In article , ~misfit~
wrote:
Hi. I've been reading here a while but not posting so much. It's mostly
above me but I'm trying to learn....

I have a problem, forgive me if this is the wrong forum in which to ask
for help. However I feel that I'm quite a way away from being able to
sort it out myself (although I do have a budget LCR meter that just
arrived from Hong Kong).


I would very much like to put a simple low-pass filter on the woofer,
with the cut-off point the same (or as close as possible) as that of
the high-pass circuit on the tweeter. However, other than the woofer
being 3.6 Ohm and the tweeter being 8 Ohm (boxes rated at 4 Ohm) I know
nothing about them. They're small Philips units, quasi-ribbon tweeters,
well finished with a good rose-wood veneer and I bought them at auction.

Ideally, you'd equip yourself and be able to do some basic measurements.

But you could experiment 'by ear' if willing to spend some time doing so.
What I can't say is if this would be worth the effort instead of replacing
the speakers entirely. Experiments may not yield a satisfactory result if
the speaker units aren't good enough to be 'improved' by such tweaks. Or if
a simple crossover isn't up to the job. Lacking measurements or experience,
trying what you propose may involve a lot of trial and error without ending
up getting a good return!

Does you have a meter that gives a reliable AC voltage measurement that
doesn't vary much with frequency across the band from about 50Hz up to a
few kHz? If so, it could help you experiment. (I'm not sure if your "LCR
meter" also measures voltages.)

The problem with an LCR meter is that it may just do this at one frequency,
and not give a useful results for L/C/R for something that has complex
behaviour. Going that route you may really need to be able to check the
impedance at various frequencies.

Assuming you can measure AC voltages...

To test the meter, you could connect it as a voltmeter to measure the
output of your power amp and play some test tones from a CD, say, see if
the reading for the voltage stays steady as you change frequency. However
note that a cheap multimeter may only give sensible AC voltage readings for
50-60Hz.

By ear or by meter, the simple way to experiment is to try putting
something like an inductor in series with the woofer. Lacking measurements
you'd have to guess what may be the right value for inductance. Then listen
(and/or measure the effect on the ac voltage at the woofer) to decide what
effect it has had. Use that to decide if a bigger or smaller inductance
might be worth trying. Repeat until happy or exhausted. :-)

Lacking measurements you can 'guess' the speaker impedance is around 10
Ohms, then choose an inductor value on that basis. Chances are, the guess
will be wrong and the actual impedance is higher. However you can then
cheaply try connecting a resistor *across* the woofer terminals to pull
down the impedance at the roll-away point. Then experiment with resistors -
cheaper than trying different inductors. But avoid choosing a value that is
too low as the amp may not like the loading.

For real use you'd need an inductor that can handle high enough currents
and with a very low series resistance. But to save cost you could
experiment first with cheaper low-current inductors. Or even 'wind your
own'.

Beyond that, I suspect others can give you more detailed advice, and may
have experience of speaking building, etc.

Slainte,

Jim

--
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