ELECTRONIC REINFORCEMENT OF SOUND REFERENCE: SCIENCE OF SOUND, 3 rd 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) CLASSROOM80 LECTURE HALL83 SYNAGOGUE85 HOME THEATER90 LEGITIMATE THEATER90 TRADITIONAL CHURCH90 MOVIE THEATER100 FUNDAMENTALIST CHURCH100 SPORTS ARENA105 ROCK CONCERT110 Source: Long, Chapter 18

LOUDSPEAKERS DYNAMIC LOUDSPEAKER MULTIPLE SPEAKERS IN A CABINET HORN LOUDSPEAKER HORN CLUSTERS

BANDWIDTHS OF VARIOUS SPEAKERS TYPE OF LOUDSPEAKER BANDWIDTH (Hz) 1” COMPRESSION DRIVER k 2” COMPRESSION DRIVER850-10k 1” DOME TWEETER k 3” CONE DRIVER700-10k 5” CONE DRIVER350-6k 8” CONE DRIVER250-5k 10” CONE DRIVER200-4k 12” CONE DRIVER150-2k 15” CONE DRIVER ” CONE DRIVER 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