Semi-Le_Calc: Calculator for Advanced Inductance Model Incorporating Semi-Inductance
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bolserst
diyAudio Member

Join Date: Jun 2005
Location: Fort Worth, Texas
Thanks for clarification on your current testing methods. Yeah, it looks like relying on tackiness of tape to attach that much weight to a cone is resulting in some decoupling and the multi-resonance points you are experiencing. You might try using less weight instead of more. Alternatively, using magnets like mwmkravchenko mentioned works great on most cones, although you have to be careful with aluminum cones to avoid dents when the magnets suddenly click towards each other from opposite sides of the cone.

Likewise, for improved accuracy of Qms and FDD values, you would need to restrain the woofer during the measurement. Ideally it would be mounted with the cone oriented vertically and the magnet system held in a vise or clamp of some kind to a frame or bench of substantial mass. For DIY, you can get pretty close by firmly holding the woofer down by the frame. Attached is an example of what to expect. The more firmly you hold the woofer, the lower the losses imparted to the entire resonance system(woofer + restraint) and the higher the magnitude of the impedance peak. Note that Qms is the only TSP that is significantly changed. Ideally the restraint system would be infinitely stiff, so the only losses you would be measuring would be due to the woofer suspension. This is what Qms is supposed to be…a measure of the woofer suspension losses. The FDD model takes this one step further by modeling the frequency dependence of these losses. But, it requires good quality data taken with firmly restrained woofer and firmly attached added mass.

As mentioned back in Post #30, the FDD parameters are not required for accurate frequency response modeling like the Semi-Le parameters are. The FDD will, however, significantly improve the predictions of the magnitude of the different impedance peaks in a woofer + enclosure system.
Attached Images
 Woofer_Clamp.png (316.4 KB, 33 views) Zwoofer_hold_nohold.png (360.0 KB, 35 views)

Last edited by bolserst; 16th December 2019 at 05:11 AM.

mwmkravchenko
Mark Kravchenko
diyAudio Member

Join Date: Jan 2002
Quote:
 Originally Posted by bolserst Alternatively, using magnets like mwmkravchenko mentioned works great on most cones, although you have to be careful with aluminum cones to avoid dents when the magnets suddenly click towards each other from opposite sides of the cone.

I learned that the hard way. Some metal cone drivers have very thin cones. I use ferrite magnets. I never found that a very thin metal cone sounded great. And in personal design work I generally spec metal cones that are thick enough to be tough to dent. This has an added benefit of cleaning up the midrange significantly.
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Mark
www.kravchenko-audio.com

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