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Audio Tweaks - Tweak Ref. 387

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Zobel network calculator
Reference # Submitted by Submitter rating Cost
387 Morgan The Best $0.00
Source Brand
Micheal Percy Audio has nice catalog for parts n/a
All a Zobel is, is one capacitor and one resistor in series that is placed across the speaker terminals (i.e. in parallel) or anywhere after the crossover. The x-overs in premium (read... absurdly expensive) speakers typically use zobels to reduce impedence changes at different frequencies... the practical result is that the speaker looks a lot more consistent to the amplifier and sounds more uniform at all frequencies. You can experiment by using the zobel calculator referenced here and put some gator clips on it so you can switch it in and out without soldering until you get the values you want. My experience is that it makes the relation of the mid bass to the deep bass more uniform and bass in general more toneful and less thuddish or one-note burp sounding.
Here is an excellent link to a free speaker design website.. use this calculator to get your starting point values..the call this the Impedence Equalization Circuit which you will find when you scroll down:
You will need to know two values, one is the driver's "nominal impedence", i.e. 8 ohms or whatever, and its' inductance. Often the manufacturer will supply this in their data sheet... the driver manufacturer that is.. or you can buy a good quality multi function meter that allows impedence readings as well as inductance and get your info right there.
There are many variables, the quality of the drivers, complex resonances caused by ports, etc, but with this simple circuit you can make a decent speaker behave like a really good one with little expense
Be patient and willing to move values around to get it the way you like it... you can do a ton of other calcs from this website too...

Cost: varies greatly depending on parts selected
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Morgan for the Zobel values you should use the "voice coil resistance", not the nominal impedence, as I misstated above. For example, the SEAS W26, an awesome 10" metal woofer, has a nominal impedence of 8 ohms but a true voice coil resistance of 6.3 ohms. The 6.3 ohms only hold true for the middle of its working range. From 100 hz down to 20 hz the impedence quickly rises to about 40 ohms, causing it so sound thin unless you have a very powerful amp. The Zobel will tame this impedence rise and also the rise into higher frequencies so the crossover region will be more consistent. The Zobel may allow you to work with simpler crossover designs. The nice thing is that you don't have to desolder you driver wiring to test this, as it is in parallel with the driver. Put it together on a piece of mdf board (hot glue is excellent for fastening the caps to the mdf) and gator clip it to your driver terminals with everything as it was, put the driver back in, tighten it up, and listen for a while. Dick Olsher suggests 10w rated resistors for normal listening levels.

try this link for a good illustration:


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