Archived from groups: alt.punk,rec.audio.pro (

More info?)

Ben,

I guess I was just not assuming that the amp was for all practical

purposes an ideal voltage source. My post was written before we knew

that the amp was rated for operation down to two ohms. As I said, it

would be a trivial difference, but perhaps it is so trivial I shouldn't

even have bothered mentioning it. Without knowing the output impedance

of the amp, though, it's tough to say 100%. Of course most modern amps

are designed such that their output impedance is low enough where it's

not a factor. But you are right, I should have left that part of my

post out. Why unnecessarily overcomplicate the issue? Sometimes I

overthink problems....

Cheers,

Trevor de Clercq

Ben Bradley wrote:

> On Sun, 20 Feb 2005 11:18:31 -0500, Trevor de Clercq

> <declerct@REMOVETHISnewschool.edu> wrote:

>

>

>>Yes, it would be 33 Watts for the 8 ohm driver and 67 Watts for the 4

>>ohm driver. Here's a proof (using resistances instead of impedances):

>

>

>>...

>

>

>>This proof is overly long, but I wanted to walk you through it. There

>>are other ways of arriving at the same answer, of course. Drivers are

>>of course theoretically inductive loads instead of resistive loads, but

>>in this theorectical case the calculations are the same.

>>

>>In the real world, of course, speakers have both a resistive and

>>reactive component which gets you into power factors at specific

>>frequencies, but I don't think it's worth getting into that here. Just

>>know that

>> each speaker will affect the frequency response of the other

>

> ^^^^ ^^^^^^ ^^^ ^^^^^^^^^ ^^^^^^^^ ^^ ^^^ ^^^^^

>

>>because a complex impedance varies throughout the frequency range. I'm

>>guessing this is a trivial difference, but someone can correct me here

>>if I'm wrong. Anyway, people mostly match their speakers for this very

>>reason.

>

>

> Just to point out a mistake in an otherwise excellent post (someone

> will come along and point out that correcting others' posts is the

> purpose of Usenet...), two important assumptions are that 1. the

> speakers are in parallel, as you said earlier, and 2. the amplifier

> has such a high damping factor (or equivalently, low output impedance)

> that it doesn't matter what the load is on it (within its rating,

> which the OP later said goes down to 2 ohms), so that whatever

> changing impedance one speaker has in relation to frequency, it won't

> affect the voltage to the other speaker, thus its acoustic output

> won't be affected by the other speaker.

> The rest of this post shows you know what you're talking about, so

> I can only guess you either forgot the word "not" in the above, or you

> somehow got mentally turned around and were thinking the speakers were

> wired in series.

>

>

>

>>WARNING: The real issue here (as you may see) is that you are putting

>>an effective 2.67 load across your amp. Most amps are only rated for a

>>4 ohm load or higher. So while your drivers may be fine and be high

>>enough wattage, your amp may melt down becuase you are drawing too much

>>current from it.

>>

>>Cheers,

>>Trevor de Clercq

>>

>>CLASSACT@BRICK.NET wrote:

>>

>>>If I have two drivers, one of which is 8 ohm, the other being 4 ohm,

>>>and I wire them in parallel, then put 100 watts through them, how many

>>>watts will go through each driver?

>>>I assume it is not merely 33, 67, respectively.

>>>

>>>--Bryan

>

>

> -----

>

http/mindspring.com/~benbradley