question about THD

[NathanW]

I don't remember where I read it but most manufactures use a small feedback loop (feeding a small amount of the output back through the input) to greatly reduce the THD ratings for their amps. This however is more of a marketing gimmick to see who can get the most zeros behind the decimal point and doesn't actually produce better sound quality as most people would think.

As a result you see some amps with 0.000x and others with 0.xx THD numbers and because most people don't really understand THD ratings (I still don't fully understand it myself) they look at the 0.000x as being much better when it probably sounds worse (most people don't actually audition amps like they do speakers before buying so they never know).

Just something to keep in mind when choosing an amp.

[TheMonolith2001]

Basically there IS a standard for measuring THD, but you don't have to follow it. Any quality company will though. It's like with home amplifiers where you can measure RMS watts with the FTC standard for CEA standard. Some manufacturers will use whatever allows them to put a higher number on the box while some will use what is more accurate. Another thing to keep in mind is they will always do this at the highest ohm load (usually 4 in car audio) where distortion is lowest. If you are looking at THD and then you are going to run it at 1 ohm it's probably not telling you all that much.

You have to use common sense too. A Class D amp is going to be 0.0X at MOST, and it is very rare to see any better than 0.X, if they are claiming any better they are probably full of shit. You usually don't get into 0.0X or better unless it is class A/B