schreef in bericht
oups.com...
While slightly o/t, the subject is related to the nature of
manufacturer's published, and measured speaker resistance specs. It's
just a question of which, if any, specs to take seriously. Personally,
I just hook up the speakers, and if the amp gets too hot at normal
levels, the speakers go back.

If you knew the minimum impedance you would'nt have bought them at all
and you wouldn't have run the risk of damaging (blowing up) your amplifier.
Ronald Berger

schreef in bericht
oups.com...
While slightly o/t, the subject is related to the nature of
manufacturer's published, and measured speaker resistance specs. It's
just a question of which, if any, specs to take seriously. Personally,
I just hook up the speakers, and if the amp gets too hot at normal
levels, the speakers go back.

If you knew the minimum impedance you would'nt have bought them at all
and you wouldn't have run the risk of damaging (blowing up) your amplifier.
Ronald Berger

schreef in bericht
oups.com...
While slightly o/t, the subject is related to the nature of
manufacturer's published, and measured speaker resistance specs. It's
just a question of which, if any, specs to take seriously. Personally,
I just hook up the speakers, and if the amp gets too hot at normal
levels, the speakers go back.

If you knew the minimum impedance you would'nt have bought them at all
and you wouldn't have run the risk of damaging (blowing up) your amplifier.
Ronald Berger

"Richard Crowley" wrote in message
...
CU's measurement of 4 ohms sounds like the minimum impedance
at some (unspecified) frequency. This seems normal to me. Look
at any impedance curve and you can see that the variation between
minimum and maximum impedance can sometimes be 2x or even 4x.

Or 10x!.

The fact that CU is reporting the minimum impedance (without any
apparent explanation or context) is just indicative of their questionable
understanding, judgement, and reliability in technical areas.

Very true.

No offense, but the notion that "measurements are measurements
not opinions" is not a safe world-view to subscribe to.

It's quite correct. It's when you are basing an opinion on questionable
measurements that problems arise.
Only when you know exactly what is being measured, and the uncertainty of
those measurements, is it is possible to arrive at a valid conclusion.

ALWAYS
question how the measurements were made and what is the hidden
agenda of the person reporting them. In CU's case, reporting 4 ohms
for nominally-rated 8 ohm speakers makes them look like consumer
champions giving you valuable information worth paying for.

Well spotted.:-)

TonyP.

"Richard Kuschel" schreef in bericht
...

I have measured many loudspeaker systems en still do. My advice: Don't
ever
trust the manufacturers ratings.
Ronald Berger.



I wouldn't trust frequency response, but impedance is a pretty simple
thing to
measure with the right gear.

I think it isn't a question of whether measurements are simple or difficult
, but can we
trust the specifications of the manufacturer? It is very, very easy to print
any curve and specs you want. I have measured rated 8 Ohm speakers
with minimum impedances of 2.3 Ohm and that was not the DC resistance of a
driver! The question is can we trust the manufacturers or not. Some we can
and
some we can't.


It is highly unlikely that two "8 Ohm" cabinets will be all that far off
that
it will be a consideration plugging thm into an amplifier rated for 4
ohms.

I agree, most of the time it wil be no problem. But if you have very low
efficiency loudspeakers with very low impedance properties mentioned above
you can run into trouble. Your amplifier has to deliver high currents to
obtain reasonable sound pressures and can be running out of steam when you
demand higher volumes, with risks of damage to the speakers as well. If
your amplifier is overloaded it starts to produce bits of DC (chopped signal
waves). This is very dangerous for speakers. The speaker can be damaged in a
split second. You haven't even the chance to react. But if you have a
massive amplifier and you are overloading the speakers you have time
to readjust the volume of your amplifier.

I have been running a set of 6 ohm speakers from a power amp designed for
8
ohms for years with no problems.

I believe you. If the 6 Ohm speakers are reasonable efficient and don't have
very low impedances there are no problems for an 8 Ohm amplifier. The point
is how much current a loudspeaker needs to play loud enough for you and if
the
amplifier can deliver this current without problems. If it can there wil be
no problems.

Ronald Berger