Fostex FE167E TL project - diyAudio
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Old 30th April 2005, 04:19 AM   #1
Lensi is offline Lensi  United States
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Default Fostex FE167E TL project

hi all,
I've just finished a year-long project to build my first full-range speaker. Until I fired them up for the first time I had never even heard a full-range, single-driver speaker. I wouldn't have even attempted this project without the valuable information provided by Martin King at www.quarter-wave.com. Although I didn't copy his plans, I did use his Mathcad applet. Thanks, Martin! And thanks to all the posters at diy forum, among others who convinced me to give this a shot.


FYI, I'm using a Fostex FE167E. Internal wiring is DHLabs T-14. Binding posts are Cardas unplated copper. The cabinets are internally braced with dowel rods. Cabinets are 44" high, driver is 37.5" up from the floor. Acousta-Stuff inside, as well as 1/2" and 1" acoustic foam.

Lensi

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Old 30th April 2005, 09:02 AM   #2
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Is it a straight ML-TL or is it folded?

dave
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Old 30th April 2005, 12:36 PM   #3
MJK is offline MJK  United States
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Old 30th April 2005, 02:41 PM   #4
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Reminds me of Bob's Mk1 FE1600 design, albeit with the round port he's used in his latest Mk2 variant. Looks good to me!
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Old 30th April 2005, 02:49 PM   #5
Lensi is offline Lensi  United States
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The enclosure is a straight MLTL. I designed a BSC and impedance correc tion before I finished the cabinets, but the bass was so profound that I had to take out the BSC entirely. I'm tweaking the impedance correction by ear. So far , I'm getting the best mid-high frequency reproduction using a parallel combination of 6.8uF, 5.6uF, 4.3uF and a film and foil .47uF. In series with that is 13 Ohms of resistance.


Lensi
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Old 30th April 2005, 03:57 PM   #6
MJK is offline MJK  United States
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If the bass is too much with the BSC, just drop the value of the parallel resistor. Even with a small resisitor of 1 or 2 ohms it will be a big improvement.
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Old 30th April 2005, 07:18 PM   #7
GM is offline GM  United States
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Quote:
Originally posted by Lensi
In series with that is 13 Ohms of resistance.
Lensi
Greets!

Yikes! 3-4 ohms + BSC I can see, but 13 with a medium Qt driver?! This would push the base effective Qt up to ~0.86! More 'boom tube' than ML-TL WRT SQ if not tuned super low (like ~25Hz) and stuffed to a fare-thee-well (at least 1.0lb/ft^3).

Oh well, different strokes..........., or is this a typo?

GM
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Old 30th April 2005, 08:51 PM   #8
Lensi is offline Lensi  United States
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GM,

I've done some more testing/tweaking. The over-abundance of bass was due to room lift. The BSC's I had tried were 1.8mH with various resistors, 6 Ohm, 5 Ohm, 4 Ohm and lastly 3.3. Still too much bass boom, but at the time I hadn't done any testing on room modes.
The impedance correction that I was using (16.7uF + 13 Ohm) was serving to remove some of the room resonance creeping up into the vocal range, giving singers a chesty resonance. The impedance correction helped remove some of that, but didn't solve the underlying problem. I have just repositioned my listening chair to solve the room mode issue, and have made a subsequent change in the impedance correction, using now 6.8uF + 13 Ohms (as well as re-installing the bsc : 1.8mH, 5 Ohm) I also changed the port tube (I have three lengths), using the longest of the three, about 4". This has smoothed out the bass response, making it more articulate with being boomy. I'll keep you posted as I move toward a permanent configuration.

Lensi
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Old 1st May 2005, 03:36 PM   #9
weidok is offline weidok  Netherlands
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Hi Lensi.. what amp are you using ??
I have found out playing with the FE 167 E in a ML TL
the amp is very very important !!!!

The little T amp sounds wonderfull ..
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Old 1st May 2005, 08:08 PM   #10
Lensi is offline Lensi  United States
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hi Weidok,

I have a Cayin TA-30 (www.cayin.de) that I've modified. I removed the preamp stage and feedback circuit. I also replaced all electrolytic capacitors with Black Gates, all film caps with AudioCap Thetas. I replaced the stock bridge rectifier with a home-built bridge using Ixys soft recovery diodes.

Now regarding my previous post....


I spent most of last night zeroing in on a final BSC and impedance correction for the speakers. After repositioning the speakers and the listening chair to reduce the effects of room modes, I settled on a BSC of 1,8mH + 5 Ohms. The impedance correction circuit is now 6,8uF+4,3uF+0.47uF Film & Foil with an 11 Ohm resistor. This combination produces the most strikingly realistic vocals I've heard.

I guess the moto is: you have to accurately identify the problem before you can create a solution. The values above are quite in line with the values calculated during the design phase of this speaker. I knew something wasn't quite right when I was testing impedance correction with values of 16-17uF and resistances of 13-15 Ohms, but I just didn't think about room modes as the source of the sonic problems.

I'm frankly blown away by the sound this Fostex MLTL produces. Cavernous soundstaging, beautiful timbre and excellent dynamics.


Lensi
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