I was looking at SNR for several manufacturers and some report very high numbers (aka 100+ db) for their amps and others (PG, JBL) report fairly low numbers (aka 85dba). I chalk this up to different test parameters but am not sure because I doubt there is that much difference...can anyone help? Just trying to learn.

From a tech perspective, S/N ratio numbers can be raw or weighted (such as "A" weighting).

Some manufacturers claim that raw numbers are superior to weighted numbers. Zapco makes this claim.

You need to know the convention used.

But S/N is an interesting number. Your CD player is 90+.

But the dynamic range possible in a moving car is such that your car's noise floor is much higher than any of your equipment.

In recent years, it's become more apparent that speakers perform differently with large signals than with the small ones we always used to measure. Similarly, the distortion characteristics of a piece of electronics - whether it sounds good with music or not - are usually not captured by S/N, THD, or numbers like that.

I suggest finding a copy of Robert Harley's The Complete Guide to High End Audio. Whether you end up agreeing with everything or not, it's well worth the read.

Well put Ken.

Most enthusiasts forget that the noise floor of the average automobile will be far worse than any well manufactured/designed product currently on the market.