SNR vs THD, which is more important (or more noticeable) for amplifiers
 

Ok, so trying to pick out an upgraded amp for next year and I am kind of stuck on something.

On Crutchfield.com, their amps typically fall into one of two categories for the higher end items:

1. Amps with high Signal to Noise Ratio (100 or above, which is good) but higher Total Harmonic Distortion around 1% (which is not so good).

2. Amps with lower Signal to Noise Ratio (85-90, which is not as good) but lower Total Harmonic Distortion around 0.05% or less (which is better).

The question is, why dont they sell amps with 100+ SNR and less than 0.05% THD?

Even the $900 Focal has a THD of 1% and 92db SNR. Is there more to it that I am missing?

I think your reading to much into specs just my opinion. You want a low noise ratio but more important is good grounds for the amps. You may hear hissing in some cheaper amps when no music is playing and the volume is up but not with higher end amps.

Agree at looking a little too hard at the specs. SNR, as you may know, is a ratio between strength of a reference signal (like a sine wave) versus measured noise; or a simple difference between the two in dB. Recall dB is logarithmic (similar to the concept that to increase power by 3dB, you need to double power), so 92dB represents a HUGE difference between signal (music) and noise, almost to the point of being negligible.

THD is measured the same, but it can be "tricked" depending on how the manufacturer rates their amps. THD increases as the amp's power increases, until it clips; that's where THD spikes up. Most manufacturers rate the power at that clipping point (usually 1% THD), so you'll usually see that spec.

However, some manufacturers under rate their amps (like RF) - it still clips to 1% at the maximum power (say 150W for a rated 100W amp). But since you're taking the THD measurement at rated power, it's much lower (like 0.05% to 0.1%).

Practically speaking, you'll only hear this when you're over-driving the amp, and you'll only notice at what power it starts to clip. Within it's power envelope, however, you won't hear the difference between an amp that has 0.05% THD to one that has 0.1% THD.

Any of the high-end amps will deliver excellent sound. So look for the amp that has the power and features you need. But most important, as bigaudiofanatic has said, once you get the amp, installation quality is what should be focused on.

Thank yo0u for this, to busy with work to go into details. +1 :tup:

Thanks for the details! Can you recommend an amp for two channel speaker setup (two 6x9 Polk Dxi690's)?

Hehe - how much you willing to spend? :D

Those Focals are mighty nice and extremely recommendable. :tup:

Depends, nothing at the moment but now that the wiring is done, everything is basically a quick swap upgrade. I heard that, like Infinity Kappas, the Focal 6x9 speakers can be harsh up top. Not sure about their bass response but the Polk 6x9's I have now do put out a nice kick and have great clarity throughout the range.

I have the Crutchfield Sound Ordnance 2100 amp (75W x 2 @ 4 ohms) and its rated at 95db SNR for 1% THD. I have no static at low volume and a nice grounding setup so no complaints. Was only $100 too.

8 gauge fosgate wiring for the power/ground and 12 gauge StreetWires speaker wire.

My RCAs were like $18 at BestBuy but the audio quality is great, no static at all so far. Made sure to keep the power wire far away from the RCAs. Running them from the preamp out on a JVC headunit.

Still though, wonder what it would sound like with a Focal amp, Focal 6x9's and a nice set of Monster Cable RCA's. :)

Rcas are all hype even more so with monster, focal is nice if you like higher output tweeters, if your looking for a smoother sound look at audison amps and image dynamics speakers.

Interconnects in the car: prioritize shielding and flexibility. As long as they're good here, you're fine. So your RCAs from BB is just fine. Power/signal wire separation during install even better. :tup:

If you've got the dough, Focal & Audison are great. You can buy more inexpensive amps and still get just as good sound (especially in the car): Alpine, Boston, JL, Rockford; typically at 30-50% the cost of those expensive amps.

I'm not too familiar with Sound Ord amps. You say you want to upgrade, but don't really indicate why. Something you don't like about your setup? Seems to be installed and working fine...

Always in the pursuit of better sound I guess, but no I am very happy for now. Probably will upgrade to the JL Audio amp eventually and call it a day.

I agree all except for the JL for a cheaper brand over priced for what you get. If you get a used one or one off ebay or something that is a different story.

then go with a good 6.5 and tweeter, not a 6x9 in the door.

Hehe, then save up for an Audison. Those babies are sweet and smooth.