Fostex FE208 Sigma
"Getting Horny"
Stage 1
Deep Thoughts
After reading about single driver speakers and why they sound better, I am convinced that a back-loaded horn is what I will need for my low wattage amp. Go to The Single Driver Web Site for details on why single driver speakers sound better.
Since the speaker is cheaper to build than the amp, I decided to transfer all funding towards this project... including the money destined for tweaking my preamp. I'm a bit sick of modifying it so on to something new for now. I can always put my solid state preamp back into duty while the speakers are evaluated and I wait for my amp parts. Because the amp has a volume control at the input, I can just control my volume there and be done with it all... The only problem is that I want to add a phono preamp and turntable some time next year. So I will definitely continue tweaking the preamp at a later date.
I don't have much for now, except for the original Fostex diagrams and my drawing (converting to inches).
Feeling Backed Up?
I've gone back and forth on which cabinet to build. The BK201 seems to be winning out as I can more easily add curves to the folded sections of the horn. Also, I found a good amount of tips from one builder who posted on AudioAsylum.com. Here's what he recommended:
Posted by redsetter <mailto:siwan@acadinfo.co.uk> (A) <http://cgi.AudioAsylum.com/scripts/mail.pl?user_ID=13530> on July 29, 2002 at 06:58:25
After much time spent building and tuning my BK201 Fostex 208Sigy speakers I can testify that they are indeed a very good design - but there is much involved in getting them to sound right. Initially they sounded horrible - boxy and just plain colored with no bass (even with well run in drivers). Then the serious work of trial and error started - this is the work of horn builder (i guess! not being a specialist)
1 - double skin the whole speaker (especially the front panel) in a dissimilar material to the main cabinet. I used block board for the main and veneered chipboard for the double skin
2 - brace the cabin - a few well placed dowels work wonders and a heavy 'floor grade' tiles attached to the base of the speaker
- 1 dowl horizontal near the exit
- 1 at 45 degree to vertical between the rear of the first curve and the last angle - (this is a good one)
3 - line the compression chamber directly behind and around the driver in 1/2 round 1 cm profile trim to deflect rear pressure waves whilst
minimizing absorption - also 1 square patch of carpet felt - 8x10 inch
4 - i treated the fostex units with 1 coat of dammar lacquer
5 - cork lining for the horn exit up to about 1/3 way up
6 - coat the whole speaker in urethane to get the last once of see throughness
7 - cork line the rest of the compression chamber (not already lined in 1/2 round profiles with cork)
Finally found a tweeter from an old pair of Linn indexes and added 1.5mf cap in series with +ve terminal and she sings like a good un. (also tried a Visaton TL16 here but they did not like each other company??? can't figure this one out - but would like to?) After the list of mods - sound changes from boxy, to free of the speakers - warm and detailed with quality bass (not masses but enough for most my friends who do like bass. I am talking about smooth detailed warm real sound with dynamics) As ever I was wondering what a real horn speaker would sound like in
comparison to my own - so I bought a pair of Beauhorn reference DX4's. It is hard to compare two different designs - but on the whole I would refer back to Dick Osler description of the Basszilla with fostex and with lowther. The Fostex sounding rounder and warmer - giving up detail for muscular presence whilst the Lowther gives up some umph for detailed presence. A audiophile friend of mine who is not known to be polite about some of my experiments said of the comparison - 'it now comes down to the subjective - one is not obviously better than the other - they are just different' - which is the most complementary this he has said so far.
All in all the BK201 Fostex 208Siggy stands up more than well to the Beahorn - considering the price difference.
Rest of the system consists of a Welborn lab Laurel, Borbely line stage pre-amp (very good by the way) and Marantz CD7. If you have built a pair of BK201's and did not have much luck with them - try these mods and see what happens.
By the way - the full modded speakers weigh in at about 45kg each but they are half the size of the Beahorns.
redsetter
So with that said, I am leaning towards the BK201 cabinet. Here are the plans in metric measurements.
They don't seem too hard to build... It's just the angles that get me worried as I am an impatient person. I want easy angles!
Construction
September 29, 2002 - Construction has begun. Since I don't own a truck, the 3/4-inch MDF was expensive as I had to buy the small pre-cut 2 x 4 feet sheets at $6 (US) per sheet. Also, I wanted to make sure the cabinet was dead to vibrations so I bonded the 3/4-inch boards with 1/2-inch MDF boards to create 1-1/4-inch thick cabs. The interior horn would still be made with the 3/4-inch stock material. Total cost for wood so far = $90. This is somewhat higher than expected.
I've made some of the big cuts but have not gotten to the meat of the project, so pictures are not available yet.
