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Old 6th May 2005, 03:32 PM   #1
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Default TL quandry (post is not the project )

Ok i am questioning if this is wrong forum or not but here foes the question. If its wrong place forgive me but you guys are all about the TL here.

This is where my problem came up.....
OK lets try this 2 way Morel

is the original post

I thought i had this TL thing licked math wise but apparently i was wrong ? I am putting this picture here and question so i can "visually' understand what was said to me in the above linked post. I dont understand how 70 odd inches applies to any driver as i said i n that post so if one of you can pick this picture apart and tell me where the math doesnt apply. I would appreciate it.

I have exhausted myself reading on the web on TL's and the theorys vary. I love a good problem, but not one with no consistent answer.

SO the picture example is like using two 8 inch woofers with a front firing port. I used the drivers combined Sd and 35 hz as a set point. Internal dimensions are 22 inches high 28 inches deep and 10 wide. You can move the inner walls in your head where your math takes you. But i am not getting 72 inches for the drivers Sd times the Frequency for a wave length (rough math, still like +/- 5 inches ).

Please help, i have half cut wood lying around for my morel 10 " and Planar project.
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Old 6th May 2005, 05:59 PM   #2
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Wait. 2 x Sd = line width minimum ? with 2 drivers. I am getting near 96 inches line length for 35 hz plus the Sd minus the Bass reflex box tuning by volume which = 84 inches with the numbers in my head.

Tell me its not this easy. Is it just a box long enough to fit 96 inches of line length in it ? Regardless of Sd and Bass reflex volume ?

Have i complicated it too much ?
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Old 6th May 2005, 06:03 PM   #3
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Default Re: TL quandry (post is not the project )

Quote:
Originally posted by Madmike2


Please help, i have half cut wood lying around for my morel 10 " and Planar project.
ANddddd am i not to include the 'pressure chamber' closed end as part of the line length.

Sorry that i ask so many questions but i need to 'see' whats being told to me so i get it.

>edit> stupid picture didnt come with the quote <edit<
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Old 6th May 2005, 08:51 PM   #4
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84" sounds a little long for a 35Hz TL tuning. I get a figure closer to 77" long.

Note that driver Fs translates into the TL length. Sd is needed for the volume of the line.

A TL gives much more bass than most people expect...do you really need two drivers?

:)ensen.
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Old 6th May 2005, 09:53 PM   #5
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I have tried to read your thread, it seems to ramble in different directions. I have no idea what your question is or how you determined the lengths. You need to simplify your question.
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Old 6th May 2005, 11:16 PM   #6
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Quote:
Originally posted by purplepeople


Note that driver Fs translates into the TL length. Sd is needed for the volume of the line.


ensen.

ooooooooo here i am trying to 'tune' the box. I think i get what i was missing before. The driver you use, the Fs of that driver is what the box is tuned to ?

Somewhere around the web i read that the Sd of the driver was to be removed from the length of the line. And then i found that that was the cross sectional area minimum of the line.

> A TL gives much more bass than most people expect...do you really need two drivers? <

Thats was an example i popped off in my head. My actual project is a 10 " Morel and a BM Planar.

> 84" sounds a little long for a 35Hz TL tuning. I get a figure closer to 77" long. <


Sound divided by the wave length divided by 4 multiplied by the number 12 inches in a foot = 96 inches for 35 hertz ? ? ?

MJK > I have tried to read your thread, it seems to ramble in different directions. I have no idea what your question is or how you determined the lengths. You need to simplify your question.

Ya i am stupid like that. I sort of have a stream of consiousness way of typing or expressing myself. Drives people nuts. See ? there i went again. My question was ... changed now. Ill ask it the way it is in my head right this moment.

Single fold multi-fold , Straight pipe. They all dont work out the same even though it is all 1/4 wave length.

Why are no two design formulas the same for designing a TL enclosure ?
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Old 7th May 2005, 12:41 AM   #7
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Quote:
Single fold multi-fold , Straight pipe. They all dont work out the same even though it is all 1/4 wave length.
Why? If the cross-sectional area is constant they should all be approximately the same length.

Quote:
Why are no two design formulas the same for designing a TL enclosure ?
Because everybody else is wrong, just ask any TL "expert".

Now a serious answer.

The newer computer modeling methods for designing a TL are all consistent. The computer models use the same assumptions with respect to how the stuffing acts and how the line geometry effects the tuning frequency. They also produce essentially the same modeled responses for the same driver and geometry.

Pre 1999/2000, most of the TL design methods were based on voodoo and black magic. The biggest error was assuming that the fibers moved and dramatically reduced the speed of sound in the TL. This was just plain wrong and was the basis of almost all of the TL design rules of thumb since the 1960's. Anybody telling you that the speed of sound in a TL is dramatically reduced by the fibers moving is totally out to lunch. There are a lot of people still preaching this theory as a fact so you need to be very careful when reading TL documents on the web or in the literature. Pick a source you have confidence in and follow his/her methods.
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Old 7th May 2005, 12:50 AM   #8
Stocker is offline Stocker  United States
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because although many people have experimented, very few have taken the time to do the research to get consistent results.

one of the members here has apparently and wrote a long .pdf paper about it. Unfortunately I remember neither the membername nor the filename. Sorry.
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Old 7th May 2005, 12:58 AM   #9
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Please let me know if you remember! 8^)
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Old 7th May 2005, 01:50 AM   #10
ScottG is offline ScottG  United States
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Quote:
Originally posted by MJK
I have tried to read your thread, it seems to ramble in different directions. I have no idea what your question is or how you determined the lengths. You need to simplify your question.

well.. his moniker is "M A D mike2"
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