Speaker A/B Switch

[clkelley564]

On my Clam Shell T@B, I've got a Coby TV/DVD unit installed from the factory. It appears that they bypassed the internal speakers and just wired four speakers to the unit. (Two on the inside of the T@B and two outside in the kitchen.) Myself and two other people have poured through the instruction manual, and through every control on the TV and the remote, and it appears there is no way to control which speakers the sound is coming from.

When I installed my XM radio I saw up in the closet where the speaker wire is attached to the wires they hardwired to the TV.

A couple of folks have told me that I can easily just add an A/B switch to the wires at that point, then I can control which speakers are on. Is it that simple?? Or do I also have to provide power to the switch somewhere?? My son says I don't even need a fancy A/B switch, just a couple of toggles. Somebody else tells me if turning off the outside speakers is my objective, just one toggle on the outside speakers is the only thing necessary.

(This is important to me because when I'm taking my afternoon nap and want to have XM on or doze through a movie, I have to turn up the volume a bit to hear over the CoolCat, and I don't want to blast my campground neighbors with the speakers in the kitchen).

So, what's the best/easiest solution?? :-)

Thanks!!

[rbeemer]

clkelley,
I am no stereo expert but here are my thoughts

I think for your situation you will need 2 toggle switches - one for left and one for right. Put the toggle on the positive side of the speaker only this should prevent any feedback from a loose ground.

The other thing you can check is to see if your TV can go through your radio(aux input) and use the radio controls- this is assuming your radio is at least four channel(left, right, front and back)

If you know anybody who does soundwork for theatre or sets up sound equipment they may have a better idea for you

[clkelley564]

Don't have a separate radio. The AM/FM radio is built into the Coby TV unit. I used the auxillary ports for the XM Radio home kit dock.

[Gerald_G]

in that case ask for a double pole single throw toggle switch.

It will have 4 terminals on it.

Run left rear, and right rear positive wires through it, and flicking one switch will kill the rear speakers.

Only thing I wonder about is if they are wired in series or parallel, and if the resistance of the speakers will be out of spec for the TV without the back pair.

It's not too likely to hurt it I don't think, but it's a consideration.

For instance of you have two 4 ohm speakers wired in series, then the values add up to an 8 ohm resitance on that channel, which may be what the TV expect to drive.

Two 8 ohm speakers in parallel will result in a 4ohm resistance.

Simply switching off speakers / disconnecting can change the resistance for the TV.

[Greg M]

Only thing I wonder about is if they are wired in series or parallel, and if the resistance of the speakers will be out of spec for the TV without the back pair.

It's not too likely to hurt it I don't think, but it's a consideration.

For instance of you have two 4 ohm speakers wired in series, then the values add up to an 8 ohm resitance on that channel, which may be what the TV expect to drive.

Two 8 ohm speakers in parallel will result in a 4ohm resistance.

Simply switching off speakers / disconnecting can change the resistance for the TV.

That's easy to find out. If the sound goes away completely when you cut the positive wires to the outside speakers, then they're wired in series, and the lower impedance of just one set of speakers could (but not likely) be a problem for the TV's amp. In that case you will need to re-wire them in parallel before you get sound again.
If the sound stays on, then they're already wired in parallel, and the higher impedance of one set of speakers will not hurt the amp at all.

-Greg

[Gerald_G]

Good point Greg - Thanks for the note.

[Joanne]

One more option.

If you want to have either the inside speakers on OR the outside speakers on, here's how I would do it. I would buy a double pole, double throw switch. I would run the positive lead for each channel from the radio to each center terminal. Then attach the positive wire for each front speaker to one set of terminals and the positive wire for each rear speaker to the other terminals. Tie the common lead of the front and rear left channel speakers together. Do the same on the right channel. Flipping the switch routes the sound to one set of speakers or the other.

I think maybe a drawing would be easier to understand.

Joanne

[clkelley564]

We got it done. The solution and instructions are in my Blog.

Carol

[nikwax]

problem with A/B switches: solid state amplifiers don't like a variable load on them, they are usually designed for a certain load. Hang too many speakers on them and you can drop the impedance down to a level that will cause the amplifier to nuke.


Ask me how I know