Switching speakers on and off

[Steven]

Now something completely unrelated to F1...

On a hifi system I want to connect 2 speakers to centre. That is with regular red-black cable (so two seperate contact points on both ends of the cables).

Anyway, what I want is to switch on and off each speaker seperately. Do I need any special kind of switch to do that? I mean to not harm sound quality?

[Caito]

I must be really bad switch or welding for you to notice a difference. If you are not using high quality cables, it makes no sense spending money on expensive switches.

If they're red and black wires, they're probably bad quality. You'll not notice any difference unless you have good ear and high quality amp and whatever you use to play whatever you play(music, dvd, etc).

Just buy one that is rated for power, to avoid heating. Anyway it's not good idea to use that switch while their is music playing. Speakers are big inductors and di/dt are big no no, unless you want a spark.

[747heavy]

Hi Tomba,

I may not 100% understand correctly what you would like to do, but you will need to keep one thing in mind.
If you have one exit on your amplifier, this exit will have a power and an impedance rating something like 150W @ 8ohm
Now if you connect two speakers in parallel this is going to halve there impedance, meaning 2x 8ohm speakers will give a 4ohm impedance. This can cause problems for your
amplifier. If the amplifier has a max. current limitation, that´s may o.k. if not it can damage/destroy your amplifier channel.

You could connect 2X 16ohm speakers in parallel onto a 8ohm exit, and if you switch one off, you have a 16ohm impedance on an 8ohm exit. this will not cause damage to your amplifier, but the speaker will be less loud.
As Caito says, avoid switching under load, if you can. If you take the speaker of under full load, the voltage spike can damage your amplifier.
The more expensive switches you can buy may have an internal dummy impendance to counteract these problems.
Hope that makes some sort of sense.

It goes back to R=U/I --> I=U/R
so for a given Voltage U the current I will be higher if you have less resistence (R), for a speaker this is called impendance.
The higher current I can damage your amplifier, if it does not has a overload protection to limit max. current (I)

[Caito]

Interesting to note that, even if you have less impedance, say you connect 4 ohms in an 8ohm exit, you will never get rated power.


Imagine the equivalent(simplification) of your circuit


and your speaker being the load (forget the values and that they're only resisitive).

You'll get max power transfer when Rload=Rthevenin, else you'll always get less power.

If you mismatch your impedances, probably nothing happens, unless you start to crank your volume up.

If the equipment is new, it probably has the necessary protection, but I would avoid it anyways. Doing it would probably shorten its lifetime, and increase the heat.



So, although it may seem odd, if you put higher(or lower) impedance, your power consumption will be higher for a given volume.