DOCUMENTRESUME ED 025 910 EF 002 252 By-Palmer, Fred M. Public Address Systems. Specifications InstallationOperation. Pub Date Jan 66 Note-5p.; Presented at the Fifteenth Annual Meeting, Eastern Regional Croup, National Association of Physical-Plant Administrators, Hotel Biltmore, N.Y.C., Jan. 1966 EDRS Price MF-$0.25 HC-$0.35 Descriptors- ,*AudioEquipment.BuildingDesign,*BuildingEquipment,*Campus Planning, *Communications, *Construction Programs, Facsimile Communication Systems, Provisionsforpublicaddressinnew construction of campus buildings (specifications, installations, and operation of public address systems), are discussed in non-technical terms. Consideration is given to microphones, , and the placement and operation of various different combinations. (ES) all 1.pem to have different resonantpeaks which clash in the vicinity of 4i;,c;-loudSpeakers. Also, it V bad practice tohave live mikes around where 04Ahey'tin pick up conversation or thatare/not meant for thepublic.

:.:liiAhe classroom, laboratory or lecture roomthat is large enough to exists. It is )7;imie,Votce 'amplification desirable,quite another condition gimpraotleal;to have an operator for everysession where the p.a.is used AW,Pso some:compromise must be made toenable the professor toactivate the Wbuilt-in'system with a minimum oftechnical know-how, He is usually will- plug it in ingto bring a neck fromhis office, put it on and 4C:and,that is about all that thespeaker himself can beexpected to do except ',!A:fitill[the plug and return the miketo the office. I have here the Palmer ,':proftssor-proof switch which I designedand built for the specificsitua- into the jamb, a micro- tioniust described. As the mike plug is inserted What :...switchAs activated which turnsthe a.c. on for theamplifier power. is.mo're important, when the mikeplug is removed, the amplifieris auto- x.Maticallyiturned off -- a chore thatthe professor has troubleremembering to a mike ttv.ifo. The concealed amplifierhas been adjusted previously I attention Y:.ietting well below the pointand should need no further utless tamOered with.

: . :Incidentally, this professor-proof switch wonsecond prize in the dgets, gimmicks and witchcraft contestat the annual meetingin Raleigh whichYgave me quite a thrill as well as$30, in Yankee money.

'-We will discuss the placing ofmicrophones a little later sothis might be a good place to stop forquestions that you mighthave relative to microphones.

r, A relatively new unit, designedfor the border-lineapplication where , amplification is needed, combines alectern with a -v on y a little speech transistorized to ,- columnarloudspeaker and battery operated, reinforce the voice enough for upto 500 people whereacoustics are good, that this unit will is now available as shown. Don't let anyone tel you audiences out-of-doors ,,. take the place of a publicaddress system for large This is an Ampli-Voxunit selling A orwitere there is competitive . for about $350 complete withbatteries.

Choice of an amplifier isdictated by the variousacoustical require- and the area to be ments, the type and number ofinput devices to be used dining hall, a two covered with sound. Assume t't we are planning a new story building with a largelounge on the ground flooralong with public dining room for seat- rest rooms and storage, etc.The second floor has a It is desirable ing 500 and an adequate kitchen andfood preparation area. building all day and an to have back-ground FM radiomusic in all of this banquets and adeqUate p.a. system for announcementsat meal time and for We immedi- special occasions that may forcetheir way into thisfacility. ately realize that the only way todistribute the sound isthru numerous loudspeakers located in the acousticalceilings.Using of rule of roughly discover that twice the ceiling height for spacingof these speakers, we in the a total of twentywill be required, ten inthe dining room: four In this kind of lounge, two in.the serving area andfour in the kitchen. application', indoors, five watts perspeaker should be amplevolume for should be adequate anroCcasion and therefore, 100watts of amplifier power for.this entire.system. PUBLIC ADDRESS SYSTEMS

SPECIFICATIONS - INSTALLATION -OPERATION

Fred M. Palmer a

systems and Jty, Certainly all of you have beenexposed to public address have had, but we hope to vou may have had asmuch experience as I IrIl5`.torne 'of and be helpful to bring. out points today that willbe of interest to all . of public addressinstalla- mostrof you. We will touch upon several types tions but wish to dwell mostly onthe provisions forpublic address in be divided into 'new construction in campusbuildings. My short talk will and the placement and ,21):' four parts: Microphones,amplifiers, loudspeakers operation of various differentcombinations.

, Before we proceed, there is a commonmisnomer used in thisbusiness it is as wrong ,that,makes.me boil. When a mike is called a device which as calling 1spark plug a truck tire. A microphone is a ,LconVerts*.sound waves into correspondingaudio frequencyelectrical which moves in accor- Y:Leiter#.,. It contains some formof flexible Ag605dance with sound wave variations. The movement, inturn,.generates a WT'ljninute voltage which is fed tothe input of an amplifierwhere it is microphone available amplified many times. There are several types of Mut they all operate on the sameprinciple. with micro- Since we are only considering publicaddress, let's stay phones best suited to this purpose. Generally, lOkes are mounted on a by a cord around floor.stand, a lectern, a tablestand, hung on the person units for all these the neck or hand held. I have here some typical purposes which areprobably familiar to you. Medium priced mikls are frequency of 60 generally adequate for publicaddress use if they have a (the to 10,000 Os and aredesigned especially tominimize feedback Also, most public familiar howl or squeal oftenheard over p.a.systems.) high impedance inputs; address systems, especiallythe portable ones, have impedance units used in and this type mike isless expensive than low required broadcasting and recording andelsewhere where long cables are high between mike and amplifier orcontrol panel. It is possible to run appreciable losses in thehigh impedance lines as much as100 feet without impedance frequencies. .Farther than100 feet or installedin conduit, low ideal for public lines should be used. So,..-called cardiod microphones are pick-up at the front and address as they are designedto give maximum feedback troubles start. ignore sounds from theloudspeakers which is where There are many They permit close talkingand are rugged andtrouble-free. noise rejection, other models for special purposessuch as high background speech clippers and long range spot pick-up, stereoeffects, close talking telephonl taps, but we will nottake time for them here.

Assuming that a Combination ofmicrophones is required for a convoca- operator be at tion, for instance, it is mostimportant that a competent He the controls at all times if asmooth and proper jobis to result. should be familiar with the program sothat he will have only the proper the moment and be ready mike or mikes turned onwhich are being used at Pre- to reduce the gainimmediately if feedbackshould start to develop. venting feedback is mucheasier if only one mikeis on at a time because

-3- allIppem to have different resonantpeaks which clash in the vicinity of mikes around where loudtpeakers, Also, it i.bad practice to have live they't0 pick up conversation orsounds that are/not meant forthe public.

4:"..,..-10:the classroom, laboratory or lecture roomthat is large enough to ak4Notce amplification desirable, quiteanother condition exists. It is ''I'AmprAct.idal,to have an operator for everysession where the p.a. isused t;VPSO sope :compromise must be made toenable the professor to activatethe built..in'system with a minimum oftechnical know-howe He is usually will- plug it in hg. to bring a neck microphone fromhis office, put it on and and,that is about all that the speakerhimself can be expected todo except nll.the plug and return the miketo the office. I have here the Palmer 4:i;:.'professor-proof switch which I designedand built for the specificsitua- tiOnAust described. As the mike plug is insertedinto the jaMb, a micro- %..switch.is activated which turns the a.c. onfor the amplifier power. What -,As.mdreAmportant, when the nine plugis removed, the amplifieris auto- i'..MiatiCillyittirned off -- a chore that theprofessor has troubleremembering been adjusted previously to amike gr. ,titvd6 The concealed amplifier has -, well below the feedback pointand should need no furtherattention titiler0.-tamliered with.

'Ancidentally, this professor-proof switch wonsecond prize in the gimmicks and witchcraft contest atthe annual meeting inRaleigh g1:141chYgave me quite a thrill aswell as $30, in Yankee money.

f. . . 4, :-We will discuss the placing ofmicrophones a little later sothis have relative ..1.-might be a good place to stop forquestions that you might

, to miicrophones. where relatively new unit, designed forthe border-line application alectern with a .:!,..-.ontY,a little speech amplificationis needed, combines columnar loudspeaker and batteryoperated, transistorizedamplifier to good, reinforce the voice enough for up to500 people where acoustics are that this unit will is tiow available as shown. Don't let anyone te4/ you take.the place of a public addresssystem for large audiencesout-of-doors unit selling or where thereis competitive sound. This is an Ampli-Vox for about $350 complete withbatteries.

Choice of an amplifier is dictatedby the various acousticalrequire- ments, the type and number ofinput devices to be usedand the area to be , dining hall, a two covered with sound. Assume t'17. we are planning a new story building with a largelounge on the ground flooralong with public dining room for seat- rest rooms and storage, etc.The second floor has a It is desirable ing 500 and an adequate kitchenand food preparation area. building all day and an to have back-ground FM radiomusic in all of this banquets and adeqUate p.a. system for announcementsat meal time and for We immedi- special occasions that may forcetheir way into thisfacility. ately realize that the only way todistribute the sound isthru numerous roughly loudspeakers located in the acousticalceilings. Using of rule of discover that twice the ceiling height for spacingof these speakers, we in the a total of twentywill be required, ten inthe dining rooms four In this kind of lounge, two in.the serving area andfour in the kitchen. application., indoors, five watts perspeaker should be amplevolume for amplifier power shouldbe adequate any occasionand therefore, 100 watts of for.this entire,system.

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-4- Student help is used for part of this food operation so this equip- t .ment must.be.behind-locked doors to avoid tampering and loss. But where the manager's office on the floor above is the only safe place, so, in it goes, assembled in a rack-type cabinet with a radio tuner, record player, speaker switching panel, monitoring speaker with volume control and meter to indicate level of sound at all times. A conventional time clock switch is added to turn the unit on at 8:00 a.m. and off at 8 p.m. when the help has all left the building. Most stock amplifiers of this size have two Microphone inputs, high impedance, and two radio and phono inputs. This meets our requirement except that mike inputs should be low impedance to accuumodate the long runs to the dining room (three receptacles) and the first floor lounge (two receptacles). Transformers are inserted at the amplifier and low impedance mikes are to be used. Remote volume control for each room is a must with the control mounted at the wall receptacle in each case as it is difficult to be sure that the volume is correct when you are not in the room with the listeners. Also, moving the micro- phones around may change the feedback situation and require adjustment of the volume controls quickly, and someone should be ready to do this immedi- ately if the old feedback bug starts to bite.

Since we are supposed to be considering amplifiers only at this time, let us get back to them. Although p.a. amplifiers have a good frequency range, they are not to be confused with so-called hi-fi amplifiers princi- pally because of their different functions and controls. Tube type amplifiers are still most practical and inexpensive, but transistorized units are now available which have advantages of small size and cool opera- tion. They are more.expensive but my be expected to have a longer life with less matntenance with_special advantages in portability and space savings where that can be.a factor.

The watt is the measuring unit for amplifier and loudspeaker power capacities and amplifier units are available from 10 to 1000 watts. Seldom would more than 100 watts be found in a stock package, but all kinds of combinations of drivers and boosters are possible to create a tremendous amount of audio power.

Having'extra wattage inan amplifier is like having a car powered to go 120 miles an hour although you never intend to exceed 70. It should deliver all the volume you require without any distortion which is of primary importance. A 100,watt amplifier would cost about 20% more than a.50 watt unit, so specity oversize. The power.consumption and upkeep are not appreciably higher. Stock amplifiers with only two microphone inputs can be adapted for any nuMber with transistorized mixer boxes so that hav- ing more than two mike inputs is not really necessary.

We must.discuss loudspeakers and the importance of their placement and phasing. Dozens of manufacturers make hundreds of models of speakers but only a few of these are designed for public address purposes. For voice amplification out of doors, the old trumpet type horn is hard to beet. The low range is limited and music i4 not well reproduced, so other types of weather-proof speakers are available for this broader application. It is desirable to have the speakert located in one place so that sound will agpear to come from where the person is seen speaking. Usuay this is not quite possible, so speakers should mount at each side of the speaker's

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platform and cover theentire area from there. In an open outdoor area speakers toward any hardvertical surface thatwill bounce In a football game sound back'iOwiraitiViiidrelied-tausing reverberation. 10,000 persons would set-up, for instance, asmall installation to seat located at the score- require a 100 watt amplifierand four 25 watt trumpets be a useful figurein board or press box. Ten watts per 1000 people can speakers for footballstadia. deciding power requirementsfor anplifiers and and simply meansthat Phasing of loudspeakersis extremely important in con- that all diaphragms movetogether as one and they will be so wired thru the junction with the naturalsound itself. Electrical energy flowing the coil to travelin voice coil winding of aloudspeaker driver causes flow of currentdecides the gap of a powerful magnet. The direction of the not movingtogether, the direction of the movement, so,if the diaphragms are The speaker reversing the leads of onespeaker will correct themovement. from the amplifier diaphragm is the medium bywhich the electrical energy corresponding in fre- air in front of itwith sound waves can vibrate the and with much quency withthose put into the diaphragmof the microphone traveling together greater force and amplitude. When all diaphragms are loudspeakers as one. Any they move the whole air massin front of the where they diaphragms that are out-of-phasetend to cancel sound waves listening people. overlap and, not only reducetotal:power but confuse

from technical terms We have tried to keepthis disiussion as free could grasp the wholepicture as possiblein the hope that all of you and volumes of easily. This is a very complicatedand interesting field it adequately, data and hours of discussionwould be necessary to cover so with thislament, we must close.

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