Stephen has made these remarkable and very beautifully constructed cabinets:
Detailed design plans were provided by Don Nordstrom, after considerable discussion concerning specifications. The enclosures are 62 inches tall, are 10.3 cubic feet (310L) , and weigh an estimated 210 lbs. With the Tannoy Silver 15inch drivers. The finish is cherry wood veneer ( not as dark as in the picture). The shape is "bat-wing" or polygonal with no internal angles. They have all been rounded on the interior. The inside is heavily braced. There are minimal damping materials. The ports are 4 inch in diameter and were "tuned" to a length of 8 3/4 inches each, read more about this below. Most sides, bottom and top are 1 inch MDF, and the front baffle is 2 inch Baltic birch. The drivers are mounted from the outside. I am using a modified version of the Gold 15" Monitor as a crossover, (using all new parts, including Ultra-tone silver in oil and Hovland capacitors, Mills resistors, and Perfect-Lay inductors), although this is a work in progress.
The crossover in the box:
What's in the box: Silver Ultra-tone cap (2 uF on HF) with the 4.0 mH inductor from Jensen. Other caps are Jensen and Hovland. I paralleled a 10uF Hovland cap with a 1.5 uF Jensen cap on the woofer circuit. Resistors are Mills. Actually, everything sounds very good at all levels of the audio spectrum to my ear and to the ear of several others.
The amplifiers are 845 SEt's with about 22 W output. They were made by Nori Komuro and have superb bass, as does the system in these cabinets. The 845 amp is now replaced by 300B SET-monoblock Amplifiers using the Tamura Permalloy transformers and the TJ Full Music mesh plate 300 B tubes
A method is described for port construction and tube length determination using port covers which are available in various sizes from Madisound in the U.S. ($2.50 each for the 4 inch diam. size). PVC pipe is availble from most any plumbing supply store and is quite inexpensive. The method is based on the assumption that several different port tube lengths may be necessaery to determine the "optimal" length or tuning. Further, damage to the cabinet may occur if repeated tight fitting tubes are forced into hole created in the cabinets( the sort of tight fit you would like with the completed cabinets).On my speakers I used 4 inch diameter ports; 4 for each cabinet. Drill the cabinet holes so that the "top" grade 4 inch PVC pipe fits snugly in the hole. The "top" grade PVC pipe has a thicker wall than the lower grade PVC ( The 4 inch internal diameter ,of course, remains the same). The point of my method is that it is an easy way to rapidly change tube lengths for "aural tuning", which I believe to be necessary for an individual cabinet system. After drilling the port hole for a snug fit for the top grade PVC pipe, purchase also the lesser grade PVC pipe which has a more narrow wall thickness: cut various lengths in groups of 4, and place them over the port cover. Because the flared port covers with the attached thinner guage PVC tube will slip easily into the port holes, wrap each one with a single wrap of weatherstripping which will provide an air tight fit. By listening to the various port lengths (aural tuning), you can rapidly determine which length is optimal. Once that is done, cut the lengths of the top grade PVC and place them for the snug fit. Thus, the port covers are used for "sizing" only, and not used in the finished product. In this way, you do not damage the cabinet during tuning of the various lengths. I do not believe you can just accept a computer generated recommended tube length, and you need to tune the port lengths by ear, just as you would listen to other key parts of a system to determine which is best. Stephen
© PE1MMK Hans Hilberink & Stephen Wangensteen. 2001.
