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Topic: Acoustical impedance

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Sound impedance

Particle velocity

Particle amplitude

Sound intensity

Particle velocity level

Acoustic theory

Sound intensity level

Acoustics

Speed of sound

Sound energy flux

Characteristic impedance

Density of air

Sound

Sound power

Sound pressure level

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	Ultrasonic transducer and examination method - Patent 4205686
		The characteristic acoustic impedance of the transformer material is approximately the geometric mean of the characteristic acoustic impedance of the emitter and the subject.
		The acoustic impedance transformer 28 is a quarter wave transformer and consists of a portion of epoxy material formed in a concavo-convex configuration having a radius of curvature substantially equal to that of the emitter 22.
		It is preferably that the characteristic acoustic impedance of the material of the transformer 28 be approximately equal to the geometric mean of the characteristic acoustic impedances of the emitter material and the subject.
	www.freepatentsonline.com /4205686.html (4155 words)

	Ultrasonic log grading - Patent 5097881
		The ultrasonic wave 46 transmitted through the log 14 is delayed in the log an amount of time determined by the acoustical impedance of the portion of the log in the path of such sound wave before it is received by the selected receiver transducer 40.
		Such acoustical impedance is determined by the density of the wood in such log and defects in the log, such as knots, change such density which affects the speed that the ultrasonic wave traverses the log.
		The computer 30 determines the acoustical impedance or density along the log and compares it with predetermined acoustical impedance or density information stored in the computer for different species of wood to determine the grade of the log from the time interval signals received at inputs 50 during the scanning of the log.
	www.freepatentsonline.com /5097881.html (5083 words)

	What is acoustic impedance?
		Acoustic impedance is a ratio of acoustic pressure to flow (and is somewhat analogous to electrical impedance).
		Like electrical impedance, acoustic impedance is complicated by the fact that the current and pressure are not necessarily in phase -- the maximum voltage may be ahead of the maximum current, or vice versa.
		The acoustic impedance of the flute for any particular fingering is one of the major factors which determines the acoustic response of the flute in that fingering.
	www.phys.unsw.edu.au /jw/z.html (1616 words)

	With impedance matching means - PatentStorm (Site not responding. Last check: )
		An acoustic matching member that is incorporated into an ultrasonic transducer for transmitting and receiving ultrasonic waves, includes: at least two layers including a first layer and a second layer that have different acoustic impedance values from each other.
		An acoustic matching member 1 is used, when a sound is propagated from a first object to a second object, for matching an acoustic impedance of the first object and an acoustic impedance of the second object.
		An acoustic impedance-matching transformer includes a tapered acoustic energy transmission (metal) block, having an acoustic impedance less than that of a piezo-electric transducer in a metric direction toward that of the acoustic propagation medium of the waveguide, and by an amount that allows...
	www.patentstorm.us /class/367/152-With_impedance_matching_means.html (1563 words)

	Peavey.com :: Impedance in Audio Technology
		When discussing a technical subject such as impedance, it is necessary to employ mathematics to illustrate the relationship between voltage, current, impedance, and the resultant power produced in the circuit.
		Third is the impedance of the air or the acoustic impedance that the combination loudspeaker/enclosure encounters.
		Since the acoustic signal produced by the loudspeaker is now restricted within the walls of the horn, the speaker is said to be loaded by the horn.
	www.peavey.com /support/technotes/concepts/impedance_2.cfm (2696 words)

	Acoustic impedance (Site not responding. Last check: )
		The acoustic impedance Z (or sound impedance) is the ratio of sound pressure p to particle velocity v in a medium or acoustic component.
		The characteristic impedance of a medium (usually air, but also for instance exhaust gases in a muffler) is the ratio of sound pressure p to particle velocity v in open field (i.e.
		The acoustic impedance Z of an acoustic component (in Pa·s/m) is the ratio of sound pressure p to particle velocity v at a transition with a previous component:
	www.punweb.com /article/Acoustical_impedance (248 words)

	Acoustical Impedance
		The electrical analog is a transmission line, a cable with an impedance change at a point or points along the cable.
		Impedance is a function of frequency and resistance is not.
		An acoustic impedance is one ohm (cgs) when a sound pressure of 1 microbar produces a volume velocity of 1 cubic cm per second.
	nde.appliedphysics.swri.edu /pipermail/nde/1999-August/006291.html (348 words)

	Absorptive sonar baffle (Site not responding. Last check: )
		A compliant mass is acoustically coupled to the fluid to augment fluid particle velocity through the screens and to further absorb energy.
		Acoustic baffles are often used with sonar arrays to provide discrimination against noise sources in certain directions as well as to alter the shape of the array's directivity pattern.
		The construction of the acoustical mass is such that the rigid plates 66 distribute the incident acoustical energy evenly across the volume of the foam core 68 and the encapsulating jacket 70 serves to protect the foam core from deterioration from sea water exposure, for instance.
	www.stickebana.com /scitech/pheological_measurement/absorptive_sonar_baffle.html (2632 words)

	Acoustical Terms
		Acoustics - The science of sound and its properties/effects on a given environment.
		Impedance - The resistance to the flow of electric energy measured in ohms.
		Gates are ideal for greatly reducing acoustical noise on stage.
	www.learnchurchsound.com /definitions/acoustical-terms.php (1846 words)

	Engineering Acoustics/Electro-acoustic analogies - Wikibooks, collection of open-content textbooks
		Acoustical resistance models loss due to viscous effects (friction) and flow resistance (represented by a screen).
		Namely, for impedance analog, pressure is analogus to voltage and volume velocity is analogus to current, and vice versa for mobility analog.
		Impedance and Mobility analogs for acoustical generators of constant pressure and constant volume velocity are as follows:
	en.wikibooks.org /wiki/Engineering_Acoustics/Electro-acoustic_analogies (437 words)

	Ambient noise canceling physiological acoustic monitoring system & method invention
		The processor is further configured to amplify the filtered audio output signal, route the filtered audio output signal and the set of input data to the display, collect an ECG signal and an impedance pneumography signal to distinguish an onset and an offset, and synchronizing the onset and the offset.
		The ambient environment is also monitored (immediately adjacent to the patient microphone), as well as the audible vibration frequencies from the patient bed/stretcher that are transferred from surrounding structures that are generated by engines, transmissions, generators and other noise sources in the environment.
		An ECG input 234 and an impedance pneumography input 236 are inputted into the processor 230, and are utilized in an algorithm with the noise canceled input signals 218, 220, 222, 224 to produce a filtered audio output 238.
	www.freshpatents.com /Ambient-noise-canceling-physiological-acoustic-monitoring-system---x26--method-dt20070104ptan20070003072.php (1863 words)

	Electroacoustical transducer comprising piezoelectric element (Site not responding. Last check: )
		In front of the element is a resonant acoustical cavity that matches impedance of the element to that of the ambient medium and comprises concentric axially short large and small diameter cylindrical chamber portions, the small diameter portion providing a front outlet from the large diameter one.
		It is well known that piezoelectric acoustical transducers have heretofore been relatively inefficient because of an inherent mismatch between the acoustic impedance of the transducer element of such a transducer and the impedance of the medium in which the device is intended to operate.
		It is also a specific object of this invention to provide an electroacoustical transducer having a transducer element which is electro-mechanically efficient and having compact means for closely matching the acoustic impedance of the transducer element to that of the ambient medium in which the element operates.
	www.emergenthomestore.com /techcat/marine_transmission/electroacoustical_transducer_comprising_piezoelectric.html (2121 words)

	Droplet Switching (Site not responding. Last check: )
		Acoustic energy is increasingly utilized, directly or indirectly, in a large number of fields, including medical ultrasound diagnostic imaging, thermal bubble-jet inkjet personal printers, piezo-jet inkjet personal printers, non-destructive testing, sonar, and microphone technologies, to name a few.
		For example, for acoustic microswitching, the acoustical impedance and acoustic attenuation of the fluid/bubble are important, whereas these are not important for the referenced prior art visible optical energy microswitching.
		Practitioners of the acoustic arts are aware that the ability of a bubble to totally block acoustic propagation is primarily related to its high acoustic reflection coefficient due to the abrupt change in acoustic impedance traveling from fluid to the vapor (or gas) bubble.
	www.ipfoundry.biz /microdroplet_switching.htm (10729 words)

	ORION - GLOSSARY
		This ratio is usually given as the amount of energy measured in Decibels at a distance of one meter from the input of one watt of electrical energy.
		In practical terms, this means that most Drivers are assigned a certain nominal impedance based on their DC voice coil resistance and mechanical stiffness.
		Sometimes known as an Acoustic suspension type, the sealed enclosure is a simple design in which each woofer is mounted in a sealed, airtight box or compartment with a specific internal volume for precisely the woofer being used.
	www.orioncaraudio.com /Technology/Glossary.aspx (5228 words)

	Acoustic Circuits
		Therefore, we identify the acoustical inductance as L' = ρL/A. Acoustical inductance is the consequence of the kinetic energy of the air.
		This is the characteristic impedance of the pipe.
		The acoustic impedance is higher at the small end, or throat, and lower at the large end, or mouth, so the conical horn is an impedance transducer.
	www.du.edu /~jcalvert/waves/acoucirc.htm (9232 words)

	Fundamentals of Ultrasonic Imaging and Flaw Detection- Developer Zone - National Instruments
		The factor that describes this relationship is referred to as acoustical impedance and the acoustical impedance ratio.
		The acoustical impedance ratio is the impedance of the second material divided by the first.
		For example, when ultrasonic waves are passed from water to steel, the acoustical impedance is approximately 20 to 1; whereas, when ultrasonic waves are passed from air to steel, the acoustical impedance is approximately 100,000 to 1.
	zone.ni.com /devzone/cda/tut/p/id/3368 (1537 words)

	Car Audio - Passive Crossovers
		Impedance rise occurs more often in midrange loudspeakers (usually at the upper frequency range of the loudspeaker).
		A Zobel is a filter used to stabilized loudspeaker impedance in a crossover-speaker circuit.
		The net result is neither a rise or fall in resistance to the amplifer or acoustical output at the crossover frequency as indicated by the yellow line between the low pass and high pass curves.
	www.the12volt.com /caraudio/cross.asp (1283 words)

	MMD Archives: Reeds and Resonators in Organ Pipes
		It is a _high_ impedance device, impedance Z = P/Q. As a contrary, a flue mechanism converts the blowing pressure into a jet of high velocity but a very low pressure, almost zero, same magnitude as the audible sound pressure.
		A high impedance source (reed) connects to where there is a pressure maximum and flow minimum, essentially a _closed_ end of the resonator.
		To be efficient a low impedance source should be connected at a pressure minimum and flow maximum, that is, to an _open_ end of the resonator.
	mmd.foxtail.com /Archives/Digests/200004/2000.04.18.06.html (1912 words)

	The Enigma of Sound Power Measurements at Low Frequencies
		The investigation of the influence of impedance on the radiated power of a sound source was carried out by determining the change in the sound pressure level in the middle of the room when the sound source was placed at different distances from the walls and corners of the reverberation room.
		If the impedance in the room should have a significant influence on the radiated power, it should clearly show up in these measurements, as the room impedance is different close to the wall than at some distance from it.
		This is to be expected as the impedance close to the wall at lower frequencies is always higher than the impedance in the middle of the room.
	www.zainea.com /enigma.htm (6458 words)

	Pro Subwoofers At Parts Express
		Acoustical performance is certainly something to consider, but size, shape, and of course cost are also factors that are best established before the project goes very far.
		The transmission line, or TL, is also known as an acoustic labyrinth because of the long and somewhat complicated path that the rear radiation of the speaker must pass through before exiting the enclosure.
		The horn serves as a transformer that matches the high acoustical impedance or pressure presented by the driver at the small throat of the horn to the lower acoustical impedance seen by the air at the larger mouth of the horn.
	www.partsexpress.com /webpage.cfm?&DID=7&WebPage_ID=239 (7113 words)

	Audio Glossary of Terms for Audio Editing, Audio Restoration, Audio Enhancement and CD Making
		Acoustical impedance is the total opposition provided by acoustical resistance and reactance to the flow of an alternating pressure applied to a system.
		Acoustical reactance is the imaginary part of the acoustical impedance.
		The cable exhibits a characteristic impedance which is independent of cable length (after past a few wavelengths) which is of a constant value related to its ratio of distributed inductance and capacitance.
	www.enhancedaudio.com /terms.htm (5148 words)

	The Physics of Dreamtime: An analysis of the acoustical properties of a didgeridoo
		It's important to note that the Acoustical Impedance and the area are inversely related, and that every change in diameter will result in a reflection of some sound waves.
		I say that the overtones appear in decreasing intensity "for the most part" because in addition to the intentional accentuation, there is a spike at around 300 Hz is which is significantly louder than its neighbors in all the tones, and is the loudest component besides the drone fundamental.
		Since changes in diameter give a change in Acoustic Impedance, and therefore a place for reflection (an opening being an infinite change in diameter), it's reasonable to assume that these irregularities in the shape of the didgeridoo are strengthening the overtones its fundamental.
	www.didjshop.com /physicsDidjDreamtime.html (4283 words)

	Measurement and simulation of the acoustical impedance of an internal combustion engine exhaust
		The objective of this research is the determination of the acoustical impedance of an internal combustion engine exhaust.
		The method uses the transfer function between two microphones positioned on a waveguide connected to the impedance to be measured.
		Some special cases are simulated, to determine the engine components, which contribute primarily to the acoustical impedance.
	www.mech.kuleuven.be /mod/past/past_01_01.en.html?printable= (297 words)

	IEN - Acoustics Department
		The Acoustics Department carries out research and measurement activity in the field of applied and physical acoustics in two principal areas: first, the realization and maintenance of the national standard of sound pressure and its direct application to acoustic measurements and secondly the investigation of photoacoustic and photothermal phenomena in solids and gases.
		As to the measurement of acoustical properties of materials, the traditional certification activity has been completed by a research activity concerning the development of mathematical models for the prediction of sound transmission in multilayer structures.
		The static pressure, which influences the acoustical impedance of the coupling between the microphones, is now measured at each step and the uncertainty is reduced, in particular when the weather conditions are not stable during the measurement.
	www.ien.it /ar97/ac.htm (1078 words)

	Boston Audio - Mat 1 Turntable Mat
		Through the use of pure carbon and proprietary tuning techniques, the Mat 1 offers a unique acoustical impedance ideally suited to the platter/vinyl interface.
		The specific grade of carbon selected for the Mat 1 was painstakingly chosen from a variety of samples that differed significantly in their acoustical properties.
		The physical design was also chosen to enhance the beneficial effect of using pure carbon graphite, including a 0.5mm cut out that accommodates the paper label of all records, ensuring the maximum contact between the mat and vinyl.
	www.boston-audio.com /mat1.html (391 words)

	Characteristics of Piezoelectric Transducers
		Optimal impedance matching is achieved by sizing the matching layer so that its thickness is 1/4 of the desired wavelength.
		For contact transducers, the matching layer is made from a material that has an acoustical impedance between the active element and steel.
		Immersion transducers have a matching layer with an acoustical impedance between the active element and water.
	www.ndt-ed.org /EducationResources/CommunityCollege/Ultrasonics/EquipmentTrans/characteristicspt.htm (651 words)

	AES 115th Convention: PAPERS - SESSION G
		To fully describe the sound field at a listening position in an acoustical environment, the distribution of energy arriving from varying spatial directions is required, which this research accomplishes through the use of microphone array beamforming.
		The method relies on an MLS (maximum length sequence) excitation signal to measure the acoustical impedance of a specimen of material placed at the termination of a long tube.
		Whereas the traditional methods require that measurements be made at multiple locations within the tube, either using a multichannel data acquisition system, or by physically moving a single microphone from one location to the next, the novel method requires only a single measurement at one location in the tube, using a single microphone.
	www.aes.org /events/115/papers/SessionG.cfm (856 words)

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