Lungster.Com - sonosub

Using the above guidelines, I assembled parts for the Sonosub from various sources. Many of the items were things I already had on-hand (goal #3). Other parts came from the local surplus/recycled materials dealer.

16 inch (inside diameter) cardboard "storage tube" by Sonoco, 3 ft long. I found this at a local surplus dealer. Note that this is not a typical Sonotube. The cardboard in this tube is 1/2 inch thick, twice the typical 1/4 inch thick concrete tubes. The thicker wall is nice, but adds to the weight and is not easy to work with if it's not almost perfectly round. My tube was almost round. Luckily, the imperfect parts were at one end, where I was able to simply shorten the tube by the offending amount. Cost : $2.00
Funiture grade plywood in varying sizes averaging 2 ft square. These also came from the same surplus dealer. Both sides are veneered with what looks like birch, with an 'A' side and a 'B' side. Thickness is roughly 3/4 inch though it varied from sample to sample. Cost : $2.00 per sheet, 2 sheets used.
Particle board, 5/8 inch thick. I had remnants of a 2 ft x 4 ft sheet originally intended for some long-forgotten project. There was enough for one round endcap. Cost : ?
Construction grade plywood, 3/4 inch thick. More remnants. Cost : ?
3/8 inch thick cherry veneered plywood. Yet more remnants. Cost : ?
Roofing felt. Leftovers. Cost : ?
Two 3/8 inch threaded steel rods, 3 ft long; plus washers, lock washers, and nuts. These came from the local home warehouse. Cost : $7.00
An INF-10 driver. Cost : $34, not including s&h.[INF-10, port tube and terminal cup; 7,814 bytes]
A plastic tube for the vent; 3 inches I.D. by 9 inches long. I was all set to use a piece of plastic plumbing tube when I realized I already had just the right size tube. The tube was the center to a roll of paper from a local paper mill. This roll happened to be 9 inches wide. Cost : $0.00
A terminal cup. I already had one. Cost : ?
Spray-on finishes, namely Rustoleum's American Accents Stone Creations (two cans, $14.00) and Clear Matte spray (one can, $6.00), plus primer ($3.00). Cost : $23.00
Ball feet. A downward firing sub must be elevated. I used four wooden balls (not entirely round; each had a small flat part) I already had. I don't know what I originally paid for them, but I found some at the local crafts store for about $3.00 each sold as "doll heads". Cost : $12.00
Parapix amplifer, with transformer and wiring connector. At $39.00, this was a much cheaper and simpler solution than building my own LM-12 amplifier. The transformer for the LM-12s would have easily cost $20.00 or more and I would still have a lot of work to do. With shipping and other charges, the final cost : $49.00. Note that as of this writing, the Parapix amplifier is sold out and no longer available from Apex Jr.

Total cost is $131.00 of the above itemized goods; darn good for both a subwoofer and amplifer. Cost could easily have been reduced further by changing the appearance of the unit - use latex paint instead of the Stone Creations; use simple wooden blocks for feet, etc.

Building the Speaker

Below are the notes I took during construction, plus any tidbits added via hindsight. The steps are not the most streamlined but represent the actual steps taken; not the optimal ones. This gives the feel of what was actually done.

Note - in all cutting and milling steps, remember to account for the "good" side of the stock. Most woodworking operations have a higher risk of tearing or damaging one surfaces than the other. Properly orienting the stock can minimize damage to the important surfaces.
Make the endcaps.
- Cut down the tube to the desired length of 24-1/4 inches. Scribe a line around the tube and cut it with a jigsaw. Cut from one or both ends of the tube so that any deformation of the tube (likely near the ends where it's weaker) is cut off leaving the rounder center portion. Cleaned up the edge as needed.
- The tube has an inside diameter of 16 inches. The tube's wall thickness is 1/2 inch. Each endcap consists of an inner 16 inch diameter insert and an outer 17 inch diameter cap.
- Mill two 16 inch diameter round inserts. I made one from plywood and one from particle board; it's what I had on-hand. These must fit snugly inside the tube. Don't assume the tube is exactly 16 inches in diameter. Make the inserts to fit, not to what it should be. To determine the actual inside diameter, I took masking tape, taped a circle inside the tube until it overlapped itself, marked the tape where it overlapped, removed it and measured it with a tape measure. This gave me the exact circumference. Divide the circumference by pi and get the diameter.
- In retrospect, my use of cheap plywood was a bad idea. While it satisfied my goal of using up stuff I already had, it lowered the quality of the top endcap. See the section on results.
- Mill the two outer round pieces from cabinet grade plywood. One is the baffle (bottom) the other is the top. I made them 17 inches in diameter to cover the 1/2 inch thick tube walls. I should have made them larger so that they stand a little proud of the walls. This would help hide any irregularity between the endcaps and the tube wall. [Four circles; two inner and two outer; 11,806 bytes]
- We now have one small and one large circle for both the top and bottom. My circle cutting jig uses a 1/4 inch hole as the center pivot point. This lets me use a 1/4 inch dowel to align each pair of circles at their centers.
- Pick one of the outer pieces to be the top - probably the better looking one; put that one aside. Align and two bottom pieces together to make the baffle. I used regular yellow wood glue. Clamp and let dry overnight. [Endcap glued and clamped; 15,123 bytes]

29-September-2000

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