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105 low frequency alignment

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Senior Contributor 200+

Joined: 29 Aug 2011
Posts: 215
Location: Finland

PostPosted: Fri Oct 21, 2011 8:47 am    Post subject: 105 low frequency alignment Reply with quote

I have read from Keftopics about 105 low frequency alignment. However I did not fully understand this topic, or topics did not explain all aspects of alignment.

As far as I understand, large 450-480uF serises capacitor is used to increase second order slope to third order and filter unvanted low frequency information. When LP was no 1 audio source, rumble was main reason for this.

Kef Topics explain that resonance peak is lower on impedance curve and this allows driver to draw more current from amp, this improves efficiency. The part I do not understand is, how this series capacitor improves efficiency close resonant frequency of woofer.

Also it is not clear to me what this does to electrical damping of woofer. I suppose source impedance will increase due capcitor. If more current is goinig to woofer, does load actually become lower... does this mean that inferior damping is result for higher efficiency.

No free lunch here either?

It would be interesting to know if anybody have any ideas about this topic.

Best Regards
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VIP Contributor 750+

Joined: 18 Nov 2005
Posts: 997
Location: Green Hut, Tovil

PostPosted: Sat Oct 22, 2011 11:24 am    Post subject: Reply with quote

I'm sure I've explained this type of third order alignment somewhere on this forum before. I'm sorry but I don't have time to find it atm. You'll have to search for yourself (now you know it's there).

The method came about as a result of the work on acoustic Butterworth for tweeters. It became clear that a simple series capacitor could extend the bass if the driver and box parameters were configured to suit. It works for the same reason that using a large series inductor, to have a low LF xo frequency cut off, does not work. You need to look at the equivalent circuits and see what happens. A simulator which will plot curves would be ideal.
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