ELECTRONIC REINFORCEMENT OF SOUND

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ELECTRONIC REINFORCEMENT OF SOUND
REFERENCE SCIENCE OF SOUND, 3rd ed., CHAPTER 24
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SOUND SOURCES IN A ROOM
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SOUND FIELDS
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POWER CONSIDERATIONS
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LOUDSPEAKERS
DYNAMIC LOUDSPEAKER
HORN LOUDSPEAKER
MULTIPLE SPEAKERS IN A CABINET
HORN CLUSTERS
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LOUDSPEAKER SYSTEMS
SINGLE CLUSTERMAINTAINS PROPER RELATIONSHIP
BETWEEN THE SOUND SYSTEM AND THE APPARENT
SOURCE MULTIPLE CLUSTERSPROVIDES GOOD COVERAGE
BUT SPREADS THE APPARENT SOURCE COLUMN
MOUNTED---SUSCEPTIBLE TO INTERFERENCE
EFFECTS DISTRIBUTEDSHOULD INCLUDE TIME DELAY TO
MAINATAIN PROPER RELATIONSHIP WITH DIRECT
SOUND PEWBACK SYSTEMSPROVIDES GOOD COVERAGE IN
CHURCHES
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TIME DELAY
SOUND THAT ARRIVES UP TO 50 ms AFTER THE DIRECT
SOUND WILL REINFOCE THE DIRECT SOUND AND YET
PRESERVE THE APPARENT DIRECTION OF THE SOUND
SOURCE. TIME DELAY IS ESPECIALLY IMPORTANT IN
THE CASE OF SUPPLEMENTARY SPEAKERS POSITIONED IN
PROBLEM AREAS, SUCH AS UNDERNEATH A BALCONY OR
FOR SPEAKERS MOUNTED ON SIDE WALLS.
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HORN LOUDSPEAKERS
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LOUDSPEAKER PLACEMENT
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LOUDSPEAKER DIRECTIVITY
UNSATISFACTORY ARRANGEMENT OF LOUDSPEAKERS

RADIATION PATTERN AND DIRECTIVITY FACTOR Q FOR A
TYPICAL 8-INCH CONE LOUDSPEAKER
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ACOUSTIC FEEDBACK
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EQUALIZATION
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ENHANCEMENT OF REVERBERATION
ADJUSTMENT OF REVERBERATION TIME IS DESIRABLE IN
MULTI-PURPOSE HALLS. MAXIMUM CLARITY OF SPEECH
DEMANDS A SHORT REVERBERATION TIME, BUT A PIPE
ORGAN SOUNDS BEST IN A REVERBERANT ROOM. ONE
SOLUTION IS THE USE OF ELECTRONICALLY ENHANCED
REVERBERATION OR ASSISTED RESONANCE ONE METHOD
OF ENHANCEMENT PLACES A LOUDSPEAKER AND
MICROPHONE IN A REVERBERATION CHAMBER ANOTHER
USES A NUMBER OF TRANSDUCERS MOUNTED ON A THIN
PLATE OR FOIL (KUHL PLATE) DIGITAL REVERBERATORS
USE DIGITAL SIGNAL PROCESSING (DSP) TO SIMULATE
REVERBERATION
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ASSISTED RESONANCE SYSTEM
REVERBERATION TIME IN THE ROYAL FESTIVAL HALL
(LONDON) WITH AND WITHOUT ASSISTED RESONANCE
(Parkin and Mogan, 2970).
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REINFORCEMENT FOR THE HEARING IMPAIRED
SPEECH INTELLIGIBILITY CAN BE IMCREASED BY
PROVIDING A WAY TO ENHANCE THE SOUND AT THE
LISTENERS EAR. THIS CAN BE DONE BY ONE OF FOUR
TYPES OF WIRELESS TRANSMISSION-RECEIVER
SYSTEMS MAGNETIC INDUCTIONEMPLOYS A LARGE LOOP
OF WIRE TO SET UP A MAGNETIC FIELD THAT CAN BE
PICKED UP BY HEARING AIDS FM BROADCASTING(FCC
HAS RESERVED A BAND OF HIGH FREQUENCY AM
BROADCASTINGOPERATES IN THE BROADCAST BAND OR
BELOW INFRARED LIGHTDONT OPERATE WELL IN
BRIGHTLY-LIGHTED ROOMS
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MICROPHONE PLACEMENT
MICROPHONES ARE GENERALLY PLACED IN THE DIRECT
FIELD OF THE SPEAKER OR PERFORMER SO THE
MICROPHONE OUTPUT IS REDUCED BY 6dB FOR EACH
DOUBLING OF THE DISTANCE. THIS REDUCES THE GAIN
BEFORE FEEDBACK BY 6dB BUT IT ALSO MEANS THE
PERFORMER CAN MOVE A LITTLE WITHOUT PRODUCING A
LARGE CHANGE IN LEVEL WHEN A MICROPHONE IS A
SMALL DISTANCE ABOVE THE FLOOR, CANCELLATION OF
CERTAIN FREQUENCIES (COMB FILTERING) CAN OCCUR.
FOR EXAMPLE, IF THE MICROPHONE WERE 3 m FROM THE
SOURCE AND BOTH WERE 1.5 m ABOVE THE FLOOR, THE
PATH DIFFERENCE OF THE DIRECT AND ONCE-REFLECTED
SOUND WOULD BE 1.23 m AND THE CANCELED FREQUENCY
WOULD BE ABOUT 140 Hz.
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OUTDOOR SOUND SYSTEMS
SOUND POWER TAKES ON CONSIDERABLE IMPORTANCE
SINCE THERE IS NO REVERBERANT FIELD FOR
REINFORCEMENT. MULTIPLE LOUDSPEAKERS AND LARGE
AMPLIFIERS ARE GENERALLY USED. LOUDSPEAKERS
SHOULD HAVE AS HIGH EFFICIENCY AS POSSIBLE.