Re: [DML] Amplifiers.

["Marty Galbreath" <marty@xxxxxxxxxxxxxxxxx>]

Time for me to chime back in. First of all, I am 48 years old. I 
have been an audio professional for 26 years now. The explanation 
offered by Andy is completely correct, IMPO (and appreciated, as I 
type by hunt-and-peck). I do not listen to rap or any similar music 
genre, I prefer classical, female vocalists, blues, and yes even the 
occasional rock ditty. 

My system contains a new Sony head unit with an advertised power of 
30 WPC. As Andy has inferred, it would be lucky to actually have 
7.5 WPC. The restrictions and regulations of how power amplifiers 
are measured in the professional realm do not apply to the car 
stereo industry. As a result, the advertised power rating of these 
devices is usually grossly over valued, usually by a factor of 4. If 
a manufacturer were to use the correct rating criteria, their units 
would appear less powerful than their competitors and would not 
sell. So a vicious cycle of boasting unrealistic power claims 
continues.

Most people would be surprised to learn that the wattage level they 
are experiencing at "normal" volumes is quite low, usually less than 
one watt. But as Andy again pointed out, every increase in level of 
3 dB doubles the power requirement. 3 dB is not a very large 
increase in actual listening level. It is regarded as the minimum 
amount of power increase that can be perceived by the human ear 
as "it got a little louder". So if we take our theoretical one watt 
and turn up the volume just enough to hear a difference, how many 
times can we do this before we run out of steam? 1 - 2 - 4 - 8 - 16 -
 32 = 64 - 128 ...it runs out of juice fast. So we can see that the 
difference between a 20 watt amp and a 70 watt amp is only a matter 
of 4 dB or so. 

So why add the external power amp if we are usually listening to 
such low levels anyway? While it's true that the 7.5 watt amplifier 
in my head unit will produce voice and most music at a reasonably 
sufficient volume, if you want to enjoy music with a large dynamic 
range at a level approaching that of a live performance, more power 
will be required. Here's why:

The human ear is far from being a linear device. It is much more 
sensitive to high frequency sound than low. So it is easy to power 
loudspeakers with enough high frequency energy, say above 500 Hz, to 
sufficient levels to make a person uncomfortable fast. It is the 
lower range of sound that becomes the challenge.

Lower frequency sound requires much larger speakers to reproduce. It 
is because the wavelength of these frequencies being much longer 
than HF, require more air to be moved in order to be generated. The 
transducers of low frequency energy, woofers, are therefore much 
less efficient that the HF counterparts, tweeters, and will use up 
most of your amplifier power. Coupled with this the lower 
sensitivity of the ear at these frequencies, you can see where all 
the power is going. 



I spent a great deal of effort and money attempting to improve the 
acoustic environment of my Delorean. This being my second D 
restoration, I recalled how noisy the first car was and was 
determined to improve that for this one. I completely removed the 
interior and installed two layers of Dynamat extreme to all of the 
fiberglass surfaces. A layer of TACMAT was installed over that on 
the rear firewall and below the parcel shelf. Above that a layer of 
Dynamat Dynaliner closed cell foam. In the area behind the door 
headliners, I used the Xtreme and a layer of the Dynaliner foam. 
Finally, I fabricated a new rear wall from 3/4 MDF and put my rear 
speakers, 7" Polk db component models, and my amp, a Soundstream 245 
amp there. The amp has 25 watts RMS x 4 channels and 100 watts RMS x 
1 for the subwoofer. Real watts, from a time when these specs on 
these amps were regulated. The storage compartment behind the 
driver's seat perfectly accommodates a Kicker L5 12" square 
subwoofer without modification, so that's where it went. In the 
dash, I replaced the 3.5" speakers with 4" MB Quart coaxials by 
making a custom mounting ring. The resulting system sounds really 
good. It's not a competition boom car, just a quiet ride with a 
nicely balanced full-range sound system. When Holly Cole or Diana 
Krall belts out a tune in my car the sound is rich and accurate. 

At first, I had the front speakers connected to the head unit and 
the rear speakers powered from the amp in bridged mode, for 50WPC. 
The fronts were dull and lifeless. Moving them to the external amp 
brought them back to life. Lowering the rears to 25 watt by doing 
this made a little difference, but only on the loudest passages of 
music. 

I fear I have strayed a little from the original question: does it 
make a difference having the external amp? For myself and my desires 
for the car, definitely yes.

Marty Galbreath
#3765





--- In dmcnews@xxxxxxxxxxxxxxx, Hank <heskin@xxxx> wrote:
> > The bottom line is some people view their car stereo as 
something to
> > generate background music for long trips - for others it's a 
huge part of the
> > driving experience, and for those of us whom are the latter - an 
external  amplifier
> > is a requirement.
> > Andy
> 
> 
> That's a great explanation, thanks.. but I've got to believe, 
based on
> the actual volume of the Delorean cabin (very small), that after a
> certain point (i.e. number of watts of output),  that it just 
doesn't
> matter - the volume would be deafening before you actually "heard" 
a
> difference with more watts.   (diminishing returns, if you will).  
So,
> for argument sake, suppose you have a great head unit that puts 
out 20
> watts per channel.  Is a 70 watt stereo *inside a Delorean* really
> going to sound better at the same tolerable volume?  From your
> explanation, the wattage ratings (assuming similar component 
quality
> and build) only matters at very high volume, which makes perfect
> sense... but listening to 70 watts inside the car has got to be 
beyond
> ear-damage level, no matter the type of music one is listening to.
> 
> If you're going for max watts and ear-drum busting and ground 
shaking
> bass, sure, that argument makes sense - but what about normal,
> everyday listening habits?
> 
> -Hank







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