Newsgroups: rec.audio.car

OOPS!
I did it again and forgot power is 10log(P1/P2) while voltage gain and
spectrum analyzer displays are 20Log(V1/V2).  Reason is
  Power=Voltage*current=V*I=V^2/R
Thus if talking power gain where the formula is dbW=10log(P1/P2) and you
want to convert to voltage gain, then db=10log[V1^2/V2^2]=20log[V1/V2].
Anyway, I hope I have the units right this time in this distortion
discussion:
>>|> (Alan Jones) writes:
>>|>Anyway, why do cars require so much power to produce quality music?
>>|>Most good systems seem to include hundreds of watts of amplifier power.
>>|>My home system has only 45 watts, and it's so loud I never turn it up
>>|>past 50%.  The area inside a car is so small - I'd expect that you
>>|>wouldn't need much power to fill it with quality music.  What's the
>>|>deal?
>>
>Addressing the home system first, with 45 WPC, it is most likely distorting
>quite a bit and distortion sounds MUCH louder than clean music.  If you excuse
>the EE terms, the power-spectral-density of an undistorted signal looks like
>this on a spectrum analyzer:
>
>   Clean 1kHz signal a 10W  on a system with .01% THD @ 10W
>
>40 (=100W)
>
>20         ^
>           |
>0 dbV (=1W)|
>           |
>-20        |
>           |
>-40        |
>           |
>-60        |       ^
>           |   ^   |   ^   ^
>-80        |   |   |   |   |   ^
>-----------------------------------
>      .1   1   2   3   4   5   6   7  kHz
>
>Note that the distortion products are 80dB down and so you don't
>really hear them unless you have a "golden ear" in a very quiet room
>or a van at rest camping. 8-)
>===================================================================
>
>Now, a Badly Distorted 1kHz signal a 100W (say with a 45 Watt rated amp):
>
>40         ^
>           |       ^
>20         |   ^   |       ^
>           |   |   |   ^   |       ^
>0 dbV      |   |   |   |   |   ^   |   ^
>           |   |   |   |   |   |   |   |   ^
>-20        |   |   |   |   |   |   |   |   |
>           |   |   |   |   |   |   |   |   |
>-40        |   |   |   |   |   |   |   |   |
>           |   |   |   |   |   |   |   |   |
>-60        |   |   |   |   |   |   |   |   |
>           |   |   |   |   |   |   |   |   |   ...and on at sin(s)/s decay
>-80        |   |   |   |   |   |   |   |   |
>           |   |   |   |   |   |   |   |   |
>-100       |   |   |   |   |   |   |   |   |
>------------------------------------------------
>           1   2   3   4   5   6   7   8   9   kHz
>
What I've shown is a 1kHz signal overdriving an amplifier such that it
is trying to put out a sine wave, but is really putting out more of a
square wave.  I have many CDs that I listen to at home and have measured
0.001 (-30dbW or -60dbV) WPC avg power at listening levels and then
draws 125 WPC for short bursts (say the 1812 Overture cannon shot,
Bolero, Telarc Time Warp, ...)  This music is requiring dynamic range of
my system of 20log(125/1)-20log(.001)= 102 dB (or 51dBW)!  Note that I
can hear amplifier noise during the very quiet sections with my ear next
to the speaker.

>Of course, most music isn't this demanding, but can still require 60-80 dbV
>dynamic range.  With clean, undistorted power, the big sound peaks aren't
>that dangerous to you hearing, but the distorted ones are since it is
>easy to get 10 times (20dbV or 10dbW) more power than you should get since the
>distortion products fall-off at a slow rate with frequency - sin(s)/s.
>These distortion products are what fries tweeters!
>
>I've been told that rock bands that want to sound "LOUD" set-up their
>amps to distort.  As a consequence, there is a problem with many rock
>musicians going deaf.  (From a good friend that is a professional bass
>player that plays in the SF Bay Area with Ray Charles and others - Ray
>Charles headlines - his band is the "other act").
>
Kirk (hope I got it right this time!) out
+---------------------------------------------------------------------+
| Kirk Lindstrom - OCD Product R & D | Hewlett-Packard Co.  M/S: 91UA |
|   Engineer/Scientist, Hardware     |                                |
|------------------------------------| Optical Communication Division |
|     kirk_lindstrom@sj.hp.com       |                                |
|    Kirk Lindstrom / HP0100/UX      | 370 W. Trimble Rd.             |
| ph 408 435 6404 | fax 408 435 6286 | San Jose, CA  95131-1096       |
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Newsgroups: rec.audio.car