My Fostex FE 108EZ project, Part 2 - diyAudio
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Old 15th March 2006, 08:28 PM   #1
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Default My Fostex FE 108EZ project, Part 2

Here are pics of prototype cabinets in the X-baffle design in 'real' wood I finally worked out the construction details and the compression chamber issues.

The box on the right is the one I will go with, although, aesthetically, I would prefer it be 3 or 4 inches shorter. I may do that in the final build.

This is prototype #6. I'm can say with certainty that foam works great for prototyping. Other than an increase in resolution and tightened bass, the overall sound did not change from foam to wood. I'm working on stuffing right now. Without it, they "honk" on vocals. Stuffing made a world of difference. I don't know the exact amount yet.

How do they sound? I think great. They have a huge soundstage. It's hard to find a sweet spot (I don't know if that is a good thing or a bad thing). Beaming issues are minimal that I can tell. Highs are sweet and crisp. Mids are as expected from this driver (excellent) Bass is a lot better than I expected. Put them right into a corner, and they actually got boomy on some recordings (I think this is an issue of bracing more than anything).

H x 45 inches, W x 16 inches, D x 12 inches. Baffle angle is 36.5 degrees.
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Old 15th March 2006, 08:31 PM   #2
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another view
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Old 16th March 2006, 05:51 PM   #3
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Comments, questions?

I'm rather surprised at the lack of response. This is an entirely new cabinet design for this driver, or any other driver as far as I can tell.

At least help me give it a name

Doug
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Old 16th March 2006, 08:57 PM   #4
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They look pretty interesting. What materials will you be using in your final set?
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Old 16th March 2006, 10:22 PM   #5
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I will certainly use baltic birch at a minimum. The front baffles as they now stand are quite dead even with 1/2 inch (18 mm?) MDF. This is due to the internal bracing. The curved back will have to be thicker or better braced as it still resonates quite a bit at the bottom. I'm still working on how best to overcome that. So I'm thinking 1/2 inch material for the front and 3/4 for the back.

Curving the back was the hardest part of construction. I thought I could bend a 1/2 inch piece of MDF that size. HA!. No way with one person and a bunch of clamps. I had some 1/4 inch plywood that I doubled up that barely worked (look at all the screws in picture #2). To do a curved back, I will have to either build a form and pre-curve the back or laminate thinner peices. 1/8 ply should be quite easy, using epoxy for glue. I could also do a V-shaped back, but the curve looks too cool to not have it.

The other option is solid wood. It can be done with this design. The only problem I see is attaching the top. I have some air-dried quartersawn maple that would work very nicely. I always thought clear pine would make nice-sounding speakers too, but that's just a guess.

All in all, I'm quite happy with the sound so far.

Doug
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Old 19th March 2006, 07:47 AM   #6
kiang is offline kiang  United Kingdom
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well taperwood , interesting design - would try it
Taperwood seems an appropriate name for it
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Old 19th March 2006, 04:12 PM   #7
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I like different. How about some info regarding the guts and the sonic purpose of the "V" below the driver?

You could call them "Bremertones".
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Old 19th March 2006, 05:15 PM   #8
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"Bremertones" Well, that's a lot better than "Prototype #6"

In summary, I chose this design trying to get the benefits of OB and BLH together. I started with Fostex's recommended enclosure for this driver, using the internal dimensions of their box. The internal line length is 77'ish inches, and the compression chamber is 1,560'ish cm2. (sorry, my notes are in the shop).

I then played around with different mockups in 1/2 inch foam until I came to this basic design, doing fast-switching near-field A:B testing extensively. There is much to be discovered yet, though. I can say this with certainty that the V below the driver "livens" up the sound considerably. If you leave the V on top of the driver (see left speaker in Post #1), the sound is too "live," for this driver anyway.

I'm very happy with the use of 4-inch ABS plastic pipe to mount the driver. It's a perfect fit. Drilling the hole was quite an adventure . The increase in music resolution was quite noticable over a box-type compression chamber. The volume of the ABS pipe accounts for about half the total volume of the CC, with the rest being a V-shape inside the cabinet. I will attempt to find or build a more 'elegant' solution on my final build, but it will be circular.

Here is a photo with the top off. The small stuffed V in the front is the rest of the compression chamber. The backwave exits downward from the driver about 8 inches, goes up to the top (see the middle baffle), and then goes downward again at the back of the cabinet to the bottom, exiting the vents. I originally tried a two-part line (like Terry Cain's BIB), but it misses something. Doing it in three three parts just sounds better to me.
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Old 19th March 2006, 06:11 PM   #9
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Just to clarify, if this is in fact a new design for speakers (I doubt it, but I have yet to find a prior example), I would like it's general description to be referred to as an "X-Baffle."

That's my 0.02

Doug
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Old 19th March 2006, 06:13 PM   #10
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I don't really follow the OB part.

That rear pathway looks like some kind of torture chamber. Don't stick your arm in there.

Are the pathways of equal cross sectional area, so it results in some type of MLTL, or are those interior panels angled? Have you plugged the dimensions into MJK's spreadsheets?

With those size panels you definitely need some bracing and until you do so, you won't know what kind of bass you're getting, because I think you've got some resonance mixed in.

Other than bracing, my only recommendation would be to try a large piece of foam as a front baffle around the driver. I believe your tonality will flesh out quite a bit with deeper 1/2 space launching of the front wave. It will make for a good easy A/B comparison for you.
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