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Old 7th November 2009, 11:02 PM   #1
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Default Transmission line ?

OK, so I am tired of reading through everything with the search button and not really finding any answers to my question. How do you choose a speaker for a t/l? what makes a person choose one model over another? what are the limitations of a t/l? I think I understand how they work I just need a little more than a nudge... ( more like a shove) in the right direction.. I wish I could afford to go back to school for the missing knowledge just to support my hobby, it just isn't cost effective to do so. So reading and asking q's are are what I have to work with.

Mike
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Old 8th November 2009, 01:25 AM   #2
juxta is offline juxta  Australia
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I'm the same mate but I don't know what a transmission line is!
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Old 8th November 2009, 01:49 AM   #3
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You guys need to spend some time over at Quarter Wavelength Loudspeaker Design studying Martin King's landmark work on modeling TL's. Click on his theory link and go thru all of his papers more than once and all your questions will be answered.
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Old 8th November 2009, 02:04 AM   #4
robocow is offline robocow  United Kingdom
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I'm starting on the T-Line road myself. I chose the Vifa PL18WO09 on a couple of recomendations for a cheap t-line driver and a SEAS Prestige 27TFFC (H0881) Textile Dome tweeter to match. I'd be interested if anyone has an opion on those choices!

Pearls from Martin J King Quarter Wave Design

Was a good place to start, after the basics of any speaker design.
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Old 8th November 2009, 03:31 AM   #5
rcw is offline rcw  Australia
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My standard definition of a transmission line is that it is an over large and elaborate type of loudspeaker enclosure that when optimised can be shown to transform into a bass reflex.
rcw.
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Old 8th November 2009, 04:55 AM   #6
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In other discussions rcw has shown little appreciation for the merits of TLs, and the above comment shows doesn't really understand them.

Don't let him discourage you.

dave
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Old 8th November 2009, 04:58 AM   #7
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Good lord.. I have a long way to go on this learning curve.. I will be back to this after I go back to school for degrees in physics and a lot more math. I need a little matrix schooling plug me and away I go.


Discouraged! No! It may take me till I retire to figure it all out but someday. I think for now I will stay with the sealed and ported enclosures (I know these are not the proper terminology)that @ least I thought I understood. Some of you guys definately make me feel stupid on occasion. I didn't really come to appreciate sound reproduction until after listening to a very few demonstrations that blew me away. So what I do know and understand has all been from lots of reading ( I havent even gotten to the must read books yet) with a lot of trial and error, and the added perk of some small success that helps to keep me moving forward.

Mike

Last edited by MykeysToy; 8th November 2009 at 05:09 AM.
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Old 8th November 2009, 06:36 AM   #8
rcw is offline rcw  Australia
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On the contrary Dave I do understand transmission lines very well.

What I don't understand is the constant if not assertion then at least implication that they posses some sort of mystical property other methods do not have.

I also find the assertion that if a person does not agree with this then they obviously do not understand the technique, laughable, to put the best face upon it.
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Old 8th November 2009, 06:41 AM   #9
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All speaker designs use a mix of science and black art. In transmission lines the Black Art is a little more prominent than say a bass reflex which uses a little more black art than a sealed. If your going to build a T/L for the first time I suggest using a design already tried and tested, then you can experiment.

Terry
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Old 8th November 2009, 07:07 AM   #10
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With the introduction of Martin King's Model & the accompanying software, the black arts involved became no greater than any other speaker enclosure.

Before MJK (and Augspurger's parallel model) TL designers followed a reciepe, and not a very good one.

One significant discovery was how, if you take a bass reflex with normal dimensions, and then start stretching the aspect ratio (keeping the port at the far end of the cabinet) the BR behaviour transitions into something completely different (dubbed an ML-TL). The impedance plot is broadly similar to a BR's but one look at the ANSYS simulations of the behaviour of the air inside the box quickly shows that box is doing something quite different (published in MJK's ML-TQWT article). More than one designer has found that their tower "bass-reflex" is not funcioning as simmed... it is because the box is not a BR it is an ML-TL.

Or you can take a strongly tapered pipe and damp fairly heavily to get a rool-off similar to a sealed box, but with a dramatically lower impedance peak. The example is somewhat less than could be achieved, but were constrained by other aspects of the box.

Click the image to open in full size.

TLs in their broadest sense are very versatile and useful devices. Like any speaker design you need to choose your compromises.

Personally i avoid standard bass reflexes, i find that being tightly tuned (using a set of scalar T/S parameters) they move around in the bass as the T/S change as f(V). For a standard BR to work well you would have to choose a driver with flat T/S curves.

TLs are naturally tolerant, and you can mutate a BR to be more tolerant.

dave
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