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Old 27th March 2020, 01:11 AM   #21
Jack Hidley is offline Jack Hidley  United States
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Active subwoofer Q
Charlie,

Yes. Around 20 years ago, Bag End came by NHT to show off their stuff. We had a many hours long conversation about all of the issues with the design. There were definitely some disagreements about some of the effects, more specifically the magnitude of the effects. At that point I spent a few months doing analysis and testing of the design to figure out what the magnitude of the effects were.

Power compression is going to be a significant affect, but it is directly related to the bandwidth of the signal. When there is no low bass, the sub actually has less than typical power compression. When there is low bass, the sub has much more than typical power compression.

There definitely is a reduction in THD from the improved compliance linearity (spider + surround + air in box), however with any typical low cost motor the increased distortion from flux modulation is both higher and more audible.

As a prototype this led me to construct the DeafStar. Six 12" woofers in a 19" cube. Qtc was about 0.7. Fcb was around 80Hz. 2.83V sensitivity at 100Hz was around 105dB. With typical music (>40Hz), it was awesome. If you played a lot of stuff with low bass it was so much less impressive, that you were fairly disappointed. With one driver on each surface, it was nearly impossible to move!

When we did the Evolution subs, they all had aluminum cones to help with the power compression. With the Xd sub (XdW) it had two woofers with aluminum cones, shorting rings and a very saturated top plate to help get rid of as much of the flux modulation as possible.

Fro man overall performance standpoint, your best option is to use a box as large as possible and make sure that the suspension is as soft as possible to maximize the overall compliance linearity. Keep Mms as low as needed to hit the Fcb that you need.
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Old 27th March 2020, 11:12 PM   #22
hifijim is offline hifijim  United States
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When I started this thread, I had two objectives (1) start an interesting conversation, and (2) confirm my existing design before I actually started cutting plywood. My design is a 12 inch driver in a 75 liter box. I went with a very linear approach which will need minimal EQ.

Well the plywood has been cut and the cabinets are being glued, so that part of the problem has been made moot. However the discussion has been very interesting. Thanks !
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