Woofer "Speed," high Xmax vs. low Xmax in Uframe and Sealed Enclosures - diyAudio
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Old 21st February 2011, 07:06 PM   #1
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Talking Woofer "Speed," high Xmax vs. low Xmax in Uframe and Sealed Enclosures

First of all I'd like to introduce myself to the board. I'm a long time lurker, and have enjoyed the wealth of information and discussions on the board. I'm a pro audio guy by trade, and a long time audiophile. There is sometimes some cross pollination between my work and hobby observations....

One of them is this whole notion of woofer "speed." Some will dismiss this term, but most I would say have experienced the phenomenon in one way or another. To my ear there is a huge difference in the perceived speed of lighter, low Xmax, pro audio woofers as opposed to the newish generation of high Xmax "subwoofer" drivers.

I've been running Magnepan 1.6's with Bag End ELF Subs for some time at home and have been quite happy with the setup. The Bag Ends use lightweight cone pro audio drivers, and walk all over the "slow and sloppy" sounding Dayton Titanic 15" Sub Kit(3cu ft sealed)I was using in terms of sound quality, if not output. The Bag Ends are a great compliment to the Maggies, but I've been curious about dipole/cardiod subs.

After perusing the board for some time, I decided to give it a go. I took a jigsaw out, and literally cut the back of the Titanic enclosure out. Now I have a U-frame.

Anyway, after some Spectrafoo analysis, and DSP tweaking, there is no doubt that I have better transient response, pitch definition, etc, than the Titanic in the sealed box--BUT--it still has a subtle quality of being "behind" the Maggies. The Bag Ends do not.

The cardioid pattern effect is interesting, as is the trembling of the room with the pulses of the U-Frame as opposed to the more punchy sound of the Bag End.

My next step is to try an Eminence Sigma 18 or similar in a U-Frame and compare the results. Does anyone have any thoughts on this? Mine are that it is a simple issue of trying to accelerate a heavy diaphragm too far....One that may be difficult to measure but not so difficult to hear.

Kind Regards,
Brett
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Old 21st February 2011, 10:32 PM   #2
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My background is similar to yours, i've been running concert rigs for the last 20 years so I know what you're talking about. The titanic series are, as you have noticed, mud motors (Qts: .49). Great for home theater "BOOM-n-rumble" not so good for music. Compared to the Selenium 15SWS800 15" (Qts: 0.37) the motor power to cone weight ratio is poor.
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Old 22nd February 2011, 04:02 AM   #3
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Yes I'm curious as to why people don't spend more time talking about this. The difference is quite startling. I'm a theatre guy so I'm looking for low frequency extension and absolute fidelity. Cost isn't really an object but size is often an issue. I've been thinking about ordering some of the Exodus Maelstroms, but am concerned with this being a problem with them. I've used the old Adire Maelstrom for years for LF effects w/Linkwitz Transform in sealed boxes with great success....But they were only 13mm Xmax, and still arguably not as tight or "quick" as the Bag Ends(which might have to do with them being a below resonance system unlike the LT). These other drivers are double that 13mm. Thats a loooong way. I've always wondered why Bag End used what are essentially Eminence Sigma's in their boxes, as they are ridiculously displacement limited...Maybe this is why. I'm thinking about setting up a U-Baffle or Flat Baffle test with the Titanic, Exodus, AE Dipole or IB series, in kind of a shootout, to get to the bottom of this. I was hoping to do the job with a couple of Exodus 18's or 21's per side. Maybe the answer is 6-Sigma's in some sort of space-saving sealed enclosure or some stacked W-bin ala Linkwitz.
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Old 22nd February 2011, 04:44 AM   #4
cbdb is offline cbdb  Canada
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You need to figure out how woofer speed and freq are related. The woofer only has to be fast enough to produce its highest freq.
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Old 22nd February 2011, 04:48 AM   #5
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In this case, for the purpose of discussion, lets say 90 Hz, as that is the LP frequency of the Bag End ELF integrator, which I'm using as a benchmark.
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Old 22nd February 2011, 04:50 AM   #6
cbdb is offline cbdb  Canada
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From this I guess you can say that you can determine a woofers "speed" by its high freq cutoff. (the woofer mass is just one of the variables )
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Old 22nd February 2011, 06:06 AM   #7
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Quote:
Originally Posted by cbdb View Post
(the woofer mass is just one of the variables )
Dan Wiggins did a study on woofer speed that to my eyes had no faults that I could see. Not that great sample size. Mass had nothing to do with "woofer speed" if I recall correctly.

Here is a link to an earlier thread on the subject with a link to Wiggin's paper as well:
Woofer speed/Inductance
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Old 22nd February 2011, 06:08 AM   #8
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Part of the problem is with the processing circuit. Graham Maynard has explored this area and came up with a discrete subwoofer circuitry which he claims is perceived to be faster sounding than conventional approaches. His circuit also operates the cone below Fs.
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Old 22nd February 2011, 06:54 AM   #9
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Before we get into the old debate about "woofer speed", it might be worth waiting for FR curves for the boxes under test. I strongly suspect the "faster" woofer will have much less response below 80-100Hz, and that leads to the perceptual difference.
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Old 22nd February 2011, 01:03 PM   #10
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Originally Posted by pinkmouse View Post
Before we get into the old debate about "woofer speed", it might be worth waiting for FR curves for the boxes under test. I strongly suspect the "faster" woofer will have much less response below 80-100Hz, and that leads to the perceptual difference.
My benchmark, the Bag End ELF System, is almost ruler flat from 8-90 Hz. It is the tightest, deepest, most articulate woofer system I have ever heard, and I have used them in bedrooms and 2000 seat theatres to the same effect.

Its perplexing--I'm not one to jump on ideas that are the not scientifically sound. I've just empirically seen this phenomenon too many times to dismiss it....Thanks for these other thread links, I'll have to check them out and see if there is anything that jumps out.
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