EP0473095A2 - Amortisseur de son hybride - Google Patents

Amortisseur de son hybride Download PDF

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Publication number
EP0473095A2
EP0473095A2 EP91114279A EP91114279A EP0473095A2 EP 0473095 A2 EP0473095 A2 EP 0473095A2 EP 91114279 A EP91114279 A EP 91114279A EP 91114279 A EP91114279 A EP 91114279A EP 0473095 A2 EP0473095 A2 EP 0473095A2
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EP
European Patent Office
Prior art keywords
absorber
sound
hybrid
passive
active
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EP91114279A
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German (de)
English (en)
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EP0473095A3 (en
Inventor
Fridolin Peter Prof. Dr. Mechel
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MECHEL FRIDOLIN PETER
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MECHEL FRIDOLIN PETER
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Publication of EP0473095A2 publication Critical patent/EP0473095A2/fr
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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1785—Methods, e.g. algorithms; Devices
    • G10K11/17861—Methods, e.g. algorithms; Devices using additional means for damping sound, e.g. using sound absorbing panels
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1787—General system configurations
    • G10K11/17875—General system configurations using an error signal without a reference signal, e.g. pure feedback
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/10—Applications
    • G10K2210/112—Ducts
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/50—Miscellaneous
    • G10K2210/509—Hybrid, i.e. combining different technologies, e.g. passive and active

Definitions

  • Mufflers are mostly lined with "passive" sound absorbers.
  • the interaction of the absorber lining with the sound field in the muffler duct is essentially due to the acoustic surface impedance of the absorber lining.
  • There is a so-called optimal surface impedance which is clearly described by the winding point of the so-called absorber function between the first and the second silencer mode. Realization efforts in the specialist literature have shown that it is fundamentally not possible to maintain this winding point impedance over a larger frequency range with purely passive absorber elements.
  • the noise to be reduced is superimposed by an electro-acoustic system on a sound wave generated by this system in such a way that there is a canceling interference in the direction of sound propagation (method of anti-noise).
  • Silencers are used to reduce the passage of sound through openings. In most applications, these openings are the clear cross sections of channels. Mufflers - and thus also the muffler according to the invention - are also used to reduce the passage of sound through joints (for example door joints) and through openings for material or for people to pass through (for example in soundproof capsules of machines and in soundproof booths). The openings are collectively called "channels" below.
  • the characteristics of the hybrid sound absorber according to the invention must be adapted to the shape of the clear cross section of the silencer duct.
  • the idea of the invention is developed here as an example for rectangular cross sections, as shown in Figure 1 , but is not limited to this shape.
  • the invention can also be used for other cross-sectional shapes, for example in the case of round or annular channels.
  • Silencers with a sound-absorbing lining basically have a sound-absorbing effect by fitting an absorber lining on the entire circumference or on part of the circumference of the clear duct cross-section, which (mostly only in parts, for example the air enclosed in porous materials) is excited to vibrate by the sound wave and thereby interacts with it, so that the sound wave is dampened as it propagates through the channel.
  • the clear cross section of the channel is often subdivided by sound-absorbing backdrops.
  • Such a backdrop silencer is shown in Figure 2 .
  • the idea of the invention is also applicable to such forms of absorber lining. Each gap in the backdrop is then treated like a silencer according to Figure 1 .
  • Sound absorbers are called "passive" if the resonance of the absorber lining is caused by the sound wave solely through mechanical (acoustic) interactions. The strength and phase of the resonance is then determined by the arrangement, the dimensions and the material properties of the absorber lining.
  • the selection of the components of the passive absorber in the silencer according to the invention is not restricted by the inventive concept. These can be, for example: porous sound absorbers made of fiber materials (mineral fibers, metal fibers, plastic fibers, organic fibers, open-cell foams, porous sintered ones Materials etc.), flexible plates, foils and membranes, perforated sheets, fabrics, fleeces etc.
  • These components of the passive absorber can either be in direct contact with one another or at a mutual distance from one another. For a more complete description of such absorber components and their acoustic properties, reference is made to reference [2].
  • the active subsystem consists of one or more sound recorders, one or more signal formers and one or more sound generators (usually: loudspeakers).
  • the sound pickups are mostly microphones, but can also be structure-borne sound pickups.
  • the signal formers for the output signal of the sound pickups are combinations of amplifiers, frequency filters and other electronic components known per se.
  • the sound generator is set into vibration by the electrical output variable of the signal shaper according to the inventive concept in such a way that its vibrating surface (for example a loudspeaker membrane) assumes an acoustic impedance according to the invention.
  • the electronic signal formers can in turn consist of passive and active electronic components (according to the language used in electronics); these can be known “analog” or “digital” functional units.
  • FIG. 3 A diagram of the active subsystem with the sound pickup (1), the signal former (2) and the sound generator (3) is shown in Figure 3 .
  • the loudspeaker of the active subsystem is arranged on the side of the passive absorber layer facing away from the channel and represents an acoustic terminating impedance Z b for this.
  • This arrangement hereinafter referred to as “series connection”, serves in the following as Example of the development of the inventive concept. It is shown schematically in Figure 4 . However, it is not the only possible arrangement according to the invention.
  • the channel-side surface of the sound-absorbing lining consists of an arrangement of "passive" and “active” partial areas.
  • the passive areas are formed by the surface of passive sound absorbers
  • the active areas are formed either by the surface of the loudspeakers or by mouths of loudspeaker chambers, which on their part can again be completely or partially filled with passive absorber components. This arrangement is also referred to as "parallel connection”.
  • Figure 5 contains a schematic representation .
  • Figure 8 shows the frequency curve of the damping D h of the lowest damped mode in a rectangular gap channel when the absorber function U of the absorber lining is at the winding point U wp at all frequencies.
  • the abscissa of this (and all of the following) representation of the damping D h is the product f ⁇ h in [Hz ⁇ m], because silencers can be summarized that meet certain "similarity laws". Note the logarithmic plot of the damping.
  • the publication DE 34 25 450 Al [20] also deals with the same aim, namely to reduce the depth of the link elements.
  • the cited document indicates that with a backdrop arrangement of backdrops of the same thickness with backdrop gaps of equal width in the intermediate region of such a jump, the channel width either loses sound absorption if the backdrop column increases proportionally with increasing channel width, or the pressure loss the muffler increased inadmissibly if you add another backdrop with increasing channel width and the backdrop column is reduced so that the added backdrop finds space.
  • the problem is to be solved by using scenes with different thicknesses.
  • suitable A combination of these makes it easier to realize a predetermined overall width of the link arrangement without having to change the ratio D / H, which is decisive for the damping and the pressure loss. Suitable combinations are given in detailed lists in this document.
  • FIG. 12 The principle of active sound attenuation, which is often referred to as “noise abatement through antisound", is shown in Figure 12 .
  • the sound wave from a noise source hits a microphone (1) in a channel. Its output signal is given to a loudspeaker (3) via a signal processor (2) (with amplification, filtering, delay time shift, etc.), which essentially Radiate sound that is intended to interfere with the sound of the noise source in a way that cancels it.
  • this interfering extinction is effectively only possible in one direction (forward direction); in the backward direction the sound tends to be amplified in most active systems.
  • a microphone (4) is also arranged behind the loudspeakers, the output signal of which is used to adaptively improve the parameters of the signal processor (2) via a controller (5) in the direction of minimizing the sound pressure at the location of the microphone ( 4).
  • Another loudspeaker technical problem is that the sound velocity of the Loudspeaker membranes must be about the same size as the sound velocity of the noise, but the sound pressure is almost zero due to the desired compensation.
  • the loudspeaker thus works on a sound field with a low field impedance.
  • the mechanical impedance of the loudspeakers must also be very low; the membranes must be light and soft and must make large strokes (at least at low frequencies).
  • Such loudspeakers are in turn not suitable for being exposed to turbulent flow.
  • a technical problem arises from the fact that the control microphone (1) on the side of the noise source not only picks up the sound field to be suppressed, but also the anti-sound emitted to the rear by the loudspeakers.
  • a method and a device for active sound attenuation are described in the published patent application DE 27 12 534 A1 [21]. It also defines the principle known as active damping, which consists in “that the energy content of (a) wave can be reduced by combining the primary wave with a specially generated secondary wave in such a way that the dilutions of the secondary wave with the Compression of the primary wave collapse and vice versa ".
  • active damping which consists in "that the energy content of (a) wave can be reduced by combining the primary wave with a specially generated secondary wave in such a way that the dilutions of the secondary wave with the Compression of the primary wave collapse and vice versa ".
  • the aforementioned publication emphasizes that the secondary wave must be generated exactly in relation to the primary wave to be canceled by it. It describes the difficulties in the precise generation of the secondary wave the principle of active damping and deals exclusively with methods and devices for obtaining the control signal for the sound source of the secondary wave.
  • the object of the invention is therefore to combine the absorber lining of a passive subsystem and an electroacoustic active subsystem in such a way that both work together to bring about a significant improvement in sound absorption compared to dampers of a known type.
  • a hybrid silencer consists of a passive absorber lining (passive subsystem) and an active electroacoustic system (active subsystem), which is characterized in that the electroacoustic active subsystem acts on the combined passive absorber in such a way that in the hybrid absorbers thus formed, the acoustic impedance of the channel-side surface of the absorber lining results in an absorber function U, which in a desired frequency range reaches or approximates the value of the absorber function U wp of the winding point between the first and the second silencer mode (main claim).
  • the absorber function U should therefore come sufficiently close to the value U wp of the absorber function in the upper winding point of the lowest damped mode, ie between the first and second damper modes, over a wide frequency range, especially at low frequencies. "Sufficient" should be measured by a significant improvement in sound absorption compared to dampers of known design.
  • the passive subsystem is a linear acoustic four-pole.
  • the terminating impedance Z b with which the absorber function U wp is achieved on the front of the hybrid absorber, results from the formula Z h is the front impedance of the passive subsystem alone if it is sound-proof on its rear side (idle case), and Z w is the front impedance of the passive subsystem alone if it is soundproofed on its rear side (short circuit -Case).
  • a passive subsystem consisting of a layer of thickness d of a porous absorber material, which is covered on its front by a thin cover layer.
  • the cover layer with the series impedance Z s consists of an acoustic parallel connection of a friction resistance R s with a mass reactance of a mass m s related to the area. Then the series impedance Z s of the cover layer follows: with the air density ⁇ o . If one chooses the resistance term R s large against the reactance term (2nd term in the denominator), then Z s describes the series impedance of a cover layer consisting of a (mass) foil. Conversely, if one chooses the reactance term large against R s , then one has a pure friction resistance, as is represented, for example, by woven and non-woven fabrics. If the cover layer is applied tightly to the porous absorber layer, the reactance of the elastic cushioning through the porous layer must still be connected in parallel. Since this is only a demonstration of the procedure, this further complication is dispensed with.
  • the terminating impedance Z b required according to the invention is thus known for the selected example of the passive subsystem.
  • Figure 14 shows an example of the so-called "locus" of the terminating impedance Z b in the complex plane with running frequency variables f ⁇ h in Hz ⁇ m.
  • the points drawn in the curve lie at thirds intervals of these variables.
  • the curve is composed of arcs, which are known to be simulated by resonance systems (see below under "Active subsystem”). At the circular arc to the right of the imaginary axis, sound energy goes into the active subsystem; here it basically represents an electronically controlled passive absorber.
  • FIG. 15 shows the associated locus of the terminating impedance Z b .
  • the locus here consists of an arc of a single-circuit resonance system at low frequencies and approximately the vertical straight line of a spring reactance at high frequencies.
  • the active subsystem must deliver energy at all frequencies.
  • a porous absorber layer in the passive absorber is not inevitable (although, as will be shown below, it is advantageous) for the realization of the inventive idea.
  • a porous absorber layer can be replaced by an air layer of the same thickness by using for it in the formulas ⁇ an ⁇ j and Z an ⁇ 1.
  • the structure of the passive subsystem according to the invention is not limited to the exemplary layer made of a porous absorber with a cover layer.
  • a method for determining the front-side impedance of an M-layered absorber is described in [16, Section 4.4]. whereby individual layers can also be air layers and the layers can also each have outer layers.
  • the determination of the termination impedance according to the invention is also not limited to the calculation methods exemplified here of an analytical-numerical description of the passive subsystem using dimensions and material data, although this route is preferable because it provides the best information for the dimensioning of the active subsystem (see below) .
  • the terminating impedance Z b formed with the measured values according to Eq. (7) can then be subjected to a numerical regression using known methods.
  • the structure of the active subsystem can expediently be taken into account (see below).
  • the determination of the terminating impedance Z b according to the invention is an intermediate step for the design of the active subsystem.
  • Z b is the acoustic input impedance of this active subsystem connected in series.
  • the essential part of the active subsystem is the acoustic impedance Z m of the loudspeaker diaphragm, since only it can be influenced by electronic control.
  • the terminating impedance Z b generally still contains acoustic components which cannot be influenced electronically. Such a portion is provided, for example, by the "loudspeaker box" with which the loudspeaker is bordered on the back.
  • Such a loudspeaker box is usually necessary, firstly, to avoid the sound of the loudspeaker vibration being released to the outside is radiated, but also to avoid that the pressure of the channel flow presses on the membrane.
  • Figure 18 shows schematically a hybrid absorber lining according to the invention including a loudspeaker box.
  • the loudspeaker box is partially filled with sound absorption material in order to avoid disturbing resonances of the membrane mass with the spring stiffness of the air cushion in the box (however, it can also be advantageous to use this resonance in a targeted manner to create one of the resonance loops of the local curve from Z b acoustically!).
  • the loudspeaker box is again to be described as a layered absorber with a reverberant termination.
  • speaker membranes are incompressible and thin compared to the sound wavelength (at least in the frequency range of interest here).
  • the terminating impedance Z b is still determined according to Eq. (7).
  • the input impedance Z e is obtained by using the calculation method for the input impedance of stratified absorbers described in [16, Section 4.4]. This subtask can thus be solved in the same generality as the determination of Z b .
  • Figure 19 shows the locus curve of the membrane impedance Z m to be set according to the invention of a structure according to Figure 18 , the air gap in front of the loudspeaker (for the meaning see below) here being 10% of the layer thickness in front of the loudspeaker and the loudspeaker box 80% with absorber material is filled.
  • the variable f ⁇ h points on the curve again at intervals of thirds) runs through the value range from approx. 4 [Hz ⁇ m] to 100 [Hz ⁇ m].
  • the passive absorber is layered in front of the loudspeaker with M absorber layers (including possible air layers) of thicknesses d i with length-related flow resistances ⁇ i and cover layers with series impedances Z s, i .
  • M absorber layers including possible air layers
  • cover layers with series impedances Z s, i .
  • M box absorber layers including any air layers with the thicknesses d i . Since the mass reactance of cover layers is mostly negligible at low frequencies, Z si ⁇ R s, i goes against the frictional resistance of the cover layers.
  • Z b becomes a linear polynomial in k o h and in Z m there is a reactance with the sign of a mass reactance and the frequency dependence of a spring reactance.
  • the electronic synthesis of this approximation in the active subsystem is very simple. This approximation is used below for examples of damping curves for silencers according to the invention.
  • the active subsystem supports the passive absorber by generating an appropriate terminating impedance Z b .
  • the admittance G p for any layered passive absorber can then be determined using the method described above. Furthermore, the terminating impedance Z b and / or the membrane impedance Z m of the active part, which in turn can contain a layered absorber between the channel-side surface and the loudspeaker membrane or can be terminated with a loudspeaker box, can be determined by the methods there.
  • the hybrid absorber lining can consist of mixed types of series connection and parallel connection of the passive subsystem with the active subsystem.
  • the two basic types are spatially arranged next to each other in a simple but complex apparatus as shown in Figure 20 .
  • Figure 21 Of particular interest is the embodiment of the invention as shown in Figure 21 , where an active subsystem works both in series and in parallel to a passive subsystem. This makes it possible to implement favorable frequency curves for the transfer function of the signal former.
  • FIG. 22 A preferred mixed form of the hybrid absorber according to the invention is shown schematically in Figure 22 .
  • the front of the loudspeaker works in series on a passive absorber, and the back creates a parallel admittance G a in parallel.
  • the parallel admittance G a must have the character of a passive admittance, but the terminating impedance Z b , as the examples above show, often has the character of a negative passive impedance.
  • This change of sign occurs automatically when you use the front and the back of the speaker diaphragm as an active signal generator.
  • This shape of the Invention also save the space required for a loudspeaker box, and the pressure equalization of the flow pressure via the loudspeaker is also given.
  • control signal for the active subsystem can, depending on the expediency, be recorded either in the part of the series connection or in the part of the parallel connection by the signal pickup (microphone).
  • the active subsystem with the schematic structure of a possible embodiment of the invention according to Figure 3 has the task of generating a prescribed acoustic impedance.
  • This impedance is the ratio of the sound pressure on the vibrating surface (membrane) of the signal generator to the speed of this surface averaged over the surface.
  • Another significant advantage of the invention compared to the task of active sound insulation is that the required control signal detected by the signal sensor (No. (1) in Figure 3 ) is not the sound pressure without the contribution of the active subsystem, but the actual sound pressure , which is a superposition of the sound pressure of the noise to be reduced, which penetrates from the front through the passive absorber, and the sound pressure of the loudspeaker of the active system.
  • the above-described difficulties of control in the case of active noise protection namely having to first eliminate the contribution of the active system from the control signal, are completely eliminated in the present invention from the approach of the inventive concept.
  • FIG 23 shows a basic diagram of the active subsystem in a basic form for realizing the invention.
  • a microphone (1) takes the Sound pressure p in front of the loudspeaker (5). Together with a microphone amplifier (2) that may be required, the pressure p is transmitted into an electrical voltage u 1.
  • a loudspeaker (5) produces a sound velocity v of its membrane by driving the loudspeaker via a power amplifier (4) with the electrical voltage u2.
  • the subdivision of the passive subsystem shown is a functional subdivision rather than an enumeration of necessary components.
  • the required amplifications can also be easily integrated into the signal former.
  • the function of the signal shaper according to the invention becomes particularly clear if one assumes that both on the microphone side the relationship between p and u 1 is linear and regardless of the frequency and on the speaker side there is such a relationship between v and u 2. Then the transmission factor u 1 / u 2 to be achieved by the signal shaper is, apart from a frequency-independent factor, equal to the terminating impedance Z b according to the invention or the membrane impedance Z m .
  • the remaining frequency dependency of the loudspeaker is included in the frequency dependence of its transfer function to be achieved by the signal former (as multiplication of transfer factors or by addition of transfer measures, which are known to each other); it is then referred to as the "combined" transmission factor of the signal converter.
  • loudspeaker frequency response in the combined transmission factor of the signal shaper according to the invention makes the application of the invention largely independent of the chosen type of loudspeaker (electrodynamic, electrostatic or magnetodynamic loudspeaker).
  • the selection can be made according to aspects of the transmission range of the Loudspeaker, by cost, by operational reliability and by simple implementation of this combined transmission factor.
  • the realization of this combined electrical transmission factor is then the last subtask to apply the invention.
  • the function of the signal shaper in the considered basic form of the implementation of the invention is essentially that of a frequency-dependent electrical filter.
  • the filter characteristic required according to the invention (frequency curve of the transmission factor according to amount and phase) is known for the subtasks by using the described solution methods.
  • an advantage of the hybrid absorber according to the invention is that, by suitable selection of the components of the passive absorber, the locus of the terminating impedance Z b can be given shapes which can be implemented by simple electronic circuits in the active subsystem.
  • Figures 4, 5, 18, 20, 21, 22 each show a hybrid absorber element according to the invention.
  • a silencer in the basic form of the invention, several of these elements are arranged one behind the other in the direction of the channel axis (direction of sound propagation) until a length of the silencer is produced which provides the required transmission loss.
  • Figure 24 shows schematically that in this embodiment of the invention, neither the control microphone nor the signal former need to be repeated for each element.
  • these level and phase changes in the excitation of successive loudspeakers are simulated in an electrical chain circuit.
  • loudspeakers are reciprocal converters; This means that they are not only useful for sound generation, but can also be operated as sound recorders.
  • the loudspeaker of the active subsystem is switched in "switching breaks" as a sound pickup, which measures the sound pressure which penetrates from the damper channel through the passive absorber. Periods of one to a few seconds are sufficient for these switching breaks.
  • the control microphone can thus be omitted; it is replaced by a timed switch.
  • the active subsystem according to the invention its implementation is essentially an electronic control task, which incidentally is seen as an advantage of the invention over the methods of active noise protection, since these basically represent a control task.
  • the function of the active subsystem according to the invention can also be conceived as a control task. The principle is explained using the schematic figure 25 .
  • the sound velocity v of the membrane is recorded by a structure-borne noise sensor (4) placed on the loudspeaker membrane.
  • the signal shaper is thus controlled using control technology methods known per se so that the quotient of the pressure p recorded by the microphone and the sound velocity v recorded by the structure-borne sound sensor forms the terminating impedance Z b required according to the invention.
  • This configuration As a control task, it can be useful "to compensate for changes in the properties of the passive subsystem that are difficult to predict, be it, for example, due to fluctuations in the production of the passive absorber, be it due to difficult to predict temperature profiles in the latter, or be it due to changes during the operation of the muffler, for example by Dirt deposits.
  • the primary target variable of the silencer namely the drop in sound level over a distance ⁇ x of the channel
  • the primary target variable of the silencer can also be used as a control variable for optimizing the terminating impedance according to the invention.
  • a first tacitly accepted standard situation is the existence of a predominantly symmetrical sound field, which, coming from the noise source, falls on the silencer (symmetrical means: in-phase vibration of the sound field on both sides of the symmetry plane of the damper channel). In fact, this is usually the case. However, probe cases of the sound source and / or the duct in front of the muffler are also conceivable, where the sound field vibration is predominantly antisymmetric (opposite in phase on both sides of the plane of symmetry). Then the determination equation (6) applies instead of the determination equation (5).
  • a second standard assumption is that the channel-side surface of the absorber lining is homogeneous, that is to say without defects and structures.
  • Silencers in technical systems are often used at elevated operating temperatures. These change the acoustic properties of the sound-conducting medium in the damper duct.
  • design steps presented above have been described in dimensionless form. They therefore apply to any gaseous medium, in particular also to a medium that has been changed from normal air by an increased temperature and / or composition (flue gases!). These operating conditions only manifest themselves when you use numerical values for the material constants that occur.
  • density ⁇ o in Z o ⁇ o c o
  • viscosity and the adiabatic exponent in ⁇ and thus in ⁇ an and Z an The influence of temperature and gas composition on these quantities is known from thermodynamics. It can therefore be included in the determination of the terminating impedance Z b if one wishes to design a silencer according to the invention for a specific operating temperature and / or gas composition. If operating temperatures change frequently and significantly during operation, it may be necessary to provide a self-adaptive active subsystem rather than operating with a specific operating temperature. As a rule, this will make digital or hybrid electronic control technology necessary for the signal former, in which the consideration of an operating temperature recorded by means of a thermometer does not pose any fundamental problems.
  • the consideration of a flow superimposition essentially means an exchange of the constant U wp .
  • an expedient embodiment of the invention consists in introducing this change in the constant U wp into a self-adapting active subsystem using known control engineering methods, using the display of a flow velocity Measuring device. With simple frequency responses of the combined transmission factor, this can be accomplished in electrical analog technology, with more complex frequency dependencies, regulation in hybrid or in digital technology can be indicated.
  • D d 14 dB.
  • a target price per square meter of backdrop area results in a silencer price of around DM 0.5 million.
  • the flow loss in the silencer which must be provided by the blowers to push the air through the silencer, is around 3,000 kW; with an efficiency of 80% of the blowers, an electrical output of around 3 800 kW is applied.
  • the silencer causes annual operating costs of 3.33 million DM / a due to its pressure loss, i.e. many times its purchase value.
  • a normal temperature T o was still calculated for a gas flow.
  • the power loss increases by a factor of (T / T o ) 2.5 for the same mass throughput, i.e. at an operating temperature of around 300 degrees Celsius by around a factor of 5.8, which results in annual operating costs of around 19.3 million DM / a leads.
  • the damping curve with the passive absorber alone is shown in dashed lines.
  • Figure 28 also shows the damping curves of a hybrid absorber (solid) with a structure and an exact locus for Z b as in Figure 15 , whereby an approximation to the exact curve was used here as well, and (dashed) the damping curve with the passive absorber alone.
  • the last figure 29 finally shows corresponding damping curves for a passive absorber lining already dimensioned broadly according to figure 10 , namely that described in figure 16 .
  • the Termination impedance is not obtained from analytically derived approximations, but through interpolation of measured values, as described above. Since the limitations of an analytical approximation are eliminated in such a procedure, the damping achieved comes closer to the optimum value.
  • the implementation of the active subsystem is an electronic control task instead of - as with the active silencer - a control task. This is seen as an advantage, since experience has shown that tax tasks are easier to solve than standard tasks. Nevertheless, the active subsystem according to the invention can be supplemented with control technology, which allows changes in the operating parameters to be “tracked”.
  • control variable is the total pressure at the measuring location and not - as in the case of the active silencer - the sound pressure of the incident wave, which has to be recovered from the measured sound pressure using complex algorithms.
  • the use of the silencer according to the invention is independent of the sound field distribution in the silencer duct. This is important because the sound pressure distribution in technical systems can neither be reliably predicted nor kept constant.
  • the silencer according to the invention can therefore be developed and dimensioned independently of the noise source in which it is to be used, while active silencers have to be adapted to the respective noise source.
  • the acoustic field impedance to which the loudspeaker of the active subsystem works can be set over a wide range by appropriate selection of the parameters of the passive subsystem. This has the advantage that relatively "hard” speakers can be used. These are usually cheaper and more robust in operation.
  • the hybrid absorber is connected in series, the sound pressure level at the loudspeaker - and thus the required elongation of the loudspeaker diaphragm - is reduced by the upstream passive absorber.
  • the upstream passive absorber can be used as a heat insulation layer in hot gas flows, since porous fiber absorbers generally also have good heat insulation.
  • the upstream passive absorber can also take on the function of a dirt filter in the invention.
  • Another advantage of the muffler according to the invention compared to the active muffler is seen in the fact that, in the event of a failure of the active subsystem (during maintenance or in the event of a fault), the passive absorber can ensure a certain remaining sound absorption.
  • Another advantage of the muffler according to the invention over the active muffler is that the transition to other channel cross sections can essentially be taken into account by changing the constant U wp and that - unlike with the active muffler - new algorithms for regulating and new arrangements of the loudspeakers do not develop Need to become.
  • a porous absorber layer in a silencer provides thermal protection for the active subsystem; it is a dirt and turbulence filter; it lowers the sound pressure level at the location of the active subsystem due to the internal one Propagation damping in the absorber material and thereby makes loudspeakers with a smaller stroke possible; it acts as a passive damper at high frequencies; it ensures residual damping in the event of a fault in the active subsystem; as a passive damper, it ensures the damping of higher channel modes; As a resistance rectifier, it accomplishes pressure equalization in the transverse direction in the case of non-uniformly vibrating loudspeaker membranes.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)
EP19910114279 1990-08-30 1991-08-26 Hybrid sound attenuator Withdrawn EP0473095A3 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE4027511 1990-08-30
DE4027511A DE4027511C1 (fr) 1990-08-30 1990-08-30

Publications (2)

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EP0473095A2 true EP0473095A2 (fr) 1992-03-04
EP0473095A3 EP0473095A3 (en) 1993-02-24

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EP19910114279 Withdrawn EP0473095A3 (en) 1990-08-30 1991-08-26 Hybrid sound attenuator

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Country Link
EP (1) EP0473095A3 (fr)
DE (1) DE4027511C1 (fr)

Cited By (2)

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WO1999021395A1 (fr) * 1997-10-22 1999-04-29 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Moniteur acoustique adaptatif
PL442352A1 (pl) * 2022-09-24 2024-03-25 Kfb Acoustics Spółka Z Ograniczoną Odpowiedzialnością Tłumik pasywno-aktywny do redukcji hałasu w kanałach

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US5812686A (en) * 1992-03-24 1998-09-22 Hobelsberger; Maximilian Hans Device for active simultation of an acoustical impedance
CH685657A5 (de) * 1992-03-24 1995-08-31 Maximilian Hobelsberger Vorrichtung zur aktiven Simulation einer akustischen Impedanz.
DE4226885C2 (de) * 1992-08-13 2001-04-19 Bayerische Motoren Werke Ag Schallabsorptionsverfahren für Kraftfahrzeuge
DE4342133A1 (de) * 1993-12-10 1995-06-14 Nokia Deutschland Gmbh Anordnung zur aktiven Schalldämpfung
DE4421803C2 (de) * 1994-06-22 1997-11-20 Stn Atlas Elektronik Gmbh Vorrichtung zur aktiven Schalldämpfung
US5498127A (en) * 1994-11-14 1996-03-12 General Electric Company Active acoustic liner
ATE203849T1 (de) * 1996-05-14 2001-08-15 Fraunhofer Ges Forschung Reaktiver schalldämpfer
DE19750102A1 (de) 1997-11-12 1999-06-02 Stankiewicz Gmbh Gasdurchströmte Leitung mit Schallabsorptionswirkung
DE19861018C2 (de) 1998-12-15 2001-06-13 Fraunhofer Ges Forschung Gesteuerter akustischer Wellenleiter zur Schalldämpfung
DE19910169B4 (de) * 1999-02-24 2004-01-29 Deutsches Zentrum für Luft- und Raumfahrt e.V. Verfahren zur aktiven Geräuschminderung in Strömungskanälen von Turbomaschinen
DE10118187C2 (de) * 2001-04-11 2003-03-27 Siemens Ag Einrichtung zum Gestalten der Akustik eines Raumes
DE10338786B4 (de) * 2003-07-18 2006-03-09 Weiss Klimatechnik Gmbh Zuluftdecke
DE102007000568A1 (de) 2007-10-24 2009-04-30 Silencesolutions Gmbh Schallabsorber
DE102008015929A1 (de) * 2008-03-27 2009-10-01 J. Eberspächer GmbH & Co. KG Abgasanlage
EP2314783A1 (fr) 2009-10-21 2011-04-27 Thorsten Flörsheimer Absorbeur de bruits ambiants
GB2532796A (en) * 2014-11-28 2016-06-01 Relec Sa Low frequency active acoustic absorber by acoustic velocity control through porous resistive layers
DE102019101358A1 (de) 2019-01-21 2020-07-23 Dr. Ing. H.C. F. Porsche Aktiengesellschaft Luftfahrzeug

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EP0227372A2 (fr) * 1985-12-18 1987-07-01 Nelson Industries, Inc. Amortisseur de son actif hybride
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EP0227372A2 (fr) * 1985-12-18 1987-07-01 Nelson Industries, Inc. Amortisseur de son actif hybride
GB2204916A (en) * 1987-05-19 1988-11-23 British Gas Plc Gaseous flow silencer

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Publication number Priority date Publication date Assignee Title
WO1999021395A1 (fr) * 1997-10-22 1999-04-29 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Moniteur acoustique adaptatif
PL442352A1 (pl) * 2022-09-24 2024-03-25 Kfb Acoustics Spółka Z Ograniczoną Odpowiedzialnością Tłumik pasywno-aktywny do redukcji hałasu w kanałach

Also Published As

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DE4027511C1 (fr) 1991-10-02
EP0473095A3 (en) 1993-02-24

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