High Fidelity Engineering Co.
ALTERNATE TUNING
Model HDT206EM
High Definition Loudspeakers
ALTERNATE TUNING GUIDESince the release of the HDT loudspeaker design in 2003 we have come up with what we feel is a substantial improvement in overall performance of the HDT loudspeakers. If you’ve researched the design you know it was originally developed as a two-way loudspeaker in 1996 using a conventional 8 inch driver and 1 inch tweeter. When the design was adapted for the Fostex FE206E driver in 2003, the tuning of the ports and
passives was raised to accommodate the higher fs. This allowed the cabinet and Fostex to work together and with the addition of our Phase Guide to the driver the end results were quite good.
We found while comparing the original 1996 speaker with the HDT that the higher tuning of the ports and passives reduced the fundamental operation of the multi-chamber design. In the original speaker there is no treatment inside the enclosure or any of it’s chambers yet it has the most liquid midrange you’ve ever heard. The Fostex based HDT on the other hand was more congested. It saw most of it’s loading from the primary chamber leaving the secondary and averaging chambers doing little work and hence emitting little energy. This prevents the speakers from doing as good a disappearing act as the original 1996 model.
Since the cone of the FE206E driver is so thin it is important when you build a pair of HDT speakers to know exactly how to treat it and with what. This paper will describe the proper procedure for treating the inside of the cabinet. It will then cover the optional alternate tuning that we suspect will be received as a significant improvement even though we can find nothing bad written about the 200 pair that have been built to date.
The alternate tuning is optional because many will be perfectly fine with the way they sound now. And it requires an additional modification to the drivers, new passive radiators and different length ports. The ports can be easily modified once the driver and both passives have been removed from the cabinet.
The alternate tuning when combined with the correct treatment of the inside of the enclosure will result in a significant increase in bass and extension of bass frequencies. It will remove the congested sound in the midrange and treble and activate the complex beauty of the enclosure design to make all the chambers work resulting in a head shaking disappearing act.
CABINET TREATMENT
The material used for all internal cabinet treatment is 1 inch thick egg crate foam like that used as mattress toppers. You can find it at Wal-Mart, Target, and most fabric stores. After you have removed the driver and both passives, or when you are building the cabinet new you should install this foam in specific places, cutting each piece for a snug fit.
Piece 1 is a 12x12 square that fits in the bottom of the averaging chamber. It can be installed though the square port in the lower rear of the cabinet or from the top through the transmission line.
Piece 2 is a 16x7 rectangle that fits on the rear panel behind each passive opposite the oval cut-outs. It should be pushed to the top of the chamber. You will have one of these pieces for each side of the enclosure.
Piece 3 is a triangle that fits in the top of the primary chamber above the driver.
Piece 4 is a 4 inch strip that mounts under Piece 3. It should be cut to a length to cover all three sides of the primary chamber.
Piece 5 is cut to match piece 4 and located just below the driver opening where as piece 4 is located just above the same opening. Piece 5 will also just cover the bottom of each oval cut-out so it should be notched so as not to obstruct the opening.
DRIVER MODIFICATION
The driver should be returned to Decware for a special viceoelastic wax glaze on the cone which lowers Fs slightly and improves midrange.
PASSIVE RADIATOR REPLACEMENT
The passives should be replaced with the alternate design available from Decware.
PORT LENGTH MODIFICATION
Front port should be lengthened from 6 to 11inches and the side ports lengthened from 8 to 17 inches. Use PVC
cont.
Note: This is available as a .pdf file
https://www.decware.com/HDTALTERNATETUNING.pdf