 Digital hearing aid |
| Therefore, it is an object of the present invention to provide a digital hearing aid which can ... |
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| Apparatus for creating 3D audio imaging over headphones using binaural synthesis |
| Accordingly, it is an object of the present invention to provide an apparatus for creating three-... |
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| System, apparatus, and method for improving speech quality in multi-party devices |
| A method, system, and apparatus are provided, such that cross talk terms may be removed from speech ... |
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| Speaker excursion control system |
| OF THE PREFERRED EMBODIMENT Referring initially to FIG. 1, there is shown a sound system which may ... |
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| Portable information terminal device with radio selective-calling receiver |
| In view of the foregoing, it is an object of the present invention to provide a portable ... |
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| Digital graphic equalizer |
| An object of the invention is to remedy the major problems of prior digital graphic equalizers and, ... |
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| Electric artificial larynx |
| It is an object of the present invention which has been made to solve the above problem to provide ... |
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| Audio reproducing apparatus corresponding to picture |
| In view of such aspects, an object of the present invention is to provide an audio reproducing ... |
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| Electro-optical device |
| With the above-mentioned problems with such prior arts in view, the present invention has been ... |
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| Method of transmitting an audio signal |
| What is claimed is: 1. A method of transmitting an analog audio signal in digital form to be ... |
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Reactive sound absorber
| Details |
Inventors: Krueger, Jan; Leistner, Philip; Fuchs, Helmut; Lippold, Roland;
Assignee: Fraunhofer-Gesellschaft (Munich, DE)
Primary Examiner: Mei; Xu
Assistant Examiner:
Attorney, Agent or Firm: Crowell & Moring LLP
A reactive sound attenuator which includes a sensor for detecting a sound parameter in a space, e.g. a duct, consists of a signal amplifier that is used to amplify a detected signal, an electroacoustic transducer and a cavity with at least one membrane. The membrane, which is capable of moving in a vibratory manner, is part of a wall of a space, e.g. a duct wall. A sensor, which is disposed in the immediate vicinity of, in or on the membrane, detects the vibrations of the membrane. The sensor's signal, which is amplified and inverted by the amplifier, controls the membrane vibration via the electroacoustic transducer. |
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DETAILED DESCRIPTION The invention relates to a reactive sound attenuator consisting of a cavity with sound-proof limits and including at least one membrane, an acoustic sensor in the immediate vicinity in or on said membrane, as well as an electroacoustic transducer and an inverting signal amplifier.
With reference to FIG.
5, so-called anti-noise systems shown therein are based on a simple concept.
(Nelson, P.
A.
, Elliott, S.
J.
: Active Control of Sound and Vibration.
Academic Press Limited, London: 1992).
These systems are most frequently aimed at and refined in active noise control in order to attenuate noise in ducts and passages.
Here, an incident primary sound wave is detected by a microphone which is located in a duct and distinctly offset in front of the remaining components in a direction that is toward the noise source.
The detected microphone signal is arithmetically rotated through 180.
degree.
as precisely as possible by means of a signal processor 11.
This rotated signal serves to control a loudspeaker 9 which subsequently emits a secondary sound wave.
In an ideal case, both waves are superimposed on one another along the direction of the sound wave's propagation until the wave is cancelled.
This cancellation can be monitored by means of a second microphone 10 in the direction of the sound wave's propagation.
This second microphone 10 outputs a signal which, at the same time, may be used to adapt the signal processor to possible variations of sound propagation in the respective duct.
This procedure can be successfully performed very precisely by means of advanced signal processors at least under laboratory conditions.
However, their practical application is characterised by a high responsiveness and sensitivity to superimposed air flows or temperature variations, as well as by a high cost for electronic elements and signal processing means.
German patent document DE 40 27 511 discloses a hybrid sound attenuator as shown in FIG.
6.
This system is used to realize an optimum acoustic impedance of a duct wall 1 located on the front side of a known passive sub-system 12 via a supplementing active sub-system on the rear side
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Audio Signal Processing 
