Newsgroups: rec.audio.car

>Joshua R. Poulson
>|> (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?
>
>Ah, yes. The perennial question. At any rate the answer is difficult to
>express without demonstration... but it revolves around two important
>points: realism, and dynamic range.
>
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 SNR=100dB and .01% THD
   (most car amps have 80-100db SNRs)

40 (=100W)

20         ^
           |
0 dbW (=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 dbW      |   |   |   |   |   ^   |   ^
           |   |   |   |   |   |   |   |   ^
-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 (-60dbW) 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!  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 db
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 (20db) 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").

>When you go to a concert that is properly set-up, you find yourself the 
>focus of thousands of watts of musical power and you can hear each note
>in the magajoules of energy directed at those delicate bones in your ear.
>The reason for so much power there is to give everyone the benefit of 
>hearing the slightest noise in the band's performance... the nuances...
>the individual sounds.
>
Why do most sane people wear ear-plugs at rock concerts if this is true?
Is it because most aren't "properly set up?" 

Also, most of the live recordings I've listened to have MUCH less dynamic
range than a good studio recording or live classical recording of unamplified
music.  My impression is that rock concerts rely more on sensory overload
and the fun of "being there" rather than providing quality music. (I haven't
been to that many as I didn't enjoy the music and worry about my hearing).

>When you attend a concert like an unpowered orchestra there is still
>a massive amount of amplification by the very design of the hall, and 

I don't think halls amplify since they don't add energy.  They do a nice
job of focusing what energy is there though.

>again there are many sources of music and you shouldn't wonder that they
>all sweat. (It ain't just because of the tuxedos).
>
8-)

>At home, it takes less power to give hints to this dynamic range, but the
>truly incredible sound setups in the home are again megawatt extravaganzas.
>My personal setup features 1200 watts of power... The neighbors seldom
>complain if I invite them over for movie nights.
>
Same here with about the same amount of power.

>In the car, a lot of energy is lost because of poor speaker placement, the
>materials in the car damping the sound and several other factors. The
>reason my car is running at a rated 770 watts is for the dynamics. Kick
>drums sound like kick drums. Guitars with distortion don't get extra 
>distortion from nasty speakers and overdriven amplifiers, and the concerts
>in my car do a fair job of approximating the concert experience.
>
What speaker efficiencies are you running?  My MB Quarts are pretty low,
but they seem to go from ear-splitting levels at 80 WPC-peak to low noise
levels (1-10mW?? maybe).  I'm running rf460sd which is 30WPC with pk power
of 80 WPC (at least on the graph they supplied).  It seems to handle all but
the very most demanding music (Telarc Time Warp, for one).  Is the 770 total
watts peak?  If so then you have 20log(770/320) or another 7.6 db headroom
which is quit a bit - can it handle TimeWarp?

>No one's car or home system can approximate the real thing (not until the
>recording industry goes up a few notches, and the rest of the audio
>industry follows their lead) but you can get closer with a lot of power
>and signal processing.
>
I actually enjoy home and auto sound more since I can turn it down!

>Dynamic range: the difference between the quietest and loudest discernible
>sounds on playback.
>
and this only matters when you aren't driving, just listening!

>Realism: Does it sound like it did when the band recorded it?
>
>-- 
>Joshua R. Poulson, Systems Programmer, Computing Services, Widener University
>jrp@cyber.Widener.EDU, jrp@netman.Widener.EDU, poulson@cs.Widener.EDU, et al.
>----------
Kirk out
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| 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