[rescue] Workers of the World, Unite!

[Tim H.]

On Mon, 22 Jul 2002 12:36:30 -0400
Joshua D Boyd <jdboyd at cs.millersville.edu> wrote:

> My recall is that 10ohm speakers on a 4 ohm amp puts to much
> load on the amp, and that if you aren't going to match the amp to the
> speaker, then at least the speaker should be a lower ohm-age. And it
> should be easy enough to add a circuit to adjust for the different
> speakers.   A 6.6667ohm resistor network in parallel with the speaker
> would bring your resistance down to the desired amount.
> 
> -- 
> Joshua D. Boyd

Please NO!  higher "ohmage" is less load, low is high load.  It is a
measure of impedance, which is related to resistance.  Using a higher
load (10 ohms instead of 4) will just mean less volume.  Using less load
(2 Ohms) will make it louder until the magic smoke comes out.

Impedance is an average, at mechanical resonance the coil in a speaker
will have significantly lower impedance than rated, while higher
frequencies will have increasingly large impedance.  This is why a well
built sub box will use air to stop the speaker from moving a lot at it's
resonance, to stop that horrible oomph sound that car audio wannabes
like so much, and to protect the amp.  

With an audio sweep generator and an oscilloscope you can actually watch
this happen, as well as being able to measure the actual impedance
profile of your speaker, which will help you design the box better, and
you can test the effectiveness of your box by comparing the impedance
profile of your speaker naked and in the box.

And if you want to get smoother base out of a sub, avoid tuned bandpass
boxes, they are extremely efficient at an extremely narrow band of
frequencies, often less than 10Hz wide, which really ruins good music of
any genre.

The easiest way to get good sounding loudspeakers involves large boxes,
which are often inconvenient at home, and impossible in a car, so you
have to compromise somewhere, but homemade bandpass enclosures are hard
to get right.  After all, Bose spends lots of money on engineers to make
their boxes, and Pros universally dislike the Bose lifestyle stuff
because it does nasty things to the sound.

OK, I'll get down from my soapbox now :-}

Tim