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Lets do it all again: TL Sub.
Lets do it all again: TL Sub.
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Old 9th May 2006, 01:26 AM   #1
Relax is offline Relax  United States
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Default Lets do it all again: TL Sub.

Whats up everyone. I read the majority of posts on subwoofer TLs, but I still have a few questions.

I read about multiple ways of designing a TL from the ground up based loosely on a tuning frequency I would select and the Sd of the driver.

I plan on using two of these:

http://www.partsexpress.com/pe/showd...number=295-460

I want to make 2 TL's As skinny as possible (11.5 inch width) and approximately 54 inches tall.

Depth is not really an issue, although I would like to stay under 18 inches. I want to build out of 3/4 inch MDF.

Is it reasonable to think a TL can be made in these dimensions which will have its -10 dB point below 20 hz?

If so, what design?

If not, how big do I need to go?
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Old 9th May 2006, 02:26 AM   #2
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Default Re: Lets do it all again: TL Sub.

Greets!

Drivers with a tiny Vas to fit in small cabs typically don't do well in low tuned TLs since its CSA is so small (low gain). To tune it to Fs to get to below 20 Hz requires a ~152" long pipe with only a ~25"^2 CSA, so you should be able to fold it up in the allotted size with a half space ~18 Hz F10 if the specs are reasonably accurate. Tuning this low also shifts its 3rd harmonic down into a sub's BW, so there's basically a 'black hole' in the response from ~70-100 Hz.

GM
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Old 9th May 2006, 03:00 AM   #3
Relax is offline Relax  United States
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The hole in response would be perfectly acceptable, since I plan on crossing over to them around 60-80 hz anyways.

Will increase the CSA result in any benefits? Its kind of hard for me to fit a 10 incher that is around 6 inches deep in a 25 inch cross section. Is a CSA of 50 or so possible?

With this line length and CSA is the response flat till what?

Is it possible to go lower without getting alot bigger?

Last question, I swear!

Other than the smaller Vas, is there any other reasons to not use this driver for a TL for low tuning?

Thank You so much!
~Jerick
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Old 9th May 2006, 03:28 AM   #4
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Greets!

You're welcome!

Increasing the CSA will increase peaking at each end of its response. Adding a short section just big/long enough to mount the driver won't affect the response enough to matter. It will just look a bit funky standing proud of the baffle if you don't bother to cosmetically blend it in.

There's nothing in the driver's published specs to indicate it won't work, but there's only one way to find out for sure.

See the first plot. Upping the CSA to 50"^2 and length to 175" looks good to really drive the room modes (2nd plot).

GM
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Old 9th May 2006, 03:30 AM   #5
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Old 9th May 2006, 03:47 AM   #6
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so perhaps a line length of 175 and CSA of 50 with filter at 40 hz?

I really like to see that extension into the sub 20hz frequencies.
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Old 9th May 2006, 04:55 AM   #7
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Greets!

I'd start with 60 Hz/4th order since the room's modes are going to chop it all up anyway, so you'll probably need EQ to smooth it out somewhat. The potentially big problems are running out of Xmax if there's not enough room gain and/or they're too far out of spec.

Anyway, a mini-review would be nice.

GM
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Old 10th May 2006, 04:31 PM   #8
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Thanks again GM!

I have started drawing up plans, but I do not know how big to make the end of the line.
I assume it is just the same as the starting, but want to doublecheck.

Will putting a curve at each bend help anything? I have seen it on a few designs, and i think I could easily make it if it will help.


Also, just for fun, are there any other TL geometries that might work better than a straight TL? If anything I would like to compare two types of TL. Maybe Straight versus Tapered or Expanding. (expanding might get too big for even I.)

Other than those few questions, I should be building soon. Won't be testing till I get my 2 plate amps though. I think I am going with the Rythmik Audio 350 Basic.

~Jerick
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Old 11th May 2006, 01:03 AM   #9
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Greets!

You're welcome!

This is a simple 1/4 WL pipe, so it has a constant CSA. If it had a forward expansion it would be a horn and if reversed, then a TQWT (aka ML-TQWT, which is more accurate).

Adding curves to better preserve the expansion through the bend only helps its HF BW, so isn't necessary in a limited sub/LF/midbass BW alignment.

An offset driver ML-TQWT will be smoother in the 3rd harmonic - up BW, but this isn't an issue for you so I see no reason to go to the extra effort and increased footprint.

A < 20 Hz basshorn will be huge by most folk's standards even if mass loaded and/or 'tapped', though of course it will have considerably more gain than a straight pipe simply because of its greater Vb.

GM
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Old 11th May 2006, 03:23 AM   #10
Relax is offline Relax  United States
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I see I see.

So I have two choices now, the CSA of 25 and 152" line

or the CSA of 50 and 175" line.

Now after thinking about your comment about making a larger chamber for the woofer that is at the end of the line, I think I may go with the smaller CSA for an overall smaller box.

Heck, I am so confused I may build them both! Now that I am done with school I have all the time I need.

Last question, could I lengthen the line and keep the CSA down to get the extended shelf like the longer and larger csa of 50 box?

I really like the predicted response of the larger box, but the smaller one is of course smaller and would be nicer to have. I figure I could fit a CSA of 25 line of length of around 190 ". If I can get a larger shelf(preferably flat to 20 hz.) I would like to.

Even if I can't thanks very much for the 2 designs already, and for your excellent explanations. Have a good one.

~Jerick
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