Modern midranges do NOT Resonate.
They just don't; not substantially. Any well-made, foam-roll midrange
should not have a problem with resonance. And I suspect the same for
most tweeters.
Audio companies are hiding the Zobel, which must be used with drivers
for them to operate properly. If you don't have the Zobel then,
hearing their bad sound, maybe you'll invest more money in those
lieing, cheating audio companies instead. Maybe get an equalizer, or
new speakers (still without the Zobel), and still have a flawed sound.
One of the things they use to hide the Zobel is the notion of
resonance, which does exist. It may have been a problem with stiff
paper surround (cheap) drivers, but is not anymore. Yet they still
mention it. Even if it were needed, the RLC circuit they recommend is
over-designed and over-complex for what the speakers need for a
corrected sound. Just keep the impedance at a low value outside the
range of the driver.
If we have to be concerned about both inductance (Zobel) and
resonance, then being frustrated we may ignore the whole mess, and
not install the Zobel. And buy more speakers or equalizers to correct
a problem that the Zobel would solve easily.
Please install the Zobel on your woofers and midranges, and don't
worry about midrange resonance, (which I worked on in the thread
above). Tweeters are built different, but I strongly suspect
manufacturers have likewise tamed its resonance substantially.
It would not hurt to install a Zobel on your tweeters (though it may
require rebalancing for volume), but I've noticed no real improvement
in sound with the Zobel on a tweeter. Your ears may be new and
improved over my 50-yr old version.
My midranges use a soft butyl surround, (the soft thing at the edge
which allows the cone to move). This was advertised as a method to
dampen resonance, so I was not surprised that they do no resonate but
just a little, ignorable amount.
But I tested an old computer speaker built by Samsung found on a
Windows 95 system, not especially hi-fi. It is 3" and has a foam roll
surround; not the softer butyl. Also, its spider was relatively large
for the cone size. Its resonance was minimal and still ignorable;
just a little more than my Speakerlab midranges.
However...
The Zobel circuit is necessary. The coil-driven speaker cannot be
balanced properly without it. It is not expensive. It is not so
difficult for the rest of us to install. You will hear the results
immediately. And it is forgiving of variations in component values.
The Zobel: •-----/\/\/\-----| |------•
Rz Cz
It is connected in parallel with its driver. It causes the crossover
to see a constant 8-ohm (or 4) impedance as advertised.
Expected Woofer Response Actual Response without Zobel
_____ ____
\ ----___
\
Expected Midrance Response Actual Response without Zobel
___ __
/ \ / ----___
/ \ /
The Zobel is sized according to coil specs. But it is flexible.
Lacking information about the driver (the inductance) should not
prevent you from installing something. I would suggest...
Rz = 8 ohms (or 4 for 4 ohm speakers.) Rated 10 watts.
Cz = 30 uf, for the woofer. (Try 20 uf for a 2-way.)
Cz = 10 uf for the midrange.
For 4-ohm systems, the capacitor values may be reduced for the smaller
coils. My speakers are all 8-ohm, so I have no experience with 4-ohm,
but the electronics is the same. You can reduce capacitors to half
the suggested values and see how that works.
All parts are available at Radio Shack. Bipolar caps work fine. Do
not use polarized capacitors. Putting two 8-ohm resistors in parallel
will give a 4-ohm resistance, reducing it. However, putting three
10-uf capacitors in parallel will give a 30 uf capacitance, increasing
it.
So, for a 2-way that is rated at 4-ohm, the resistor would be 4 ohm
(or two 8-ohms in parallel), and the capacitor would be a 10 uf (or
two 4.7 uf in parallel).
You can experiment with values, (though that may be a waste of time),
and with rebalancing the speakers afterward. The driver above that
one which has the new Zobel may need a boost; a reduction in
attenuation -- maybe.
--
Michael
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