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Old 10th April 2005, 10:07 PM   #1
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Default Transmission line question(s)

Hello

I have a diy speaker using a Seas P17REX paired with a Morel MDT29 tweeter. I like the overall sound of both of these units. They are in a vented enclosure, modelled using lspcad i believe many years ago.

Recently the amplifier used to drive these has changed, to something with a lot less power output. My idea now is to buy another pair of P17REX and build a new enclosure. I thought of making a transmission-line type this time, and realise i know nothing of how to model these speakers. I think i remember a software being mentioned somewhere, to atleast give oneself a basis for experimentation.

Are the woofers particularly unsuited for a transmission line?
Their stats are, i believe, Fr=34Hz, Vas=30.5, Qts=0.24, Z=8ohms with a sensitivity of 89dB/SPL.

I was thinking about a design similar to the "Thor" kit,
http://www.madisound.com/pdf/Kits/au...r%20Review.pdf

Ive only read that review in passing, however, and it seems that some(all?) of the math required can be derived from that document. My main question is, is there a piece of free software which simplifies experimentation with TL speakers?

I have access to a non-professional measurement setup, so i might be able to utilize this in the crossover tweaking and enclosure adjustments.

rgds Kristian
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Old 10th April 2005, 10:16 PM   #2
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Quick reply, just about to eat my dinner, good place to start is Martin J King's website: http://www.quarter-wave.com/
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Old 11th April 2005, 08:45 AM   #3
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Default Re: Transmission line question(s)

Quote:
Originally posted by yacuza
Their stats are, i believe, Fr=34Hz, Vas=30.5, Qts=0.24, Z=8ohms with a sensitivity of 89dB/SPL.
Qts is rather low for a TL... other important TL resources are my site (URL below) and Bob Brines

http://geocities.com/rbrines1/

dave
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Old 11th April 2005, 03:49 PM   #4
kneadle is offline kneadle  United States
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Default Low Qts

As Qts is an equation using qes and qms, how does one know when qts is smallish for a given TL enclosure? A smaller driver is going to have a smaller Qts. Wouldn't that make it unsuitable only for a large TL enclosure?

Or does the science of TL teach us that "Transmission" only works in certain physical circumstances?

Dave
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Old 11th April 2005, 04:55 PM   #5
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Quote:
A smaller driver is going to have a smaller Qts. Wouldn't that make it unsuitable only for a large TL enclosure?
The Qts from a smaller speaker isn't lower per definition, compared to the qts of a large driver. The Qts is the total quality factor for a speaker and is a good way to see the strenght (and efficiency) of any speaker.
Basically a low Qts means a big magnet and vice versa.

I use a driver with an Qts of 0.29 in a TL and it works very nice, while giving good low end extension. It has a smaller mouth as throat and was easily modelled with AJ-horn. Modelled with the mouth the same size or larger than the throat it gave poor results.

Mvg Johan
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Old 11th April 2005, 08:10 PM   #6
kneadle is offline kneadle  United States
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Quote:
Originally posted by Rademakers


The Qts from a smaller speaker isn't lower per definition, compared to the qts of a large driver. The Qts is the total quality factor for a speaker and is a good way to see the strenght (and efficiency) of any speaker.
Basically a low Qts means a big magnet and vice versa.


Mvg Johan
Now looking at the actual equation, your explanation makes perfect sense. I learned something today!



Dave
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Old 11th April 2005, 08:16 PM   #7
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Quote:
Originally posted by kneadle
Now looking at the actual equation, your explanation makes perfect sense. I learned something today!


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Old 11th April 2005, 08:45 PM   #8
kneadle is offline kneadle  United States
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My new mantra: "high qts is the TL ch'i."

Dave
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Old 11th April 2005, 09:32 PM   #9
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Hello

The first TL I built using a 6.5in driver was with the P17REX, using an " IPL Acoustics " design, and the results were excellent. It was this that proved to me that low Qts drivers were the way to go for lines. So I would go ahead and try them. I still have the original plans, but you might achieve even better results by using Martin Kings worksheets

Roy
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Old 11th April 2005, 10:02 PM   #10
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Quote:
Originally posted by Roy Lewis
I still have the original plans, but you might achieve even better results by using Martin Kings worksheets

Roy
If you happen to have these in some sort of electronic format, and would not mind, i would very much like to receive those plans, if nothing else to use as a sanity-check for my own design. Email is kristian (at) renegade (dot) se

After reading some more on various places it seems to me one of the more important factors to decide upon is the length(and thus resonant frequency) of the line. Using two drivers, should i start with a point between the two drivers, or at the topmost driver? Perhaps it is best to use a middle point, so that both drivers experience an equal amount of "detune" from their optimum tl length.

Or should i just shut up and build a line, it seems to me it is a good idea to build it from cheap board on the first go, and get a sense of it, then build it again with higher-quality woodwork.

I want to thank everyone for replying, and hope to receive more of them, in spite of my tendency to lengthy posts.

rgds,
Kristian
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