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 ½ 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/images/mileva-FE127-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.
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 ½ 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/images/mileva-FE127-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.
The forum has sugested to me this thread (when creating this one) - http://www.diyaudio.com/forums/multi-way/180438-what-happens-when-tl-open-both-ends.html - 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.
Not much interest for the matter in 2011... maybe things changed since then.
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
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.
http://www.diyaudio.com/forums/swap-meet/227884-frugal-horn-mikasa-fostex-126e.html
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.
http://www.diyaudio.com/forums/swap-meet/227884-frugal-horn-mikasa-fostex-126e.html
Last edited:
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.
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.
I would really like to see a simulation! actually more than one.
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?
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...
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...
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.
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.
Yep. That was a very good video. I think we know now why you don't see TL's designed like this. I can't envisage a situation where multiple harmonics would be desireable.......
I am familiar with Hornresp and the people who made it could make one that does open pipes... but there is no interest... however there are other much stronger mediums of simulation out there, people who are engineers and work with them might know how to do such a simulation without a "special" software dedicated to TL. It's much more simple for average people to make a hole in a pipe and put a loudspeaker in there.
By the way - I believe there is no (written) word on the issue from MJ King... someone who should have a hole attic full of various monstrous/frankensteinian shaped pipes that never see the light of day.
By the way - I believe there is no (written) word on the issue from MJ King... someone who should have a hole attic full of various monstrous/frankensteinian shaped pipes that never see the light of day.
Yes, ideally BEM simulation would do arbitrary shapes. That's an aspiration of mine, but I'm not there yet.
actually, I think Martin might have far fewer failed franken-projects kicking around than most of us
and, a pipe organ as any type of TL - really?
and, a pipe organ as any type of TL - really?
Ok, this does not work as I was hoping so I’m going to be more specific about it – the reason I’m interested to see a simulation (the most important is a typical straight line with driver mounted at equal distance from the open ends) is to see how the null situation is – I don’t remember what caused the nulls problem, those frequencies at which the sim’ always shows a crevasse (for example if you tune at around 50 hz you get the problem at 175-225 hz). I suspect there will be more nulls as there are more harmonics “singing” out of the pipe. Then there is the driver offset situation – how does that remedy the problem of the nulls? And how do all of these work in reality… nobody has 1000db crevasse in real life.
The nulls where related to main cone / terminus interaction (cancellation)… now if you have a second open end with an offset driver… everybody is playing something else, how will it sound at distance … that’s why I want that simulation.
The nulls where related to main cone / terminus interaction (cancellation)… now if you have a second open end with an offset driver… everybody is playing something else, how will it sound at distance … that’s why I want that simulation.
So, what you saying? You were leading us up the garden path and round the corner into the mysterious secret garden to see if there were any monsters there because you were afraid to go alone........or something
The monsters are in my closet and under my bed where I can keep a close eye on them 😉
If I could do that simulation I would, cause I'm really curious about it.
If I could do that simulation I would, cause I'm really curious about it.
How about you knock something up out of a couple of tubes that you could slide in and out of each other, That would give you a couple of variables to play with
- Status
- Not open for further replies.