[sdiy] Re: crystal clear

[Magnus Danielson]

From: Don Tillman <don at till.com>
Subject: Re: crystal clear
Date: Fri, 9 May 2003 21:58:44 -0700

>    > Date: Thu, 08 May 2003 15:12:18 +0200 (CEST) From: Magnus
>    > Danielson <cfmd at swipnet.se>
>    > 
>    > Pbigamp = Ptotal = Ptop + Pmid + Pbas + Pcrossover
> 
> Sorry, I assumed you were referring to something else...
> 
> Imagine a simple biamping system:
>   Low amp: 100 watts
>   High amp: 50 watts
> 
> The obvious single amp version of this would suggest that a full range
> amp equivalent would be 150 Watts.
> 
> But because the maximum amplifier voltage is proportional to the
> square root of the maximum amplifier power, the full range amp's power
> rating will need to be able to handle the sum of those voltages:
> 
>   Full range amp: (sqrt(100)) + sqrt(50))^2 => 291 watts
> 
> This is somewhat bogus reasoning because you will only use those 
> 291 watts during occasional peaks.  But it does mean that biamping
> allows you to handle more peak power than you'd expect.
> 
> (And if something goes wrong, it keeps the 150 (or 291) watts out of
> the tweeter.)

Thanks Don, *I* had forgot that part of the argumentation... don't say 10 years
brings flaws into your memory-bank ;O)

Actually, I remember this reversely as getting more dynamics, which you do in
a sense. You could also use the bandwidth reasoning, but it all boils down to
having the same meaning as the peak/voltage vs. peak/power argumentation.

Do I have to care about peak voltage? This is another issue which seems to be
not well understood. The ratio of peak/rms voltage known as the Crest factor
comes into play. What is the maximum Crest factor I need to expect?

The higher Crest factor, the higher headroom you will need in order for the
amps not to clip even if you are at the limit of what the elements can handle
in power (RMS level is effective value and tells you how much power you toss).

Anyway, when you do the math just biamping gives you effectively more dynamics
for the amount of power your amp totals. So, several smaller amps can do better
than a amp having the same total power.

So, big is not necessarilly beutifull ;O)

Cheers,
Magnus