[sdiy] SOT: speakers & theory...

[Magnus Danielson]

From: Nils Pipenbrinck <np at inverse-entertainment.de>
Subject: [sdiy] SOT: speakers & theory...
Date: Sun, 05 Jun 2005 15:35:07 +0200
Message-ID: <42A2FF8B.304 at inverse-entertainment.de>

> Well, once again a guitar amp related question. Tried to get some help 
> elsewhere, but I'd like to have a technical answer instead of a flamewar :)
> 
> 
> Say you have two 8 ohm speakers connected to an output transformer.
> 
> How does the frequency response and efficiency factor changes if you:
> 
>  * connect them in series, and feed them from the 16 ohm transformer tap.
>  * connect theem in parallel and feed them from the 4 ohm transformer tap.
> 
> I've noticed a *huge* difference in tone and perceived volume when I 
> change the configuration. But to be honest I don't understand why it 
> makes any difference.

There are a few things going on here:

Your amplifiers output impedance must always be considered when relating to
damping, which comes into play of the tone characteristics. When you parallel
the elements (I assume they are two equalent 8 Ohm elements, or else we are
really out on deep water here) you get 4 Ohms and when you serialize them you
get 16 Ohm of "nominal" impedance. In reality the impedance changes alot with
frequency.

Your amp may not be suitable for 4 or 16 Ohm operation. 4 Ohm requires higher
current load where as 16 Ohm requires higher voltage swing. Which works best is
really related to what your amp is designed for.

Sometimes you are actually better off with separate amps.

That's the short story. However, I am by no means supprised to hear what you is
experiencing, it is normal effects in my experience. If the amps can handle it,
I would probably go for paralleling, but then I might be spoiled by the amps we
had since they could pump current.

Now, did that make sense? Do you want the long story giving some more theory
and all?

Cheers,
Magnus - former PA systems designer