Building a pair of Back-Loaded Horn Speakers for Fostex fe166es-r Drivers
Zowie! Yeah man! Dig it!
Yup, I bought a pair of those special edition Fostex FE166ES-R back in January 2005 and built a back-loaded horn (abbreviated BLH) for them, and I am now a happy horn owner.
In 2004 I built a pair of the Adire HE12 speakers and learned a lot - last year it was horn time and I learned even more... Those are the Adires on the left below, and the back-loaded horns are on the right. I took (bad) pictures through the whole process, and I'm finally getting around to building the page on the new speakers!
The grain on the sides is not that blotchy in person, figured veneer with burls and trickly swirly grain - lost a lot of time finishing the sides (twice). All trim is figured maple. Internal braces, such as they are, are also maple. Threaded rods run across the cabinets for additional resonance tweaking.
These are based on the Fostex 'factory' plan on the Madisound site - and they are deceptively big, a little more than two feet deep.
I doubled the top and back, and added the maple baffle, all are mild deviations from the oiginal Tetsuo Nagaoka plan,
as internal sizes were maintained from the plan (except for one correction noted later).
*Heavy* suckers - almost two entire sheets of 4x8-3/4 birch veneer ply in each cabinet.
Makes you think hard before you start moving these around, or even flipping them over.
For those of you just starting on this path, well, keep going. It just gets better and better!
Thanks to the late-great Terry Cain for inspiration and advice, to Steve Killian for periodic checkups, to Jim Dowdy for being the DowdyLama that he is, to Fostex for making these schmancy drivers, to the forums for keeping me going, and finally - importantly - to Blithe, who has far more patience for the parade of homebuilt audio through the living room and the evenings and weekends in the shop than I ever expected or deserved!
What's so great about the Fostex FE166es-r?
The driver is based on a normal Fostex FE166 with some radical tweaks
Because of the magnet size this driver has a very high 'Q' and can really only be used in some sort of horn. The same 'Q' makes the response rise through the bass and lower midrange, then level out and extend up to almost 18kHz before starting to drop again. This response curve matches well with BLH horn loading - the bass horn behind the driver loads the driver and cuts down on dopple distortion, and a drop in horn efficiency through the mid band can be tailored to match the riding response of the front radiation so that, in theory, you get a relatively flat response at high efficiency and no electrical crossover to complicate things and smear the signal.
In my case it seems to have worked - and there is another bonus in that these drivers are directional - not so directional that your head must be locked in a vise, but enough that some significant room interactions are reduced.
OK, if these are so wonderful, where can I find a pair of drivers?
Break-in procedure for DriversPretty much everyone agrees that it takes a long time to break-in most Fostex drivers, and the fe166es-r is no exception - I put several hundred hours on them before final assembly of the horns, and they continued to change even after that extensive burn-in.
(Also need to apply ductseal and felt before soldering the leads onto the connection tabs)
Update on FE166ES-R Horns
But they are a lot deeper than the Adires -- and heavier!
Better have a lot of clamps on hand for this project - I used the 'free' side to help hold the interior walls in place as I glued up one side completely, then applied oil finish to the interior before gluing the free side permanently
I used bags of play sand to assist in gluing the double-thick side panels - also added threaded rods through the cabinets in three places to help locate everything during the repeated glue steps
From the other side... note the plastic film used to prevent the interior joints adhering to the free side until the final step
Getting close to hearing them now - checking the fit of the figured maple baffle/soundboard and trim, with cocobolo widgets to separate the horn edges from the baffle