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Want to build a TL subwoofer - driver advice needed
Want to build a TL subwoofer - driver advice needed
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Old 5th March 2018, 03:31 PM   #21
solid7 is offline solid7  United States
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Quote:
Originally Posted by planet10 View Post

Your image does not show… attach it to a post.

dave
I did attach it to the post. I can see it. Let me see if I can find another one.

Thanks for the info.

EDIT:

Here's an example of what I'm asking about:

Click the image to open in full size.

Last edited by solid7; 5th March 2018 at 03:37 PM.
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Old 5th March 2018, 04:05 PM   #22
solid7 is offline solid7  United States
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So, I read through all of Martin King's scholarly breakdown, on how he derived his conclusions. I half glanced through a pile of messy differential equations. He even made a nice reference to Maple V software. (which is used to do symbolic math - very nice) However, I'm not sure that I really got down to the heart of the matter of what the actual final product looks like.

He seems to have done most of his testing on a straight box, with variances approaching terminus. (flared and tapered) He seems to be saying that a tapered design is the best, but trickiest to get right. And then, his website states that his design software hasn't been available to new users since 2014, with restricted access to existing users.

I like his work. He's meticulous, and he really did a deep dive into the subject matter. But how can I put it into practice?
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Old 5th March 2018, 04:28 PM   #23
jplesset is offline jplesset  United States
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I would not characterize the cabinet shown as a "transmission line", but rather as a bass reflex type, with a very small cabinet and a very long reflex tube... I doubt you would be happy with the results if you model it.
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Old 5th March 2018, 04:40 PM   #24
solid7 is offline solid7  United States
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Quote:
Originally Posted by jplesset View Post
I would not characterize the cabinet shown as a "transmission line", but rather as a bass reflex type, with a very small cabinet and a very long reflex tube... I doubt you would be happy with the results if you model it.
Ok, I get that - it was just an example. But what I am asking is whether or not it's possible to optimize that type of design, according to the T/L design parameters.

In other words... If I were to create the proper size and length opening, would it fit the design intent of the T/L? Or is there some other fundamental difference?
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Old 5th March 2018, 07:46 PM   #25
planet10 is offline planet10  Canada
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Want to build a TL subwoofer - driver advice needed
The picture shown is called a horn by the manufacturers, but is a mess. It is designed like an air cavity/end loaded horn, but acts like an undamped TL/quarter wave resonator. For a typical 3” driver will be way longer than practical, the smooth curves make the ripple caused by unwanted harmonics worse — squared off corners act as additional LP filters. It also uses translam construction, pretty shape, but a waste of material, and the "pretty” brings no sonic benefit. Further it is MDF which is not the best material for building
speakers.

One does not even have to look at the math to get what is needed out of Martin’s papers.

dave
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Old 5th March 2018, 07:49 PM   #26
planet10 is offline planet10  Canada
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Want to build a TL subwoofer - driver advice needed
Quote:
Originally Posted by solid7 View Post
Ok, I get that - it was just an example. But what I am asking is whether or not it's possible to optimize that type of design, according to the T/L design parameters.
Yes, with a TL modeller. One puts the driver into a box and plays. It takes a lot of that. Successful TL design takes a lot of playing, fortunately the modelers mean you don;t actually have to build boxes. You can get a lot of clues from those that have some expertise and take things like taper. driver offset, and restricted terminus from what Martin has written and that many of us have practically shown by building boxes based on his and others TL modelers.

dave
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Old 5th March 2018, 07:55 PM   #27
solid7 is offline solid7  United States
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I have been modeling a folded labyrinth, like the one shown, using the parameters from Keith Webb's spreadsheet at Transmission Line Theory.

I selected the 10" Dayton woofer that was mentioned earlier, as well as the 8" version of it. (I'm modeling both in a CAD program, as I'm interpreting the data)

The only thing that I'm not really sure about, is how much of the total volume is the line, vs the driver chamber.

How do I figure driver offset? I'm not sure that I'm seeing that - or if I am, I'm not recognizing it. (in the spreadsheet)
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Old 5th March 2018, 07:58 PM   #28
planet10 is offline planet10  Canada
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Want to build a TL subwoofer - driver advice needed
The SS is an expression of Martin’s tables in a SS. There is no dtiver chamber, just line, the offset depends on the taper and the SS dhould just spit it out.

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Old 5th March 2018, 08:08 PM   #29
solid7 is offline solid7  United States
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Oh, I see. So the mounting of the driver would need to occur in such a way that the drivers is perpendicular to the line.
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Old 5th March 2018, 08:15 PM   #30
planet10 is offline planet10  Canada
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Want to build a TL subwoofer - driver advice needed
At the frequencies involved perpendicular has no meaning. The driver taps into the line, ideally at the optimum offset. This is refered to as the Zd.

dave
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