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Old 25th December 2002, 04:19 AM   #1
tom1356 is offline tom1356  United States
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Default t-line subs for a DIY line array

I have been listening to just the two bottom modules of the array I'm building and have come to the conclusion that they would benefit from a very nice sub. I originally wanted to go with a pair of 12" Shivas or Lambdas in a sono tube T-line, but now I'm thinking a little bigger.
Nelson Pass's "El-pipe-o" has inspired me. Two 21's are a little big but...two 18's might work. Has anyone tried the ACI SV18?
I have 8" ceilings so thats a limit. Any other sugestions? hints?

You can see my progress on the arrays here.

Ouch! $100.00 for brass mounting hardware
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Old 26th December 2002, 01:16 AM   #2
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What's the avantages of an array like that? Seems like a lot of work.

The copper phase plugs are hollow? If you turned them on a laith there's no way to make them hollow. So I'm assuming they're solid. This heavy weigh must influence the frequency response of your drives greatly, right? Is this what they're for mainly?

If you have 18" subs and use sono-tubes you will need to form a bend in the sonotubes if you want them vertical and tuned to 20-30 Hz. You could build the bends out of fiberglass maybe. But easier thing would be to cut triangular or techically trapazoid shaped cylinders (looking at the cylinder from the side) to form the bends. And glue them together. An upside-down slim horseshoe, with the ends facing the ground would look good and produce optimium sound, I think. Although they would be 90 degrees out-of-phase and right next to each other. Don't know if that's a problem.
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Old 26th December 2002, 05:33 AM   #3
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Tom,

Your arrays are awesome. What a super job you’ve done, my complements.

See the drawing I’ve done below as a suggestion of a possible solution for your ceiling height problem. It’s a tapered tube within a 24” sono-tube. This double the available TL length in the same space, as long as you sign up to the tapered tube approach (you‘ll have to calculate your own taper).

I respectfully call it “El Pipe-Dopo”.

Rodd Yamashita
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Old 26th December 2002, 03:48 PM   #4
tom1356 is offline tom1356  United States
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Hello Rod,
Thank you for the kind words. Your idea is an excelent solution but I think it is beyond my mathamatical abilities and design understanding. I can follow directions but comming up with the math for a new design is more than I want to tackle.
If i switch to two 10" or 12" subs in the "el pipe-o" form, will I be able to hit ~20hz in a 14' x 14' x 8' room?
What qualities do I look for in a driver? There are to many options for the uneducated.
Should I build them with one driver per tube as NP ended up with or two drivers per tube as in his first model?

P.S. I really want to stay with a 250 watt amp per driver which should be plenty since I don't listen very loud.
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Old 26th December 2002, 04:58 PM   #5
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Quote:
Originally posted by tom1356
Hello Rod,
Thank you for the kind words. Your idea is an excelent solution but I think it is beyond my mathamatical abilities and design understanding. I can follow directions but comming up with the math for a new design is more than I want to tackle.
If i switch to two 10" or 12" subs in the "el pipe-o" form, will I be able to hit ~20hz in a 14' x 14' x 8' room?
Not necessarily.
Quote:
Originally posted by tom1356
What qualities do I look for in a driver? There are to many options for the uneducated.
Should I build them with one driver per tube as NP ended up with or two drivers per tube as in his first model?

P.S. I really want to stay with a 250 watt amp per driver which should be plenty since I don't listen very loud.
Tom,

El Pipe-Dopo is pretty conceptual in its mechanical design, but principles on which the design is based have been shown to have credibility. I merely combined Mr. Pass’ El Pipe-O with the idea of a folded/tapered TL. This has all been done before.

The trick with the TL’s and EL Pipe-o is the length of the line or tube. That’s why I suggested the pipe with in a pipe. El Pipe-O is 14’ long, and it a quarter wave tube (like pipe organs). That means the full wavelength is 4 X 14’ = 56’. That is the length of a 19.6Hz wave, so El Pipe-O is tuned to ~ 20Hz.

If we apply this to El Pipe-Dopo where the tube is sitting on a 24” tall box, and the column is 7’ tall, the tube section can be 5’ (give or take 6”). Therefore the tube in a tube is totals to a length of 10’. Again using the quarter wave principle, 4 X 10’ = 40’ which is the length of a 27.5 Hz wave. This is a respectably low tuning frequency if it were acceptable to you.

There are other considerations. El Pipe-Dopo is only conceptual. I would hope to get the nod from some of the more knowledgeable on TL’s before moving forward. Furthermore El Pipe-Dopo is a tapered design. My understanding of TL’s is limited, but the calculation of the exact taper is not crucial, but the compromises in the performance are unclear. Next is the driver selection. Usually, you select a drive and tune the pipe length to the drivers fs (which you can still do), but box design also has something to do with the performance. Here again, I would have to defer to the more knowledgeable on TL’s.

If Dave (Planet10) doesn’t respond to this call in a timely manner, then send him an email. I’m sure he can provide some guidance here.

Most 12” or 15” bass drivers are fairly efficient. In 99% of the home situations 250Watts will be plenty of power to rattle the walls with.

Rodd Yamashita
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Old 26th December 2002, 07:38 PM   #6
jmiyake is offline jmiyake  United States
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Default Consider a bass array?

Since you like arrays, you should consider a bass array.

This would be a series of subwoofers across the front of the listening room. They would only need to be separated by about 1/4 wavelength at the crossover frequency apart from each other, so about 5' should do it. This will behave much like a line array, coupling and providing a much more uniform wavefront, and it would be less affected by the room modes than a single sub, or 2 subs separated by more that 6'. Ideally it would be one in each corner and then one evenly spaced with no more than 5' separating them across the front. I certainly think that this is superior to having a vertical array of subwoofers in the left and right corner, which is fashionable in the very high end these days, but would tend to be probematic depending on the room dimensions.

James
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Old 26th December 2002, 08:26 PM   #7
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Tom,

I recently finished a pair of subs using nested sonotubes as Rodd has suggested. Mine don't have the box at the bottom, but rather have the driver firing down at the floor and the terminus at the ceiling.

I was able to get nearly 12 feet of line in a 7 foot column, using two straight pieces of tube. Essentially each cabinet consists of one 16" in diameter sonotube inside a 24" in diameter tube. The 16" tube has a closed end opposite the driver magnet and the open end adjacent to the driver. The 24" tube has the terminus at the ceiling, with the closed end holding the driver at the floor. The idea was to launch an axial wave from the driver, which is located at about 50% of the line length, that would find it's way to the 16" endplate and then up the void created by the distance between the two tubes to the terminus. This assembly would in turn excite the corner at the floor and at the ceiling (something a very good friend of mine recommended years ago as a good configuration for a sub) and if everything was right, would require a fresh box of Depends (tm) for each listening session. The only thing that made this even possible for me to consider, since I am not an engineer, mathematician or even a really smart guy, was the availability of Martin King's MathCAD worksheets.

I was able to use the MathCAD files to model the nested cylinders as a mass loaded tapered quarter wave tube, using the different tube diameters as a slight taper value in the worksheets. Fortunately, the drivers I used fit the model quite well and perform pretty much as anticipated, given my relatively crude measurement equipment (a Excel value calibrated RS SPL meter). I measure fairly flat response to 20Hz with both subs driven at my listening position, which is what I wanted to achieve. The really cool thing is, that they stand in the corners of the room, really don't look that large, and for the Feng Shui enlightened, offer the added advantage of improved chi flow, which incidentally Martin's worksheets don't really address .

Given how well King's worksheets correlate with the finished product, I can't encourage you enough to take a look at them. They initially look pretty daunting (mostly because of the visible strings of calculations, which you don't have to know anything about), but are exceptionally easy to use and can help you get close to a workable solution, before you drag the bridge formwork into your living room.
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Old 26th December 2002, 10:45 PM   #8
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I think Dana should show us the picture of those tubes
hanging out of the back of his car. Whadya say?
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Old 26th December 2002, 11:43 PM   #9
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Unfortunately, I don't have a lot of photographic evidence of this project, but I did come across two images; the candid "two guys and a 24" tube trim jig" shot (note the look of utter disbelief on the Altendorf operator's face; he is on the left - incidentally, the strategically placed "dot" is nothing more then a camera artifact, not one of the modern digital techniques meant to imply something needs to be hidden from the general public) and every speaker builder's favorite "my enclosures are bigger than my car" photo, which while interesting visually, drove home the point that if you are really serious, you got to get a larger vehicle.

If anyone is interested, I do have a set of pdf drawings I can email that explains more clearly what I did than my verbal description. Once again, probably not everyone's cup of tea, but it kept me off the streets for a few weeks and has given me countless hours of pleasure explaining to those outside the orbit of this forum, why anyone in their right mind would build something so...
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Old 26th December 2002, 11:44 PM   #10
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