I have a system installed at a customers house which is the following:
Crestron Pyng hub (control)
Crestron C2N-AMP-4x100
Autonomics MMS-1e (connected to Input 1 on Crestron Amp using 3' Crestron RCA audio cables)
2 rooms being used on Crestron Amp
Autonomics is the only source

The issue is this:
If system has been off for a while (can't provide an exact time) when turning either audio zone on the speakers sound like the drivers have been blown.

When I was onsite today I connected the same RCA cables connected to the MMS-1e into the analog out of the cable box (currently not a multi-room source) with the rooms on, and the blown speaker sound disappeared. Connected the audio cables back to the MMS-1e and the speakers continued to sound normal.

I had the system off for a while (about 30 minutes) and turned it back on and the speakers sounded like they should.

During the original install I was experiencing the same issue and in troubleshooting replaced the RCA cables 3 times thinking they were bad cables but that didn't resolve the issue. I tried different inputs and outputs on the amp which didn't resolve the issue.

Because I can't recreate the issue I am at a loss as to what may be causing the speakers to sound like this. I believe I have narrowed it down to either the MMS-1e or Crestron Amp. If the speakers were bad no matter what the source was the speakers would always sound bad.

Can you please provide some insight into troubleshooting and narrowing down what device may be causing the issue so I can get a replacement unit if necessary

I don't know the exact equipment, therefore don't know exactly how it's connected, but here's exactly the way this could happen. It was a common problem back in the days of discrete transistor input circuitry.

Let's say an audio source goes through a Y cable to the inputs of two amplifiers. If one of those outputs connects to something that craps it up, you'll have what you're talking about.

Let's say these amplifiers have input stages that consist of about the simplest type of amp input: a high value resistor to ground, followed by a capacitor in series with the signal, fed into the base of a transistor with minimal series resistance. The transistor will have various components connected to it so that when the power is on, the proper DC voltages are present at the transistor so that it amplifies.

Those "proper DC voltages" make the transistor look like a relatively high impedance load compare to what it looks life with the power off. Without the DC voltages, the connection of audio through the base of the transistor through its emitter looks to the input signal like a diode in series with a resistor.

Such a load will sharply cut off the upper or lower half of any part of the waveform of the signal that exceeds about 0.7 volts. The transistor craps up the audio. Since this amp isn't on, you don't hear the problem from this amp. You hear it from the other amp.

THE CIRCUIT THAT'S NOT ON CRAPS UP THE AUDIO OF THE CIRCUIT THAT IS ON. We used to find this all the time in analog equipment hooked together where one amp might be on and the other off.

One or both amps might crap up the signal of the other amp. It depends on their input circuitry.

The cure is to turn on the other amp. Then the DC voltages that bias the transistor for proper operation keep it from looking like a diode in series with a resistor.

And if you turn off one of the amps? It's possible for residual small amount of voltage to keep this from happening for some period of time. That explains the "sometime" nature of this.

What's the cure? Don't split the signal with a simple Y that's just a piece of wire. Instead put a resistance, say 1000 ohms, in series with each output of the Y. Even better, put the signal through 1000 ohms; from that point put, say, 4.7k to ground and put 1000 ohms in series with each output of the Y. You have to make this; you can't just add these parts to a Y connector or Y cable.

Does any of this match the details of how you're wired or when the problem occurs?

Thanks for the informative information Ernie.

The system is connected as follows:

MMS-1e - Analog Audio (Factory made RCA cables) - Crestron Amp input 1(internal of the Crestron amp will then distribute the source to the speaker amplifiers)

I don't have any Y cables installed in the system.

From what you have stated it is sounding more like an amp issue than a source issue? The question I have is; if this is an amp issue why would the problem go away when using the same input but changing the source connected to that input? Nothing is changing (number of zones on, audio cables, zone volumes) except for the source feeding input 1.

I really need a schematic of your connections to see if I can find what's going on, if it's the kind of thing I'm talking about.

Why would it work differently with different sources? The problem I mentioned would be worse with a high impedance source than with a low impedance source so switching one amp from a high impedance source to a low impedance source would make the problem go away.

See if the problem EVER happens when all amps are powered up. If not, then it's probably this issue and more information would pin down exactly where it is. Our cure back in analog days was to have all the amps on or all the amps off. (I also cured it with series resistors as I described.) You didn't just turn on that old Nikko or Sansui receiver when you wanted zone 2; it was always on when the main amp was on.

YOU might not be using a Y connector, but a source with two outputs might be built as though it's a simple Y connector. When we hear about "buffered outputs" they're talking about an output amplification stage (even unity gain) for each output that isolates one output from another so that influences downstream can't affect the signal back where it's coming from.

Ernie might be on to something. I'm not familiar with these units, but a complication with diagnosing this could be the exact time a unit is powered down. When the operator shuts down a unit, the unit may mute or go to minimum output for a while before actually powering down. This is done as part of an anti turn ON/OFF "thump" strategy.

Another wild card is the possibility that an unused input will be shorted when not selected. This is an attempt to minimize crosstalk (such as a Tuner leaking into the Phono). For example, when Phono is selected, Tuner input is shorted. In a multi-zone situation, shorting unused inputs can cause this sort of issue. In my delayed power down case suggested above, this 'short' could go away after a while -- complicating the diagnosis. In the old analog days, this unused input  'short' would be mechanical, and very obvious to diagnose. With modern design approaches, this 'short' will be an electronic scheme that effectively changes series or parallel impedance. When all modern circuits are powered, everything is under control. When a circuit is not powered, ugly things can happen. With our old mechanical switch a short is a short unless heavyweight currents blow something away. (Diagnose by following the smoke!)

"Might be on to something"? Gee, thanks!

I stated this, which would put us a lot closer to an answer:

I didn't mention the shorting of unused inputs because his original description didn't seem to imply that any source switching was going on. There was just horrible sound when everything was connected and one of the amps was powered down. His description EXACTLY matches the problem I was describing.

Sounds like a 3' RCA cable from source to amp. Do you really need a diagram to figure this out?

MMS-1e----------------------Amp

I have one of these amplifiers, log into it using toolbox and open text console. In text console, type restore. Worked on mine (different issue) but it sure can't hurt.

I have replaced the RCA cable 3 times and still having the same issue.

I will try a restore on the amp the next time I am onsite.

Was referring to Ernie's request for a diagram of a 1 source, 1 amp system.

Yeah, it now looks more mysterious than it did at first. I somehow thought two amps were involved, even internal to one chassis... I'm baffled.

There are two amps involved but are internal to the Crestron 4x100. The Crestron unit is similar to any other multi-room audio amp where it has a set number of analog inputs and a set number of speaker zones. In this case the Crestron amp has 6 analog inputs with 4 output zones (8 speakers).