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Old 10th January 2002, 11:55 PM   #1
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Question Pros and Cons of Transmission Line speakers

Hi friends!

I want to build a pair of speakers and have my eyes set on the seas Thor transmission line speaker designed by dr d'Appolito himself ( http://www.seas.no/thor.htm ). The reason for my interest is the many good reviews their previous top-of-the-line DIY kit Odin got. ( i never liked the look of Odin and dont want a stand mount speaker. ) So when they launched a better design ( in their view ) that looked better i got interested.

Im a bit put of by it beeing a transmission line speaker. If it was a sealed box i would probably build it immediatly. Do you have any experiance with TL speakers?

I listen to most kinds of music, but dont need earth moving bass energy. I like the bass to be fast and tuneful. ( mind it, i dont MIND deep bass if the music is recorded like that. Its just not my top criteria for choosing a speaker )

I would much appreciate your view if you have experiance of your own.
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Old 11th January 2002, 12:14 AM   #2
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Transmission lines have a high cool factor in my book. There are two reasons I'm not currently running transmission lines--the size would be prohibitive in my case, and they're not a good choice for servo feedback loops, which happens to be something I want to play with for a bit.
I've used them off and on for years. Properly designed, they are a wonder.

Grey
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Old 11th January 2002, 12:40 AM   #3
Geoff is offline Geoff  United Kingdom
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Robert

Having built and used transmission lines at various times during the past 30 years, my advice is don't be put off. Properly designed, transmission lines offer the best subjective bass response of any type of enclosure. Tight, fast and deep. The only time I have not used a transmission line is when the available space has prohibited it.

Geoff
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Old 11th January 2002, 03:20 AM   #4
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If you hear a properly designed transmission line you will never go back to sealed box again. A TL has effectively NO RESONANCE! The bass is incredibly tight, and the woofer is finally given room to move. The bass will not be earth-shattering, it will be clean. I built a pair of transmission lines to go with my electrostatics. I will never own another sealed box.

I have published a preliminary report on a TL on my ESL website. You may find the construction pics and plans informative. Click on the "Hybrid ESL" tab.

http://home1.gte.net/res0f2t3/index.htm

Good Luck!

-M.A.
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Old 11th January 2002, 08:06 AM   #5
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M_Anker:
You're not quite right about TL's having 'NO RESONANCE'.
The whole principle of a TL is based on using one resonancefrequency, damped to a low Q, to increase bandwith. That's why the pipe is getting smaller, the further from the speaker You get.

But it does sound resonance-free, properly constructed.

Some years ago (@12) I did some research on damping materials for TL's, and came to the conclusion that 'long-haired sheep-wool' was best suited, since it had 6dB less attenuation at 30Hz than the best synthetic alternative, but had the same attenuation at higher frequencies.
I also found out that if I stuffed the 1/3 of the line closest to the speaker tight, the next 1/3 less tight, and the last 1/3 loosly, I'd get not only the best attenuation of undesired frequencies, but also the best sound.

Bedroc:
Go for it.
Put some effort into experimenting with the damping-material. It has a big influence on the final result.
Have a look at : http://www.t-linespeakers.org/index.html

I love TL's too.
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Hoffmeyer ;0)
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Old 11th January 2002, 08:34 AM   #6
yeti is offline yeti  Germany
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Default width of the line

It seems to be that there is no physicsal reason for the line to get
tighter at the output.
Years ago i buildt one with a linear cross-section and there was no differnce in frequency response.
In fact the resonant frequency is determined by the length of the tube.
The rest you'll get by proper damping.

regards

Arne
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Old 11th January 2002, 12:54 PM   #7
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The reason the TL appears to have no resonance is because of the tapered-pipe configuration. There are only two parallel surfaces(the sides), and the rest of the pipe is not parallel. This effectively removes any chance of standing waves; therefore, the TL has effectively no unwanted resonance. Hoffmeyer is correct, but what I am saying is that you will not experience any unwanted resonance coming from the enclosure. I am comparing the TL design with sealed box enclosures in which I've always had unwanted resonances.
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Old 11th January 2002, 03:25 PM   #8
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If you taper both sides, or use a design that subdivides a rectangular cross section into triangular pipes, you can remove even that potential resonance.
One thing I've always wanted to try is to take a PVC pipe (yes, Bryan, Sonotube would work as well, and probably be cheaper), then roll a triangular piece of 1/2" foam into a tube and slide it inside. Since the triangle would taper the inside of the foam roll, you would achieve progressive damping, and due to the circular cross section and foam, there would be no chance for unwanted resonances at all. It would also be ridiculously easy and inexpensive to construct.
I think I'll build one this afternoon. (Just kidding...got heatsinks to fiddle with and amps to build, not to mention going to see my bees.)

Grey
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Old 11th January 2002, 04:37 PM   #9
navin is offline navin  India
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tapering a trans. line gives to advantages.
1. breaking/spreading resonances
2. less volume required

a thumb rule could be cross section of line being about 1.25-1.5 times Sd (area of woofer) to about 0.75-1 time Sd.

Hope this helps

regards
Navin
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Old 11th January 2002, 06:35 PM   #10
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Hi bedroc,

I have designed and built a couple of TLs over the years. Not bad technique, certainly better than BR. The last were a sub using 4 x 12" drivers each side, each with their own line. They were about 1000 litres each, per side. My friend still uses them.

I am into horns these days, but I have found a couple of items that might interest you, both by people who actually design gear for a living and have a long track record.

It's your choice, but I'm not impressed with the Thor. The LF and HF responses are too rolled off and it's only about 87dB midband efficiency. Can you say compression? Also the two midbasses have substantially different path lengths to the port. Tsk.

Lynn Olsen's Amity would be a better bet. Read the theory and development article (and the others in the library on the same site) to get the details: URL below. It's easily 75-20k FR, 94dB sensitivity, flat impedence, and there are a number of constructor groups around the world that can help too. It uses common, reasonably cheap drivers ( Vifa midbass, Scan tweet) and produces outstanding results, but is probably a bit more difficult to build than the Thor. Tonally accuracy and dynamics are it's strongest points.

http://www.aloha-audio.com/Ariel.html with v6 being the latest and best.

For some general reading on TL principles, take a look at John Risch's posts on AA. He is an engineer and designer for Peavey I beleive. Go to http://www.teresaudio.com/haven/ look at the subwoofer page (designed to match the Ariel: TL design too!) and next to the 4th pic there is a link.

For stuffing the line, carded and well supported long hair wool, or Acousta-stuff is best.

Hope this helps.
Cheers
Brett
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