DerrickM

I already ordered it, but still wanted to get any feedback everybody might have. It's 400W at 4-ohms, and my sub is an Infinity "perfect 12.1" in 4-ohm. (My current 200W RF isn't keeping up with the rest of the system, and this was the most I wanted to spend on yet another upgrade).

Also, what exactly is a class-D amp, and why are all the sub amps class-D?

elduderino

Class D is the class of power supply modulation.

Class A, Class B, and sliding Class A-B are the ones most people are familiar with.

CLass D uses a high-speed square wave method of modulation that results in a more efficient amp. Class AB is 50% efficient as a general rule. Class D can reach 80%. Smaller amp, less heat sink (which is the most expensive part often, when costs of shipping it are added in), more watts.

Because the switching signal creates noise that can creep into the audible spectrum, Class D full-range amps have been rare. Sub amps that don't play above 200 Hz or so are very easy to filter.

There are some purists that don't like the phase delay of the low-pass filtering as it affects sound quality. Since you have to have pretty sophisticated time alignment to overcome that fact that your woofer is the farthest speaker ANYWAY, it's not really a deal in most systems, IMO.

However, those amps can also generate FM radio interference. We have seen some Hifonics Brutus amps totally trash the already poor FM reception in a TSX due to being very close to the window anttenna and the C-pillar FM amplifier. JL Audio is the only Class D that I know of that has been reported as for sure NOT causing this issue, and Hifonics are the only ones I know FOR SURE do, but I ahve heard of older MTX amps doing it anecdotally (didn't even think of that until just now, dude... sorry I didn't mention it earlier, just recurred...)

I don't know that your car would be susceptible to the same FM issues that a TSX is, or if your amp is a "bad actor" in that regard, so don't mean to raise a panic or anything...

bcae1.com has a section on "amplifier classes" that has some pretty graphs... : )

DerrickM

Thanks Ken! Congratulations on your new vendor status! We can always count on you for advice.

I almost never listen to radio anyway--so I wouldn't notice it anyway. I wonder if it could affect satellite radio?! That would be a drag. I'm sure it's probably fine, since these are extremely popular amps, and most sub amps are class D nowadays anyway.

But, now that you've got my curiosity up, I'll go peruse MTX's website to see what they say.

PS - I took your advice on putting sawdust in the last layer of resin on the sub box.

DerrickM

MTX says pretty much the same thing you just did. They do say they've addressed the issues of noise and radio interference:

http://www.mtx.com/caraudio/technology/ampClassD.cfm