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|13th August 2007, 03:58 PM||#1|
Join Date: May 2003
Dipole Sub EQ question
I'm in the process of building a dipole sub, similar to the W-frame design shown on the Linkwitz website. At this point, it's still a paper design. However, I'm considering a Peerless 830845 rather than the 830500, but I cannot find much on the 830845 used in a dipole application. Theses drivers appear to be very similar, except that Qts is 0.45 and 0.2, respectively.
I think I understand the ideas behind the equalization of a driver used in this application, but not completely. The two basic mechanisms are the dipole slope equalization and a Linkwitz transform.
Both Linkwitz and Kreskovsky indicate that if Qts < 0.5, there are 3 poles, all of which are "real". For the case of Qts > 0.5, the poles are complex, and an additional pole appears. However, both seem to only deal with the case where Qts < 0.4, such that the first pole is one octave or more below Fs. Then, both authors describe an example using a driver with parameters similar to the Peerless 830500.
So, the basic question is how do I equalize the response when the poles are relatively close to Fs?
In the case of the 830845, I believe the poles will appear as follows:
Fp1 = 15 Hz (this doesn't meet the condition described by Kreskovsky)
Fs = 23 Hz
Fp2 = 37 Hz
My concern is that the first pole at 15 Hz cannot be treated as Linkwitz or Kreskovsky suggest.
Another question in this is how far will Fs and Qts move once the driver is installed in a W-frame cabinet?
How close does Qts need to be to 0.5 before I can stop worrying about the Linkwitz transform?
And finally, assuming that Qts is close to, but less than 0.5, can a series resistance be added to bring the drivers up to 0.5 as suggested in this post [http://www.diyaudio.com/forums/showt...346#post861346]? When would this be a bad idea?
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