ms@dvamc.UUCP (07/11/83)
In reply to Shane: I didn't think I had enough of an address to reply by mail. There is a publication called Speaker Builder, comes out four times a year, it is a sister pub of The Audio Amateur. (P.O. Box 494, Peterborough, New Hampshire 03458). As the title suggests, it is devoted to speaker building information. There are also some books available: Loudspeaker Design Cookbook by Speaker Research Associates is good, and more can be found by looking at the back issues of Speaker Builder (which I believe can be ordered). Also check the classified section of Audio magazine for places like Speakerlab, they have kits and components. I built my own speakers a few years back and am still happy (a Rogers LS3/5a copy and 9f' transmission line subwoofers - biamplified). Just for fun I'd like to build electrostatics, ah, one of these days. Good luck, I'd be happy to help in any other way. Marc Sabransky decvax![duke,mcnc]!dvamc!ms
dbg@ihldt.UUCP (10/10/83)
I recommend building from scratch. I also recommend going with an uncomplicated two way system, with a simple 6db/o crossover (cap in series with HF driver, coil in series with LF driver). If you try to get real fancy with your design, you'll almost certainly get burned. I know that from experience. I've designed speakers following the popular equations, and I've designed speakers ignoring all parameters and just going on trial and error and intuitive feel. I would recommend a mix that tends toward intuitive feel. Select a LF driver and enclosure, based on Thiele's equations, that suit your needs (power, efficiency, low end, cabinet size, etc) Experiment heavily with port size and depth, be generous with fiberglass wool inside the enclosure (fasten it loosly to the walls), and seal the enclosure permanently at the rear. Don't spend too much on the drivers and always front-mount them. Any access needed to the inside of the enclosure can be done thru the driver mounting holes. The enclosure should be made of particle-board. You can always add brazilian rosewood veneer when you're done if they sound good enough. Select a HF driver by whatever means you can (price, brother-in-law's recommendation, trial and error, etc), but be sure the efficiencies are compatable. Don't use a horn tweeter with an inefficient LF design. (Don't use horns at all. The good ones cost too much and the cheap ones sound cheap) Finding reasonably good, inexpensive drivers is part of the trick. There are plenty of driver manufacturers around that produce reasonable drivers -- CTS, Eminence, Peerless to name a few of the older, not so expensive companies. Altec, E-V, JBL charge big bucks for their drivers. I used to buy what I considered a pretty decent tweeter from CTS by the case ($60 for 12). It was generally referred to as the "phenolic ring" tweeter. The quality went way down during their strike of the mid seventies, but I believe they're back in production out of CTS of Brownsville, Texas. I can't offer any real recommendations for driver selection as I've been out of the business for a while and no longer have any accounts with driver manufacturers. Another option that seems to have merits is a subwoofer system. A pair of 6" two way units and a common subwoofer would be an interesting project to try to build from scratch. If you want to experiment, you might consider getting the McGee Radio catalog from 1901 McGee St, Kansas City, Mo. Lately they've been carying 10" and 12" subwoofers with dual voice coils (no fancy circuits to derive a common channel for the sub woofer). happy building, ihldt!dbg
rjr@mgweed.UUCP (10/13/83)
After reading ihldt!dbg's thought on building speakers, I thought I would throw out mine: I have experimented with many speaker box designs. There were quite a few articles in "Popular Electronics" (I think the author's name was Webb) about building cabinets, mostly dealing with bass reflex types. I never had good luck with ported, or bass reflex designs. After consulting with a friend of mine who is an acoustical engineer at a well known acoustical lab affiliated with IIT, it seemed the best bet was to go for the infinite baffle design. It is a good one since, for one thing, the enclosure size is not critical, as it is with vented enclosures. One can try all kinds of speakers in the box without worrying about cone resonances etc. The main rules for constructing a cabinet (which apply to many types) are to make it heavy. Don't use 1/2 inch plywood. Use 3/4 inch stuff at least. If the cabinet is much larger than a bookshelf size, fasten ribs inside to stiffen the sides and back. It is a matter of choice whether you want to use screws or nails, but definetly use glue as well! The only exception to this is the front or back, if you want to be able to remove it. Put at least 4 or 5 inches of fiberglass padding on all inside surfaces, except the front. The idea is to make the box look as large, acoustically, as possible. I mounted a screw terminal strip on the back and brought out all speaker wires individually. The crossovers are mounted on the outside of the cabinets. I prefer a 3-way crossover system. My cabinets have a 12 inch woofer, a 8 inch cone type mid-range unit, and a horn tweeter. I selected crossover frequencies of 500 and 2500 Hz. My crossover is a 12dB/octave design taken from an old audio handbook. I wound the inductors with 22 Ga wire using laminations from a couple of old power supply filter chokes. The capacitors are all mylar or paper types. Do not use electrolytics! Even the non-polarized speaker caps that are sold (Radio Shack and others) are back-to-back electrolytics and the tolerance is lousy and they deteriorate after some years. If you have room, you can even use oil types. My measured crossover characteristics came out very close to the design figures. The low frequency crossover turned out at 535 Hz rather than the intended 500, but otherwise there were no other departures. For serious listening to classical music, I also use a pair of "Ionovac" tweeters. These have a high impedance input and I connect them across the existing horns. Today, I would recommend one of the dome tweeters. They are clean and efficient. One should connect the tweeter to the crossover through a "L" pad. Many speaker systems used to incorporate one as a "brilliance" control. It helps balance out the system. Single driver wide range "coaxial" speakers are OK for background use only, as far as I am concerned. I don't think one can expect a 10 or 12 inch cone, being pounded by bass, to simultaneously work well on the mid and high frequencies. Be sure the high and mid range speakers have solid backs so the back-wave from the woofer does not reach them. Bob mgweed!rjr