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Old 20th October 2012, 01:49 AM   #8251
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Quote:
Originally Posted by BudP View Post
If you PM me with an email Dave may allow me to send you a copy of the construction diagram that the prototypes I have were built to.
Feel free to distribute. The drawing does not entail the final details of pushing the box heavily towads aperiodic.

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Old 20th October 2012, 02:12 AM   #8252
TerryO is offline TerryO  United States
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I've listened to Bud's system many times, as well as the Planet10 assortment...or at least several dozens of them. Excellent designs all.

I certainly do like Bud's setup, as it does everything extreamly well, without having hype'd anything to catch your attention. An excellent, yet honest musical presentation.

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Old 20th October 2012, 03:45 AM   #8253
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Originally Posted by ScottG View Post
I've never heard of a truly aperiodic alignment before.
I tend to think of aperiodic as some measure of flow resistance or targeted compliance damping. It doesn't really matter what the size of the box is (or the resulting response), rather it "focuses" on flattening impedance around Fb - whatever Fb happens to be. (i.e. some measure of a mechanical version of a series LCR at Fb.)
I must mention an experience I had around 1975, even though I can not provide much technical support for it. I have tried, but cannot find any reference to this.
There was an article in Hi-Fi News, I think, (or Gramophone?) around 1974 mentioning a bass enclosure configuration dubbed by the designer "acoustic feedback". The claim was that two bass drivers mounted back to back in a box would control each other at the point of fundamental resonance such that the result was utterly non-resonant (or a-periodic, I guess). It ran counter to intuition on a couple of scores, but the claim was intriguing enough for me to try to build one as a sub in a 3 piece sub-satellite system I was building at the time, where the sub was mono. What really got me interested was the claim by the designer that the measured impedance of the system right through what normally would be the resonant frequency of the system was essentially flat, 1 ohm or so.

I built a box and duly mounted a pair of cheap CTS 12" foam surround woofers with Fs's of around 20Hz and tried it. The box was too small to allow deep extension, but what I heard was the cleanest, most non-resonant bass I think I had heard to that point and, possibly, since. The design's counter-intuitive aspect was that the drivers' placement in the box was symmetrical. I think there was a presumption that the drivers' resonant frequencies was the same, since the tendency for one driver to resonate controlled the same in the other.

I know - it smacks of perpetual motion and such, and I didn't have the equipment to run a sweep through it, but I can say that it did sound exactly the way you would expect a bass system to sound with resonances miraculously and completely removed, and it was a revelation and a treat.
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Old 20th October 2012, 03:57 AM   #8254
nuconz is offline nuconz  United States
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don't recall the name of the company but i remember a "motional feedback" system that had some type of connectivity to the back of the amp/receiver. saw one of these in a hi-fi shop in "gatorville". might have only been a servo controlled system.
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Old 20th October 2012, 04:16 AM   #8255
BudP is offline BudP  United States
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I know - it smacks of perpetual motion and such, and I didn't have the equipment to run a sweep through it, but I can say that it did sound exactly the way you would expect a bass system to sound with resonances miraculously and completely removed, and it was a revelation and a treat.
Yup, exactly that sits in my living room. And since Dave said I could show, while he does the tell part, I have attached the one document I have.

Bud
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File Type: pdf FonkenWoofTL-0v8-map-120508.pdf (52.0 KB, 305 views)
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Old 20th October 2012, 04:36 AM   #8256
ScottG is offline ScottG  United States
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Originally Posted by Russell Dawkins View Post

I built a box and duly mounted a pair of cheap CTS 12" foam surround woofers with Fs's of around 20Hz and tried it. The box was too small to allow deep extension, but what I heard was the cleanest, most non-resonant bass I think I had heard to that point and, possibly, since.


That's a system running purely off of compliance (below Fb ..and perhaps well below it). Plus it should be well below any standing waves in the enclosure.

Nonlinear distortion however will be horrendous - depending on the bandwidth used/playback material and if "E.Q.ed" to a reasonably flat in room response.

2 drivers back to back and in phase are a bipole. What's particularly pertinent is that Vas is now double that of 1 driver - effectively cutting your enclosure volume in half.


Bag End does all their subs as "compliance" based systems. (..don't know if they do bipoles or not.)
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Old 20th October 2012, 08:15 AM   #8257
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Originally Posted by BudP View Post
unstuffed rectangular cross section slant load transmission line
It does not have much stuffing near the driver where you can see inside (except for Ultratouch felt lining), it would be better to say that they are carefully stuffed with at least 3 different materials.

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Old 20th October 2012, 10:35 AM   #8258
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The Great Plains Audio 416B-16 (Alnico magnet, 16 ohms) appears to have more magnet than the traditional Altec 416. I wasn't getting very good data from the measurements (flaky software), but the Qts seemed to be 0.19 or so, and other methods for estimating efficiency indicated something around 99 dB/meter, not the 97 dB/meter that Altec used to quote in their literature.

I also want to thank Planet10 for giving me some good starting points for the resistive-vent enclosure. I have no interest in "aperiodic" enclosures per se, since it is probably an unattainable goal. A deliberately lossy vented box, though, is another thing.

The problem with a standard Theile/Small vented box is the box-loss term, denoted as Ql. This loss term unfortunately introduces a zero in the response around 1 Hz - morever, it is impossible to get Ql much beyond 8~12 in practical enclosures, so the very low-frequency zero is always there, randomly chuffing the voice coil in and out of the gap, which in turn varies the IM distortion of the driver. Some of the perception of blur of vented systems is actually the result of this low-frequency zero.

If you're willing to discard some bass extension, the bass can be re-aligned so the system transfer function is midway between a closed-box and a vented-box. The vent, rather than being as close as possible to a true inductance, has an intentional loss term introduced, and becomes more resistive.

Instead of being an unwanted and uncontrollable loss term, it becomes part of the LF alignment. There's also a desirable side effect of the system becoming less sensitive to dynamic variations of Qts. Using a very wide or tall vent, with felt lining, introduces resistive loss, as well as damping organ-pipe modes. Rather than "aperiodic", it is simply an enclosure that is transitional between vented and closed-box, with the vent primarily resistive rather than inductive. What I like is the woofer is no longer so critically dependent on amplifier damping, a good thing if the speaker is going to be powered with zero-feedback triode amplifiers.

As for 2012 RMAF news, Radian will be announcing some interesting compression drivers before the end of the year. Can't say more than that.

Last edited by Lynn Olson; 20th October 2012 at 11:00 AM.
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Old 20th October 2012, 01:00 PM   #8259
ultrafi is offline ultrafi  United States
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Hey Lynn, nice to finally meet you at RMAF. I think Altec sensitivity was measured at 4 feet, not one meter. Dunno, if you took that into account or not.
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Old 20th October 2012, 05:47 PM   #8260
Pano is offline Pano  United States
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Altec did measure at 4 feet - that is correct.
FWIW, I have not yet measured a vintage or remagged 416-A that was anywhere near 0.21 Qe. Double that, mostly. Wonder what the difference is?

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Originally Posted by nuconz View Post
saw one of these in a hi-fi shop in "gatorville". might have only been a servo controlled system.
Do you remember when that was?
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