I am trying to choose a 12-inch driver for a bass guitar speaker to be
used at roughly 100 Watts. I'm looking for some rule of thumb advice
about the Xmax needed to support this application. These speakers tend
to be in the 96 dB sensitivity range, with Xmax values ranging from
2.5 to 6 mm.

"Georg Grosz" wrote in message
om
I am trying to choose a 12-inch driver for a bass guitar speaker to be
used at roughly 100 Watts. I'm looking for some rule of thumb advice
about the Xmax needed to support this application. These speakers tend
to be in the 96 dB sensitivity range, with Xmax values ranging from
2.5 to 6 mm.

Here's a good article about the topic:

http://www.linkwitzlab.com/thor_splmax.htm

Rule of thumb is that all drivers with a given cone area will put out the
same SPL; given the same frequency, the same enclosure, and the same Xmax.

The first plot on the page shows max SPL versus frequency for a 12" driver
with 12.5mm Xmax which just happens to be a Peerless XLS 830500. If you
drop the SPL line by 6 dB (half the sound intensity), you'd approximate the
results for a driver with 6.25 (half 12.5 mm) mm Xmax. Drop by another 6
dB, and there's the calculated results for a driver with 3.12 mm Xmax.

This driver has about 90 dB/W sensitivity, so it would take only 1/4 the
power shown on the plot for your 96 dB/W driver.

These results are for a closed box. A vented box will have less Xmax around
the box resonance because the output from the port will become significant
and help quite a bit. At frequencies well above the port resonance, the
Xmax/SPL situation will be pretty much the same. At frequencies well below
the port resonance, the vented box is basically a disaster, as far as SPL
and XMax goes.

Hope this helps!

If you are trying to decide upon a speaker for bass guitar application,
leaving the techie stuff to one side for a minute, I can speak from my
personal experiences being a seasoned bass player.

I use 10" drivers and 15" drivers, 12" tend not to work too well with bass,
but are more suited to six string guitar.

I use Eminence Kappa drivers in my 4 x 10" cabinets, rated at 200w each
giving 800w continuous handling capacity and provide a good punchy bass
response.

Most applications that require a single driver would benefit from a 15" unit
thus providing a better low frequency response. Most 15" bass drivers have a
frequency response of about 35-2500 hz (the open 'E' string being 44hz).
Although depending on your style you may require a HF horn for the highs.

While cabinet design (mine are all ported) does play an important part, I
have found that listening to the sound quality is more beneficial...I have
tried drivers that have superb specs and sound terrible and vice versa.

Try and stick with Eminence bass or K/Board drivers or Celestion bass
drivers.

A rule of thumb....multiple driver cabinets = 10", single driver cabinets =
15" ....for bass guitar anyway.

AlunP

"Alun P" alun.priddle@NOSPAMblueyonderDOTcoDOTuk wrote in message . uk...
If you are trying to decide upon a speaker for bass guitar application,
leaving the techie stuff to one side for a minute, I can speak from my
personal experiences being a seasoned bass player.

I use 10" drivers and 15" drivers, 12" tend not to work too well with bass,
but are more suited to six string guitar.

I use Eminence Kappa drivers in my 4 x 10" cabinets, rated at 200w each
giving 800w continuous handling capacity and provide a good punchy bass
response.

Most applications that require a single driver would benefit from a 15" unit
thus providing a better low frequency response. Most 15" bass drivers have a
frequency response of about 35-2500 hz (the open 'E' string being 44hz).
Although depending on your style you may require a HF horn for the highs.

While cabinet design (mine are all ported) does play an important part, I
have found that listening to the sound quality is more beneficial...I have
tried drivers that have superb specs and sound terrible and vice versa.

Try and stick with Eminence bass or K/Board drivers or Celestion bass
drivers.

A rule of thumb....multiple driver cabinets = 10", single driver cabinets =
15" ....for bass guitar anyway.

AlunP

Thanks Arny and Alun for the tips. I agree with the rule of thumb. It
seems to come from the fact that a 12" is neither fish nor fowl -- too
small to put out enough SPL, too big for multiple drivers in a box.

The rather specialized exception to this rule is the one that I happen
to fit into. A lot of jazz bassists are happy with combo amps feeding
roughly 100 Watts into a single 12" driver in a small box. There are
some respectable amps in this category. I use a Gallien-Krueger
MB150-112 combo -- the whole thing is a cubic foot and 24 pounds. It
is widely accepted that this amp cannot keep up with a loud band, but
the portability is pretty compelling.

Meanwhile, I have figured out something interesting. The bass guitar
puts out a waveform that looks roughly like an equal mixture of the
fundamental and the first few harmonics. In other words, the amplitude
of the components in the excursion limited danger zone are much lower
than the total amplitude. This may explain why you can get away with
an Xmax value that would be insufficient for dealing with pure sine
waves.