So what should I be looking for in the specs?

 

- Signal to Noise Ratio

- Phases

- Effeciency

- Power RMS

- Power Max ( get subs that are in the upper half portion of your

amp power )

 

Some of the more important specs are signal to noise ratio (higher is better), current output, or the amps ability to drive low ohm loads. Power ratings are often deceiving, because most of the time, they are derived from driving the amplifier with a set tone instead of real music, and real music is much more demanding than test tones.

The most important spec is how does the amp sound? Does it's features meet your need for your application? Does the amp have the ability to perform when called upon, without distorting, clipping, or compressing the sound? These questions are much more important than a white paper from the manufacturer stating specs in the lab. After all, you are the one who has to listen to the thing every day. Buy what sounds good to you.

 

Read the Output Power carefully and look for something like

"100 Watts per channel, both channels driven into 4 ohms at less than 0.5% total harmonic distortion".

The rest of the "max power" BS is just that, BS. "Music Power" or whatever they want to call it, it's garbage. That levels the playing field.

 

also the big thing almsot everybody forgets is what the amp's power rating was rated at voltage wise. also are you using it for subs? maybe look at something w/ a 18db or 24db octave rolloff. it will cut out the higher tones a little better.

 

Also look for what freq range the amps power was rated at. As rustdawg said, you want to look at the THD (I prefer .05%) as well as the freq range.

Some companies will rate their amps at xxx watts at .1% THD @ 1K Hz. Well that's great if you plan on listening to AM stations giving crop yields all day. :sillylol:

You want to look for (at least) 20-20K Hz. That's the full spectrum of the human ear.

AJ

 

Specs are junk. All of them. Good amp, crap amp, it doesn't matter. On the good amps, the power is under-rated, so it means nothing. On junk amps, well, they're junk. They play games with power ratings to make them look substantially more powerful than they are.

all of the other stuff (S/N ratio, distortion %, frequency response, blah blah blah) is all mostly useless. Even the cheap amps have high S/N ratios, low distortion (at least in the amp's linear operating range) and cover a full 20-20khz frequency range.

When you need to buy an amp, talk to a sales person about the application and your budget. Buy the most power you can with your money (that DOESN'T mean buy the one with the highest power rating). Listen to it at the store and see how loud it gets. If you stick with quality brands, then buy the most amp you can afford, you'll be happy. If you think you're getting a deal on that 1,000 watt Boss, don't get pissed when your buddy's 200 watt Kicker amp blows you out of the water.

If you're into SQ and not worried about maximum output, you still need to stick with the good quality stuff, but you can get away with lower power. You'll be hard pressed to find sound quality differences from one quality amp to another, but by all means feel free to audition them all and judge for yourself. Just keep in mind that virtually no car audio stores have level-matching equipment, and unless the 2 amps that you're auditioning are set to have a 100% identical output level, you'll be biased toward the louder one.

 

A note about Good quality amps power output being underrated. They are not actually underrated. This is a little known fact. Nobody bothers to check CURRENT DRAW. It is listed in the amps specs. Good quality amps are HIGH CURRENT amps. That is how some amps rated at 50 watts RMS sound twice as loud as other amps rated at 50 watts. REmember those old orion HCCA amps? 22watts per channel but they could easily run a pair of subs...or 3 or 4? They were good, solid high current amps. Remember the Coustic power logis amps? Not bad amps, but their power output seemed wimpier per-watt than say, Punch amps. Punch amps were high current amps too. Look into it and youll see what I mean. The more current an amp uses the more power it can create. Any of you EE majors out there already know this. No secrets, just often overlooked.

 

It's not really that simple. You can't escape ohm's law. I=E/R. Current flow is directly proportional to voltage. This means that no matter how much current you pump into a driver, you're still going to have a known voltage level in order to achieve a particular wattage.

An amp that's driving a 4 ohm sub at 100 watts is pumping 5 amps and 20 volts into the driver, regardless of whether it's a Pyramid or a Rockford.

What it boils down to (and where the "current" wives tale comes from) I believe is in the amp's power supply circuit. Because you're dealing with a finite voltage source, it's necessary for the power supply to handle massive current levels in order to provide adequate voltage & current to the amplifier transistors.

The "resistance" of a transducer is very dynamic and does not stay constant. It also has a j-term (inductance/capacitance) which further complicates the issues, and presents a difficult load for the amp to handle. An amplifier that has adequate current capability will be able to handle the complex impedance, where a lesser quality amp will simply clip.

Since *most* amps are a-b style amps, their efficiency is relatively similar (usually around 50%). Because of this, the maximum current draw of an amplifier is a fair indicator of its output capabilities, but not quite for the reasons that Recluse stated.

I do admit that I need to brush up on my long forgotten amplifier knowledge in order to provide information that's any farther in-depth than this.