Modifying a driver for lower Fs

[DeonC]

Hi guys

This is a question for the speaker gurus on the forum. I want to modify a driver so that the Fs is reduced, but without radically altering it's sensitivity. It would be nice if the Qts goes up a bit as well. I want to use the driver in question on an open baffle, so VAS is not a factor at all. The driver specs is as follows:

Resonant Frequency (fs) 40Hz
Electromagnetic Q (Qes) 0.54
Mechanical Q (Qms) 6.56
Total Q (Qts) 0.49
Compliance Equivalent Volume (Vas) 293 liters

Ideally I would like the Fs to go as low as 20Hz, but 25Hz will also be acceptable (but that is the upper limit). Qts must ideally be about 0.7, but as low as 0.6 or as high as 0.9 is still usable. I do have a professional speaker repairer\rebuilder that can help me with these mods, but I need to know what to do. Any ideas?

Thanks,
Deon

[454Casull]

Slice up the spider. :P

[DeonC]

I was wondering if loosening the suspension might do the trick. But how will that affect the rest of the parameters?

[Ron E]

Modifying the suspension would reduce Fs, but it would also reduce Qes, Qms and Qts.

Try a "Linkwitz transform" (pole-shifting circuit) if you want to use the driver you have. You can modify cutoff and Q independent of midband sensitivity.....

Reducing Fs to 20Hz seems like it would not be especially useful in an open baffle speaker because it would be deep in the rolloff region anyway.

[DeonC]

Thanks Ron. I was starting to think that all I will be able to do is a Linkwitz transform below the cut-off of the other driver. The only disadvantage is that I was hoping to get away with a simple passive XO, but then again life is seldom as simple as we want it to be. Thanks for the help.

Deon