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Old 30th January 2006, 07:51 PM   #1
flaevor is offline flaevor  United States
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Default T-Line help...can somebody do a sim

Do I have any volunteers for a mathcad sim of a t-line for the Tangband W5-1138SG using two drivers.

TSPs here

I understand the basics of esentially making it one quarter wave of Fs but I have seen lots of designs that do not use this simple formula and I do not fully grasp what the advantages and disadvantages of deviating from that formula are.
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Old 30th January 2006, 09:53 PM   #2
Wizard of Kelts
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If nobody else volunteers, I think I'll have time later tonight.

Were you planning on a straight TL, or a Mass Loaded Transmission Line, (MLTL)?

Also, where you planning on

A) Hooking them up in parallel, to make a 2 ohm unit?

B) Hooking them up in series, to make an 8 ohm unit?

C) Hooking each up to separate amplifier? If that is what you are doing, and plan on crossing these subs over passively, what crossover point were you planning on using, and, (not necessary to answer) did you have an inductor coil size picked out? If so, what is the model number or the DCR of the coil.

The last two questions do not necessarily have to be answered, but would be nice to know.
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Old 31st January 2006, 12:10 AM   #3
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Hi flae,
Quarter wave of Fs is a simple calculation for a very ideal and theoretical model. You must to consider the acoustical impedance of air or other filling material. This is why the efective lenght drops down to about +- 80% of theoretical lenght. Other parameters are important too, like T-S par, sectional areas of begining and closed/open terminus, straight or folded etc, etc
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Old 31st January 2006, 06:36 AM   #4
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Sorry, flaevor.

I worked on it, and had something that looked kind of nice but it went bad somehow transferring from Sections to TQWT program.

To briefly summarize:

I assumed each speaker was driven by a separate amp or channel, so I kept the parameters the same except doubled the Vas and the Sd.

I came up with something like this:
Line length = 75 inches.
Area at top of line= 1 Sd.
Area at opening of line =0.3 Sd

Driver center to top, (closed end), of line = 25 inches
Stuffing density = 0.4

The response curve was not much different from a closed box of equal size, but the cone excursion was cut about in half.

Late here, will resume tomorrow with some graphs.
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Old 31st January 2006, 07:15 AM   #5
Wizard of Kelts
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Well, what the heck. Here is some sims for a Mass Loaded Transmission Line. That is a transmission line with a port at the end. This is done in the TQWT worksheet.

It's a place to start, anyway.

Pretty good response for a subwoofer. Here are the parameters and setup for the box. Sorry about the units-that metiric stuff doesn't take over here, and certainly not at this time of the morning. Plenty of online calculators to help you convert.

Remember, the Vas and Sd are doubled in the user input section, because you are using two in the box. I am assuming you are connecting each driver up to a separate channel. Everything else is the same as Tangband's specs.
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File Type: gif tangband five incher.gif (6.7 KB, 402 views)
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Old 31st January 2006, 07:17 AM   #6
Wizard of Kelts
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Here is the frequency response. Two five inchers giving significant response down into the twenties. Very nice.
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File Type: gif flaevor tangband freq resp.gif (4.9 KB, 412 views)
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Old 31st January 2006, 07:19 AM   #7
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Here is the output of the cone (red), and the port (dotted blue).
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File Type: gif flaevor tangband woofer adn port ooutput.gif (5.2 KB, 367 views)
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Old 31st January 2006, 07:21 AM   #8
Wizard of Kelts
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Here isi the step response.

Curves are not perfect, but maybe a beginning to start from. Assuming you are using this as a subwoofer, you could use it "as is".
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File Type: gif flaevor tangband step presponse.gif (4.2 KB, 342 views)
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Old 31st January 2006, 09:11 AM   #9
flaevor is offline flaevor  United States
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wow!!! thanks a million. I had read an article about a mass loaded T-line and the interesting thing was that the bassreflex sim netted the same internal volume. So I took the interior dimensions of the cabinet I had in mind (not mass loaded but with two bends) and plugged them in to see what the bass reflex results would be and they were way less then ideal. Since I don't have mathcad and have never used the sheets I thought I'd see if you guys could help.

as far as the other details go...I had planned to put both speakers in the same line wired in series.

A german magazine often puts two drivers in one line, one at one third and the other at one fifth of the line(to minimize certain resonances). Then I remembered reading that the resonances occur independent of the placement in the line, or at least to some extent. So I figured why not place the speakers as close together as possible at the beginning of the line. I like the looks better.

In the end I was fishing for suggestions and your sims helped thanks again.
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Old 31st January 2006, 01:17 PM   #10
Wizard of Kelts
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Flaevor:

Well, in this unit the driver position ratio is 0.5. which menas the centerline between the drivers is halfway down the length. Line position does affect the response, although somewhat less in a Mass Loaded TL than a standard TL.

I can redo the sim with both drivers in series. It won't change much, except that the sensitivity will be 3 dB less throughout the sim. I can alos rerun the standard TL I was talking about for you.

A couple of questions:

Are you crossing over passively, with inductors in the Line? Or are you planning to use a separate amp/crossover to run this sub?

And what frequency do you plan on crossing over?

Incidentally, a Mass Loaded TL does give somewhat different response from a bass reflex. The response an octave above cutoff is somewhat enhanced in a Mass Loaded TL.
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