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Combining Speaker Output

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After successfully configuring dual radio operation I am now looking at how exactly I want to install things. Because I don't have a good place to install another speaker and there would be some difficulty running another cable I am looking at potentially combining speaker audio from the two radios at the primary radio. My plan would be build an adapter similar to wiredwrx's to breakout the connections between J500 and the control head cable which would allow mixing the audio and sending it up the interface cable to the single speaker I'm currently using.

Since audio isn't really my thing, I'm trying to make sure I have everything in line design-wise before I try anything. Since it is only the two radios I'm thinking a simple resistor bridge would work without introducing too much loss. Has anyone had success using one with Motorola radios? I've used these a couple times for other projects but never with balanced audio. Would the Speaker Lo connections just be tied together, or would they also be bridged? How are the resistor values determined?

Rather than build my own circuit, I am also looking at using an RDL STD divider/combiner, but again I'm not sure which resistance value would be appropriate.
 

axel

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You absolutely want to make sure each radio's speaker outputs stay isolated from each other and ground. That's like rule #1 when working with moto radios.

The RDL combiners are essentially just resistive bridges in a fancy case. If you want to go that route, the lower the impedance value the better. Higher impedances will result in lower volumes, and in a mobile setting that's definitely not ideal. I think RDL made a 150Ω version of their splitter/combiner, so that would probably be your best bet.
 

jry

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Well I would possibly look at mixing in the second audio at a lower level

You may have to add the access to the points you need in the audio circuitry

The accessory connector does have RX audio but its at a fixed level so that would need to get mixed in before the level control but after the squelch.

Have never dug into this so its just a different approach from combining at the speaker outputs.
 
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Thanks, axel. I'm well aware of the no grounding rule, just wasn't sure about combining the speaker low outputs. I was looking at the RDL combiner because of the better packaging.

I've got to take a look again, and may just end up going with another speaker. I have individual speakers for the other radios and the spatial diversity is helpful for localizing the source radio. Space is an issue so I'll have to get a little more creative to add another. The convenience of using the existing speaker is tempting, though.
 
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tuckerm

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I have my audio combiner still if you want it, I don't think I'm going to end up using it...
 
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I have my audio combiner still if you want it, I don't think I'm going to end up using it...
I'm thinking I might go that way. Should have just had you bring it up last weekend. I'll contact you offline.
 

Astro Spectra

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Lateral thinking: most vehicles today have at least three midrange speakers, left door right door, and console. Why not leave the entertainment connected to the passenger door and use the driver's door for the secondary radio and the console for the primary?

If you're chicken about cutting into the looms, a lot of vehicle entertainment boxen have connectors that you can easily source aftermarket adapters for. They're available from vehicle audio houses and some auto parts stores. Use those to make a break out adapter that allows access to the relevant speaker pairs but enables the removal of the radio fit down track when you need to return or on-sell the vehicle.
 

RFI-EMI-GUY

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Bridge three 70.7 V audio transformers together.
 
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