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      11-20-2010, 01:31 AM   #1
ctuna
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Auto amp Specs question for power

When reading auto amp specs for power should you believe the 14.5 Volt output rating or the 12.5 Volt rating for real world power. Also is the class of amp relevant ? Does a class AB amp and a class D amp with the same or close power rating perform the same? Are there any articles on this anywhere.
Also is a distortion spec of 1 % at rated power significant.

I remember being impressed by the JL Slash Specs as it maintained power across the full Spectrum. (to 20k)
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      11-20-2010, 02:00 AM   #2
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When the car isn't running, or when your lights are on, or your defogger, your car won't be at 14.4.

12.5 is a reasonable voltage with the engine off or with a heavier load.

The rest of your questions could fill a book.

Class D amplifiers initially did not sound as good as Class AB with mids and highs. Bass was fine. The consensus now is that current technology has eliminated the difference.

But you have the "all amps sound alike" school and the "all amps have their own signature sound" school.

You won't navigate those polar extremes in a forum like this.

Distortions differ in type and spectral distribution. Harmonic, intermodulation, odd-order, even-order...

The baseline for a high-fidelity amplifier is to be flat from 20 to 20k, with less than 3dB of deviation (much less).

My approach is that power, noise rejection, and dynamic headroom are the most important aspects for car audio. A Class AB amp with more dynamic headroom sounds better than a Class D amp without dynamic headroom - even with the same RMS power rating.
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      11-20-2010, 02:35 AM   #3
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If you are running at less than full power?

If you are running at less than full power won't any amp have some dynamic head room ( More power when a higher Input signal comes along) or maybe I don't understand this correctly. I used to read these specs a lot when selecting a home system but haven't done that for awhile.

As far as every amp sounding the same I know thats not true as Sony Receivers in the 70's were noted for having a thin an tinny sound no bass where pioneer and HK could always do bass and mid range better and HK always underrated there power.

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      11-20-2010, 12:04 PM   #4
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I know from Home Theater (watched the Blue Ray of the Rock and Roll Hall of fame 25th Anniversary last night) that I sized amps very conservatively. I use Sonus Faber speakers, which are not super efficient but give good midrange. They were never really happy until they got 200 WRMS of Pararsound each. Biggest improvement of size is in bass control, biggest improvement of quality is in high end fielity and consistency.

I have been nervous about the Class D amps since they haven't been well received in Absolute Sound and other pubs. But they do have some virtues for car audio, including size and heat.

You are right that receivers are voiced differently. Its a no brainer to hear the differences when you audition the same system and swap in different receivers. Adjust gain to match and you will hear differences. I only use my denon for the front end pre-pro. Even the larger denons did not have the sound I wanted.
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      11-20-2010, 12:41 PM   #5
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Rob G

Hows your install going?
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      11-20-2010, 02:38 PM   #6
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My point is that you will find smart, knowledgeable people who will provide data to bolster their argument that all good amps DO sound alike - and it won't get settled here. If we present our products on that basis, I will be called a shyster by some.

I am not a militant on the subject - but I think there is a lot of BS out there on the topic. The human mind doesn't work well with comparison testing of smells, tastes, or sounds - that further muddied the waters. How we got New Coke. Hard to "prove" anything.

We feel that we've eliminated the bad sounding gear, and our packages give good value for the price. But there is a diff between a 75 wpc amp with almost headroom, and a 75 wpc amp with 2.5 dB of headroom (125 watts).

There is a diff between "20 watts" of IC BTL power running off 12v, and 20 watts of discrete, 20-20k power with a real switching power supply behind it.

Those are issues you are more likely to encounter in car system design.
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