On 16/06/2017 10:14 PM, Scott Dorsey wrote:
In article , Trevor wrote:
On 16/06/2017 11:46 AM, Geoff wrote:
On 16/06/2017 1:36 PM, wrote:
Geoff wrote: "If your amp says 8 ohms minimum, then that is the lowest
Z you should "
That's what I always thought, and was instructed to
by dealers and other audio people. I guess if 8ohm
speakers become almost impossible to find in say,
10-20 years, I can always connect resistors in-line
to make up for the difference. IE: 4ohm speakrs,
just add minimum 4ohm resistor to the plus side
going to each speaker, to double load to 8ohm per
channel.
This is a terrible idea,
Right, in more ways than one!
because the impedance of the speaker varies a lot
with frequency, and the impedance of that series resistor does not. So now
you have a resistive divider whose ratio changes with frequency, and you will
find that the frequencies where the speaker impedance is low are suddenly
accentuated.
Actually where the speaker impedance is low, the series resistor will
attenuate more than when the speaker impedance is high. (more voltage
dropped across the larger impedance in a series network) Therefore the
frequencies where the speaker impedance is *high* are accentuated Vs
where it is low since the resistor remains constant.
FAR better to simply connect two 4ohm speakers in series on each channel
if absolutely necessary.
This is even worse, because now you have a weird impedance in series with your
speaker. If the two speakers are identical and have identical impedance
curves, then their peaks and dips match to exaggerate one another.
Rubbish, as long as they are identical the response will be the same as
for one, neglecting any *acoustic* comb filtering that may occur
afterwards. All peaks and dips in the impedance curve should be close
enough so the voltage will share equally. And obviously the current is
identical.
However you are right, I did forget to add *identical* speakers in
series. Not some stupid mismatched combination.
Since on
the whole you'll tend to have level dips corresponding with impedance peaks
(admittedly a generalization) this will tend to exaggerate any response
aberrations in the speaker.
A speaker may have a perfectly flat response despite a large variation
in impedance when driven from a low impedance source, such as any modern
amplifier.
The Bose 901 is the finest example of how series drivers can go terribly wrong.
Right, but not for the reason you suggest.
Can't imagine why you wouldn't want (or need)
to replace your (already old) amplifier in 10 or 20 years as well though.
I'm still running the 1961 vintage Citation II as the studio monitor amp.
It sounds good and it's paid for. Occasionally I'll swap it out for something
more modern just to make sure I'm not missing something.
I doubt any JVC amplifier is in the same league however.
Trevor.