Claims
- 1. A method for attenuating the reflections of the sound pressure wave radiated by a sound reproduction apparatus into an acoustic space, said method comprising the steps of:taking a sample signal from a signal intended for reproduction of the original sound, in the sound reproduction apparatus reproducing the original sound, processing the sample signal to set its properties including the delay, phase inversion and amplitude, passing the processed sample signal to a cancelling loudspeaker, and converting the processed sample signal by means of said cancelling loudspeaker into a cancelling sound radiated into said acoustic space for attenuating reflections of said original sound, wherein blocking essentially entirely the signal components having a sufficiently high frequency to create a diffuse sound field in said acoustic space during the reproduction of said signal components, from being passed for reproduction by said cancelling loudspeaker, and setting the volume of the cancelling sound below the level of an original sound.
- 2. The method according to claim 1, wherein said step of blocking undesired sound components from being passed to said cancelling loudspeaker is essentially entirely effected on cancellation signal components having a frequency greater than 200 Hz.
- 3. The method according to claim 1 or 2, wherein said sample signal is low-pass filtered in order to clean said sample signal free from said frequency components capable of forming a diffuse sound field.
- 4. The method according to claim 1 or 2, wherein said blocking of said diffuse-sound-field forming frequency components from passing to said cancelling loudspeaker is effected by taking the sample signal from the bass channel signal of the sound reproduction apparatus, which bass channel signal consists essentially of low-frequency signal components whose emission into said acoustic space causes essentially ordered reflections.
- 5. The method according to claim 1, wherein said cancelling sound is radiated at least at one reflection location of the original sound.
- 6. The method according to claim 1, wherein the amplitude of said cancelling sound is set essentially equal to the amplitude of said reflected wave of said original sound, whereby the change caused by the reflected wave in the sound field can be attenuated without cancelling the low-frequency components of the original sound.
- 7. The method according to claim 1, wherein the amplitude of said cancelling sound is set so that the acoustic output level of the cancelling sound in the vicinity of said cancelling loudspeaker is from 4 dB to 6 dB below the acoustic output level of the original sound.
- 8. The method according to claim 1, wherein the processing of the sample signal for setting the desired delay comprises the steps ofproducing said cancelling sound signal with a plurality of different delays, observing the degree of attenuation of acoustic reflections as a function of varying delay, and based on the observation results selecting a suitable delay that is different from the time of propagation of sound waves from the original sound loudspeaker to the location of the cancelling loudspeaker.
- 9. The method according to claim 1, wherein the loudspeaker used as said cancelling loudspeaker is of a type adapted to radiate low-frequency sounds only, such as one known as a subwoofer.
- 10. The method according to claim 1 for use in conjunction with a stereophonic or multichannel sound reproduction system, wherein the multichannel signal is combined into a single sample signal for said setting ofcancellation signal delay, phase inversion and amplitude and passing to said cancelling loudspeaker.
- 11. A sound reproduction apparatus comprising:a signal source serving to provide a reproducible original sound signal in electrical form from a sound recording, a sound reproduction signal path connected to said original sound signal source for passing said signal to be reproduced, said signal path including an amplifier for amplification of said signal to be reproduced, at least one loudspeaker connected after said amplifier on the sound reproduction path thus facilitating the conversion of said signal to be reproduced into an acoustic sound radiated into said acoustic space, a cancellation sound signal path connected to said signal source of original sound for taking and passing a signal sample, said cancellation sound signal path including control means with delay, amplification and phase-inversion facilities for the processing of said cancelling sound signal, and at least one cancelling loudspeaker connected to said cancellation sound signal path for generating said cancelling sound and thus attenuating the reflected pressure waves of the original sound radiated into said acoustic space, wherein said apparatus includes signal separation means connected to said cancellation sound signal path for removing such signal components, whose frequency is sufficiently high for forming a diffuse sound field in conjunction with their reproduction in said acoustic space, from said canceling sound signal and thus from the cancelling sound being radiated by said canceling loudspeaker.
- 12. The sound reproduction apparatus according to claim 11, wherein said signal separation means are adapted to remove signal components having a frequency higher than 200 Hz.
- 13. The sound reproduction apparatus according to any of claim 11 or 12, whereinsaid sound reproduction signal path includes a selective frequency band divider integrated with said amplifier for dividing the original signal into separate frequency bands, and said cancellation sound signal path is adapted to pass via said amplifier of the sound reproduction signal path and its integral frequency band divider so that the cancellation sound signal path is passed via the low-frequency band of the band divider, whereby said frequency band divider also acts as said signal separation means.
- 14. The sound reproduction apparatus according to claim 11 or 12, wherein said cancellation sound signal path includes a low-pass filter acting as said signal separation means.
- 15. The sound reproduction apparatus according to claim 14, wherein said low-pass filter is connected on said cancellation sound signal path prior to said control means.
- 16. The sound reproduction apparatus according to claim 11, wherein said control means include a digital delay circuit comprisingan AD converter for converting a signal into digital format, memory circuits for storing a digital signal, a DA converter for converting a digital signal back into analog format, and a microcontroller for connecting a digital signal from said AD converter to said memory units and, after the lapse of a set delay time, further from said memory units to said DA converter.
- 17. The sound reproduction apparatus according to claim 16, wherein said digital delay circuit is adapted to generate a delay which is a function of frequency.
- 18. The sound reproduction apparatus according to claim 11, whereinat least one of said loudspeakers is a low-frequency radiator such as a subwoofer, and at least one of said cancelling loudspeakers is at least for its frequency response of a similar type of low-frequency.
- 19. The sound reproduction apparatus according to claim 11 for reproduction of stereophonic or multichannel sounds, wherein said apparatus includes means for combining and passing signals from the different channels in a combined format over said cancellation sound signal path to said control means.
- 20. The sound reproduction apparatus according to claim 19, wherein said means for combining the signals from the different channels are placed on the cancellation signal path prior to said signal separation means.
Priority Claims (1)
Number |
Date |
Country |
Kind |
981409 |
Jun 1998 |
FI |
|
CROSS REFERENCE TO RELATED APPLICATION
This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/FI99/00534 which has an International filing date of Jun. 17, 1999, which designated the United States of America.
PCT Information
Filing Document |
Filing Date |
Country |
Kind |
PCT/FI99/00534 |
|
WO |
00 |
Publishing Document |
Publishing Date |
Country |
Kind |
WO99/66492 |
12/23/1999 |
WO |
A |
US Referenced Citations (3)
Number |
Name |
Date |
Kind |
4899387 |
Pass |
Feb 1990 |
A |
5559891 |
Kuusama et al. |
Sep 1996 |
A |
5832095 |
Daniels |
Nov 1998 |
A |
Foreign Referenced Citations (1)
Number |
Date |
Country |
6062499 |
Mar 1994 |
JP |