Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
  • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
  • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
  • H04R1/28—Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means
  • H04R1/2869—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself
  • H04R1/2876—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself by means of damping material, e.g. as cladding
  • H04R1/288—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself by means of damping material, e.g. as cladding for loudspeaker transducers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
  • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
  • H04R1/227—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only  using transducers reproducing the same frequency band
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
  • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
  • H04R1/28—Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means
  • H04R1/2869—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself
  • H04R1/2884—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself by means of the enclosure structure, i.e. strengthening or shape of the enclosure
  • H04R1/2888—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself by means of the enclosure structure, i.e. strengthening or shape of the enclosure for loudspeaker transducers

Definitions

• the invention relates to the field of electro-acoustic transducers, in particular transducers consisting of at least one loudspeaker mounted in a resonant acoustic enclosure, intended to be Q connected at the output of an electrical modulation source to restore the sound signal. corresponding.
• the subject of the invention is a method for equalizing the amplitude / frequency response of this type of transducer. It also provides a - new transducer assembly making it possible to operate according to the invented method, as well as preferred modes of use of the new transducer assembly.
• equalizers are generally selective networks, most often incorporated in the acoustic enclosure, and intended to correct the electrical input signal from the transducer, to compensate for irregularities in the amplitude / frequency response of the loudspeakers.
• This equalization method is for example carried out by using passive anti-resonant circuits inserted between the amplifier and the acoustic enclosure, and effecting a selective weakening of the output signal of the amplifier.
• the filters themselves are a distortion factor of the signal, due to the r unable to give them a perfect linear transfer function in their bandwidth. They are also subject to variations in their response characteristics as a function of the ambient temperature, or even of their aging.
• equalization circuits brings constraints in this. which relates to the characteristics of the loudspeaker corrected to avoid unfavorable indirect effects, such as for example the damping of the loudspeaker (cf. "Engineering technique”; E 2613-9; paragraphs 2, 32).
• the equalization of the response curve of the electro-acoustic transducers is also approached by making precise choices on the parameters of the enclosure, in relation to the parameters of the speaker (s) mounted in the enclosure.
• FIG. 3 represents the uncorrected response curve (curve A) characteristic of known transducers, and the response curve after correction (curve B), using known techniques, such as for example the so-called “Thiele and Small” techniques.
• this involves acting on the resonance frequency, the overvoltage coefficient, or even the equivalent volume (V as ) of the loudspeaker, in relation to techniques for damping acoustic phenomena. speaker noise, for example by stuffing its internal walls with a "choking" material (glass wool).
• these known techniques do not have a homogeneous effect on the entire frequency spectrum, owing to the fact that the cyclic weakening phenomena introduced by the transducers are very different in the low frequency domain (less than 300 Hz ) compared to higher frequencies.
• the known damping techniques then act relatively effectively at low frequencies, owing to the fact that the responsibility of the loudspeaker in the irregularities of the level of restitution of sound signal is preponderant, on the other hand, the correction of the irregularities in the field of mediums. and treble, that is to say where the parameters related to the constitution of the speaker are predominant, is much less well performed.
• the objective of the present invention is therefore to overcome these various drawbacks of the existing equalization methods.
• a first object of the invention is to provide a method for correcting the amplitude / frequency response curve of the electro-acoustic transducers, without affecting the efficiency of the electric amplifier + electro-acoustic transducer system.
• a second object of the invention is to provide such a correction method applicable whatever the specific response curve of the transducers. electro-acoustic used, provided that their amplitude / frequency response curve presents "cyclic" irregularities around an average value of the level of restitution of the sound signal.
• a complementary object of the invention is to provide an equalization method which operates over the entire spectrum of the audible frequency spectrum, in particular up to the highest fundamental sounds (4000 Hz).
• electro-acoustic transducer in the form of a succession of alternations of axima and minima levels; in that said electro-acoustic transducer is used in cooperation with at least one second electro-acoustic transducer connected in parallel to the same modulation source, and operating on the same frequency range, said second electro-acoustic transducer
• D acoustipque being chosen so that it has an amplitude / frequency response curve complementary to that of the first transducer, to form by adding the sound signals of said transducers, a resulting sound signal corrected due to the mutual compensation of the irregularities inherent in each transducer .
• said transducer will exhibit all the more “exploitable” natural irregularities as its efficiency is high, that is to say that it is devoid of any damping device and is at its maximum sensitivity.
• the second transducer a transducer identical to the first transducer is used, said second transducer having an adjustable resonant frequency so as to allow an offset of its response curve relative to that of the first transducer, to achieve mutual compensation of their respective irregularities.
• the response curve of said second transducer is shifted by action on one of the following parameters: value and configuration of the volume of the enclosure; modification of the air flow in one or more vents made in the enclosure; modification of the characteristics of a passive speaker mounted in the enclosure of the adjustable electro-acoustic transducer.
• the equalization process thus defined can be implemented in particular in a set of twin transducers, consisting of two speakers each provided with at least one speaker, said speakers having a common wall at least a portion of which is movable so as to adjust the volume of each of said speakers.
• FIG. 1 shows the implementation of the method according to the invention in a set of two Hel holtz cavities, each provided with a loudspeaker, and having a common side wall;
• FIG. 2 shows the implementation of 1'invention in a set of two paired cavities Helmholtz and J each provided a loudspeaker, and having a common bottom wall;
• FIG. 3 shows the response curves A and B, before and after correction according to known techniques respectively, for a conventional transducer of the type with enclosure fitted with a loudspeaker;
• FIG. 4 represents the offset of the amplitude / frequency response curves of two paired electro-acoustic transducers according to the method of the present invention;
• FIG. 5 represents the resulting curve of equalized amplitude / frequency response for the transducers of FIG. 4 (curve D), in comparison with the curve obtained by using known techniques (curve B).
• FIG. 4 illustrates the fundamental principle of the production method according to the invention.
• the response curve A corresponds to a first electro-acoustic transducer intended to operate for example over a range I of frequencies ranging from 60 Hz to 3000 Hz or more.
• This response curve presents alternating irregularities, which result in a variation in the level of sound reproduction (ordinate axis in dB), around an average level 1 ⁇ located around + 2 dB, in the case shown.
• the principle of the equalization method according to the invention consists in using at least one second electro-acoustic transducer, in cooperation with the first, the second transducer being chosen so as to have a response curve C similar to the response curve A of the first transducer, but offset from it.
• the offset of the two response curves A and C corresponds substantially to the value of a half-period of the irregularity cycles of the transducers. It follows that the frequency intervals for which the response curve A of the first transducer exhibits a significant relative attenuation substantially correspond to a maximum level of restitution of the response curve C of the second associated transducer.
• the restored signal corresponding to the addition of the signals coming from each of the transducers is therefore equalized over the entire frequency spectrum, by mutual compensation of the irregular response curves of each transducer.
• the equalization of the resulting restored signal will be all the more perfect when the following two conditions are met.
• the mutual compensation of the irregularities of the response curves A and C of the twin electro-acoustic transducers will only be effective if the irregularities in question are of alternating shape, that is to say that they occur under the form of a succession of attenuations and maximum levels, at intervals which coincide with frequency.
• the irregularities must be in the form of alternation of attenuations and maximum levels, of substantially equal amplitude around an average level of restitution for each pair of neighboring positive and negative alternations, of so that the offset of curves C and A by about half a period makes the positive alternations of one curve coincide with the negative alternations of the other, according to the method, exact coincidence is of course advantageous, but results are extremely satisfactory from the point of view of equalization are obtained even for approximate coincidences.
• FIG. 4 constitutes an illustration for demonstrative purpose of the basic principle applied in the equalization method according to the invention.
• it has been found experimentally that a completely satisfactory equalization is obtained even if the succession of positive and negative alternations of the amplitude / frequency response curves of the transducers is not carried out according to regular periods, or if variations in amplitude of these alternations are relatively uneven.
• Another essential advantage of the invention is shown in FIG.
• the implementation of the equalization method according to the invention provides an extremely precise method of adjusting the tone, or even the timbre, audio signals reproduced.
• This extremely advantageous characteristic of the invention adds to the equalization effect.
• compensation is in the form of a transducer adjustment system, which makes it possible to adapt the same set of transducers to the compensated reproduction of signals recorded using different techniques.
• Examples include the generation of sound effects on sounds produced by electronic instruments, or the adaptation of transducers to the acoustics of the listening room.
• Figures 1 and 2 show preferred embodiments, of course not limiting, of sets of electro-acoustic transducers implementing the equalization method according to the invention.
• transducers of the Helmholtz cavity type each provided with a loudspeaker and a vent.
• the method according to the invention applies to any type of transducer, provided that the amplitude / frequency response curve which corresponds to it at least partially satisfies the two conditions highlighted above.
• the implementation of the equalization process is obtained by using two Helmholtz cavities 10 and 20, each provided with a loudspeaker 11-21, and a vent 12-22 .
• the cavities 10-20 are paired so as to present a common side wall 15.
• the two cavities have identical, or almost identical, characteristics. This means that they each have a response curve amplitude / frequency of substantially identical configuration, in particular from the point of view of the frequency of succession of the irregularities, and of the amplitude of the half-waves.
• the adjustment of the offset of the response curves allowing the equalization according to the invention is carried out here by adjusting the resonant frequency of the transducers. More specifically, a coarse adjustment is performed by movement of the wall 15, and a fine adjustment by movement of the lower block 16. These movements are made for example 'through systems threaded-rod nuts 17, 18; 37, 38 controlled by flywheels 19, 39 mounted on an outer wall of the twin cavities.
• the modification of the resonant frequency of each of the two paired transducers is carried out by modification of the configuration and of the internal volume of the two cavities 10-20 respectively, from the made of the displacement of the wall portion 16.
• the effect obtained can be illustrated from FIG. 4. It can in fact be considered that the curve A corresponds to the amplitude / frequency response curve of the transducer 1, and that the curve C corresponds to the amplitude / frequency response curve of the second transducer 2.
• the resonance frequency f 2 of the transducer 2 is around 40 Hz.
• the resonance frequency corresponds to a point on the weakening slope characteristic of any acoustic resonant system (slope of the order of 18 dB per octave), on the amplitude / frequency response curve.
• the response curve A of the transducer 1 remains fixed, the effect of the displacement of the articulated portion 16 of the common wall 15 on the offset of the curve C will be illustrated approximately by the curve d f .
• This curve d f is in fact traversed by the point P of the resonant frequency of the transducer 2, on the response curve C, when the internal volume of the cavity 20 of the transducer 2 is varied.
• This curve d f illustrates 1 • influence of the variation in the volume of the cavity 20 on two essential parameters:
• the increase in the volume of the resonant cavity 20 causes the resonance point P to rise towards the first maximum of the response curve C.
• FIG. 1 allows adjustment of the equalization by varying the volume of the enclosure, thanks to the displacement of a portion of the common wall.
• the dimensions of the articulated wall portion 16 are not a limiting characteristic of the invention, and must be adapted to the characteristics of the transducer, and to the desired adjustment precision. In particular, it is possible to plan
• ⁇ D example by action on a shutter (not shown) closing the vent more or less completely, or even by adding a neck of adjustable length or shape.
• Another technique for adjusting the resonance frequency of at least one of the transducers consists in
• the adjustment then consists in controlling the resonant frequency of the diaphragm, by acting on its mass, on the elastic return force of the diaphragm, or by any other means.
• the action on the flow of air through the vent can be considered, in certain applications, as less advantageous than the action on the volume of the cavities: a variation in the volume of the resonant cavity has indeed in general no influence on the transducer efficiency, unlike the action techniques on the vent.
• the two transducers of the same set can perfectly be completely separate from each other, and therefore not have a common wall.
• FIG. 2 represents a variant of the embodiment of. FIG. 1, in which two transducers 3, 4, of the Helmholtz cavity type, are paired by presenting a movable common bottom wall. Each of the transducers is provided with a speaker 31-41, and a vent 32-42.
• the common movable internal partition 35 is inclined, so as to avoid the unfavorable effects of reflection which would be induced by a straight partition, and would imply the use of a damping technique detrimental to performance.
• a prototype corresponding to this figure was produced by means of a box, the total interior volume of which (covering the cavities of the transducers 3 and 4) was 80 liters.
• the two speakers are similar, and had an overall diameter of 190 mm.
• the nominal surface of each of the vents, 2.5 dm 2 is adjusted by a flap.
• This implementation configuration of the method of the invention has the advantage of combining the equalization phenomenon already described, with a second phenomenon of controlling the directivity of the acoustic radiation of the system.
• This directivity control is obtained by supplying the two transducers 3, 4 from the same modulation source, but by actuating them simultaneously in phase shift, preferably in phase opposition.
• Control of the directivity can then be obtained by acting on one or other of the parameters such as: the value of the phase shift (constant or not as a function of the frequency); the orientation of the emission of each transducer; the intensity and the lobe of their radiation; the distances between transmitters; the range of frequencies concerned; among others.
• the embodiment of FIG. 2 is extremely advantageous when it is desired to have a possibility of adjusting the equalization of the restored sound signal, combined with a directivity effect, and possibly with a possibility of action. on the tone, all this being possible without affecting the performance of the installation.
• a completely preferential application of this electro-acoustic transducer system is the high power sound system of congress halls, concert halls, or more generally of any public event.

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• Health & Medical Sciences (AREA)
• Otolaryngology (AREA)
• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Circuit For Audible Band Transducer (AREA)
• Transducers For Ultrasonic Waves (AREA)
• Amplifiers (AREA)
• Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=9341840

Family Applications (1)

Country Status (7)

Cited By (1)

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Citations (10)

• 1986
  • 1986-12-12 FR FR8617423A patent/FR2608343B1/fr not_active Expired
• 1987
  • 1987-12-11 AT AT88900235T patent/ATE91838T1/de not_active IP Right Cessation
  • 1987-12-11 AU AU10515/88A patent/AU1051588A/en not_active Abandoned
  • 1987-12-11 WO PCT/FR1987/000494 patent/WO1988004513A1/fr active IP Right Grant
  • 1987-12-11 DE DE8888900235T patent/DE3786672D1/de not_active Expired - Lifetime
  • 1987-12-11 EP EP88900235A patent/EP0335892B1/de not_active Expired - Lifetime
• 1988
  • 1988-08-10 KR KR1019880700960A patent/KR890700298A/ko not_active Application Discontinuation

Patent Citations (10)

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