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From: gary@ke4zv.UUCP (Gary Coffman)
Newsgroups: sci.electronics,misc.consumers,rec.audio,rec.ham-radio
Subject: Re: Need Modest Public Address System
Message-ID: <1496@ke4zv.UUCP>
Date: 1 Nov 90 01:12:55 GMT
References: <90303.202207DBG@SLACVM.SLAC.STANFORD.EDU>
Reply-To: gary@ke4zv.UUCP (Gary Coffman)
Followup-To: sci.electronics
Organization: Gannett Technologies Group
Lines: 50

In article <90303.202207DBG@SLACVM.SLAC.STANFORD.EDU> DBG@SLACVM.SLAC.STANFORD.EDU writes:
>
>Does anyone have relevant experience with PA systems for modest-size
>groups? We don't want a bull-horn, and don't need rock-band volume, but
>want good fidelity and enough volume to handle say 100 people inside a
>community-center-type room (typically hard walls, tile floor, acoustic
>tile ceiling).

There are numerous tradeoffs in a PA system. The fidelity/cost tradeoff
is one of the toughest. First let me urge you to avoid wireless microphones
if possible. Good wireless systems with diversity receivers and using
crystal controlled clear frequencies (requiring a license) are very expensive.
Nothing less is satisfactory except in rare conditions. Without diversity
reception you will have null zones with sudden fades and odd noises. Without
crystal control you will have drift problems similar to those you described.
Expect to pay upwards of $1000 for a decent wireless microphone system.

If possible use a podium mounted stick mic such as an Electro Voice EV635, this
is the best all around microphone you can buy. It's extremely rugged, you
can drive nails with it, and it has good voice fidelity. Most broadcasters
use it. If the speaker must move about, use a lapel mic like a Sony ECM50 or
let him hand hold the EV. Using a hand mic properly is a skill that some
speakers find difficult to master.  These are professional microphones in the 
$50 to $90 dollar class.

For a hall holding 100 people you need an amplifier of about 50 watts.
With very efficent speakers you can get away with 20 watts. You will need 
an equalizer to balance the system and prevent feedback. Bogen makes a
suitable amp for about $150. If the PA is to be a permanant installation,
ceiling mounted speakers sprinkled about the hall are best. No one gets
blasted and people in the back can hear clearly. Cost will be about $10
each for 5 inch ceiling mount speakers and 70 volt line transformers.
Otherwise you will need two or three floor standing speaker cabinets. If 
you want good fidelity, and you do else feedback becomes very difficult 
to control, these can be very expensive. Expect to pay at least $150 each 
for floor standing speakers. You can make suitable speakers yourself out of 
plywood and speaker components by EV or even Radio Shack. Cost about $50 each.

An empty hall and one containing 100 people have very different acoustics.
Try to get some volunteers to sit in the seats while you are equalizing
the system. Otherwise you will be unpleasantly surprised. Also a system
that sounds plenty loud in an empty hall will be inadequate when sound
absorbing bodies are present. Try to do all your testing with the hall
filled.

So with care you can put together a system for around $300 that will do
a fine job. Get to know your local sound reinforcement technicians and the
distributors where they shop. You'll learn a lot.

Gary KE4ZV