On Thu, 04 May 2006 22:22:41 +0100, Owain
wrote:

Tom Harvey wrote:
Please excuse the stupid question...
I have 2x 4 ohm speakers which I intended to run from 2 x amps bridged,
but on the amps it says to use a minimum of 8 ohm speakers in bridged
mode. Can I use them in this way, will it cause any damage to the
amps/speakers, sound problems, or should I have to have a re-think?
Any explanation in idiot proof, layman's terms would be gratefully
received.

If you use 2 x 4ohm speakers in parallel, the load on the amplifier will
be 2ohm, which will be much too low. The amplifier is very likely to die.

If you use 2 x 4ohm speakers in series, the load on the amplifier will
be 8ohm, which will be about right. Caveat: the impedance rating of
speakers is nominal. The actual impedance of the speakers may still be
too low for the amplifier, especially if you crank up the volume.

Bridging effectively doubles the voltage the amplifier can supply.
This means that into the same load, if also doubles the current it
will try to supply. Power is voltage multiplied by current. Hence,
twice the voltage and twice the current equates to four times the
power.

This means that for bridging, 16-ohm speakers should be used for an
amplifier rated for driving 8 ohms non-bridged (or 8-ohm speakers for
an amplifier rated for driving 4 ohms).

(The above is a simplification of the real situation, but is usually
sufficiently good for practical purposes.)

From the specification you give, running the speakers in series is the
only option. Running them in parallel will probably either damage the
amplifier or cause its protection circuits to operate, adversely
affecting the sound.

--
Chris Isbell
Southampton, UK