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Old 20th March 2013, 03:46 PM   #1
tpelvis is offline tpelvis  United Kingdom
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Default Transmission Line Build and Play

Hi

I am new to posting on this site, but thought that the project I am undertaking might be of interest to some of this site's members.

Together with a good friend of mine, I want to look a bit further into replacing conventional oil and mineral based absorption material with alternatives such as wood fibre, sheeps wool, hemp and other natural fibres.


As the title of this post suggests, we want to trial these materials in a transmission line speaker, constructed by us, from an IPL Acoustics kit (IPL M1TLm Ribbon Transmission Line).


We are aware that long haired wool has often been used to fine tune, but we want to look at the bigger picture of replacing the profiled foam that runs along the labyrinth with a natural alternative.



We don't want to do this just to provide a greener alternative, although that is good news too, we want to see if we can improve on the sound.


Neither of us had previously heard TL speakers before, but when we listened to them, at the kit supplier's home (Ivan @ IPL Acoustics) we were seriously impressed and both commented on the unique nature of their presentation.

The supplied kit comes with profiled foam and a small quantity of long haired wool, for fine tuning, so our intention is to build the speakers as per kit, with one small change. We will gasket (draught excluder) and screw one side panel to enable us to gain easy access for changing over the absorption materials.

To give a why to all of this, I part own a sheep wool business and have experimented with different types and quantities of wool in closed box and ported speakers. This has produced some interesting and quite unexpected (by us) results.

Both my friend and I, were astonished at the impact differing absorption materials have on balance, definition, imaging and timbre not just between synthetic and natural fibres, but between wools!

We will/are taking photos as we go to provide something a bit more interesting to look at than just text! Pics here Flickr: theacousticshepherd's Photostream


Have just glued outer box, less one side panel.
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Old 21st March 2013, 10:27 PM   #2
tpelvis is offline tpelvis  United Kingdom
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What a bizarre site! Don't know if I have just posted in the wrong section or whether a TL speaker build designed to experiment with alternative cab absorption is just to dull to attract any interest/comments on a DIY Audio site!?
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Old 22nd March 2013, 12:02 AM   #3
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I'm sure there would be interest if you showed us the measured results,
"some interesting and quite unexpected (by us) results" is a bit vague...
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Old 22nd March 2013, 01:13 PM   #4
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So you guys think this is a brand new, revolutionary idea?
You're not gertting much interest because folks have been thre and done that, and as stated previously, you're using vague "magazine" terms that have also been done before.

Folks will need some objective results to get interested, and even then it's still pretty ho-hum.


Quote:
Originally Posted by tpelvis View Post
What a bizarre site! Don't know if I have just posted in the wrong section or whether a TL speaker build designed to experiment with alternative cab absorption is just to dull to attract any interest/comments on a DIY Audio site!?
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I was so much older then, I'm younger than that now.
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Old 22nd March 2013, 03:57 PM   #5
tpelvis is offline tpelvis  United Kingdom
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Quote:
Originally Posted by fastbike1 View Post
So you guys think this is a brand new, revolutionary idea?
You're not gertting much interest because folks have been thre and done that, and as stated previously, you're using vague "magazine" terms that have also been done before.

Folks will need some objective results to get interested, and even then it's still pretty ho-hum.
That's fantastic news! Clearly we are not old enough or well versed enough to have come across this before.Could you perhaps point us in the direction of any of this info/data please? Would really help us out knowing what has gone before.
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Old 22nd March 2013, 03:59 PM   #6
tpelvis is offline tpelvis  United Kingdom
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Quote:
Originally Posted by PeteMcK View Post
I'm sure there would be interest if you showed us the measured results,
"some interesting and quite unexpected (by us) results" is a bit vague...
Thanks Pete, as we are, as mentioned, rather new to this, could you perhaps suggest what you feel we could measure?
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Old 22nd March 2013, 04:06 PM   #7
tpelvis is offline tpelvis  United Kingdom
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Quote:
Originally Posted by fastbike1 View Post
you're using vague "magazine" terms
Nearly forgot, could you perhaps explain where and what?
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Old 22nd March 2013, 05:29 PM   #8
pkitt is offline pkitt  United States
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Have you looked up George Augsperger? He developed alignment tables and software for modeling TLs using polyester fiber, fiberglass, and other materials for the stuffing. Martin King developed his TL modeling software and alignment tables based on polyester fiber effects. Maybe these two sources could be useful for your experimentation.
Paul

Quote:
Originally Posted by tpelvis View Post
Nearly forgot, could you perhaps explain where and what?
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Old 22nd March 2013, 06:53 PM   #9
tpelvis is offline tpelvis  United Kingdom
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Quote:
Originally Posted by pkitt View Post
Have you looked up George Augsperger? He developed alignment tables and software for modeling TLs using polyester fiber, fiberglass, and other materials for the stuffing. Martin King developed his TL modeling software and alignment tables based on polyester fiber effects. Maybe these two sources could be useful for your experimentation.
Paul
Thanks Paul, really appreciate your help. Do you happen to know if any of this is web based, or is this research paper based?

Cheers T
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Old 22nd March 2013, 08:17 PM   #10
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re measurement, look for cumulative spectral decay (waterfall) plots, & freq response;
Martin Kings site: Quarter Wavelength Loudspeaker Design
I think some of Augsperger's work is in pdf form if you google
Probably worth having a look at Baily's Wireless World articles as well for historical perspective
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency

Last edited by PeteMcK; 22nd March 2013 at 08:41 PM.
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