ELECTRONIC REINFORCEMENT OF SOUND
REFERENCE:
SCIENCE OF SOUND, 3rd ed., CHAPTER 24
LONG, ARCHITECTURAL ACOUSTICS, CHAPTER 18
SOUND SOURCES IN A ROOM
SOUND FIELDS
POWER
CONSIDERATIONS
MAXIMUM SOUND LEVELS FOR VARIOUS USES
TYPE OF USE
MAXIMUM LEVEL (dBA)
CLASSROOM
LECTURE HALL
SYNAGOGUE
HOME THEATER
LEGITIMATE THEATER
TRADITIONAL CHURCH
MOVIE THEATER
FUNDAMENTALIST CHURCH
SPORTS ARENA
ROCK CONCERT
80
83
85
90
90
90
100
100
105
110
Source: Long, Chapter 18
LOUDSPEAKERS
DYNAMIC
LOUDSPEAKER
HORN
LOUDSPEAKER
MULTIPLE
SPEAKERS IN A
CABINET
HORN
CLUSTERS
BANDWIDTHS OF VARIOUS SPEAKERS
TYPE OF LOUDSPEAKER
BANDWIDTH (Hz)
1” COMPRESSION DRIVER
2” COMPRESSION DRIVER
1” DOME TWEETER
3” CONE DRIVER
5” CONE DRIVER
8” CONE DRIVER
10” CONE DRIVER
12” CONE DRIVER
15” CONE DRIVER
18” CONE DRIVER
1200-16k
850-10k
2000-20k
700-10k
350-6k
250-5k
200-4k
150-2k
80-1250
70-1000
Source: Long, Chapter 18
LOUDSPEAKER SYSTEMS
SINGLE CLUSTER—MAINTAINS PROPER RELATIONSHIP BETWEEN
THE SOUND SYSTEM AND THE APPARENT SOURCE
MULTIPLE CLUSTERS—PROVIDES GOOD COVERAGE BUT SPREADS
THE APPARENT SOURCE
COLUMN MOUNTED---SUSCEPTIBLE TO INTERFERENCE EFFECTS
DISTRIBUTED—SHOULD INCLUDE TIME DELAY TO MAINATAIN
PROPER RELATIONSHIP WITH DIRECT SOUND
PEWBACK SYSTEMS—PROVIDES GOOD COVERAGE IN CHURCHES
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.
HORN LOUDSPEAKERS
LOUDSPEAKER PLACEMENT
LOUDSPEAKER
DIRECTIVITY
UNSATISFACTORY
ARRANGEMENT OF
LOUDSPEAKERS
RADIATION PATTERN
AND DIRECTIVITY
FACTOR Q FOR A
TYPICAL 8-INCH CONE
LOUDSPEAKER
ACOUSTIC FEEDBACK
EQUALIZATION
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
ASSISTED RESONANCE SYSTEM
REVERBERATION TIME IN THE ROYAL FESTIVAL HALL (LONDON) WITH
AND WITHOUT ASSISTED RESONANCE (Parkin and Mogan, 2970).
REINFORCEMENT FOR THE HEARING IMPAIRED
SPEECH INTELLIGIBILITY CAN BE INCREASED BY PROVIDING A WAY TO
ENHANCE THE SOUND AT THE LISTENER’S EAR. THIS CAN BE DONE BY ONE
OF FOUR TYPES OF WIRELESS TRANSMISSION-RECEIVER SYSTEMS:
MAGNETIC INDUCTION—EMPLOYS 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 BROADCASTING—OPERATES IN THE BROADCAST BAND OR BELOW
INFRARED LIGHT—DON’T OPERATE WELL IN BRIGHTLY-LIGHTED ROOMS
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.
MULTIPLE OPEN MICROPHONES
WHEN THERE ARE SEVERAL MICROPHONES IN USE AT THE SAME TIME,
THE SIGNAL FROM THE LOUDSPEAKER CAN BE PICKED UP BY EACH OF
THEM AND COMBINED AT THE MIXER.
IT IS GOOD PRACTICE IN SPEECH SYSTEMS TO USE AN AUTOMATIC
MICROPHONE MIXER SO THAT THE SYSTEM GAIN IS THEORETICALLY
THE SAME AS IT WOULD BE IF ONLY ONE MICROPHONE WERE ON A A
GIVEN TIME.
GRANOFF MUSIC CENTER
TUFTS UNIVERSITY
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.
SPEAKER CLUSTER AT PRITZKER PAVILLION
PRITZKER PAVILLION IN MILLENIUM PARK,
CHICAGO
JAY PRITZKER MUSIC PAVILION
CHICAGO
PRITZKER PAVILION
VIEW OF AUDIENCE FROM THE STAGE