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
US6665413
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
US2002085723
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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Process for the preparation of
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Pressure sensing device adapted
to corrosive or explosive atmospheres and with means to filter
disturbance frequencies
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Resonator device for e.g. non
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INLINE HELMHOLTZ TYPE RESONATOR
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clutch of motor vehicle
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Hydraulic system for motor
vehicle
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COOLING DEVICE AND ELECTRONIC
DEVICE COMPRISING SUCH A COOLING DEVICE
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LITHOGRAPHIC APPARATUS HAVING
ACOUSTIC RESONATOR
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Microphone for audio source
tracking
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Novel Helmholtz resonator
CN101435356
EXHAUST DEVICE FOR STRADDLE-TYPE
VEHICLE AND STRADDLE-TYPE VEHICLE
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MICROREACTOR DEVICE
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Noise attenuation device for a
centrifugal compressor discharge or suction nozzle
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MEASUREMENT OF SOUND SPEED OF
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Method and device for achieving
better heat transfer when using pulse heaters
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SILENCER OF INTERNAL COMBUSTION
ENGINE
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Supply gas cooling circuit for
overheating turbo-compressor of motor vehicle
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Acoustic liner for gas turbine
engine manufactured by an additive fabrication process
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HANDHELD ELECTRONIC DEVICE HAVING
OFFSET SOUND OPENINGS
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MOTORCYCLE AIRBOX WITH HELMHOLTZ
RESONATOR
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HERMETIC COMPRESSOR
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RESONATOR
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TURBINE ENGINE FUEL INJECTOR WITH
HELMHOLTZ RESONATOR
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Recess lower cross member for
motor vehicle, has Helmholtz resonator
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Cross head for dashboard of motor
vehicle, has acoustic resonator
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Apparatus for delivery of
pressurised gas
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Novel Helmholtz resonator
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Earphone with acoustical filter
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Adjustable helmholtz resonator
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INTAKE NOISE MUFFLING DEVICE AND
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RESONATOR WITH INTERNAL
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ACOUSTIC FLOW STRAIGHTENER FOR
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HELMHOLTZ RESONATOR
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Porous acoustic material for
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Silencer for an exhaust system
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PNEUMATIC TIRE
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PNEUMATIC TIRE
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SPEECH COMMUNICATION DEVICE
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Assessing Porous Media Properties
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INTAKE ASSEMBLY HAVING HELMHOLTZ
RESONATORS
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VEHICULAR SOUND-PROOF STRUCTURE
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Device for attenuating cavity
noise in a tire and wheel assembly
EP1932689
ELECTRONIC DEVICE AND SOUND
PROOFING METHOD FOR THE SAME
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Combustion Control for a Gas
Turbine
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Helmholtz resonator type marine
signal
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Combustion chamber for a gas
turbine engine
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Exhaust silencer for automotive
vehicles
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NOISE SUPPRESSOR, ELECTRONIC
APPARATUS AND CONTROL METHOD
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Vacuum cleaner equipped with a
noise-attenuation device
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Thermoacoustic Device
US2008060364
Gas turbine helicopter engine
with reduced sound emissions due to acoustic treatment of a jet
pump
EP1902948
METHOD FOR CLEANING OF SPENT
GASES...
RU2361094
Resonator device at junction of
combustor and combustion chamber
US2008041058
A SILENCER, A MARINE VESSEL AND A
METHOD OF SILENCING A MARINE EXHAUST
WO2008012501
Combustion chamber for gas
turbine of power plant system
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CENTRAL BODY OF TURBOJET NOZZLE
JP2007292064
INSULATION DEVICE FOR STEERING
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CENTRAL BODY FOR A TURBOJET
EXHAUST CHANNEL, TURBOJET
US2007272477
PNEUMATIC TIRE
JP2007269144
Handheld electronic device having
hidden sound openings offset from an audio source
US2007252810
Noise reduction of rotary mowers
using an acoustical helmholtz resonator array
US2007234699
Sound absorbing device for
FR2899537
Flushing system for a vacuum
toilet bowl, especially in an aircraft, has a Helmholtz
resonator
DE102006014011
A GOLF CLUB DRIVER HEAD HAVING
HELMHOLTZ RESONATOR
KR20070078374
Combustion chamber
DE102006007711
A GOLF CLUB DRIVER HEAD HAVING
HELMHOLTZ RESONATOR
WO2007086676
AIR SUPPLY REGISTER
JP2007139223
Acoustic resonator e.g. Helmholtz
resonator, for use in motor vehicle
FR2895714
Low-noise cabinet type air
conditioner
CN2893501
Silencer
EP1785602
Resonator performance by local
reduction of component thickness
US2007102235
Heating device e.g. oil-heated
heating device, has helmholtz-resonator
DE102005052881
Cannula handle and storage system
US2007093755
SPEAKER SYSTEM
JP2007060099
Resonating device for combustion
chamber
EP1775515
CANNULA HANDLE AND STORAGE SYSTEM
WO2007038433
Motor vehicle engine with Exhaust
Gas Recirculation ... Helmholtz resonator
FR2891015
MUFFLER FOR ELECTRONIC
EQUIPMENT...
JP2007047560
Exhaust system with external
Helmholtz resonator and associated method
US2007051556
Fuel injection device for
internal combustion engine of motor vehicle...
FR2890415
FLUID VOLUME DETECTING DEVICE
JP2007017320
INTAKE DEVICE
JP2007016652
Handheld electronic device having
offset sound openings
US2007025582
Silencer for use in exhaust
system of motor vehicle, has helmholtz chamber and resonator
pipe...
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 RESONATOR
KR20050012042
STRUCTURE INSTALLED IN CAVITY
BETWEEN HEAD LINING AND ROOF PANEL...
KR20050008931
LOUDSPEAKER SYSTEM COMPRISING A
HELMHOLTZ RESONATOR...
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HELMHOLTZ RESONATOR AIR INLET
SYSTEM FOR VEHICLE
KR20060001216
NOISE REDUCTION APPARATUS...
USING HELMHOLTZ RESONATOR
KR20010037807
RESONATOR OF ENGINE INDUCTION
SYSTEM
KR20010028178
BAMBOO SOUND-PROOF WALL
KR20010011073
COMBINED AIR CLEANING AND
RESONATING APPARATUS
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COMPRESSOR
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NOISE-DECREASING DEVICE FOR
INTAKE MANIFOLD OF A CAR
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IMAGE FORMING APPARATUS
JP2006251590
RIM WHEEL AND MANUFACTURING
METHOD THEREOF
JP2006231966
DEVICE FOR MEASURING CHANGING
AMOUNT OF VOLUME
KR20020058784
APPARATUS FOR REDUCING INTAKE
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KR20020038217
MUFFLER FOR VEHICLE
KR20020030352
Silencer containing one or more
porous bodies
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Loudspeaker which can be used
with or without stand which acts as a helmholtz resonator
GB2422066
PIPE AND ITS MANUFACTURING
METHOD
JP2006144557
Combustion chamber for a gas
turbine engine
US2006123791
Exhaust gas muffler
DE102004056889
SOUND ELIMINATING STRUCTURE AND
STIRLING COOLING BOX
JP2006105514
HELMHOLTZ RESONATOR AND AN
EXHAUST LINE PROVIDED THEREWITH
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Noise insulating partition for
an internal volume, of an automotive vehicle, in particular.
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Devices and transducers with
cavity resonator to control 3-D characteristics/harmonic
frequencies
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Fluid pumping apparatus with
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extended output and field cancellation
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Wide band sound diffuser with
self regulated low frequency absorption and methods of
mounting
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Silencer device for exhaust-gas
turbocharger, has Helmholtz resonator
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ACOUSTICALLY STIFFENED
GAS-TURBINE FUEL NOZZLE
WO2006014300
Apparatus for reducing
thermoacoustic oscillations in combustion chambers
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Apparatus for reducing
thermoacoustic oscillations in combustion chambers
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US2006014114
Determining the depth of
perforation tunnels in a wellbore using the Helmholtz
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Resonator device and circuits
for 3-d detection/receiving sonic waves
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ELECTRIC CONNECTION BOX
JP2005304162
COMBUSTION APPARATUS HAVING
INSTABILITY REDUCTION MEANS
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VIBRATION DAMPING DEVICE FOR A
COMBUSTION CHAMBER
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ELECTRONIC SURVEILLANCE SYSTEMS
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Exhaust-silencer assembly for
motor vehicle exhaust system, has Helmholtz resonator
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burner and gas turbine
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Gas turbine
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JP2004352245
Muffler with helmholtz
resonator having multiple degrees of freedom
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Device for damping
thermoacoustic oscillations in a combustion chamber
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Improvement of acoustic
situation in passenger cabin of vehicle, comprising use of
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Vortex blower having helmholtz
resonators and a baffle assembly
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Diffuser and turbine
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thermoacoustic oscillations in a combustion chamber
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Sound damping device having a
Helmholtz resonator for installations with pulsating gas flows
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eg for vehicle i.c. engine air intake silencer
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Exhaust gas silencer with
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Venting device for internal
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Tuned Helmholtz resonator using
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CHANGE OF PUMP JET ROTOR
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Contactless inner eye pressure
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Protective helmet, especially
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Hard disk drive cover that
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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
