TIMBRE CONSTANCY ACROSS A RANGE OF DIRECTIVITIES FOR A LOUDSPEAKER

• US 20160021458A1
• Filed: 03/06/2014
• Published: 01/21/2016
• Est. Priority Date: 03/11/2013
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Johnson, Martin E., Holman, Tomlinson
• Granted Patent: US 9,763,008 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04R 1/403 loud-speakers
• CPC Class Codes: H04R 2201/401 2D or 3D arrays of transducers
• CPC Class Codes: H04R 2201/403 Linear arrays of transducers
• CPC Class Codes: H04R 2203/12 Beamforming aspects for stereophonic sound reproduction with loudspeaker arrays
• CPC Class Codes: H04R 2227/007 Electronic adaptation of audio signals to reverberation of the listening space for PA
• CPC Class Codes: H04R 29/002 Loudspeaker arrays
• CPC Class Codes: H04R 5/02 Spatial or constructional arrangements of loudspeakers
• CPC Class Codes: H04R 5/04 Circuit arrangements, e.g. for selective connection of amplifier inputs/outputs to loudspeakers, for loudspeaker detection, or for adaptation of settings to personal preferences or hearing impairments combinations of amplifiers H03F3/68; stereophonic systems H04S
• CPC Class Codes: H04S 2400/01 Multi-channel, i.e. more than two input channels, sound reproduction with two speakers wherein the multi-channel information is substantially preserved
• CPC Class Codes: H04S 2400/15 Aspects of sound capture and related signal processing for recording or reproduction
• CPC Class Codes: H04S 3/008 in which the audio signals are in digital form, i.e. employing more than two discrete digital channels data reduction aspects thereof based on psychoacoustics G10L19/02
• CPC Class Codes: H04S 7/301 Automatic calibration of stereophonic sound system, e.g. with test microphone
• CPC Class Codes: H04S 7/305 Electronic adaptation of stereophonic audio signals to reverberation of the listening space H04S7/301 takes precedence
• CPC Class Codes: H04S 7/307 Frequency adjustment, e.g. tone control H04S7/301 takes precedence

Abstract

A system and method for driving a loudspeaker array across directivities and frequencies to maintain timbre constancy in a listening area is described. In one embodiment, a frequency independent room constant describing the listening area is determined using the directivity index of a first beam pattern, the direct-to-reverberant ratio DR at the listener'"'"'s location in the listening area, and an estimated reverberation time T₆₀ for the listening area at a designated frequency. On the basis of this room constant, an offset may be generated for a second beam pattern. The offset describes the decibel difference between first and second beam patterns to achieve constant timbre and may be used to adjust the second beam pattern at multiple frequencies. Maintaining constant timbre improves audio quality regardless of the characteristics of the listening area and the beam patterns used to represent sound program content. Other embodiments are also described.

Claims

1. A method for maintaining timbre constancy among beam patterns for a loudspeaker, comprising:

calculating a room constant c based on the directivity index of a first beam pattern, wherein the room constant c indicates the volume of the room and the distance of a microphone from the loudspeaker;

calculating an offset for a second beam pattern based on the room constant c and the directivity index of the second beam pattern, wherein the offset indicates the level difference between the first and second beam patterns; and

adjusting the level of the second beam pattern to match the level of the first beam pattern based on the calculated offset level at each frequency in a set of frequencies.

2. The method of claim 1, wherein calculating the room constant c comprises:

determining the direct-to-reverberant ratio (DR) produced by the loudspeaker for the first beam pattern at a designated frequency f;

determining the time (T₆₀) required for the level of a sound in the room to drop by 60 dB at the designated frequency f; and

determining the directivity index (DI₁) for the first beam pattern at the designated frequency f.

3. The method of claim 2, wherein the room constant c is equal to

4. The method of claim 2, wherein the DR(f) and T₆₀(f) values are determined using a test sound produced by the loudspeaker and sensed by the microphone in the room.

5. The method of claim 2, wherein the DR(f) and T₆₀(f) values are estimated values for a typical room.

6. The method of claim 2, further comprising:

determining the directivity index (DI₂) for the second beam pattern, wherein the offset for the second beam pattern is calculated for the designated frequency f as

7. The method of claim 1, wherein the method is performed upon initialization of the loudspeaker in the room.

8. The method of claim 1, further comprising:

driving the loudspeaker to produce the second beam pattern to emit a piece of sound program content into the room based on the adjusted level at each frequency in the set of frequencies.

9. An audio receiver for maintaining timbre constancy among beam patterns for a loudspeaker array in a listening area, comprising:

a hardware processor;

a memory unit to store a timbre constancy unit to;

determine a room constant c for the listening area based on the directivity index of a first beam pattern emitted by the loudspeaker array;

determine an offset for a second beam pattern emitted by the loudspeaker array based on the room constant c and the directivity index of the second beam pattern; and

adjust the level of the second beam pattern to match the level of the first beam pattern based on the calculated offset at each frequency in a set of frequencies.

10. The audio receiver of claim 9, further comprising:

a microphone to sense sounds produced by the loudspeaker array in the listening area, wherein the room constant c indicates the volume of the listening area and the distance of the microphone from the loudspeaker array.

11. The audio receiver of claim 9, wherein the offset indicates the level difference between the first and second beam patterns at each frequency in the set of frequencies.

12. The audio receiver of claim 11, wherein determining the room constant c comprises:

determine a direct-to-reverberant ratio (DR) produced by the loudspeaker array for the first beam pattern at a designated frequency f;

determine a time (T₆₀) required for the level of a sound in the listening area to drop by 60 dB at the designated frequency f; and

determine the directivity index (DI₁) for the first beam pattern at the designated frequency f.

13. The audio receiver of claim 12, wherein the room constant c is equal to

14. The audio receiver of claim 12, wherein the DR(f) and T₆₀(f) values are determined using a test sound produced by the loudspeaker array and sensed by the microphone in the listening area.

15. The audio receiver of claim 12, further comprising:

a network controller to receive data from external devices, wherein the DR(f) and T₆₀(f) values are estimated values for a typical listening area received from an external device through the network controller.

16. The audio receiver of claim 12, wherein the timbre constancy unit further performs operations to:

determine the directivity index (DI₂) for the second beam pattern, wherein the offset for the second beam pattern is calculated for the designated frequency f as

17. The audio receiver of claim 9, wherein the timbre constancy unit is activated upon initialization of the loudspeaker array in the listening area.

18. The audio receiver of claim 9, further comprising:

power amplifiers to drive the loudspeaker array to produce the second beam pattern to emit a piece of sound program content into the listening area based on the adjusted level at each frequency in the set of frequencies.

19. An article of manufacture for maintaining timbre constancy among beam patterns for a loudspeaker, comprising:

a machine-readable storage medium that stores instructions which, when executed by a processor in a computer,

calculate a room constant c based on the directivity index of a first beam pattern, wherein the room constant c indicates the volume of the room and the distance of a microphone from the loudspeaker;

calculate an offset for a second beam pattern based on the room constant c and the directivity index of the second beam pattern, wherein the offset indicates the level difference between the first and second beam patterns; and

adjust the level of the second beam pattern to match the level of the first beam pattern based on the calculated offset at each frequency in a set of frequencies.

20. The article of manufacture of claim 19, wherein the storage medium includes further instructions for calculating the room constant c, the further instructions to:

determine the direct-to-reverberant ratio (DR) produced by the loudspeaker for the first beam pattern at a designated frequency f;

determine the time (T₆₀) required for the level of a sound in the room to drop by 60 dB at the designated frequency f; and

determine the directivity index (DI₁) for the first beam pattern at the designated frequency f.

21. The article of manufacture of claim 20, wherein the room constant c is equal to

22. The article of manufacture of claim 20, wherein the DR(f) and T₆₀(f) values are determined using a test sound produced by the loudspeaker and sensed by the microphone in the room.

23. The article of manufacture of claim 20, wherein the DR(f) and T₆₀(f) values are estimated values for a typical room.

24. The article of manufacture of claim 19, wherein the storage medium includes further instructions to:

determine the directivity index (DI₂) for the second beam pattern, wherein the offset for the second beam pattern is calculated for the designated frequency f as

25. The article of manufacture of claim 19, wherein the instructions are performed upon initialization of the loudspeaker in the room.

26. The article of manufacture of claim 19, wherein the storage medium includes further instructions to:

drive the loudspeaker to produce the second beam pattern to emit a piece of sound program content into the room based on the adjusted level at each frequency in the set of frequencies.