Author Topic: Transmission line Speakers  (Read 451 times)

Offline Samayanaya

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Transmission line Speakers
« on: October 05, 2017, 01:36:12 PM »
What are the benefits of TL vs reflex design? And what type of drivers would work well in a TL box?

Online DRNB

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Re: Transmission line Speakers
« Reply #1 on: October 05, 2017, 02:28:40 PM »
"There is no shame in not knowing; the shame lies in not finding out." (Russian Proverb)

Offline bbe22

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Re: Transmission line Speakers
« Reply #2 on: October 05, 2017, 06:51:20 PM »
google  Paul K.  (Kittinger) and follow some of his work. He is probably the most active TL guru    out there         
Leonard Audio has a program to simulate, so go there also.

Offline Samayanaya

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Re: Transmission line Speakers
« Reply #3 on: October 06, 2017, 12:41:13 PM »
Quote
Fundamentals of TL Design.
Right, choose a speaker/subwoofer with a Qts between 0.4 – 0.6, and an fs of reasonable depth. From fs derive ¼ wavelength, chop 5% off that figure – this is your line length. Find the Sd of the target speaker/subwoofer, times it by 2, and this will be the CSA of your line. Build, wad, listen. That’s it, you’re a transmission line designer.

Seems easy enough  :point:  ;D

Offline JimGore

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Re: Transmission line Speakers
« Reply #4 on: October 21, 2017, 08:56:47 AM »
To me the biggest difference is in the the way the rear wave can be damped and the way a TL doesn't build as much pressure as a bass reflex cabinet.

My all time favorite type of speaker is still a tapered quarter wave tube (TQWT) which works on a similar principle as a TL, but with less folding. On paper it doesn't look like it performs any better than a bass reflex with a 6dB shelf, but it sure sounds very different.

Best is to just build a couple rough prototypes so you can experiment and hear for yourself.

Kind regards,
Ian.

Offline Rotelman

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Re: Transmission line Speakers
« Reply #5 on: October 25, 2017, 12:36:24 PM »
....Best is to just build a couple rough prototypes so you can experiment and hear for yourself.....

This is some great advice.

My curiosity got the better of me when I got hold of some old Tempest bass reflex enclosures housing a single 8" all range driver. The enclosure had a rectangular front mounted port. In their original form, they sounded crap.

I removed the rear panels and installed a horizontal labyrinth system internally to end at the original rectangular bass reflex front mounted port. The gap between the port invert and the enclosure internal invert was filled in with timber. I used copious amounts of damping material in the labyrinth, closed up the rear panels and gave it some juice.... End result was a huge improvement on the original. Definitely lower lows, but more then just lower lows, it was cleaner and smoother lower lows with great composure and well rounded, better defined and warmer mids and highs.

Great experiment with el-cheapo stuff made for a fun project with lots of learning (and beers) with very rewarding end results. Would recommend as a start to anyone interested in TL.







Offline Samayanaya

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Re: Transmission line Speakers
« Reply #6 on: November 07, 2017, 10:58:51 PM »
So I am busy with a design and have a couple of question...

With all the reading and calculating etc, I think I have a good grasp of what needs to be done to build a TL box.

If I make the port 10% smaller than the required size of Sd, I will add pressure to the line which might cause back pressure resulting in unwanted resonance but the bass will be tighter. By using damping material, should I able to get rid of the resonance?

My line calculation is done for 44Hz from the baffle. I read somewhere that I need to make the line 5% shorter but could not figure out why. Any ideas on this?

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Offline JimGore

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Re: Transmission line Speakers
« Reply #7 on: November 08, 2017, 08:25:42 AM »
OK,  there are a number of things to consider:

1. The smaller the opening, the less easily air can move so you will build pressure.
2. The smaller the cross section of your line, the more you inhibit airflow, thus building pressure.
3. Any bends, folds, obstacles and daming material will cause turbulence,  which in turn inhibits air flow, thus building pressure.

The air moving through the line has a certain speed and mass. Coupled with the length of the line that gives you a resonant frequency. Now if you slow down that air inside the line for any of tge reasons stated above, then the effect is that the line now looks "longer" because it takes more time for the air to propogate through the line. The result is that the tuning frequency becomes lower.

Each case will be different, so between 5 and 10% shorter line is normally recommended but it's a bit of a guess.

Also just remember that if you build a standard TL you will have massive amounts of parallel walls all through the line which causes high Q standing waves.

That's why I prefer to build tapered quarterwave enclosures - is can have 0, 1 or 2 folds and because it's tapered you immediately have less standing wave problems.

As for having "tighter" bass when using a small opening, I don't think that's an accurate description. The bass will be more constrained,  muffled, and dull perhaps but definitely not tighter.

Hope that helps?

Kind regards,
Ian.

Offline Samayanaya

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Re: Transmission line Speakers
« Reply #8 on: November 08, 2017, 09:41:04 AM »
Thanks Ian. It does make sense. I'll keep the opening the correct size.

I am doing a tapered design though. I am reducing from 1.5x Sd down to Sd. The calculated line is 156cm but will shorten that to 145cm (~8% reduction) depending on the build practicallity. I am also doing 2 folds as I want a bookshelf size unit. The 2 folds will allow a internal box depth of approximately 360mm.


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