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Old 31st January 2007, 10:42 PM   #11
GM is offline GM  United States
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Default Re: Hello Indm....

Quote:
Originally posted by Fish Chris
I have heard that horizontal pipes are not recommended, AND that they are perfectly okay....

I have heard that the pipe diameter should be no less than the driver diameter or slightly more (like 100% to 110%) AND that a 10" diameter is just about right for most 15" drivers.....

I have heard of successful TL pipes as short as 6ft, and as long as 12ft (14ft if you include the small attached enclosure at one end).

Here on this forum, GM supplied me with a chart which takes driver specs into account. It shows that a 9.7" diameter pipe, by 168" (14ft) would work optimumly with a 15" Dayton Titanic......

GM also supplied me with a calculator for a "quarter wave" pipe, which is only about 6ft in length. I believe the 168" pipe is for a half wave design.... more efficient ?
Greets!

ROTFLMAO! So that's why the B#$% Wave Cannon doesn't perform up to par!

As I noted in the other thread and MJK has devoted considerable effort in proving, the pipe's CSA is a function of all the driver's specs, though Vas dominates. That said, if you're wanting a high acoustic power rating (better damping) over efficiency to limit the effects of VC heating, then as is stated in the B@#$ WC patent, a 2:1 CR is a good compromise, so if the 15" driver's effective diameter is 12.75", then the pipe's should be 12.75*0.707 = ~9". For HIFI/HT apps though, we typically want as much efficiency as we can afford in size, so this R-O-T can be ignored.

To get a short TL to go low requires it be reverse tapered with the driver at the extreme top. The price you pay for 'short' is a very large top area since it all comes down to a minimum net Vb is required for a given driver to reach a given Fp. There's no free 'lunch' here, it's a 'robbing Peter to pay Paul' situation.

Right, the Alpha TL is a very basic end loaded 1/4 WL pipe designed to mimic the response of an IB while completely damping the driver's impedance, which is what you asked for AFAIK. Using MJK's Classic TL alignment tables and his WS to sim different alignments will net you more performance overall.

I did?! Please show me. Regardless, a closed one end (or driver), open other end is a 1/4 WL resonator, ergo the 168" pipe is a 1/4 WL pipe. A 1/2 WL resonator would be closed at both ends and have to be ~twice as long to have the same Fp as the 1/4 WL pipe. This alignment can never have more gain than the driver's IB response, but will have the lowest distortion of any alignment other than a 'perfect' horn AFAIK.

GM
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Old 1st February 2007, 01:22 AM   #12
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Default Thank you GM....

Okay, so a quarter-wave pipe it will be. Learn something every day :-)

Yes, the Omega quarter wave-length pipe you sent me the calculator for, shows a 71" to 76" inch pipe, depending on whether one uses polyfil or fiberglass stuffing.

Anyway, you said > ....then the pipe's should be 12.75*0.707 = ~9". <

....but again, I can only get sonotube in 8", 10", 12" etc. But now, before you figure out the correction for this, what would be a good length and diameter for "two" of my 15"s, in this kind of setup > http://www.teresaudio.com/haven/subs/place.jpg
Again, I think this is a pretty cool looking design.... plus, the guy says that the push-pull configuration of the drivers made a surprising improvment in overall sound clarity !
(note; there are two drivers in this box, with the driver you can't see, having the voice coil inside of the box.... and one of the drivers being hooked up out of phase)

I'll get this all figured out sooner or later :-)

Thanks again,
Fish
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Old 1st February 2007, 04:35 AM   #13
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[QUOTE]the guy says that the push-pull configuration of the drivers made a surprising improvment in overall sound clarity !

Interesting question, If Vas is infact as important as GM says, should the pipe be 1/2 the diameter? Afterall you cannot reduce the length.

I am also curious about the idea of clamshelling the drivers for push pull, I am under the impression that minimal volume between the cones is the ideal way of doing it. Any thoughts
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Old 1st February 2007, 06:02 AM   #14
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If you put most of the pipe, including the end with the driver, into another room your output will be the dotted blue line below. This is taken from bjornos' sims.

As you can see, the shape of that output will be nice, but the sensitivity will be poor, about 75 dB 1W/1M. So this is not the way to go for a high efficiency sub.
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File Type: gif long pipe response.gif (10.0 KB, 126 views)
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Old 1st February 2007, 03:37 PM   #15
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Default Hey guys....

Well Cameron, I think we might be on different pages when we are talking about "push / pull"......

Their is the one type where the faces of the two subs are litterally bolted together, with one sub wired out of phase. This gives half of the cone surface area, of what the two subs by themselves would have. I hear this makes very clean sound, but is not very efficient.

In the push / pull setup I'm talking about, the subs are on opposite sides of the small box at the bottom of the pipe, and are therefor are just as efficient as any "two seperate drivers" would normally be.

Still, I sure would like to know how the pipe might change, for two subs to be attached to it ???

Right on kelticwizard, All in one room it will be then :-)

Peace,
Fish
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Old 1st February 2007, 06:48 PM   #16
GM is offline GM  United States
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Default Re: Thank you GM....

Quote:
Originally posted by Fish Chris
Yes, the Omega quarter wave-length pipe you sent me the calculator for, shows a 71" to 76" inch pipe, depending on whether one uses polyfil or fiberglass stuffing.

...but again, I can only get sonotube in 8", 10", 12" etc. But now, before you figure out the correction for this, what would be a good length and diameter for "two" of my 15"s, in this kind of setup > http://www.teresaudio.com/haven/subs/place.jpg
Again, I think this is a pretty cool looking design.... plus, the guy says that the push-pull configuration of the drivers made a surprising improvment in overall sound clarity !
Greets!

You're welcome!

Hmm, when I decided to go ahead and post it I didn't think to change the driver's specs to the Titanic's........good thing you didn't build from it since the actual dims are considerably bigger, 113.46 - 119.65" with much larger CSAs.

Understood. Obviously, you use what's available if you're not going to box it up in wood and since we're usually more interested in best practical efficiency than max damping, then the biggest tubes you can get, but unless you have very high ceilings you won't get to take advantage of the driver's low Fs. Note that with two of these drivers you'll need two 12" tubes 125" long to reach Fs, so at least a 15"h x 24" i.d. square baffle box. Pretty decent half space 2.83 V output or an IB response to Fs if stuffed. The trade-off being a <80 Hz steep XO required if not well stuffed (~1 lb/ft^3 polyfil).

If we drop back to dual 10" pipes to get a slightly smaller box, then performance below ~40 Hz rolls off, though it will only take ~half as much stuffing to get a 'close enough' IB response. If there's decent room gain this is probably a good compromise.

Right, a bipole layout to ~cancel out any rocking coupling motion and drivers physically reversed to average out any suspension non-linearities.

GM
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File Type: jpg dayton titanic mk iii bipole pipe tuned to fs.jpg (27.1 KB, 106 views)
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Old 1st February 2007, 08:10 PM   #17
GM is offline GM  United States
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Quote:
Originally posted by Cameron Glendin
Interesting question, If Vas is infact as important as GM says, should the pipe be 1/2 the diameter? Afterall you cannot reduce the length.

I am also curious about the idea of clamshelling the drivers for push pull, I am under the impression that minimal volume between the cones is the ideal way of doing it. Any thoughts
Greets!

By '1/2 dia.' I assume you're referring to the pipe diameter reduction if the drivers are clamshell mounted. True, Isobaric driver coupling will reduce the baffle box and pipe Vb to 1/4, but the trade-off is 2x the drivers and power to = ~one driver's output, so only worthwhile when saving space is paramount IMO. As always though, YMMV.

Ideally there would be no air gap between them, but a spacer is required to allow for a sub driver's large half roll surround.

GM
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