Stereo questions

[Ti Kan]

Ameer Antar writes:
> I'm not sure what you mean by 'control the woofer'? I'm guessing this means that
> the cone movement (and thus sound) is accurate to the original signal... The thing
> is, even if the speaker is rated at 1000W, a good quality low power amp will
> always sound smooth and controlled.
> ...

It's a complicated subject and a bit off topic, but I'll explain a little.

"All else being equal", a larger woofer is going to have a lower free-air
resonant frequency (Fs).  The bass response of the system is going to be
directly proportional to Fs (amongst other things, see below).  Using
multiple smaller woofers will not lower the Fs since it's an intrinsic part
of the woofer characteristic (and varies from brand to brand and model to
model).  You can modify the woofer by coating the cone or somesuch to
increase its mass, thereby decreasing the Fs, but you give away the better
transient response of the smaller woofer.  Another way to decrease Fs is
to make the woofer's suspension more compliant, but that's not something
that could be easily modified after manufacture.

Woofer system design is always a three-way tradeoff between bass response,
efficiency, and volume (as in size of the system, including enclosure).
Some of the "trading off" is already done by the woofer manufacturer, the
rest is in the enclosure system design.

You can find 8" woofers that have Fs nearly as low as that of a 12",
and hence the potential for excellent bass, but one or both of the other
two factors are traded off to achieve it, most likely the efficiency.
Hence the requirement for higher powered amplifiers.

In reality, things get more complex because "all else is not equal".
The woofer's magnetic system and the suspension design also determine the
woofer's damping characteristics (Qts) and "Acoustic compliance" (Vas),
which in turn also influence the efficiency, bass response, and required
enclosure volume.

To achieve optimum bass performance *for a given woofer*, the volume of
the enclosure behind it must be calculated and matched.  It also depends
on what type of enclosure you want to use (sealed vs. bass reflex, etc) and
how much frequency response deviation from flat you're willing to tolerate.

A car is a very complex place to make subwoofers work optimally, especially
if it's not going to be mounted in a box (then you effectively have the
trunk as "the enclosure", with lots of little air leaks).  A woofer can be
designed to work reasonably well in such an environment (typically with a
high Qts), but that woofer will be terrible in a smallish box.

Slapping a brand X and model Y woofer into a car is an exercise in
hit and miss...  sometimes it works well, other times not.  That same
woofer that worked well in your car might not be so good in a different
car.

P.S.
This discussion could become ultra technical and go on a tangent real
quick.  It's probably better suited to a different forum! :-)

-Ti
2003 A4 1.8T multitronic (soon)
2001 S4 2.7T
1984 5000S turbo
1980 4000 2.0
--
    ///  Ti Kan                Vorsprung durch Technik
   ///   AMB Laboratories, Sunnyvale, CA. USA
  ///    ti at amb.org
 //////  http://www.amb.org/ti/
///