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Re: home stereo impedance matching

Here are some iffy ideas. If this is so, then that may be so.

You mention 8-16 Ohm speaker outputs. If you amplifier has two pairs of
speaker outputs with each speaker to be rated at 8-16, then a single 4 Ohm
speaker would be the same as driving two 8 Ohm speakers. A single 4 Ohm
speaker per channel would then be OK if no other speakers are driven in

The main problem with an 8 Ohm series resistor is that it reduces the
speaker damping. Most speakers are designed to "see" a fairly low impedance
load and depend on this to damp unwanted resonances. An 8 Ohm series
resistance presents too large a load from the point of view of the speaker,
so the damping may be inadequate. It is the damping factor that makes long
skinny speaker wires undesirable. Some manufacturers have then designed low
resistance wires which they claim sound better. Actually just using
thicker, shorter wires often achieves the same effect at substantially lower
cost. A series resistor can seriously degrade the sound, especially in the
bass region.

The main danger to the amplifier is that you will draw too much current and
blow it out. Some amplifiers have built in protection circuits which
prevent this, in which case the low impedance should not be a problem.
Protection circuitry will just turn off the sound if there is a danger to
the amplifier. If you listen at relatively low levels this should not be a
problem. Of course the 8-16 Ohm outputs are really the manufacturers way of
disclaiming responsibility it the amp. blows out. Speaker ratings are
generally according to the minimum impedance, and the actual impedance
varies considerably across the frequency spectrum. They seldom maintain
values only between 8 and 16. Often the low impedance is at a narrow band
of frequencies and will typically occur in the bass region. If you do not
listen to bass heavy music then again, the impedance may not be a problem.
The reason for the low impedance in the bass has to do with the resonant
frequency of the woofer, and the manufacturer may have adjusted the
impedance to compensate for the falling frequency response below the
resonance. If you wish to partially protect the amp. you could install a
fast blow series fuse to limit the maximum current.

The series resistor is easy to install, if you can find them.

The other thing to be careful about is the rated maximum power for the
speakers. If your amp exceeds this, it is possible to blow out the
speakers. However if your amp is rated for a much lower power than the
speaker, it is possible to blow out the tweeters. When overdriven, the amp
will produce copious energy in the high frequencies which can blow out the
tweeters. Again, listening at low volumes should be safe.

Older tube amplifiers did have multiple taps for matching to speaker
impedance, but modern ones do not. OTOH older tube amps could be damaged by
no speaker load, but survived short circuits quite well. Modern transistor
amps are just the opposite. They survive high impedance loads quite well,
but are easily damaged by short circuits.

With all of these ifs I would put in the disclaimer that neither I nor the
listserve can be held responsible for consequent damage to either speakers
or amp.

John M. Clement
Houston, TX

I have a pair of old (relatively) Bose 501 speakers that are marked as 4
Ohms, that I would like to use with a new receiver that only offers 8-16
ohm connections. From what I've been able to establish, higher end
speakers tend to be of the 4 Ohm variety due to greater power associated
with lower resistance.
What types of problems can I expect if I use 4 Ohm speakers with my 8
Ohm system?
If my only problem will be reduced performance, then I'm not terribly
concerned. If I will cause permanent damage to my new receiver I think
I'll leave the speakers in storage.
In the past, my father had wired a 4 Ohm resistor (rated at 15 Watts) in
series with the speaker so that the amp would see 8 Ohms. Is it that