RE: Amps, Speakers, & Zoning

[Keith Doxey <keith.doxey@xxxxxxx>]

Hi Paul,

Firstly, switching speakers or connecting/disconnecting whilst the amp is
turned on is no problem. Thats exactly what the AB switches on the amp do.
The only reason the speaker manufacturers tell you not to connect live is
incase the amp is really cranked up and you blow the speakers or get a
shock from the amp. With a high power amp driving hard ther can easily be
60 volts AC at the output.

A transistor amp is perfectly happy driving into an open circuit, a valve
amp is not.

Most amplifiers are capable of handling a minimun load of 4 ohms.
Most speakers are 8 ohms.
2  x 8ohm speakers in parallel gives a load of 4 ohms.
2 x 8ohm speakers in series gives a 16 ohm load.

On the attached diagram you will see 8 speakers connected up as 4 parallel
sets of 2 speakers.
Each speaker is 8 ohms so each of the 4 sets is 16 ohms. 4 sets of 16 ohms
in parallel is 4 ohms so still safe for the amp.

You will notice that each of the relays switched between a speaker or a
dummy 8 ohm 25 watt resistor to simulate the speaker still being there.
This is neccessary to keep the impedance constant and avoid changes in
volume to other speakers as one is switched in or out of circuit.

If you only need two speakers use one of the series sets eg LS1 & LS2.
This
will present a 16 ohm load to the amp.

4 sets use LS1-4 and the amp will see 8 ohms
6 sets use LS1-6 and the amp will see 5.3 ohms

If you need an odd number or the speakers arent 8 ohms the maths gets
messy.
Ideally one amp per circuit is the best method. If you are only using mono
anyway then go to a car boot sale and buy a couple of old hifi amps and use
the left channel for Zone1 right for Zone2 and just use relays to
connect/disconnect a single speaker. That way you can also adjust the
volume for each room to balance different room sizes and speaker types.

Diagram coming up.

Hope that helps.....
and I hope the thunderstorm rumbling outside doesnt crash my PC !!!!

Keith


-----Original Message-----
From:	Paul Gordon [SMTP:paul_gordon@xxxxxxx]
Sent:	29 July 2000 08:49
To:	ukha_d@xxxxxxx
Subject:	[ukha_d] Amps, Speakers, & Zoning

Morning all!

My good lady has insisted that I put some zoning in place for our Homeseer
announcement speakers. Currently, I have an old amp connected to the PC
soundcard (mainly becuase it drives two pairs of speakers - the PC
soundcard
is one of the motherborad built-in ones, and it only has a single
line-out).
To which I have currently connected a single pair of speakers, - one in the

living room, and one in the bedroom. (I don't need a stereo pair for simple

TTS announcements)


So, I need to put in some way of zoning these speakers (and some more),
that
is external to the Amp, and controllable by Homeseer.

So, what must I do to protect the amp whilst still being able to switch
speakers in/out willy nilly?  How best should I go about this? What are the

implications if I run the amp with "incorrect" speaker loads (0,
1, 2, 3,
or
4 speakers)?

--------------------------------------------------------------------<e-
BTW: Did you buy that new car yet?
If not, check this site out.
They're called CarsDirect.com and it's a pretty sweet way to buy a car.
http://click.egroups.com/1/6847/9/_/2065/_/964880919/
--------------------------------------------------------------------e>-