Is there such a thing as a TL opened at both ends ? - diyAudio
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Old 26th March 2017, 11:48 AM   #1
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Default Is there such a thing as a TL opened at both ends ?

Greetings!

Here is my transmission line question a curiosity, perhaps more is there such a thing as a TL opened at both ends? basically an open tube with a driver mounted somewhere in the middle (I suspect), no closed end here, the second end is also opened.

I have found no reference to such a design or anything what so ever on the internet or on diyaudio, maybe I am not familiar with the English name of such an enclosure.
I would also like to add the fact that an opened tube is an acoustic resonator tuned to wavelength so it must have some kind of an output/bass contribution; I am interested in simulations, designs, accounts if nothing else, and of course a comparison (advantages/disadvantages) with transmission line enclosures we all know.

A variation on the simple design (one pine / two opened ends) would be to have other brances as well and another variation would be driver placement (offset?) for example the Mileva design (http://p10hifi.net/tlinespeakers/FH/...7-MLV-0v99.gif ) seems to be made out of three branches but that one has an (two actually) open end. Any idea how branching / driver placement might play a role?

By the way I ask this question in the context of a full range driver (no additional subwoofer support) in fact I think the original idea came from imagining a hybrid enclosure between an open baffle and a bass enhancing enclosure.
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Old 26th March 2017, 11:51 AM   #2
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The forum has sugested to me this thread (when creating this one) - What happens when a TL is open at both ends - of which I was not aware because for some reason google didn't included it in the first few pages of results.
Not much interest for the matter in 2011... maybe things changed since then.
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Old 26th March 2017, 11:53 AM   #3
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It would be twice the length and half the diameter of a normal TL of the same spec, might be a useful variant in a specific application
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Old 27th March 2017, 01:25 AM   #4
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Default Like these?

I think Scott's on to it.

Image you have a working TL design. Then imagine splitting the TL lengthwise down the middle (beginning to end) with a very thin partition. Still the same only now you have 2 TL's each with the same length and each with 1/2 the volume.


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Last edited by DonVK; 27th March 2017 at 01:33 AM. Reason: added analogy
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Old 27th March 2017, 01:31 AM   #5
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Nearly hehe
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Old 27th March 2017, 08:33 AM   #6
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An untapered pipe open at both ends is a 1/2 wave resonator, i.e. has an Fp of 1/2 lambda and reproduces both odd and even harmonics. As I recall, a variation was featured about 25 years or more back in Speaker Builder magazine, which I believe was called the 'Freeline' by its author.
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Old 27th March 2017, 03:32 PM   #7
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Now that changes things a bit - this is not the same "profile" as a quarter wave resonator which has only odd harmonics - this is the biggest difference between a TL in the traditional/commonly used sense and an open end tube (this is what it suppose to be called). That's double the harmonics and to me it sounds like double the output at the vents - not SPL - just more sound coming out... and offsetting the driver would have to be done more precisely I think because there is more going on in the tube.
I would really like to see a simulation! actually more than one.
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Old 27th March 2017, 04:05 PM   #8
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There seem to be conflicting opinions, 1/4 wave, 1/2 wave or something inbetween. Having re-read the links you gave earlier and a little more research I'm not able to come to a conclusion, the interactions could be more complex than they at first appear. Do you think there are any programs that could be used to simulate it?
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Old 27th March 2017, 06:10 PM   #9
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First of all the harmonics situation is very true - Resonances of open air columns and there is a video I found (for kids) that gives an idea of the tuning frequency of there things - https://www.youtube.com/watch?v=bHdHaYNX4Tk (at 3:32).

I don't know much about simulations etc. I don't live for computers, but I doubt that there is such a thing - as an acoustic enclosure I mean - because there seems to be ery little interest for the matter - I wonder why...
The system is more complex it seems because of the harmonics situation and when you move the driver in an offset position the pipe output - at an end will not be the same as the one at the other end - how the whole thing will behave... well I don't have the brain power to simulate it; and then there are other issues - how do these things actually sound/behave as acoustic enclosures - from a subjective point of view, what about the effects on the midrange (full range driver in the pipe) etc. what about the variations on the design with additional branches...
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Old 27th March 2017, 06:27 PM   #10
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You have an interesting idea. Certainly in the Bass Reflex camps there are many variations with 1-3 tuning ports and sim models for them. Two different TLs raises some interesting tuning possibilities.

However, the only box Sim program I currently use is HornResp and I can't figure out how to model a 2 line TL on it. It will do offset drivers and damping but only for single lines.
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