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

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

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