TITLE
ELECTROACOUSTICAL TRANSDUCING
The present invention relates in general to electroacoustical transducing and more particularly concerns novel apparatus and techniques for selectively altering sound radiation patterns related to sound level.
REFERENCE TO COMPUTER PROGRAM LISTING ON COMPACT DISC A computer program listing appendix is submitted on a compact disc and the material on compact disc is incorporated by reference. The compact disc is submitted in duplicate and contains the file sharcboot_gemstone.h having 833,522 bytes created September 10,2003.
BACKGROUND OF THE INVENTION For background, reference is made to U.S. Patent Nos. 4,739,514, 5,361,381, RE37,223, 5,809,153, Pub. No. US 2003/0002693 and the commercially available Bose 321 sound system incorporated by reference herein.
BRIEF SUMMARY OF THE INVENTION
In general, in one aspect, the invention features a method that comprises controlling audio electrical signals to be provided to a plurality of electroacoustical transducers of an array to achieve directivity and acoustic volume characteristics that are varied with respect to a parameter associated with operation of the array, the controlling of the signals resulting in maintaining the radiated relative acoustic power spectrum of the array substantially the same as the characteristics are varied.
Implementations of the invention may include one or more of the following features. The variation is based on a volume level selected by a user. The compensating is based on a signal level detected in the controlled audio electrical signals. The controlling comprises reducing the amplitude of one of the electrical signals for higher acoustic volume levels. The controlling comprises combining two components of an intermediate electrical signal in selectable proportions. The controlling of the audio electrical signals comprises adjusting a level of one of the signals over a limited frequency range. Controlling the audio electrical signals includes
processing one of the signals in a high pass filter and processing the other of the signals in a complementary all pass filter.
In general, in another aspect, the invention features an apparatus comprising an input terminal to receive an input audio electrical signal, and circuitry (a) to generate two related output audio electrical signals from the input audio signal for use by a pair of electroacoustical transducers of an array, (b) to control the two output signals to achieve predefined directivity and acoustic volume characteristics that are varied with respect to a parameter associated with operation of the array, and (c) to compensate for a change in the radiated acoustic power spectrum of the array that results from the controlling of the signals.
Implementations of the invention may include one or more of the following feartures. The circuitry comprises a dynamic equalizer. The dynamic equalizer includes a pair of signal processing paths and a mixer to mix signals that are processed on the two paths. The circuitry is also to compensate for the change based on a volume level.
In general, in another aspect, the invention features an electroacoustical transducer array comprising: a pair of electroacoustical transducers driven respectively by related electrical signal components, an input terminal to receive an input audio electrical signal, and circuitry (a) to generate two related output audio electrical signals for use by the pair of electroacoustical transducers of an array, (b) to control the two output signals to achieve predefined directivity and acoustic volume characteristics that are varied with respect to a parameter associated with operation of the array, and (c) to compensate for a change in acoustic power spectrum of the array that results from the controlling of the signals. The circuitry comprises a dynamic equalizer. The dynamic equalizer includes a pair of signal processing paths and a mixer to mix signals that are processed on the two paths. The apparatus comprises a second input terminal to carry a signal indicating a volume level for use by the circuitry.
In general, in another aspect, the invention features a sound system comprising a pair of electroacoustical transducer arrays, each of the arrays comprising: a pair of electroacoustical transducers or drivers driven respectively by related electrical signal components, an input terminal to receive an input audio electrical signal, and circuitry (a) to generate two related output audio electrical signals for use by the pair of electroacoustical transducers of an array, (b) to control the two output signals to achieve predefined directivity and acoustic volume characteristics that are varied with respect to a parameter associated with operation of the array,
and (c) to compensate for a change in radiated acoustic power spectrum of the array that results from the controlling of the signals.
In general, in another aspect, the invention features an apparatus comprising a speaker array comprising a pair of adjacent speakers each having an axis along which acoustic energy is radiated from the speaker, and circuitry (a) to generate two related output audio electrical signals from an input audio signal for use by the pair of speakers, and (b) to control the two output signals to achieve predefined directivity and acoustic volume characteristics, the speakers being oriented so that the axes are separated by an angle of about 60 degrees.
It is an important object of the invention to provide electroacoustical transducing with a number of advantages.
Other features, objects and advantages of the invention will become apparent from the following description when read in connection with the accompanying drawing in which:
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
FIG 1 is a pictorial representation of an electroacoustical system according to the invention seated in a room;
FIG 2 is a block diagram illustrating the logical arrangement of a system according to the invention;
FIG 3 is a block diagram illustrating the logical arrangement of a subsystem according to the invention;
FIG 4 is a block diagram illustrating the logical arrangement of a signal processing system according to the invention;
FIG 5 is a graphical representation of control index as a function of volume level;
FIG 6 is a graphical representation of phase as a function of frequency for high pass and all pass filters;
FIG 7 is a graphical representation of radiated power as a function of frequency at different power levels;
FIG 8 is a graphical representation of equalized responses as a function of frequency at different levels;
FIG 9 is a graphical representation of radiated power as a function of frequency at different power levels for another embodiment;
FIG 10 is a graphical representation of equalization responses as a function of frequency at different levels;
FIG 11 is a block diagram illustrating the logical arrangement of an equalization module;
FIG 12 is a graphical representation of filter coefficient as a function of volume level; and
FIG 13 is a block diagram illustrating the logical arrangement of a system according to the invention.
DETAILED DESCRIPTION
With reference now to the drawing and more particularly FIG. 1, a loudspeaker system 300 according to the invention includes a left loudspeaker enclosure 302L having an inside driver 302LI and an outside driver 302LO and a right loudspeaker enclosure 302R having a right inside driver 302RI and a right outside driver 302RO. The spacing between inside and outside drivers in each enclosure measured between the centers is typically 81 mm. These enclosures are constructed and arranged to radiate spectral components in the mid and high frequency range, typically from about 210 Hz to 16 KHz. Loudspeaker system 300 also includes a bass enclosure 310 having a driver 312 constructed and arranged to radiate spectral components within the bass frequency range, typically between 20 Hz and 210 Hz. A loudspeaker driver module 306 delivers an electrical signal to each driver. There is typically a radiation path 307 from left outside driver 302LO reflected from wall 304L to listener 320 and from right outside driver 302RO over path 316 after reflection from right wall 304R. Apparent acoustic images of left outside driver 302LO and right outside driver 302RO are I302LO and I302RO, respectively. For spectral components below a predetermined frequency Fd = c/2D, where c = 331 m/s, the velocity of sound in air, and D is the spacing between driver centers, typically .081 m, where Fd is about 2 KHz, the radiation pattern for each enclosure is directed away from listener 320 with more energy radiated to the outside of each enclosure than to listener 320.
For a range of higher frequencies, typically above 2 KHz, sound from the inside drivers 302LI and 302RI reach listener 320 over a direct path 308 and 314, respectively, and from outside drivers 302LO and 302RO after reflection from walls 304L and 304R, respectively.
Referring to FIG 2, there is shown a block diagram illustrating the logical arrangement of circuitry embodying driver module 306. A digital audio signal N energizes decoder 340,
typically a Crystal CS 98000 chip, which accepts digital audio encoded in any one of a variety of audio formats, such as AC3 or DTS, and furnishes decoded signals for individual channels, typically left, right, center, left surround, right surround and low frequency effects (LFE), for a typical 5.1 channel surround system. A DSP chip 342, typically an Analog Device 21065L performs signal processing for generating and controlling audio signals to be provided to the drivers inside the enclosures, including those in the right enclosure 304R, the left enclosure 304L and bass enclosure 310. D/A converters 344 convert the digital signals to analog form for amplification by amplifiers 346 that energize the respective drivers.
The distance between driver centers of 81 mm corresponds to a propagation delay of approximately 240 us. In the frequency range below Fd, the system is constructed and arranged to drive one of the drivers in an enclosure radiating a cancelling signal attenuated 1 dB and inverted in polarity relative to the signal energizing the other driver to provide a 180° relative phase shift at all frequencies below Fd. This attenuation reduces the extent of cancellation, allowing more power to be radiated while preserving a sharp notch in the directivity pattern. By changing the delay in the signal path to one of the drivers from 0 us to 240 us, the effective directivity pattern changes from that of a dipole for 0 us delay to a cardioid when the signal delay furnished is 240 us that corresponds to the propagation delay between centers. For signal delays between these extremes, the notch or notches progressively change direction. In addition to using variable delay to alter the directivity pattern, other signal processing techniques can be used, such as altering the relative phase and magnitude of signals applied to the various drivers.
According to the invention, cancellation may be reduced below the frequency F