Hi,

I want to make a speaker selector box so I can alternate between having
the music in the lounge (2 speakers) or dining room (2 speakers) or
both.

The lounge speakers are both 6ohm, whereas the dining room speakers are
4 ohm each.

How hard would something like this be to achieve? I have often read
about impedance matching - is this hard to achieve?

basically the lounge speakers impedance is fine .. the amp's
recommended and minimum is 6 ohm. So, the 2 dining room speakers
present too little a load. Ultimately, I could add two 2 ohm resistors
to each line for the dining room speakers, as dummy loads - yes?

Problem is, could there be any way I could have all four on ? If each
lounge speaker and dining room speaker were connected in parallel back
at the amp (i.e. left lounge speaker and left dining room speaker
connected to left amp output), the impedance would be too low.

How could I match the impedance of the load to 6ohm (or something
higher than that)?

On 8 Mar 2006 16:31:55 -0800, "andrew_h"
wrote:
I want to make a speaker selector box so I can alternate between having
the music in the lounge (2 speakers) or dining room (2 speakers) or
both.
The lounge speakers are both 6ohm, whereas the dining room speakers are
4 ohm each.

How hard would something like this be to achieve? I have often read
about impedance matching - is this hard to achieve?
This is difficult but doable at the price of balancing the levels.

basically the lounge speakers impedance is fine .. the amp's
recommended and minimum is 6 ohm. So, the 2 dining room speakers
present too little a load.
Actually, the lower impedance represent too great a load.

Ultimately, I could add two 2 ohm resistors
to each line for the dining room speakers, as dummy loads - yes?
Yes but they will dissipate a substantial part of your power as heat,
not sound, and that will require that you turn the volume up.

Problem is, could there be any way I could have all four on ? If each
lounge speaker and dining room speaker were connected in parallel back
at the amp (i.e. left lounge speaker and left dining room speaker
connected to left amp output), the impedance would be too low.
Right.

How could I match the impedance of the load to 6ohm (or something
higher than that)?
It depends on how picky you are about quality. Connecting them in
series would make for a 10ohm impedance but the frequency response of
each speaker will be irregular.

So, you can add series resistors to bump up the impedance and/or you
can wire them in series but get a bumpy response. My vote is to try
the latter and see if it is satisfactory for background listening
(which is what I presume you are doing with all oc them on).

Kal

"andrew_h" writes:

Hi,

I want to make a speaker selector box so I can alternate between having
the music in the lounge (2 speakers) or dining room (2 speakers) or
both.

The lounge speakers are both 6ohm, whereas the dining room speakers are
4 ohm each.

How hard would something like this be to achieve? I have often read
about impedance matching - is this hard to achieve?

With the speakers you have and the normal hifi amplifiers this
is a little bit hard to do...

I your speakers were 8 ohms both, and your amplifier cna handle
speakers down to 4 ohms, then things woudl be easy.
Then you could just put switches that switch the different
speaker sets connected or not connected to amplifier output.
Separate switch for both speaker sets allows you to control
each speaker separately (if both are put on they are
connected in parallel to amplifier output).
Some hifi amplifiers even have two sets of speaker outputs wired
in this way, with front-panel swithes to control A and B
speaker sets on/off. I have at least one amplifier that has this.

There is another trick that some amplifiers use: when both
A and B speakers are turned on, they are wired in series.
So the impedance doubles (two 4 ohm speakers = 8 ohms,
two 8 ohm speakers = 16 ohms). This will be safe for amplifier,
but limit the maximum output power from ampifier
(you get less total power for two speaker sets than what you
get for one speaker set). The speaker series connection
work quite acceptably if the both speaker sets are exactly
same type speakers. If the A and B sets are different type
speakers (different manufacturer, different model etc..) the
sound quality can drop considerably (there will be interaction
bwrween speakers when their load impadances at different
frequencies can be considerably different.. can cause
very sonciderable frequrncy response problems!).

basically the lounge speakers impedance is fine .. the amp's
recommended and minimum is 6 ohm. So, the 2 dining room speakers
present too little a load. Ultimately, I could add two 2 ohm resistors
to each line for the dining room speakers, as dummy loads - yes?

Adding two ohms resistance in series with 4 ohm speakers will
turn the whole load look like 6 ohms to amplifier. This works.
The downside of this is that this series resistance can
affect your speaker sound quality more or less. The ideal
speaker wiring and amplifier output should have zero ohms.
Other problem is the lost power in that resistor, the problem
that you need to turn the ampifier a little bit louder to
compensate the power loss is not typically a problem,
but the problem is that the lost power ends up heating
the resistors: you need power resistors capable of handling
the lost power (around one third of what gets out of amplifier)
and have it installed so that when the resistor heat up they
do not cause danger.

Even if you have all speakers "tweaked" to 6 ohms, this
will not solve the problem. If you wire two 6 ohm speakers to
one output, the amplifier will see a 3 ohms load. It is
definately too low impedance for your 6 ohms capable amplifier.

Problem is, could there be any way I could have all four on ?

Buy an another amplifier to drive the other speaker set is
one option. This gives you the bonus of having spearate
volume controls for those different locations.

If each
lounge speaker and dining room speaker were connected in parallel back
at the amp (i.e. left lounge speaker and left dining room speaker
connected to left amp output), the impedance would be too low.

Definately too low.

How could I match the impedance of the load to 6ohm (or something
higher than that)?

The methods to try to do the matching are not very practical.
Adding series resistors will loose lots of power and definately
cause sound quality problems. Not good.

There are also impedance matching transformers for speaker
applications. Those can convert impedance quite well,
but this kind of transformers are generally quite expensive
speacial products.. Usually not economically feasible, and
still can have effect to sound quality.

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

"andrew_h" wrote in message
ups.com


I want to make a speaker selector box so I can alternate
between having the music in the lounge (2 speakers) or
dining room (2 speakers) or both.

Easiest to do with separate power amps for each set of speakers.

In the real world of receivers, easist to do with a separate receiver for
each pair of speakers. If there's an esoteric source, it could be shared by
linking the tape output of the system with that source, to the tape input of
the other sysetm.

The lounge speakers are both 6ohm, whereas the dining
room speakers are 4 ohm each.

That nets out to a load that is 4 ohms, which may put an undesirable load
on a shared power amp.

How hard would something like this be to achieve? I have
often read about impedance matching - is this hard to
achieve?

It's not so much the impedance variation, its the differing efficiencies, as
well as the control issues. You can get a servicable receiver for less than
$80, its very easy to spend that on speaker switching and level control
options that cost more.