Not IME with any of the original 416 series, though in retrospect wouldn't necessarily include GPA or others re-cones. Ditto GPA's 416-8C, which I've no experience with, though based on published specs it might need to be gapped a little from the baffle [mostly sealed] if driven with a matching impedance, but does anybody do this in a high SQ app these days?
For a truly aperiodic alignment, all would require huge cabs to hold enough stuffing.
GM
For a truly aperiodic alignment, all would require huge cabs to hold enough stuffing.
GM
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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.)
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According to the dictionary, it means ‘without period’. I take this to mean it must completely flatten the driver’s impedance at Fs as practical, not just squash part of it at Fb and the only way I know how to do it other than electrically is to do it acoustically with a compression horn or mechanically via a stuffed TL, so size and tuning does matter in this case.
GM
GM
Should include our own Dave Dlugos of Planet 10, who has also managed it with an unstuffed rectangular cross section slant load transmission line, with drivers mounted mag to mag. Impedance begins to rise below 20 Hz, using two SDX7 6.5" woofers with Dan Wiggens XBL long throw technology. Astoundingly clear, tons of texture for higher frequencies to attach to and significant output at 30 Hz and below. Easily matches my EnABL'd Lowther PM6A drivers.
Bud
Bud
I've not seen this accomplished. Sometimes close, but often not much better than a well done sealed design with some lossy venting. (..though poor examples of the later abound as well.)
The most flat impedance mechanically derived example I've seen was Gary Pimm's designs that truly were tuned resistive partitions. Technically though it was a cardioid and dipole (at much lower freq.s). Interestingly however, they weren't that big.
I think a big problem here will be changing driver conditions that will never really allow for a truly resistive impedance. The suspension changes over time. It also changes under different pressure conditions caused by increased excursion and compression. Finally, depending on the input and the motor's ability to remove heat - driver parameters can also change. (..practically speaking a compression driver can overcome these hurdles though.)
It will be interesting to see what Lynn comes up with, but in this case I'd expect just some modest flattening of impedance (..if resistive venting is used at all).
..Oooh, link please!
I think this is sort of "claimed" for the Tango RSI speakers as well, but I'd strongly bet that it's a series LCR:
6moons audio reviews: Acoustic System Int. Tango
I am a little lost with the Planet 10 organization schemes, but, here is one link
Transmission Line Speakers
and here is a link to Planet 10
planet_10 hifi
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. I do know he has gone well beyond what I have.
Bud
Transmission Line Speakers
and here is a link to Planet 10
planet_10 hifi
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. I do know he has gone well beyond what I have.
Bud
Feel free to distribute. The drawing does not entail the final details of pushing the box heavily towads aperiodic.
dave
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.
Best Regards,
TerryO
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.
Best Regards,
TerryO
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.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.)
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.
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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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.
dave
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.
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.
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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?
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?
Do you remember when that was?