[sdiy] Speaker Impedance

[harrybissell]

Bob Weigel wrote: <snip>

>  NOW....with the
> resistor you have the equivelent of an 8 ohm speaker with 7 ohms of DC
> resistance that is only making heat..no sound. So now it's half as
> potentially efficient roughly.
>

The "DC resistance" of the speaker is not just 'making heat'... the cone will
be displaced by some amount from magentic field.

Trouble is, the DC resistance of the 8 ohm speaker is WAY less than 8 ohms...
it could be as low as 2-3 ohms.

Most people try to avoid providing DC for the two reasons... it makes the cones
move off-center... sometimes so much so they leave the enclosure.  The wattage
of the DC resistance is WAY over what the speaker is designed to handle.

I agree... half as efficient.  Two speakers in series is better. If you can
afford to
lose power, the series resistor will work OK as well.

Another solution would be to take a speaker matching transformer (like a 70V
line unit) that is good for the power... and connect the amp to 0 - 8 ohm taps
and
the speaker to the 0 - 4 ohm taps (autotransformer).   This will NOT waste any
power
... but the transformer is going to be quite expensive !!!    (maybe more than
the
right, or a second speaker...)

H^) harry