"Trevor" wrote in message
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On 3/12/2014 12:21 AM, Mark Zacharias wrote:
"Trevor" wrote in message
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On 2/12/2014 12:19 AM, wrote:
geoff: My 1995 JVC receiver specifies 8-16ohms. Guess that's an
oldie then!
Many cheap receivers with limited current capability specify 8 ohms or
more, regardless of age. Conversely many good amps can handle loads as
low as 2 ohms without a problem.
Speaker impedances have not really changed - they are rating them a bit
more accurately these days.
Mark Z.
Partly true to the second part, mostly no to the first part. Some
manufacturers use the impedance minimum fairly closely these days. Others
are just an estimate of what they think the amp rating should be. But
speaker impedances HAVE generally dropped over the last 50 years or so.
First with the change from valve amps they generally went from ~16ohm to
8ohm. Then with the improvement in current handling of transistor amps
(and the increase in multiple small bass drivers vs one larger driver),
many have dropped from ~8ohm to ~6 or 4 ohm.
In any case ALL speakers vary wildly in *impedance* across the frequency
range, especially ported speakers, but the voice coil *resistance* of many
drivers has decreased. That affects the system impedance, and is easy to
measure. And some manufacturers still produce their drivers with voice
coil resistance options, or even custom make them if you buy enough.
Trevor.
What I meant to suggest is that so-called "8-ohm" speakers have always
actually been closer to 5 or 6 ohms. Should have been clearer.
mz