The Side Horn 108ES Project by Michael Zhang This project started last year. I first wanted to build the late Mr. Tetsuo Nagaoka's Super Swan, the D-108S. I bought a Japanese book with the plan and I had the fortune to get help from some Japanese Diyers, such as Mr. Nebu and Mr. Kusano who located a pair of Fostex FE 108ES drivers. I also received advice and encouragement from Mr. Nebu's forum. I had some of my personal non-audio friends in Japan (Thanks! guys.) buy and ship them to me. This 10 cm driver according to Fostex, has a frequency range from 80HZ to 22KHZ, 93dB/w (1m). The cone is made of banana fiber. It is hand made. The build quality is indeed very good and I think the pair is worth the $300 I spent for it (including shipping of course). The original D-108S plan uses 15mm thick plywood. I had to convert it to use 3/4 inch thick plywood. I tried but never finish the conversion. Then I put off the project for quite some time because I had other more important things to do. At the mean time, I learned more from reading about other people’s projects (Big Fun, All Fun, Hedlund, etc.) and frequenting James's forum and I started to have my own ideas. I want a horn with smooth contour in a manageable size. I used James' horn calculator to get the numbers and came up with a horn plan of my own. However, it was quite difficult if not impossible to compromise between the horn mouth size and the horn length within the predetermined overall size of the horn: what I got was a horn with shorter length and smaller mouth than the numbers dictate. Mr. COEF who has done some very interesting DIY horn projects and simulations, introduced me to the Nagaoka style of back-loaded horns. I basically quote here: ~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~* [chamber] The chamber volume formula is the same as yours, but Mr. Nagaoka usually sets the crossover range between 150-250Hz (corresponds to 300-500Hz cut-off). [throat Area] We use the cone area times 0.5-0.9 corresponding to Q of the driver. Wider throat gives high level and dull bass output. On the other hand, lo-Q driver can keep high speed response and difficult to get the high level bass output. That means we have to emphasize the bass for lo-Q driver such as 108ES. First fix the throat, then chamber (crossover). [length] We consider the driving force of the full-range driver to fix the horn length. Longer horn enables lower range output, but requires powerful driver. If one wants high low-end output and accepts dull bass, he goes to 4.0m horn. We usually consider the balance of the length and high-speed/dull trade off referring the successful cases as SWAN. There is no formula for folded horns in terms of length, but 2.0-3.0m will be successful. [flare rate] Flare rate is basically exponential and flare freq. goes 25-35Hz depending on the cabinet size. With the balance to the length, we sometimes use the cascade horn, e.g. 20Hz flare freq. for 1st 1/2 length, 30Hz for next 1/4 , 40Hz to exit. [mouth area] Mouth area is restricted by cabinet size with fixed length. We usually balance the length, flare rate and mouth at the same time for fixed cabinet size. ~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~* I decided to follow this approach because I think this is a proven way to make good compromises. In order to use Mr. Nagaoka's formulas, I went to http://village.infoweb.ne.jp/~fwgi5816/SP/backload.htm The way the applets are written for horn calculation shows a lot of flexibility. There are several steps. Besides entering the driver parameters, you can make decisions as to the length, mouth size and other characteristics you might want for your horn, for which the applets give some recommended values as well. With the Mr. COEF's help, I got the numbers from the applets for my horn: throat=43.2 cm2, pre-chamber volume = 1.9 liter to make a cross-over at about 225 HZ, mouth = 780 cm2, length= 270cm. The first 3/5 length of the horn expands exponentially but less so near the mouth. I want the horn to have smooth folds like the small Isophon horn for more efficiency and have a trapezoidal shape to kill the standing waves. The small front baffle where the driver is mounted and most of the air chamber, stick out of the horn body for better imaging (kind of imitating the Super Swan whose air chamber perches on top of its long neck) and the segment between the throat and the first fold should be as long as possible so that less problems happens here. This segment also has a divider in the middle so it has two branches. The purpose of this is to help with efficiency and panel bracing. Because the way the horn folds, I used a reflector at its end so that the horn mouth opens to both the right and left sides. This way the horn couples more with the floor. Each opening on the side panel is about 780 cm2 and the horn contour cross-section where the opening start is about 780 cm2 too. You can see through the two openings from one side to the other. I made an opening to the reflector so that I can put sand or lead shots in side it. On the diagram, the expansion of the horn seems not to be as much as it should, but the trapezoidal contour expands in the other dimension as well. The sidehorn plans are now available in a TurboCad zip file which you can download here (you need to unzip it). Some bitmap images are also enclosed. In spite of sore muscles and back, I enjoyed building the horn as much as designing it. I used 2 sheets of 5'x5' 13 ply 18mm or 3/4 inch Baltic plywood. I wanted to use a circular saw but I could not handle it to make precision cuts. I now think a good table saw would do the job. Anyway, except an electric drill, I used only hand tools. I used a Japanese pull saw to do all the cuts, including many angled ones. A block planer came handy when the cuts were not perfect. Clamps and wood screws were used when I assembled panels with wood glue. I also chose polyurethane glue and wood filler to make panel joins air-tight. At the horn folds, I used cement form made of paper for the curvy parts. When the pieces cut from the cement form are glued to their place, they feel as stiff as the plywood. I used a polyurethane foam ("Great Stuff") to fill the voids behind the cement form pieces. I have not given a nice finish to the horns yet but I have been listening to them for about one and half months now. The CD player is Samsung DVD 709 tweaked based on Bobwires’ recommendation and the amp is the Zen amp from Decware. The horns seem to become more and more clear and refined as the time goes by. Even though the theory says that mid and treble sound have strong directivity, the clarity improved quite a bit after I placed some old wool sweater over the mouth reflectors (I plan to use something better looking in the future). I think that for back-loaded horn that opens anywhere, be it at front, rear or side, smooth contour with few folds has the disadvantage of less attenuated mid and treble. Since I do not have any measuring instruments, all I can tell about the sound here is only my subjective impression. First of all I can listen to them for hours without feeling tired. The lyrics become very easy to understand, I now not only enjoy the melody in songs but also the way the singers do their phrasing. I do not know how low the bass goes, but I remember that my wife once asked me: "what's happening outside?" when the low level rumbling she heard was from the start of a rock song. The bass seems to have a shape, not the kind of well defined shape, but you can tell how tall and large it is. The treble is real and pleasurable to hear. As for the mid, these horns are very good at incarnating the female voices (I have not listened to much male voices yet on them). I like to listen to some old Chinese pop songs. I have to confess that I felt embarrassed to get so intimate with the voices. Thanks to Samsung 709, the soundstage is simply amazing. I recently bought an album, entitled "Chinese Bamboo Flute" on the LaserLight label for $2.99. The last tune on the album, "The Crab and the Egret", describes a dramatic fight between the 2 different creatures with a lot of Chinese drums, gongs and cymbals. I play it just for the soundstage fun. I also noticed that the speakers are sensitive to changes I made to the amp and the CD player. In conclusion, I feel that it was an interesting, educational project. I would like to thank Mr. COEF, GM from Atlanta, Mr. Kasuno and others for their invaluable advices and help. I am also grateful to all those who show their ideas and projects on the Internet I read and to James for his wonderful web site and forum, and many knowledgeable participants thereof. Michael Top