Various microphone inputs in the building are fed into an amplifier, and from there, distributed to a patch panel that feeds various speakers. To my uneducated surprise, there is no jack on any of the amps allowing me to record. The output going to the speakers should obviously not be fed directly into a microphone input (on a smart phone, for example). What do I use to step it down? I assume there is a commercial product for this. How am I assured that the step down is at the right level.



You should not use the speaker outputs to feed your mic input on anything. And unless you measure, you don't know what voltages are used on those speaker outputs.

If you do know maximum voltage swing, you could work out how much you have to attenuate the signal, but there is still a risk. Your assumption that there is a commercial product for this is not really true - it's such an odd scenario.

The best route is to actually position a microphone next to one of the speakers, but if you actually do want to do this you will need a variable resistor. Remove a speaker and wire the potentiometer's end connectors across where the speaker would go (actually probably a pot and maybe a 10k in series), and connect the ground and centre wiper to your mic jack. Start off with it turned right down low.


The signal level coming from outputs designed to drive speakers (which I am assuming are passive or not self-powered speakers) will overload any mic/line level input. Mic/line level inputs (which may have a switchable attenuation pad) will expect less current and are likely designed to handle signals in mV (millivolt) range. Or a preamp level output is more in line with what I think you are looking for (instead of a power amp output). The device you are looking at with apparently only speaker level outputs likely has a line (or preamp) level input feeding it from somewhere. Maybe you can find a diagram of the A/V system (the breakout panel is not labelled, or there is not a patch bay with labels). If you can find the source line level signal, you could try using a line level splitter so you can feed another deivce from it. Keep in mind that some power amps are just not designed to continuously drive a low impedance load, so you have to be careful when putting a purely resistive load across speaker outputs. I would exhaust all other options before trying to step down the output from a power amp (to turn into a preamp).


Use a DI with a suitable attenuation switch. 40dB of attenuation is a voltage reduction by a factor of 100. That should usually be more than enough for reducing speaker levels to line level but may be a tossup for mic levels depending on just what kind of speaker and loudness we are talking about.

I have a cheap stereo house brand passive DI here that goes from 50k input impedance to 600 output impedance, making for a voltage reduction by about 20dB already (the square root of the impedance ratio), with an additional 0/20/40dB attenuation switch.

That's the kind of connectivity you'd be using for going into a mic input.

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