I have speakers that are rated at 150W RMS, 300W max. Amp is 175W RMS (not sure what the max is, I assume 350W) . How should I set the amp output? 150W with the receiver set at normal listening level, 150W at the max the receiver would ever be set at, 300W at receiver max level?

 

Max wattage is a fake number. It's not important. Preferably, you'll want to set you gains with an O-Scope and find the maximum volume of the headunit before distortion, then turn the gain up on the amp until it starts to distort as well. If you don't have an O-Scope, just listen for the distortion very carefully.

 

The volume from the doors and rear speakers is as loud as I can stand before distortion. Is there a standard for the wattage output to match speaker specs? I.e.amp wattage set to speaker rated RMS power at typical receiver level; amp wattage set to speaker rated max power at max receiver level; etc... Assuming Watts = (VAC squared) ÷ speaker resistance

 

you can govern an amp to a set of speakers. You'll measure for a certain amount of AC voltage coming from the amp. For a 150w RMS signal into a 4 Ohm load, you'll look for 24.5 Volts of output.

 

I know that. The question is what should I set the amp output to for the best response from the speakers? 24.5V with the receiver at the typical level? 24.5V with the receiver as high as I would have it at? 34 6V with the receiver as high as it will go?

 

You want max clean output your speakers can handle, at the max clean volume the headunit can output. If 34 out of 40 is the highest you can turn the radio without distortion then that's where you'll set your gains on your amp.

 

Ok. Would that amp setting be the Max that the speakers can handle then? I.e. receiver at 34, amp gain turned up until amp output is 34.6V?

 

34.6 Volts is 300 watts of output. Your amp is only capable of a 175w RMS. Turn your radio up to 34, and turn the gain up till your music distorts, back it off just a tad more since your speakers cannot handle the power your amp does.

 

I guess I need to find an o-scope to do this properly.

 

I don't think an O-Scope is necessary here. Turn the volume on you headunit to the max volume you use. And use a multi-meter, probe the output of the amp, play a test tone 1Khz for door speakers or 50Hz for subwoofers and turn it up to 24.5 Volts of output. Forget the 34.6 volts of output. That's fake, your amp cannot produce that much voltage without distortion.

 

I already bought a cheap little handheld o-scope from Amazon. If it is crap, I'll just send it back.

 

I assume I can check the head unit's distortion with an o-scope on one RCA cable, right? i.e. 50Hz tone, o-scope on the Subwoofer L RCA.

 

Yes. a 50Hz tone for subwoofers and a 1Khz tone for the mid-bass speakers.

 

I have a scope, i need to do some googling to figure out how to do this. I have not heard of this before.

 

I am going to just cut an old RCA cable, and strip the wires to connect the o-scope.