Steve,
With all due respect, reproducing the lower portion of the audio frequency
spectrum requires much greater power than the high-end. I have bi-amped the
smaller stereo monitoring system in my recording studio and run 400 watts
RMS to the subwoofer and 50 watts RMS per channel to the satellite
speakers. If you ever go to a concert where sound reinforcement is being
used, note the mass of the low-end cabinets and the drivers they contain
compared to the typical horn drivers of the high-end. While it takes a lot
of power to move the cone drivers in the low-end, the high-end drivers are
very small and usually of a very low mass diaphram-type which would be
destroyed in an instant with anywhere near the power of the low end
apmlifiers applied to them. You are on the right track, though, regarding
peak power being occasionally reached. One of the characteristics of much
modern music, especially the urban thug type, is lots of sustained bass
notes, which means a system can be running at peak power for a good deal of
the time. A basic consideration of understanding manufacturerer's claimed
power ratings is to see if the rating is stated as RMS, Music Power or not
stated as to what kind of rating at all. Unless the rating in watts is
stated as RMS and a statement is made as to how much (in percentage) of
certain types of distortion and over what frequency range, it is most likely
inflated. Audio power amplifiers for cars seem to be the most highly
overated of all types.
Gary '73 TR6
----- Original Message -----
From: Steve Hanselman <tr6@kc4sw.com>
To: Andrew Packard <apackard@triad.rr.com>; 'R. Ashford Little II'
<ralittle2@mindspring.com>; 6-Pack <6pack@autox.team.net>
Sent: Sunday, October 20, 2002 9:50 PM
Subject: RE: Alternators and Radios
> One of the major problems with anything relating to entertainment is a
real
> inflated sense of what they are delivering. I'd never accuse them of
lying,
> but on the other hand I'd be extremely surprised if any of the 100 watt
> amplifiers delivered anything close to 100 watts.
>
> On another note the math below is incorrect. Assuming that the amp in
> question really delivers 100 watts output and that it is 75% (a
reasonably
> optimistic view) efficient this means it takes over 133 watts. Converting
> this to required current gives 10.1 amps (assuming a terminal voltage of
> 13.2VDC). Given that audio is never continuous the peak current is
probably
> closer to 20 Amps at any given instant this depends on the ratio of highs
to
> lows (highs take more power than lows).
>
> Remember these are the same folks who bring you that 6Hp compressor that
> runs on a standard 15 amp 120 outlet.
>
> Having said that I'd put the largest deep cycle battery that'll fit in the
> car and let the stock alternator run it. Just don't drive to long after
> dark
>
> Just my two cents worth (well maybe .075 cents worth)
>
> Steve
>
> tr6@kc4sw.com
>
>
> -----Original Message-----
> From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net]On
> Behalf Of Andrew Packard
> Sent: Sunday, October 20, 2002 8:12 PM
> To: 'R. Ashford Little II'; 6-Pack; Triumphs@autox. Net
> Subject: RE: Alternators and Radios
>
>
> The Ford Fiesta Bosch alternator has a 55 amp rating. The installation is
> incredibly easy. I just had to get a slightly shorter fan belt and shave
a
> bit of the mounting bracket to allow for the alternator fan blades to
clear
> it. Even the plug from my Lucas pushed right into the Bosch. I would
think
> that 55 amps would be enough to run about any reasonable stereo set up you
> would want.
> Andy
> TR250
>
> -----Original Message-----
> From: R. Ashford Little II [SMTP:ralittle2@mindspring.com]
> Sent: Sunday, October 20, 2002 5:26 PM
> To: 6-Pack; Triumphs@autox. Net
> Subject: Alternators and Radios
>
> I've got the stock alternator or my 70 TR6. I'm thinking of upgrading
> the stereo to add an external amp to my CD player, however, I'm a bit
> worried that with my stock setup it's not such a good idea. I also lack
> almost all skills related to electrical so I'm turning to those my DC
> inclined. I was given this example and would like to know if this is a
> good rule of thumb?
>
> Let's say that you have an amp rated at a total of 100 watts (either
> 25x4 or 50x2). To get the estimated draw you would take the 100 and
> divide it by 14.4 which yields 6.94 amps. Is this correct? Also there
> is supposed to be some efficiency loss in the amp so I was told that you
> would really take something like 100 x .75 (25% loss due to heat) =
> 75/14.4=5.21 amps.
>
> All amps, just like anything, are not created equal either. You can buy
> an el cheapo model that supposedly rated at X rms per channel vs. brand
> B which is a true reflection of their advertised power. How do you
> figure that in?
>
> What is the estimated draw of the lights and blower when on? This will
> give me an idea of how much excess I'm dealing with. Also, this looks
> like it might necessitate an upgrade to the Ford Fiesta alternator.
> What's the output of that again?
>
> The last thing I want to do is to purchase something that ends up
> working beautifully, but prevents me from hearing the truly melodious
> sound of my engine.
>
> TIA,
>
> R. Ashford Little II
> www.geocities.com/ralittle2
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