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folded voight pipes??? [message #21357] Sat, 10 December 2005 10:34 Go to next message
jim denton is currently offline  jim denton
Messages: 162
Registered: May 2009
Master
Recently made contact with a seller on Audiogon about some used Lowthers PM6A's and he said that these will amaze and befuddle one in a Voight folded pipe design----well, since I live in a constant state of Befuddlement....(that's located North of Texas and just South of Kansas, ) it took me a few days to, blink.... FOLDED pipe?? Is anyone up on this? I guess I've seen plans for this in a BR box design but not in a pipe design? He also mentioned the Norway Lowther guys building bigger pipe boxes for the 8" over the 6" drivers---wider and deeper at the top --almost 4" seperate the baffles??? I'm searching for some more details to this idea ...JD

Re: folded voight pipes??? [message #21358 is a reply to message #21357] Sat, 10 December 2005 11:56 Go to previous messageGo to next message
roncla is currently offline  roncla
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Registered: May 2009
Master
Built many of them for an assortment of different drivers.
Basic a folded tapered pipe in which the throat is =Sd in area and the mouth (not the port) is 4-5x Sd and the length is 1/4 wave length of the target Fc(which will only work if its a straight pipe).
Advantages over a straight MLTL is a smoother FR curve as the harmonics in the upper range are closer together. Disadvantages are that the Fc is higher.
Usually Lowthers are BHL (back horn loaded) or BLH whichever term you perfer. However they can be used in a folded pipe if adequate BSC (baffle step compensentation)can be employed or equaliziation is used. I presently design and build single driver full range BLHs for Fostex applications, well full range i guess if you dont count the ribbon tweet i have with the 208e sigma.
IMO they should be used in BLHs for the optitum performance.
Do a "Google" on Lowthers and Lowther America.
ron

Re: folded voight pipes??? [message #21359 is a reply to message #21357] Mon, 12 December 2005 08:50 Go to previous messageGo to next message
Bob Brines is currently offline  Bob Brines
Messages: 186
Registered: May 2009
Location: Hot Springs Village, AR
Master
The "Voigt Pipe" is a design attributed to Paul Voigt, incorrectly, I might add -- Voigt's patented tapered pipe is completely different. It is tapered front to back, coming to a point at the top and being rather deep at the bottom. The driver is roughly 1/2 way down the pipe and there is a port at the bottom front. The best known "Voigt Pipe" is the Lowther Club of Norway design. This design most likely used the PM6A or PM6C.

Any "Voigt Pipe" can be folded, that is bent back on itself 180 degrees. The front then is the original pipe from the port up to the driver, and the top part of the pipe folds back toward the floor. In the case of the LCN pipe, this will reduce the height from 72" to ~ 40" high. A variation of the folded "Voigt Pipe" is the "Weems' Pipe", named after David Weems.

Neither the LCN "Voigt Pipe" or the "Weems' Pipe" variation are very good designs. They were build empirically without any real science behind them. They suffer from significant and very audible roughness in the 100-500 Hz range, right where the music is. Now that we have Martin King's worksheets, we do much better. You might investigate the MLTL design.

BTW, although I may get flamed for saying so, the "Voigt Pipe" is really a type of back horn. All of the same physics apply.

Bob


Re: folded voight pipes??? [message #21360 is a reply to message #21359] Mon, 12 December 2005 10:55 Go to previous messageGo to next message
akhilesh is currently offline  akhilesh
Messages: 1275
Registered: May 2009
Illuminati (3rd Degree)
HI Bob,
Good post. Could you elaborate more on why ot;s rough in the 100-500 hz region? I'll be interested to know.
thanks
-akhilesh

Re: folded voight pipes??? [message #21361 is a reply to message #21360] Mon, 12 December 2005 15:05 Go to previous messageGo to next message
Bob Brines is currently offline  Bob Brines
Messages: 186
Registered: May 2009
Location: Hot Springs Village, AR
Master

The success of a quarter-wave speaker depends on controlling the first 2 or 3 harmonics. The normal procedure with a "Voigt Pipe", also known as a Tapered Quarter Wave Tube, is to place the driver at the node of the 1st harmonic, which is acoustically, but not necessarily physically, 1/2 way down the pipe. This completely suppresses the 1st harmonic. The problem with a poorly designed TQWT is that the 3rd harmonic (there are only odd harmonics in a stopped pipe) is not properly suppressed. The Lowther Club of Norway TQWT is much too small in volume to allow the suppressed 1st harmonic to affect the 3rd.

In an untapered Mass-Loaded Transmission Line speaker, the normal procedure is to place the driver at the first node of the 3rd harmonic, about 1/5 the length of the pipe. Suppressing the 3rd harmonic reflects both ways and helps to suppress both the 1st and 5th harmonic. Generalizations are not real good with pipes, but I have found that if a driver works at all in a quarter-wave pipe, an untapered pipe will usually lead to the smoothest output.

The graphs above are are modeled output using a Lowther PM6C diver in the LCN TQWT, a quick hack at an optimized TQWT and an optimized MLTL. The MLTL presents the smallest physical cabinet and the smoothest output. I am treading as close as I think I can to the limits of what a commercial vendor can say, but is worth at least what it cost you.

Bob

Re: folded voight pipes??? [message #21362 is a reply to message #21361] Mon, 12 December 2005 16:48 Go to previous messageGo to next message
akhilesh is currently offline  akhilesh
Messages: 1275
Registered: May 2009
Illuminati (3rd Degree)
Nice post Bob.
thanks
IN the end you said:
"I am treading as close as I think I can to the limits of what a commercial vendor can say, but is worth at least what it cost you. "
None of what you are telling us in the post above is copyrighted by you, right.. it's from Martin King's math designs?
thanks
-akhilesh

Clarifying questions [message #21363 is a reply to message #21361] Mon, 12 December 2005 16:55 Go to previous messageGo to next message
akhilesh is currently offline  akhilesh
Messages: 1275
Registered: May 2009
Illuminati (3rd Degree)
In your post above , Bob (i admit I havent really read through voigt pipes so pardon me if this is a basic question) does the harmonic = a multiple of the frequency of tuning of the port in the pipe? so a firts harmonic = the frequency of the port of the box, and so on?
thanks
-akhilesh

Good Information [message #21364 is a reply to message #21359] Tue, 13 December 2005 05:35 Go to previous messageGo to next message
FredT is currently offline  FredT
Messages: 704
Registered: May 2009
Illuminati (1st Degree)
Thanks to Bob and guys like him who are willing to challenge some of our commonly held misconceptions with real data. The Fostex FE-166E Voigt pipes I built (and sold to Jim) were loosely based on the Lowther Club of Norway design. To my ears they are pleasant sounding, especially when placed in a room whose dimensions accentuate the 60-80hz range, but they definitely are colored. Having heard Bob's FT-1600 MKII design in one room at the GPAF, with the Voigt pipes only two doors down, I have to agree that Voigt pipes aren't the best enclosure design for Fostex drivers.

Re: Clarifying questions [message #21365 is a reply to message #21363] Tue, 13 December 2005 05:49 Go to previous messageGo to next message
Bob Brines is currently offline  Bob Brines
Messages: 186
Registered: May 2009
Location: Hot Springs Village, AR
Master
Right. The first harmonic is the system tuning frequency. Higher harmonics are are multiples of this.

You have to be careful of exactly how the author is numbering things. When talking to anyone not deeply involved in the technical, I use the numbering system above. Particularly when dealing with computer programing, you will see the fundamental listed as F0, the first multiple as F1 and so on. Then there is a numbering system based on overtones. In an open pipe where all harmonics are produced, the first overtone is the second harmonic, or F1. In a stopped pipe, the first overtone is the third harmonic, or F2. Totally confusing to the casual reader.

Sorry, I couldn't resist.

Bob


Re: folded voight pipes??? [message #21366 is a reply to message #21362] Tue, 13 December 2005 05:55 Go to previous messageGo to previous message
Bob Brines is currently offline  Bob Brines
Messages: 186
Registered: May 2009
Location: Hot Springs Village, AR
Master
None of what I posted is copyrighted. It is all pretty much common knowledge. My problem is that I am coming close to proselizing my own product. That is a no-no on this forum.


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