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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Zobel's attenuation on driver posted by hZ on May 3, 1999 at 01:25:08:
The inductance of a tweter, as small as it is, will resonate to some extent with the series cap of even a first order crossover network. All higher order networks will also be prone to this problem. A 1" soft dome tweeter with an inductance of 75 uH will resonate to the tune of 1 to 1 1/2 dB without a Zobel, higher inductances to a greater degree, lower to a lesser degree.Technically, according to the textbooks, a Zobel will not cause a loss of HF due to it's presence, say, in a direct amp connection. However, if a tweeter were to have a relatively high inductance, then a suitable Zobel to make the Z flat at HF would exhibit a shelving response where it's impedance became significantly lower than that of the tweeter within the audio band.
This would not be likely to be an issue with most tweeters, but could become an issue for midranges. The inductance of many midranges is high enough to become a significant factor in the HF response. A Zobel for some nidranges WILL cut into the HF via the shelving action, but only for those with a relatively high inductance. You would be surprised at how many drivers have an electrical roll off due to the inductance and total series resistance, that actually rolls off a mechanical resonance in the top end of the driver, just like a moving magnet phono cartridge.
If you calculate the effective electrical -3 dB point, and examine the drivers FR curve, if the - 3 dB point does not correspond to the -3 dB point on the acoustic curve (it is higher in frequency), then the driver has a mechanical resonace aiding the top end. This is like a built in crossover EQ that is permanantly built-into the driver. If this -3 dB electrical roll off occurs low enough, adding a Zobel to flatten the Z curve will cause a shelved response above the inflection point.
You could try using an overdamped Zobel on the woofer to tame the slight rise, but an overdamped Zobel is much more succesful with a single HF peak or a mild peak at the top range of a driver, rather than a gentle slope. You could make the inductor bigger, and instead of a hard cap shunt, place a 1 to 3 ohm resistor in line, a highly overdamped Zobel instead of the cap, as opposed to in addition to a shunt cap. This will often tame a rising response as you describe.
Jon Risch
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Follow Ups
- Re: Zobel's attenuation on driver - Jon Risch 18:17:17 05/04/99 (0)
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