SOUND-IMPROVING MEANS AND METHOD

• US 3,624,298 A
• Filed: 03/05/1969
• Issued: 11/30/1971
• Est. Priority Date: 03/05/1969
• Status: Expired due to Term

• Current Assignee: Altec Lansing LLC (Infinity Group Holding Co. LLC)
• Original Assignee: Arthur C. Davis, Donald B. Davis, James J. Noble
• Inventors: Davis, Arthur C., Davis, Donald B., Noble, James J.
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Leaheey, Jon Bradford
• Application Number:
  US04/804,573
• Time in Patent Office: 1,000 Days
• Field of Search: 179/1.2,170.2,1D,1F,1FS 325/12 333/76,28T
• US Class Current: 381/66
• CPC Class Codes: H03G 5/10 having semiconductor devices

Abstract

A method for eliminating undesired effects produced by reverberations from structure on the quality of sound produced by a sound system which is operated in association with the structure by smoothing the sound pressure-level versus frequency characteristics of the sound; and apparatus for practicing the method in the form of a filter network for use in combination with the sound system whereby electrical signals are attenuated by different amounts within selected ones of discrete bands of audiofrequencies to shape the sound pressure-level versus frequency characteristic of the sound.

Claims

1. For eliminating undesired distortion effects produced by reverberations from structure on the quality of sound over a predetermined audio frequency spectrum produced by a system which is operated in association with the structure and which has a signal source, an amplifier, a linking circuit connecting the signal source and amplifier, and a sound reproducing device driven by the amplifier, the combination with the signal source, linking circuit, and amplifier comprising:

a plurality of electrical, band-rejection filters located in series in the linking circuit and each having a respective center frequency lying within a band in which it attenuates electrical signals, said bands overlapping each other to provide a continuous attenuation pattern across said predetermined audio frequency spectrum, the center frequencies of the respective filters being substantially equally spaced by a fraction of an octave across said audio-frequency spectrum; and

means connected to each filter for variably controlling the amount of attenuation of electrical signals within the frequency band to which the respective filter is tuned to minimize said distortion effects over said entire predetermined audio frequency spectrum.

2. The combination claimed in claim 1 wherein the respective center frequencies of said band-rejection filters are spaced one-third octave apart across at least a portion of the audiofrequency spectrum.

3. The combination claimed in claim 1, wherein the frequencies at which the attenuation produced by each filter is oNe-half its maximum value are approximately in coincidence with frequencies at which at least one filter of immediately adjacent center frequency produces one-half its maximum attenuation.

4. The combination claimed in claim 1 wherein at least a portion of the band-rejection filters are active filters having active components.

5. The combination claimed in claim 4 wherein at least some of the band-rejection filters are spaced one-sixth octave apart across at least a portion of the audiofrequency spectrum.

6. The combination claimed in claim 1 wherein each band-rejection filter has a circuit comprising:

a coil connected in series in the linking circuit between the signal source and the amplifier;

a capacitor connected in parallel arrangement with the coil and tuned with the coil in a respective frequency of resonance for attenuating electrical signals within a band including the tuned frequency; and

means in the filter circuit for reducing the decay time of oscillations within said band of the filter to improve the fidelity of the acoustical output of the sound system.

7. The combination claimed in claim 6 wherein the means for reducing the decay time of oscillations comprises a resistor connected in the filter circuit and in series with the coil and wherein the value of said resistor is selected in conjunction with the values of the capacitor and the coil to establish a bandwidth, at the point corresponding to one-half of the maximum attenuation of the band at the center frequency thereof, of substantially one-third octave.

8. The combination claimed in claim 6 wherein the means for reducing the decay time comprises a resistor connected in the filter circuit in series with the capacitor.

9. The combination claimed in claim 1 wherein the means for variably controlling the amount of attenuation of electrical signals comprises a variable resistor connected in parallel with each filter.

10. The combination claimed in claim 1 and further comprising means for maintaining, for the linking circuit, and impedance that is substantially free of variation caused by any variation in the number of filters that are used and by any variation in the attenuation of each respective filter.

11. The combination claimed in claim 10, wherein the linking circuit comprises at least two electrically conductive paths and the means for maintaining a constant impedance comprises at least one bandpass filter portion for operating in association with each band-rejection filter to short filter-current of frequencies lying within said band in which electrical signals are attenuated across the linking circuit, and wherein the means for variably controlling the amount of attenuation comprises a first variable resistor in parallel connection with the band-rejection filter and a second variable resistor in series connection with the bandpass filter, said first and second variable resistors being linked and variable together to control the attenuation of signals within said band in which signals are attenuated and to provide a constant impedance for the linking circuit.

12. For eliminating undesired effects produced by resonances induced by structure forming and contained in a room on the quality of sound over a audio frequency audiofrequency spectrum produced in the room by a system having a signal source, an amplifier, a linking circuit connecting the signal source and amplifier, and a sound reproducing device driving the atmosphere within the room to produce said sound, the method comprising:

measuring the pressure-level of said sound at intervals spaced across said predetermined audio-frequency spectrum to produce a sound pressure-level versus frequency curve for the room; and

selectively attenuating, within a plurality of contiguous frequency bands covering said spectrum, electrical signals in the linking circuit to compensate the sound pressure-level versus frequency characteristics of the sound produced in the room to cause said characteristics to corresPond to a curve which is essentially smooth over said predetermined frequency spectrum.

13. The method claimed in claim 12 wherein the step of measuring the pressure-level of said sound is accomplished by analyzing sound in the room to provide a dynamic sound pressure-level versus frequency curve for the room.

14. For eliminating undesired effects produced by resonances induced by structure-forming and contained in a room on the quality of sound over a predetermined audiofrequency spectrum produced in the room by a sound-reinforcing system having a microphone, a signal source, amplifying means, a linking circuit a plurality of contiguous electrical band rejection filters located in series and connecting the signal source and amplifying means, and a sound reproducing device driven by electrical signals from the amplifying means to drive the atmosphere within the room to produce said sound, the method comprising:

measuring the pressure level of said sound at intervals spaced across said predetermined audio-frequency spectrum to produce a sound pressure-level versus frequency curve for the room;

selectively attenuating, across said frequency spectrum, electrical signals in the linking circuit to produce an attenuation versus frequency curve which is substantially the inverse of the sound pressure-level curve for the room; and

selectively altering electrical signals in the linking circuit to eliminate any regenerative feedback in the reenforcement system caused by acoustical coupling between the sound in the room and microphone.

15. The method claimed in claim 14 including the further step of selectively attenuating electrical signals in the linking circuit to eliminate regenerative feedback in the reenforcement system caused by placement of a body of large size with respect to the microphone in close association with the microphone.

16. For use in connection with a sound system having a signal source, amplifying means, a linking circuit connecting the signal source and the amplifying means, and a sound reproducing device driven by signals supplied thereto by the amplifying means to produce sounds over a predetermined audio frequency spectrum and operating in association with the structure forming and in a room which acts on said sounds to produce undesired variances in pressure-levels therein with respect to the power levels of the signals supplied to the sound reproducing device, the method for adjusting the sound pressure-level versus frequency characteristics of the reproduced sound to improve the quality thereof comprising:

measuring the sound pressure-level versus frequency characteristics of sound in the room at intervals spaced across said predetermined audio-frequency spectrum; and

selectively attenuating, within contiguous bands having different center frequencies and covering said frequency spectrum, electrical signals in the linking circuit to alter the sound pressure-level versus frequency characteristics of the sound produced in the room to cause said characteristics to correspond to a curve which is substantially smooth over said entire frequency spectrum and to provide a balance of sound pressure-levels in the reproduced sound having a desirable correspondence to the balance of power levels of the signals supplied to the sound reproducing device.

17. The method claimed in claim 16 wherein electrical signals are selectively attenuated to alter the sound pressure-level versus frequency characteristics of the sound produced in the room to provide a balance of sound pressure-levels in the reproduced sound which emphasize selected portions of the reproduced sound material.

18. For use in connection with a sound system having a signal source, an amplifier, a linking circuit connecting the signal source and the amplifier, a plurality of variable-attenuation, band-rejection filters for attenuating electrical signals in contiguous frequency bands covering a predetermined portion of the audiofrequency spectrum, and a sound-reproducing device driven by signals supplied thereto by the amplifier to produce sounds and operating in association with the structure forming and in a room which acts on said sounds produced by the sound system to produce undesired variances in pressure-levels therein with respect to the power levels of the signals supplied to the amplifier, the method for adjusting the sound pressure-level versus frequency characteristics of said sounds to improve the quality thereof comprising:

measuring the pressure-level of sound in the room at intervals spaced across at least a portion of the audio-frequency spectrum to produce a sound pressure-level versus frequency curve for the room; and

varying the attenuations of selected ones of the plurality of band-rejection filters to produce a composite electrical attenuation versus frequency filter-response curve which is substantially the inverse of the acoustical sound pressure-level versus frequency response curve of the room, such that selected bands of electrical signals in the linking circuit are attenuated to produce a sound pressure-level versus frequency response curve for the room that is substantially smooth over said audio frequency spectrum.