relay for on/off speakers

christophe

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Hi guys, I need your help please. So i have a raspberry pi that gives audio output (AUX) to an audio interface that outputs to 4 studio monitors. I will be using the hanson 2811dc15 so that to tell xlights that it is only 4 pixels. Therefore easy on/off.

How do you guys work out what relay is required to trigger the speakers on/off? I saw online that i have to be careful in choosing the appropriate relay as they can damaged the speakers in the long run. The speakers are not constant voltage also so that's why i am a bit confused.

Thank you
 

AAH

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To the best of my knowledge there is pretty well no way on earth that the use of relays can damage speakers. In high end stereo gear relays are commonly used to isolate the speakers from the rest of the electronics at startup so you don't get a thump and also potentially damage the speakers.
Any relay could do the job really. Going to a lower current relay rather than a high current 1 gives the 2811DC board an easier time of it. A 4 pole relay will happily handle the 4 outputs as you only need to break 1 of the 2 connections. The speaker current is probably well under 5A AC so even the lightest duty relays are probably fine.
 

christophe

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Would it be easier to use a single output and turn off the amplifier?
I wanted the music to be where the lights are flashing. Therefore I have divided my layout into 4 sections and have one speaker for each section. Then program the speakers to be on/off depending on the show.
 

David_AVD

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It sounds like you're using active speakers (with inbuilt amplifier)? If so you'll need to add some resistors into the mix to stop unwanted clicks and pops as the relays enable the powered speaker audio inputs.

If you're talking about normal 4 or 8 Ohm speakers with a single amplifier, you need to be careful. To be safe, you'll need to cascade the contacts of the 4 relays. That way if more than one gets turned on at once, the amplifier doesn't have more than one speaker connected to it. This is assuming you only need/want one speaker to be on at a time.
 

christophe

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It sounds like you're using active speakers (with inbuilt amplifier)? If so you'll need to add some resistors into the mix to stop unwanted clicks and pops as the relays enable the powered speaker audio inputs.

If you're talking about normal 4 or 8 Ohm speakers with a single amplifier, you need to be careful. To be safe, you'll need to cascade the contacts of the 4 relays. That way if more than one gets turned on at once, the amplifier doesn't have more than one speaker connected to it. This is assuming you only need/want one speaker to be on at a time.
Thank you for your replies. I have two pairs of studio monitors and i thought that i could used them for my show. I think i will probably first try with 4 or 8 ohm speakers with a normal relay. Would have any idea what resistor would be needed? I see some AUX that they sell with in built resistors to prevent overloading. Would that work?
Thanks
 

David_AVD

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If you're wanting to use 4/8 Ohms speakers and a single amplifier channel, you won't need the resistors.

I'll have to draw a diagram of how the relay contact are arranged. Can you read circuit diagrams?
 

christophe

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Ideally i would prefer to go with the in built amplifer studio monitors because of the sound difference. But it seems that 4/8 ohm speakers are much easier to control and therefore will try this path first.

Yes i can read circuit diagrams. Thank you
 

TerryK

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Can you provide more details please? In your first post it seemed you already had the equipment but your last post perhaps not yet the speakers. Is your goal a single audio output to 1 of 4 speakers or any of 4 speakers? Are the speakers purchased and are they self amplified or not? Too, what wattage to the speakers are you attempting to shove as that will help determine minimum amperage rating of the relay contacts.
 

David_AVD

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Here's what I meant by cascading the relay contacts for a speaker setup.

Each relay (except the first) gets its feed from the normally closed contact of the replay before.

This creates a priority system so the lowest number output gets audio if more than one relay is energised.

Due to that, it means that the amplifier never gets more than one speaker put onto its output.

While you could try and ensure this in software, mistakes and glitches happen and this prevents a bad result.
 

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christophe

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Sorry for late respond. I have been flat out with work.

Thank you David for the diagram.

@ Terry : So the speakers are KRK Rokit 5 G4 DSP Studio Monitor 5 Inch Pair. I usually run them with an audio interface that outputs Left/Right TRS or XLR to the speakers. Each speaker has an in-built amplifier and therefore its own power. I will be running them at about 60% volume and therefore since they are rated at 55W per speaker, 33W power consumption.

What I was thinking is to split the two TRS outputs from the audio interface (2 x left and 2 x right) to the 4 speakers. I would have the 2 right speakers on the right side of my layout and the 2 left on the left.

Cut the TRS cable and used the ground with the relay switch. When I need the speaker to be on, then the contact relay would trigger the ground. Therefore 1 independent relay switch for each speaker. As David said to have a resistor, this is where I am not sure where to have them in the circuit.

Please correct me if I am wrong because it's all a learning process.

Thank you for your help
 

David_AVD

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OK, since you have active speakers with balanced (TRS / XLR) connections, you can do the switching this way.

The normally closed contact on each relay shorts the input to the speaker when not required.

When the relay activates, the signal is allowed to pass through to the active speaker.

The 4.7K resistors (wattage not important) stop the short from affecting the audio interface's output.

They also isolate each output from the other. Duplicate the circuit for the other two outputs (right channel).
 

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TerryK

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I have a few concerns; those in a moment. First, being self-amplified, relay contact amperage rating becomes a non-issue. Switching of the inputs are low level so just about any miniature (signal switching) relay will do. I would suggest gold plated contacts to help minimize contact electrical noise if input switching is the final solution.

The concerns; I find myself a bit cautious when switching inputs to powered devices; seen too many situations with unexpected results. Be that as it may I can't help but wonder if switching the AC Main may be a better solution. This would let the amp's electronics manage pop/click/thump prevention.

A question for David regarding his suggestion; I searched for and scanned the speaker's User Manual. I noticed that they have a spec-ed input impedance of 5.1 KOhm. With the balanced input and the 4.7 KOhm resistors, would that not reduce the signal level seen by the monitor speaker by approximately 65%? Electrically that would be a tad more than 6 Db, not sure what that would translate to in SPL.
 
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