Tech question on amp design

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Zaf - 29 Mar 2004 03:29 GMT

I'm planning on using an auto head unit permanantly mounted in a
weatherproof (i hope) box for a home patio entertainment system. I
plan to use outdoor home stereo speakers and would like to get as much
power as possible into these 8 ohm speakers. Will goosing up the +12V
supply I need have any impact on the delivered power of the amp? How
exactly do manufactureres measure power output for car audio? I
always get a kick out of 'RMS power', quite a meaningless measurement,
if you're talking power, you want average, RMS is abetter indicator of
waveform energy if you're talking just voltage or current.

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MZ - 29 Mar 2004 04:52 GMT

> I'm planning on using an auto head unit permanantly mounted in a
> weatherproof (i hope) box for a home patio entertainment system. I
> plan to use outdoor home stereo speakers and would like to get as much
> power as possible into these 8 ohm speakers. Will goosing up the +12V
> supply I need have any impact on the delivered power of the amp?

For the vast majority of car amplifiers available, yes. Most exhibit an
increase in power output roughly proportional to the supply voltage squared.
In other words, the efficiency of the amplifier remains relatively constant
(kinda sorta) with increasing supply voltage. I personally wouldn't go any
higher than 15v though. And, of course, you can get more power by running a
second pair of speakers in parallel.

> How
> exactly do manufactureres measure power output for car audio? I
> always get a kick out of 'RMS power', quite a meaningless measurement,
> if you're talking power, you want average, RMS is abetter indicator of
> waveform energy if you're talking just voltage or current.

I've been harping on this very issue for quite some time also. The "RMS
power" measurement is actually NOT "RMS power". All manufacturers that I
know of that use that terminology are actually referring to average power.
This terminology appears to have stuck with them, and I'm not entirely sure
why.

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Tony Hwang - 29 Mar 2004 06:01 GMT

>>I'm planning on using an auto head unit permanantly mounted in a
>>weatherproof (i hope) box for a home patio entertainment system. I
[quoted text clipped - 20 lines]
> This terminology appears to have stuck with them, and I'm not entirely sure
> why.

Hi,
Water proof? Don't forget cooling. Amp specially when pushed by
increasing supply voltage, generates more heat. RMS power can be roughly
measured by measuring current draw of the amp and power supply voltage
multiplied by efficiency of the amp, say 45%. P(rms) = V x I x 0.45.
Tony

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