Multiple radios to one speaker

515 · Post by **515** » Thu Sep 13, 2001 8:47 am

I would like to install a VHF and UHF spectra in my vehicle, but only have room for one speaker. What is the easiest and safest way to connect both to the same speaker? I would prefer something passive that requires no power.

Elroy Jetson · Post by **Elroy Jetson** » Thu Sep 13, 2001 9:55 am

You can't do that safely without special
electronics.

By the way, in case you hadn't thought about it, communications speaker usually work
just fine under the seats of the car. Or
they can be tucked up under the dash in many
cases. Be creative. You'll figure out a
way to use a separate speaker for each radio.

Elroy

Post by **alex** » Thu Sep 13, 2001 10:15 am

My speakers are between the door and the seat in the car - there seems to be enough room. I have found this allows for the audio to go up towards the celing, and get reflected better throughout the car.

Just an idea. You can buy smaller speakers too, you don't need to use the larger motorola ones, but the audio quality is quite nice from the Motorola ones.

-Alex

jim · Post by **jim** » Thu Sep 13, 2001 5:39 pm

That's an easy one. Go to Radio Shack and get an audio transformer with 8ohm/1000 ohm windings. One trans. for each radio.
The one radio's output goes to the 8 ohm side of trans. #1

The second radio's output goes to the 8 ohm side of trans #2

Both of the transformer's 1000 ohm windings tie in parallel and go to the single speaker.

I use this frequently and it works just fine.

mike38015 · Post by **mike38015** » Thu Sep 13, 2001 7:16 pm

I used two speakers from older Motorola 2600 installed cellular phones (2"H x 2"D x 4"w). Together they equal one spectra speaker, plus I get great audio out of them, I would even say its better quality.

Mike

Reslock · Post by **Reslock** » Thu Sep 13, 2001 7:19 pm

Good thought Jim, but what about radios that have DC on the audio cct?

RadioSouth · Post by **RadioSouth** » Thu Sep 13, 2001 8:45 pm

CAREFUL with Spectra audio outputs! Believe I've seen warnings on these that neither speaker wire can go to ground without blowing
the radio's audio output.

515 · Post by **515** » Fri Sep 14, 2001 8:47 am

Thanks for the idea Jim. I figured something along those lines was possible. I don't think there would be any DC on the speaker output of a Spectra. Is there any noticible volume loss or distortion in this setup from the 500 to 8 ohm mismatch?

fytnsu · Post by **fytnsu** » Fri Sep 14, 2001 8:16 pm

I was trying to do the same thing (multiple radios - one speaker) however I tried to build an audio mixer. Big Mistake. I ended up blowing the control head on my spectra.

Also, has anyone heard of using an 1:1 audio transformer that Radio Shack sells?

Thanks,
Ryan

Adamwest · Post by **Adamwest** » Fri Sep 14, 2001 10:51 pm

Hi

Why not just use a 4 pol 3 pos switch. Set pos 1 for the first radios speaker, 2 for radio speaker 2 and pos 3 for both speakers.

jim · Post by **jim** » Sun Sep 16, 2001 5:48 am

None of these radios that I've seen have DC on the speaker output. By doing it this way, you are not allowing any part of the speaker circuit to see ground either.

Microwave Mike · Post by **Microwave Mike** » Wed Sep 19, 2001 1:29 pm

You can load the speaker output with the right value resistor of 16 ohms at five watts. That will make the push-pull output of the audio amp happy. Then tap off with a 1000 ohm resistor to a mixer input set to line level input. The other side on the input to the mixer will be at ground level.
this will isolate the speaker output and pad it down a bit. The mixer to use is up to what you can find. The output of the mixer is then connected to a single audio amp and matching speaker. You then adjust each input on the audio amp for the radios you have.
You can use a switch box instead of a mixer to feed the one audio amp/speaker.
DO NOT SHORT OUT THE RADIO AUDIO OUTPUT. Pulling the audio amp in a Spectra is a :o.
Mike

jim · Post by **jim** » Wed Sep 19, 2001 5:51 pm

Using any type of a switchbox makes no sense at all- that will allow only one radio to work at a time. The idea of 1 speaker/2 radios is to use 1 speaker on 2 radios SIMULTANEOUSLY, not one at a time.

And no, the transformer offers no distortion. You will, however, notice a very slight lowerin of the volume which you compensate by turning it up louder. This isn't a problem unless you're in a REALLY noisy environment. I just did this circuit again Monday and it works just fine.

JackR · Post by **JackR** » Wed Sep 19, 2001 7:20 pm

If your Radio Shack has them, try one of their "Universal Speakers". They come in 5x7 or 4x10 sizes. What makes this work is that they have 2 seperate 8 ohm coils so they can be connected to 4 , 8, or 16 ohm outputs depending on how you hook up the jumpers. I have hooked 2 radios to them without any problems.