On 2008-04-27, Paul Stamler <pstamlerhell@[EMAIL PROTECTED]
> wrote:
> "William Sommerwerck" <grizzledgeezer@[EMAIL PROTECTED]
> wrote in message
> news:uOadneFdR68CU47VnZ2dnUVZ_h6hnZ2d@[EMAIL PROTECTED]
>> Russound used to make a speaker-selector box that kept the impedance
> pretty
>> much constant, regardless of which speakers were connected.
>>
>> One could build a speaker selector -- with a very simple circuit --
such
>> that whether you selected one, two, three, or four speaker pairs, the
>> impedance would stay constant. I ought to patent it.
>
> I doubt you could; I remember such boxes from the 1950s. We had one, in
> fact.
If the computer industry is anything to go by you probably could patent
it. I've seen things like a fairly recent patent for something I have
a text book with sample code in dating a decade or so before the patent
application. It doesn't seem to stop them.
Anyway - The original poster could always combine speakers in parallel
and series to keep the impedance right, though as each speaker changes
impedance over frequency the effects of connecting different speakers in
series could be interesting. I've not tried it so don't know whether it
would work or not. You may get all the treble in one and all the bass in
another (extreme example)
For the original poster:
Connect two speakers in series - adds the impedances.
So 2 * 8ohm speakers gives 16ohm
Connect in parallel and, if they're the same impedance you end up
halving it. (It's 1/(1/A + 1/B) so 1/(1/8 + 1/8) = 1/1/4 = 4)
So 2 in series gives 16ohm. Parallel those pairs to get 8 again.
It sounded as if you had an impedance selector switch on the amplifier.
(You asked what to set impedance to). In that case work out what you're
going to present to it and choose that.
1 in parallel = 8ohm
2 = 4ohm (Some domestic amplifiers have a 4ohm mode)
3 = 2 2/3 ohm
4 = 2 ohm
6 = 1 1/3 ohm
8 = 1 ohm
I think choosing too low is less a problem than choosing too high if at
a problem at all. My domestic amplifier has two sets of terminals and a
"Speaker A, Speaker B, Speaker A+B, Headphones" switch on the front so can
drive two pairs of speakers or 4ohm but is perfectly happy driving one.
(Relays click inside, so it may be doing something more clever to keep
things matched. I'm trying to remember if I noted any extra transformers
when I last opened it up. I don't think so.)
I'm used to stage equipment though which is very robust. The amplifiers
we used to use were rated down to 2ohm so we could connect up to 4
speakers in parallel and we had a lovely old telephone patch panel to do
it with. We rarely connected more than 2, if we wanted to drive front
of house in mono off one channel of the mixing desk and save the other
3 we had for things like rear of house or on stage effects.
For severe Hi-Fidelity you worry about impedance matching where both
ends of the wire want the same. On stage we didn't worry so much.
- Richard
--
_/_/_/ _/_/_/ _/_/_/ Richard dot Corfield at gmail dot com
_/ _/ _/ _/
_/_/ _/ _/ Time is a one way street,
_/ _/ _/_/ _/_/_/ except in the Twilight Zone
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