE102005033421

Damping device for damping frequency-variable pulsations in a hydraulic pipe has branch resonator...DE102005032319

ACOUSTIC TELEMETER SYSTEM...RU2291961

MUFFLER REDUCING HIGH FREQUENCY NOISE

JP2006283625

DEVICE FOR REDUCING NOISE OF A RECIPROCATING COMPRESSOR...KR20050018155

DISK DRIVE ADOPTING A RESONATORKR20050012042

STRUCTURE INSTALLED IN CAVITY BETWEEN HEAD LINING AND ROOF PANEL...KR20050008931

LOUDSPEAKER SYSTEM COMPRISING A HELMHOLTZ RESONATOR...KR0158885

HELMHOLTZ RESONATOR AIR INLET SYSTEM FOR VEHICLE

KR20060001216

NOISE REDUCTION APPARATUS... USING HELMHOLTZ RESONATORKR20010037807

RESONATOR OF ENGINE INDUCTION SYSTEMKR20010028178

BAMBOO SOUND-PROOF WALLKR20010011073

COMBINED AIR CLEANING AND RESONATING APPARATUSKR20000001532

COMPRESSOR

KR100273658

NOISE-DECREASING DEVICE FOR INTAKE MANIFOLD OF A CARKR960008782

IMAGE FORMING APPARATUSJP2006251590

RIM WHEEL AND MANUFACTURING METHOD THEREOFJP2006231966

DEVICE FOR MEASURING CHANGING AMOUNT OF VOLUMEKR20020058784

APPARATUS FOR REDUCING INTAKE NOISE OF VEHICLE USING HELMHOLTZ RESONATORKR20020038217

MUFFLER FOR VEHICLEKR20020030352

Silencer containing one or more porous bodiesUS7104358

Loudspeaker which can be used with or without stand which acts as a helmholtz resonatorGB2422066

PIPE AND ITS MANUFACTURING METHODJP2006144557

Combustion chamber for a gas turbine engineUS2006123791

Exhaust gas mufflerDE102004056889




10/25

SOUND ELIMINATING STRUCTURE AND STIRLING COOLING BOXJP2006105514

HELMHOLTZ RESONATOR AND AN EXHAUST LINE PROVIDED THEREWITHWO2006048557

Noise insulating partition for an internal volume, of an automotive vehicle, in particular.EP1657115

Devices and transducers with cavity resonator to control 3-D characteristics/harmonic frequenciesUS2006090959

Fluid pumping apparatus with Helmholtz-resonatorEP1647713

Loudspeaker system with extended output and field cancellationUS2006050915

Wide band sound diffuser with self regulated low frequency absorption and methods of mountingUS2006042875

Silencer device for exhaust-gas turbocharger, has Helmholtz resonatorDE102004040317

ACOUSTICALLY STIFFENED GAS-TURBINE FUEL NOZZLEWO2006014300

Apparatus for reducing thermoacoustic oscillations in combustion chambersEP1624251

Apparatus for reducing thermoacoustic oscillations in combustion chambersEP1624250

Gas-fired heating apparatusUS2006014114

Determining the depth of perforation tunnels in a wellbore using the Helmholtz resonance effectGB2416398

Electronically controlled dual chamber variable resonatorUS2005252716

Resonator device and circuits for 3-d detection/receiving sonic wavesUS2005270906

ELECTRIC CONNECTION BOXJP2005304162

COMBUSTION APPARATUS HAVING INSTABILITY REDUCTION MEANSGB1203065

VIBRATION DAMPING DEVICE FOR A COMBUSTION CHAMBERGB1274529

ELECTRONIC SURVEILLANCE SYSTEMSGB1292380

Exhaust-silencer assembly for motor vehicle exhaust system, has Helmholtz resonatorDE202005010304

RIM WHEEL AND TIRE RIM WHEEL ASSEMBLYJP2005219739

SONIC EMITTER ARRANGEMENTSWO2005051037

Burner, method for operating a burner and gas turbineUS2005106519

Gas turbineUS2005144950




11/25

RIM WHEELJP2004352245

Muffler with helmholtz resonator having multiple degrees of freedomEP1482137

Device for damping thermoacoustic oscillations in a combustion chamberEP1596130

EXHAUST PART OF THE VACUUM DEVICE WITH REDUCED NOISE LEVELSI21778

Improvement of acoustic situation in passenger cabin of vehicle, comprising use of Helmholtz-resonatorsDE102004016689

Vortex blower having helmholtz resonators and a baffle assemblyUS2005207883

Diffuser and turbineEP1559874

Device and method for damping thermoacoustic oscillations in a combustion chamberEP1557609

SOUND ABSORBING STRUCTUREJP2005146650

RESONATOR STRUCTURE IN EXHAUST SYSTEM FOR INTERNAL COMBUSTION ENGINEJP2005120853

SEATJP2005080756

Radial blower for a leaf and waste collection/removal apparatus with operating noise suppression meansUS20040715462004-04-15

SUPPORT RING, TIRE ASSEMBLY USING THE SUPPORT RING, AND VEHICLEJP2005007928

Sound damping device having a Helmholtz resonator for installations with pulsating gas flowsEP1381025

Multi-chamber resonator system eg for vehicle i.c. engine air intake silencerGB2391044

COMPRESSORJP2004360630

SOUND ABSORPTION FLOORJP2004338504

Fresh gas supply system for a combustion engineUS2003230273

SONIC DRIER AND SONIC DRYING DEVICEJP2004317066

Speaker deviceUS2004028246

Borehole telemetry systemGB2399921

HELMHOLTZ RESONATORUS2004173175

Combined active noise control and resonatorUS2003178248

Feedback resistant stringed musical instrumentUS2004134334




12/25

Active noise control system with a Helmholtz resonatorEP1313090

Radial fan for leaf and waste vacuum devices with Helmholtz resonatorDE20221007

Mud pump noise attenuation in a borehole telemetry systemGB2392762

Passenger restraint system for vehicle including a gas generator with noise reductionEP1288086

Infrasonic Helmholtz resonatorUS6665413

Broadband noise-suppressing barrierUS2003006090

Tunable active sound absorberGB2387522

RESONATORJP2003293873

Fan shroud with built in noise reductionUS2003183446

VEHICLEJP2003267214

SOUND ABSORBING FOAMWO02065447

Sound absorbing foamUS2002153199

Multiple frequency helmholtz resonatorUS2003136119

Exhaust gas silencer with combined acoustic resonator chamber and spark arresterGB2383604

MEDIUM WEIGHT SENSOR USING ACOUSTIC RESONATORJP2002214104

Exhaust gas system with helmholtz resonatorUS2002108810

SOUND ABSORBING FOAMED PLASTIC AND METHOD OF MAKING THE SAMEJP2003140659

HYDRAULIC ELEVATORJP2003118950

Venting device for internal combustion engine...DE10143686

SOUND INSULATORJP2002220817

Noise attenuation arrangements for pressurised-gas conduitsEP1176355

SOUND INSULATION STRUCTURE USING DOUBLE BOARDJP2002356934

Sound-lowing cover for compressorCN2475837

Natural gas exhaust silencer for engineCN2475836

Apparatus for damping acoustic vibrations in a combustor




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US2002000343

SOUND ABSORBING METHOD IN BUILDINGJP2002348985

RIM WHEELJP2002234305 2002-08-20

RIM WHEEL WITH CORE AND TIRE RIM WHEEL ASSEMBLY

JP2002234304

SOUND ABSORPTION STRUCTURE FOR BUILDINGJP2002227322

ACOUSTIC MATERIALJP2002189474

RIM WHEELJP2002079802

TyreEP1106395

Air induction system for internal combustion engine

US6382161

ACOUSTIC ELEMENTWO0133906

ACTIVE MUFFLING DEVICEJP2002132265

Gas detection system has a laserFR2815122

SILENCERWO0123714

Noise attenuation arrangements for pressurised-gas conduits

GB2365066

Tuned active helmholtz resonator with forced responseEP1085201

Tuned Helmholtz resonator using cavity forcingUS6758304

CHANGE OF PUMP JET ROTOR HOUSING...JP2001138990

Contactless inner eye pressure measurementDE10039896Protective helmet, especially for motorcyclistsEP1066766

Hard disk drive cover that contains a helmholtz resonator which attenuates acoustic energyUS6493180

PRESSURE WAVE GENERATORJP2001330000

RECIPROCATING COMPRESSORJP2001263232

MUFFLERJP2001248509

Sound absorbing structureUS6435303

HEAVY LOAD PNEUMATIC TIREJP2001191734




14/25

Sound absorber for sound wavesUS6290022

Combined resonator and coolant store for an IC engineGB2357141

Hydraulic noise reduction assembly with variable side branchUS6234758

Dosage arrangement in common-rail fuel injector of diesel engineDE19956077

Noise attenuating sound resonator for automotive cooling module shroudUS6309176

DAMPING DEVICE FOR DAMPING VIBRATION AMPLIFICATION OF SOUND WAVE FOR BURNERJP2000146182

Tunable active sound absorbersUS6778673

IMAGE FORMING DEVICEJP2001117451

PNEUMATIC TIRE HAVING SOUND ABSORBING CHARACTERISTICJP2000118207

Method and arrangement for sound-suppression in wheelsUS6309026

LOW-FREQUENCY SOUND DECREASING DEVICEJP2001075574

MICROMACHINED ACOUSTIC EJECTORS AND APPLICATIONS TO MICRO THRUSTERS...WO0007735

ENGINE INTAKE NOISE REDUCTION STRUCTUREJP2001020717

Vehicle heating and/or airconditioning housing with improved acoustic performancesEP0968857

Method of making composite chambercore sandwich-type structure with inherent acoustic attenuationUS6231710

METHOD FOR MONITORING WHIPPED STATE OF CREAMSJP2000321253

RECIPROCATING INTERNAL COMBUSTION ENGINEJP11351085

INTERCOOLER AND INTAKE DEVICE...JP2000310124

RECIPROCATING INTERNAL COMBUSTION ENGINEJP11336555

VOLUMETERJP2000241226

VOLUMETERJP2000241225

Mechanically coupled helmholtz resonators for broadband acoustic attenuationUS6069840

Vehicle wheelEP0936083


RECIPROCATING COMPRESSOR




15/25

JP2000161220



RECIPROCATING COMPRESSOR

JP2000161216

PULSATION DAMPING DEVICEJP11201367

VACUUM CLEANER AND SUCTION PORT BODY THEREFORJP2000126098

Sound-absorbing plateDE19841975

Combustion engine with EGR device, especially diesel engineEP0911510

Air induction device for IC engine has Helmholtz resonator

DE19833326

Device for directed noise attenuation in a turbomachineEP0974788

Variably tuned helmholtz resonator with linear response controllerEP0894970

Noise absorption device for a centrifuge motor-fan unit in an automobile air conditioning systemFR2780454

Integrated resonator and filter apparatusUS6048386

PASSIVE RADIATOR

JP11346395

Combined air cleaner-resonatorEP0896148

Noise attenuator for an induction system or an exhaust systemUS6009705

INTEGRATED DUCT AND RESONATORWO9849440

HORN LOADED MICROPHONE WITH HELMHOLTZ RESONATOR ATTENUATORWO9851122

STRUCTURE OF SOUND ABSORBING MATERIALJP11259076

INTAKE DEVICE FOR INTERNAL COMBUSTION ENGINEJP10227261

PROCESS FOR REFINING THE MICROSTRUCTURE OF METALSWO9830346

Vehicle interior noise level suppressionDE19755751

Motor air intake silencerDE19754840

TELEPHONE HANDSETJP10229435

EXHAUST MUFFLER FOR VEHICLEJP11062547




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RESONATORJP11044266

Noise determination method for road or railwayDE19726608

COGGED BELT DRIVE OF INTERNAL COMBUSTION ENGINE MECHANISMSRU2131524

DIFFERENTIAL MICROPHONE ASSEMBLY WITH PASSIVE SUPPRESSION OF RESONANCESCA2205722

REFRIGERATORJP10306972

AIR INTAKE SYSTEM FOR AN INTERNAL COMBUSTION ENGINEWO9742408

Refining microstructure of metals continuously cast by Hot Top techniqueFR2761624

Wheel tyre and road noise reducerDE19710029

SOUND ABSORBING DEVICE AND SOUND ABSORBING STRUCTURE FOR ROOMJP10227084

Refining microstructure of metals continuously cast by Hot TopFR2758101

Tunable acoustic systemUS5930371

Valve for an air flow channelEP0800030

LININGJP9175436

ResonatorEP0778399

Sound absorption structureUS5783780

Sound absorbing wheel-housing coverEP0769422

Tyre/road noise reduction arrangementEP0769421

Device for damping thermo-acoustic vibrations in combustion chamber of gas turbineDE19640980

Sound absorber element for absorber platesDE19640087

SOUND REPRODUCTION DEVICEJP10075494

Acoustic alarm employing a resonant cavity arrangementGB2316784

Sound absorptive hollow core structural panelUS6021612

STANDING WAVE SPACER FOR INTERNAL COMBUSTION ENGINEJP10008990

POLYGON SCANNERJP9311286




17/25

LINT HANDLING SYSTEMCA2174460

HELMHOLTZ RESONATOR LOUDSPEAKERWO9631106

SILENCERJP9212176

Adjustable silencer for air intake of vehicular combustion engineFR2743848

SOUND ABSORBERJP9198051

Arrangement for reducing tire/road noiseUS5839761

MAGNETIC TAG EXECUTING ACOUSTIC OR MAGNETIC INQUIRYJP8249431

System for absorption of air noiseDE19533623

SOUND ABSORBING MATERIALJP9062267

TELEVISION RECEIVERJP8322095

Assembly for reducing tyre/road surface noise.EP0680866

DAMPING DEVICE FOR THERMO-ACOUSTIC VIBRATION IN COMBUSTION CHAMBERJP7293885

Engine enclosure air inlet/discharge sound attenuatorUS5625172

Sound absorber for motor vehiclesUS5681072

HELMHOLTZ HYDRAULIC PRESSURE PULSATION FILTER OF GAS SEALED TYPEJP8240202

GAS-TURBINE ENGINE AFTERBURNERRU2117806

Apparatus for acoustic noise reductionUS5508477

Sound absorption system for automobileDE4446080

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

PRODUCTION OF SOUND ABSORBING MATERIALJP8166787

Dynamics free low emissions gas turbine combustorUS5644918

Vehicle with IC engineDE4435296

Method and composite resonator for tuning an engine air induction systemUS5572966

INTAKE STRUCTURE OF ENGINEJP8093583

ADAPTIVE MANIFOLD TUNING




18/25

WO9511373

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

RESONATOR TYPE SOUND-ABSORBING BODY AND SOUND-ABSORBING CEILINGJP8013642

Vibration-insulating panel element

US5473125

MULTIBLADE BLOWERJP7332284

Sound-proofed swimming poolFR2718479

SILENCER FOR ATTENUATING DISCHARGE NOISES...WO9419596

Quantitative determination of air present in refrigerant sampleUS5524477

RESONATOR

JP7208287

VOLUMETERJP7190834

PISTON POWER MACHINE OR WORKING MACHINEJP6213072

HAND-HELD APPARATUS RADIATING SOUNDJP6223215

GAS TURBINE COMBUSTION DEVICEJP7139738

SOUND FIELD ADJUSTING DEVICE

JP7160268

COMBUSTION CHAMBER OF GAS TURBINEJP6221563


SILENCER DEVICE FOR COMBUSTION ENGINEJP6202673

VOLUMENOMETERJP7083730




Silencer arrangement for combustion engines.EP0589516

Exhaust gas system of an internal combustion engineDE4330129

Sound absorption method for motor vehicles.EP0586831

SECONDARY BURNERJP6094227




19/25


Air intake device for an internal combustion engine.EP0569714

A refrigeration compressor.EP0561383

Piston-type engine with valve coverDE4305281

Covering element.EP0584442

Sandwich construction panel for acoustic insulationFR2700179

Noise-attenuating internal combustion engine air intake systemUS5424494

Sound-absorbing housing cladding for machineDE4241515

Piezoelectric sound sourcesUS5386479

Low frequency sound generation system for use in vehicular passenger compartmentsUS5394478

SOUND VOLUME CONTROLLER FOR PIANOJP6149232

Device for determining the volume of objects using a chamber with two resonatorsUS5385069

Earplug and hearing devices formed in-situUS5333622

SPEAKER EQUIPMENTJP6038290

Acoustic muffler for high volume fluid flow utilizing Heimholtz resonatorsUS5276291

Musical instrument incorporating a Helmholtz resonatorUS5248846

Gas turbine combustor.EP0576717

RECIPROCATING TYPE ELECTRIC RAZORJP6000261

Self-supporting wall with sound absorbing properties.EP0518305

Guard-rail with sound absorbing properties.EP0518304

CALIBRATION OF SEISMIC STREAMERS IN A HELMHOLZ RESONATORUS5210718

AIR SUCTION DEVICE FOR INTERNAL COMBUSTION ENGINESDE4215416

EXTENDED FREQUENCY RANGE HELMHOLTZ RESONATORSWO9321625

NOISE REDUCTION DEVICEJP5195746




20/25

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

SOUND ABSORBING BODYJP5158484

CVD FILM FORMING DEVICEJP5117860

Silencer arrangement for internal combustion engines.EP0481450

NOISE REDUCTION DEVICEJP5059927

No title availableJP5294230

SILENCER FOR FAN OF HOVERCRAFT(R)JP5016795

ACTIVE MUFFLING DEVICEJP4350314


Loudspeaker system.EP0456416

SOUND ABSORBING PANELCA2040076

Exhaust system for small planing boatUS5234364

Method and means to adjust sound characteristics of club head upon impact with golf ballUS5064197

ACTIVE TYPE PULSATION PRESSURE ABSORBERJP6026448

HELMHOLTZ RESONANCE TYPE WIDE BAND TRANSMITTER-RECEIVERJP4278798

ROTARY TYPE ENCLOSED COMPRESSORJP4265490

Tubewave damper probe for seismic applicationsUS5171943

SPEAKER UNITJP4369996

METHOD AND DEVICE FOR REGENERATING SOOTY SMOKE FILTER IN DIESEL ENGINEJP3242413

ROTARY COMPRESSORJP4159490

INTERNAL SIDEBRANCH RESONATORUS5162621

INTAKE PIPE WITH INTAKE RESONATORJP4109071

METHOD AND APPARATUS FOR MONITORING AND CONTROLLING A HEAT GENERATORCA2020832

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

Quasi-optical gyrotron




21/25

US5052003

LASER PRINTER DEVICEJP4000469

EXHAUST DEVICE FOR SMALL SPEEDBOATJP3295791

PULSE COMBUSTION APPARATUS

CA2013491

DIRECT RADIATION TYPE SPEAKERJP3201796

Fan silencer apparatusGB2237323

VARIABLE TENSION TRANSDUCERJP2123900

Acoustic apparatus.EP0361445

VOLUMETER

JP3108614

Acoustic apparatusUS4987601

ELECTRIC ACOUSTIC UNIT CONVERTERJP2075299

NOISE-SUPPRESSING DEVICEJP2161134

Keyboard instrument.EP0347775

IC engine exhaust system - incorporates Helmholtz resonator

DE3916429

GAS LASERJP2285686

GAS LASER DEVICEJP2281676

GAS LASER DEVICEJP2270384

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


Acoustic apparatus.EP0336303

Acoustic Apparatus.EP0334238

Method and apparatus of expanding acoustic reproduction range.EP0334217


Passive structural and aerodynamic control of compressor surgeUS5199856

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




22/25

INTAKE DEVICE FOR ENGINEJP2176113

METHOD AND APPARATUS FOR MONITORING AND CONTROLLING A HEAT GENERATORWO8906771

Sound insulation panel for preset frequency bandsIT1225514

Compressor noise attenuation using branch type resonatorUS4927342

ACOUSTIC DEVICEJP2113697

MEASURING APPARATUS OF INTERNAL VOLUMEJP2064418

ELECTRIC/ELECTRONIC MUSICAL INSTRUMENTJP2041098

ELECTRIC/ELECTRONIC MUSICAL INSTRUMENTJP2041097

PORTABLE ELECTRIC MUSICAL INSTRUMENTJP2029795

PORTABLE MUSICAL INSTRUMENTJP2029794

AUTOMATIC WASHERJP2026598

ELECTRONIC MUSICAL INSTRUMENTJP1319792



ACOUSTIC EQUIPMENTJP1254098




MAGNETIC RESONANCE IMAGING DEVICEJP1201247

VOLUMETERJP1184417



BODY RESONANCE INSTRUMENTJP1144099

VOLUME MEASURING INSTRUMENTJP1118722




23/25

PRINTERJP63239076

A silencing ventilating deviceEP0265000

Method and apparatus for nonintrusively determining mach numberUS4829813

VOLUMETERJP63298013

Acoustic inspection methodEP0242060

Sound attenuating boxUS4787473

VOLUMETERJP63113315

VOLUMETERJP63044127

Method of mounting a piezoelectric helmholtz transducer on a printed circuit boardUS4630342

ACOUSTIC DISPLACEMENT METERJP62070705

Measure for reducing the sound emitted from railway railsDE3532765

SILENCER DEVICE FOR INTERNAL COMBUSTION ENGINEJP62038815

FLUID DRIVING APPARATUSJP61265396

Heating boilerDE3517859

Exhaust system for outboard motorsUS4897060

SILENCER DEVICE OF ADAPTABLE TYPEJP61129414

Infra-sonic intensification of glow bedSE456524

Method and apparatus for acoustically measuring the volume of an objectUS4640130

Sound probeDE3439546

SOUND ABSORPTIVE STRUCTURAL BLOCK WITH SEQUENCED CAVITIESCA1214396

Exhaust system for outboard motorsUS4607723

INTERNAL COMBUSTION PISTON ENGINE USING AIR CHAMBER IN PISTONCA1242121

SPEAKER DEVICEJP61020490

Broadband matching networkUS4644505

Low noise hand-held hairdryer




24/25

US4596921

Sound-absorbing building elementDE3412432

Sound attenuating ventilating boxNL8304487

Burner for the processes of the autogenous welding technique

DE3329937

PULSER BURNERJP60038514

PULSATING COMBUSTION APPARATUSJP60033408

GASEOUS COMPONENT DETECTORJP59212761

General purpose modular acoustic signal generatorUS4602245

PIEZOELECTRIC TYPE LOW FREQUENCY TRANSDUCER

JP59190795

Method and apparatus for low frequency active attenuationUS4527282

APPARATUS FOR DETECTING GAS TEMPERATUREJP59160730

Gas pressure regulatorGB2136095

BAR FOR A POWER CHAIN SAWCA1173330

Passive acoustic absorber device also absorbing low frequencies

FR2540912

Vehicle roof liner.EP0079253

INFRARED RAY DETECTORJP59054950

Low frequency mufflerUS4501341

SOUND SUPPRESSOR LINERCA1160850

CYLINDER BLOCK OF INTERNAL-COMBUSTION ENGINEJP58107839

Directional microphone with high frequency selective acoustic lensUS4401859

Perforate tube mufflerUS4371053

Electro-acoustic transducerUS4379212

Piezo-electric ringing transducer.EP0025955

COMPACT EXHAUST SILENCER FOR DIESEL LOCOMOTIVESCA1138780

Two stroke cycle engine with sustained power strokeUS4370959




25/25

Mufflers for percussive pneumatic machinesUS4294330

ELECTRONIC AUDIO SIGNALLING DEVICE FOR TELEPHONESCA1138137

SOUND-ATTENUATING MUFFLER FOR EXHAUST GASESCA1123749

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