Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 59 - diyAudio
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Old 7th May 2006, 08:28 AM   #581
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Have had this idea steaming for a while with the extra pair of Monacor's I have. An apeirodical box where the whole back panel is made of two perforated plates, between the plates I would put damping.
In the corners of these would be screws so it would be possible to squeeze these together in order to adjust output of the back wave. The BIBs are excellent to try this on, at the moment I have two pillows on the mouths(this idea I got from listen to my mother in law way to long to keep hi freq in line

Office dividers have these plates and it is possible to choose amount of holes drilled.
I got this idea sitting examin a Dynaudio variovent which has this adjustment feature.
What do you experts say?
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Old 7th May 2006, 10:52 PM   #582
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Are you saying that the mouth should have some louvers
on it like window blinds? What a concept. Doesn't
Bose use something like that? ;-)


Back when I was playing with PVC pipe(s) I noticed the
'soundstage problem." The sound was pretty rich in
an 81 in. line but the soundstage sucked.
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Old 8th May 2006, 02:32 AM   #583
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>>> Are you saying that the mouth should have some louvers
on it like window blinds?

That seems like a cool idea to try actually... or any other way to adjust the output from the mouth/top of a BIB. Pillows sound like a good ideat too... or some acousta stuff loosley filling all or part of the entire cab.

I am going to use the Fostex 168S and wonder if i will need a sub? I have a great ACI 12" sub in a sealed box but will pair that up with the Fostex 127e project i will begin after the BIB's are done.

Any thoughts on bracing the inside baffle? I was wondering as i dry fit everything together that it might vibrate since it's so long... the back too. I may brace somehow. I was thinking of running a thin peice of 3/4" ply down the center of the internal baffle and doubling up the back and front baffles.
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Old 8th May 2006, 04:11 AM   #584
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Default Weekend progress...

Here's number 1, sides now glued, front edges routed, dry fit to its plinth. # 2 is in the same state, ready to sand. The finish will be amber shellac. Internal wire is cat 5e, using all four pairs.
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File Type: jpg p1010715.jpg (23.2 KB, 793 views)
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Old 8th May 2006, 07:15 AM   #585
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Default fe108e sigma

i noticed the dims for the fostex fe108e sigma are not on zilla's site... i believe from somewhere back in the thread i got these dimensions:
88in(224cm) line length. Driver down 17.5in from So. 33in^3 mouth area. F3 of circa 50Hz.

does that sound right? also, the fe 103e and the fe126e show 2 sets of dims, one for increased bass. would this apply for the 108ez as well? i am looking to build a bib optimized for the 108ez but that would also work well with a fe126e in the event i need more efficiency with my little tripath.

those new photos pouring in have gotten me excited to start my build!
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Old 8th May 2006, 08:45 AM   #586
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Jeff -I wouldn't worry too much about the internal baffle -it's going to be pretty solid, locked between the two side panels (side benefit: it's quite an effective brace for them too). Doubling the front and rear panels could be a good move.

My suspicion is that it is very unlikely you will need a sub with the FE168Sigma. I'd see what you think first, and if you feel it's a bit lacking in LF, add one or two afterwards. I did send you some dims for the non 'E' 168Sigma with a graph, right? Might be useful to have them up on the pages if possible.

Playing with the stuffing is always a good idea, so long as you don't go too far. A 1in thick layer of foam or some-such, about 5in deep, attached around the inner mouth might help attenuate unwanted HF too. Have to be a bit careful of course, not to begin to absorb the LF too.

The 'window-blind' idea is interesting -I've been playing with something similar, albeit in a different context and with different cabinets for a few weeks -I'll let you know later when I find if it's worked out. Watch out with the bottom layer BTW guys. Too much stuffing in that bit, and you'll end up with an odd TQWT (first half) with an aperiodic vent into a long positive tapered vent (2nd half). Not sure what that would do to the response... I might try in MathCad actually, just for fun! I'm not entirely sure that's what Peter means though -I think he's suggesting that rather than being open, forming a horn terminus, the top should be sealed off with a drilled, aperiodic vent. Either that, or the cabinet remains 'normal' but the back panel has a bit of aperiodic 'treatment' too. But I could be way off there myself!

Lousymusician -I like it! (Well, I've liked all of them so far!) Do keep us up to date.

Giantstairs -that's odd, I could've sworn I sent some 108ESigma dimensions to Jeff with a graph. Oh well, sorry about that! The ones you cite are the ones I'd use specifically for the 108ESigma. As you're thinking about trying the 126 as well though, I'd use the same line-length and driver position as you cite, coupled to the mouth area of the smaller 126E suggested dimensions (43in^2). If it booms a bit with the Sigma, just add some more damping. It should be happy enough with the 126, though it's a bit short, and you might need an additional false mounting baffle, otherwise the larger driver won't fit.

Best
Scott
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Old 8th May 2006, 09:08 AM   #587
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Default FE108EZ

Hi Giantstairs

I too noticed that the 108EZ specs had gone from zilla's webpage. I hope they were OK as I just ordered the wood! I printed a copy of the original post:

BIB for FE108ESigma
L = 88in
So = driver down 17.5" from sealed end
Sm = 33in2

so, ties in with what you have.

I tried to find in the thread why they might have been taken off, but it's too late now and I'll just have to hear how they are in a week or so javascript:smilie('')

Best,

Wilson
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Old 8th May 2006, 11:25 AM   #588
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Default fostex fe108e sigmas

thanks, scott! i do remember seeing them on zilla's site a while back. in any case i will be deciding on the width and depth shortly as i hope to get some wood this weekend.

wilson, glad to see someone else is trying out the fe108ez. what dimensions have you gone with for the cuts and what type of wood have you chosen? i would like to try the birch ply but i'm not sure how readily available that is here in spain.

cheers,
larry
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Old 8th May 2006, 01:08 PM   #589
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Larry, I have gone with 19mm MDF, after I see/hear the results of my errors I may splash-out for real wood. I have not got the tools to handle a 4 ft x 8 ft sheet of it at home so have asked my local Mr Bricolage (HD-equivalent) to do it for me; therefore, shop-cut sizes are 'compromised' by the size/cutting cost of the sheets they have in stock. So, the total height is the length of the side of the sheet = 4 ft = 1220 mm, the extra length I can cut off at home (for free) and the front and back panels cover the sides, rather than having the sides come through to the front of the cab.

These are outside lengths I have asked for for 19 mm board for shop cut (from 4'x8' sheet)
Front & Back = 1220 x 158 mm (approx. 4' x 6") = inside width of 158-2x19 = 120mm = very approx. 4.3/4"
Sides = 1220 x 178 mm (approx. 4' x 7") giving inside depth of 178 mm =approx. 7"
Bottom = 120 x 178 mm, giving area of (120x178/25.4^2) = 33.1 "^2
Baffle = 1220 x 120 mm (length will be recut once I measure it, depending on how I terminate the horn)
Spacer plate = 158 x 158 x 19 mm

Once I have these pieces, I plan to recut the lengths at home to get the 88" L. With the as shop-cut pieces the Llength is very approx (apologies to earlier posters regarding the accuracy of this) 1220 - 19 [bottom] - (178/2) [height to baffle end] + PI* (178/2) [around baffle] + (1220 - 19 -(178/2)) [up the horn] = 2.5 m, so I need to take about 13 cm off the height off of the front, back & sides for total length = 1090mm, inside = 1071mm, gives roughly 2.25 m L, roughly 88". The baffle, with the inside height at 1071 mm, it gives a length of about SQR(1071^2+(178/2)^2) = 1075 mm (point to point, ignoring thickness and termination, so a minimum of 1075 mm = 43 1/3").

I have worried about two things in particular, that the size of the driver is not too wide for the front piece (part of the reason I use a full-width front). Holes for the 108eZ are at 115 mm dia, so there is practical limit for the inside width (120mm, holes are 5mm dia) and (as mentioned earlier) the driver will touch the baffle (it does on the original 15mm drawings I did), so I will add another 158 x 158 x 19 mm spacer to the front, to mount the driver to just to be sure.

Sorry this was a bit long-winded,

w.
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Old 8th May 2006, 01:57 PM   #590
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Sorry Larry,

Baffle length is shorter than that, if total inside height = 1071 mm then the baffle length is at roughly SQR((1071-178/2)^2 + (178/2)^2) for inside width of 178mm, which gives 986 mm (ignoring how you terminate & thicknesses).

w.

1071 mm roughly 42 3/16"
178 mm roughly 7"
986 mm roughly 38 13/16"
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