Which BIB Dimensions for this Pair of FE164-s? - diyAudio
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Old 18th December 2005, 07:27 PM   #1
DMD is offline DMD  United States
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Default Which BIB Dimensions for this Pair of FE164-s?

Greetings Everyone,

I've been intensely curious to hear the BIBs ever since first reading about them, so when I retrieved this pair of Fostex FE164-s from storage I decided to go for it. I bought these on closeout a few years ago; the FE164 (featured in Martin's Project 2) is essentially similar to its successor, the FE167E, but with more excursion and slightly lower high end (Xmax is 1.0, high freq is 20K), so it should fit the box nicely.

But now after doing a BIB search of the forum, I wonder which one? Scottmoose, I certainly appreciate the abundant fruits of your R&D with the design that you've laid on us so far, and I wonder: Have you built and listened to one or more of the alternative boxes you suggested for the Sigma and such about a month ago, and/or do you have a theoretical favorite among them at this point? Anybody else? What might you do with a pair of FE164-s?

Thanks All,
Don
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Old 19th December 2005, 12:05 AM   #2
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Hi Don

I completed the latest pair last week. They were for a friend over in Sheffield actually, and were enlarged boxes to take (wait for it...) the FF225K. The very last driver you'd expect to work. Except for the fact that they did. Rather well. I didn't hear them with added super-tweeters, which their new ower is adding to take response up past 14Khz, but with 30AWG wire and a tube-amp, they were stunning. Didn't go lower than the smaller drivers, but one of the largest soundstages I've ever heard.

Hmm, FE164. Right, couple of options. Terry's original box should work fine. Plenty of people have used just that to good effect. However, quite a few FE168ESigma owners have commented that they love it, but would enlarge things a bit if they did it again. As the originals were designed for smaller drivers, this is not surprising. They are very forgiving, and should work well, but increasing some dimensions should reap some rewards. Now, the FE164, 166 / 167, despite their smaller frame, actually have a larger cone area then the Sigmas -20.56in^2 if memory serves, so they too should benefit a bit. So, this is what I would do for the 164/6/7 family (the FF165K needs a slightly longer line) assuming 3/4" build material. I don't have the original design equations etc, as I can't get hold of those Fostex Craft Manuals (try though I have), but I'm pretty sure I'm about right here, and I'm sure Terry or an owner of the manuals would straighten us out if I'm off:

External dimensions:
Height: 64"
Width: 7"
Depth 18"
Driver 28 1/2" from the top
Internal baffle ends 7 14/16" from the floor and internal front & rear baffle walls.
Stuff the point lightly, and add a layer to the base of the cabinet. Shove against a rear wall, or better, into corners. If you've an SS amp, you'll need at least 24AWG wire.

My own pair of BIB cabinets have FF165Ks. Enclosure width and depth are the same as suggested above, but with Terry's original 70" cabinet height and driver positioned 31" from the top as they have a lower Fs. Still not long enough theoretically, but I won't go taller than 70" otherwise the driver will be well above the listening height, unless you listen sitting on a bar-stool of course... To say they thunder would be a chronic understatement. Allison Goldfrapp never sounded so sexy either.

Hope some of this helps.
Scott
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Old 19th December 2005, 11:09 PM   #3
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One other thought -a suggestion I remember Terry himself making a while back elsewhere for the FE164. This driver can benefit from the whizzer cone being removed -better soundstage depth, imaging, width, loss of that annoying shout the cones always seem to have, without damage to the top end apparantly. Then you could add Dave's phase plugs. If that's a bridge too far, you could trim the whizzer back in stages, 1/4" at a time. Bit drastic, but could be worth doing.

Scott
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Old 20th December 2005, 02:35 AM   #4
DMD is offline DMD  United States
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Quote:
Originally posted by Scottmoose
Hope some of this helps.
All of it helps. Thank you.

And well, that is one sure way to eliminate the whizzer cone problem, isn't it? I knew I'd get to some of the latest driver mods, certainly phase plugs, before I got them into the boxes. I seem to remember an ancient one called "the 99 cent FE164 mod" or something like that, maybe using rope caulk...? Anyway I'm delighted to hear of this whizzer cone solution, and I'm sure I'm up for it (let's see now, the whizzer cone is this one, right? ;-)

Another subject, has anyone addressed the sizing, and effectiveness or not, of the circular false baffle? Do you use it?
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Old 20th December 2005, 10:22 AM   #5
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Oh dear. I did hope you wouldn't ask that. However, seeing that you have...

There was a thread, oh, maybe 6 or more (probably more) months back where we debated this issue, which ended up being rather... spirited, shall we say? I've pretty much stayed on the fence with this one. I have not tried them myself, primarily because a) I don't own, and cannot in the foreseeable future afford a lathe, and also because getting hold of a decent hardwood in the UK is like finding someone over here who knows how to cook a decent steak -rare. (Sorry about that!) So I can't comment from personal experience, though I'll try to offer a quick, objective critique of the situation. The problem we have here is that, just like the BIB boxes themselves, there isn't any software that can actually model these baffles in-room behaviour yet; at least, not to the best of my knowledge and I do try to keep up to date. Oh, there's several programs that allow you to model flat baffles of various shapes and sizes, but not baffles with a constantly varying radii like those Terry creates. Now, the effect of flat baffles (especially circular) sticking out beyond the edges of an enclosure is invariably not pretty in my experience. They are A Very Bad Idea then in my view, and I have seen nothing thus far that makes me even contemplate altering this stance. However, these baffles Terry creates are, as noted above, not flat. Far from it. Does this make a difference? Well, there are two questions here: 1) Do they damage the sound, and 2) Do they bring any benefits to the sound.

Looking at the response plot of the Abby at 1m as measured by Nelson Pass on his First Watt article on current-source amps and full-range drivers, I can't see anything at all that looks like a problem caused by the baffle being there, in contrast to what programs like The Edge suggest would happen if a flat baffle of identical diameter (I think it's circa 11 1/2", give or take) was there. So in answer to question 1), they certainly don't appear to be damaging the sound or causing any problems.

Question 2) is the trickier bit though. Do they improve things? Well, it's not inconcievable. If we look at Nelson's measured response of the Abby again, do you spot any sign of real baffle-step problems? No, I don't either, which is rather unusual for a tall, 9" wide cabinet with no compensation network and no active Eq (so far as I know) being applied. Which leads us to 2 possibilities. Either the cabinets were slammed up hard against a rear wall, or these little baffles were helping out a bit (or both of course). Now personally, I would've thought these podular baffles were too small to assist in this respect, but equally, I cannot see how this narrow cabinet alone could have such negigable baffle-step issues without some assistance. So it's certainly possible they help in this regard. I'll keep an open mind on this one, until someone takes some definitive measurements of two otherwise identical cabinets, one with baffles in place, and the other without.

What also intrigues me are comments suggesting that these baffles of Terry's assist in image projection etc., and it's here that the debate seems to be hottest. I see no reason to doubt the comments, but I'm always wary of purely subjective views too -if there's a difference you can measure it. (Of course, we then have to qualify this by noting that we have to know what we are supposed to be looking for in measurements, and more particularly how we are actually going to carry these measurements out. Not always as easy as people think.) Assuming they are not convincing themselves they are hearing something that isn't really there, I can offer a couple of possible explanations for this effect. Firstly, it could well have something to do with edge diffraction, and they might perhaps be dispersing some of the nasties seen here. I'm not an expert, and again, they seem rather small to my way of thinking for achieving this end, but this would go some way toward explaining it. Another, rather more obscure possibility could be that they might help negate, or perhaps again disperse, reflections off the driver surround, which is an eternal issue with all moving coil drivers. Again, sheet speculation on my part.

Conclusions? Well, for what it's worth, in my oppinion, you should under no circumstances attempt to use a flat, circular baffle. That will do things to the sound, and none of them are attractive. You'd be much better off doing without. If you're good with the old lathe, then you've nothing to loose by giving it a shot though. If you don't like them, you can always remove them after all, and you might get some benefits.

Cheers
Scott

PS -I'd go for Dave's phase-plugs as the first modification the 164s. You could try the whizzer-cone reduction / removal thing afterwards.
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Old 20th December 2005, 03:49 PM   #6
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Quote:
Originally posted by DMD


I seem to remember an ancient one called "the 99 cent FE164 mod" or something like that, maybe using rope caulk...?
Greets!

Never heard of this one, but there's the '$0.98 Mod' originally posted to tame the Lowther's whizzer, which of course works on any whizzer since its primary/secondary function is to damp the comb filtering between the whizzer and main diaphragm and mildly damp its bell modes: http://web.archive.org/web/200206282...wther/mods.htm

Use rope caulk on the inside/outside of the basket and all the motor to damp it as well as reduce reflections. Anchor wires to keep them from 'singing'.

GM
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Old 20th December 2005, 04:24 PM   #7
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Sounds good to me, and slightly less drastic too! Any thoughts regarding the box dimensions to share Greg?

Cheers
Scott
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Old 20th December 2005, 08:44 PM   #8
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Quote:
Originally posted by DMD


Another subject, has anyone addressed the sizing, and effectiveness or not, of the circular false baffle? Do you use it?
Greets!

Flat baffles will work well enough if cut into an amorphous shape to average out its eigenmodes (standing waves). Its area plus end correction plus some percentage of the main baffle's area will define its F3 baffle step point. Make it big enough to blend into the room's boundary gain and no electronic BSC is required, ergo its size is room/location/desired f3 dependent. If you're convinced any HF reflections off its sharp or modestly rounded edge are degrading imaging/soundstaging/whatever, trim it with fairly dense open cell foam, or for SAF centric audiophiles, have the S.O. make/have made some nice quilted edge covers for them in whatever pattern/colors suits their fancy and finish off the cabs in whatever complementary color/stain/whatever they choose.

Note that both these edge treatments (or similar) will negate the need for an amorphous shape, so a simple round baffle suffices, which is theoretically best since 'sound is round'.

WRT the baffle's curvature, its performance goal is to negate the need for any edge damping and a theoretically mathmatically 'perfect' decreasing radius can be derived from J.M. LeCleach's horn mouth expansion routine, which will have a rolled over flange if carried to completion, but a simple radius = the baffle's diameter suffices down in the midbass/lower mids IMO.

WRT the baffle's sonic effect other than lowering the baffle step corner, it's a passive radiator, with radiation patterns of a rigid piston of whatever curvature it has and it further mass loads the driver, so of course it will audibly affect imaging/soundstaging to some extent, and all for the better if its eigenmodes and transition from driver to baffle acoustic impedance mismatches are well damped, so I don't understand why there would be any debate, especially 'heated', per se on this subject.

If there's a debate buried in this subject, it's the potentially audible difference between a narrow baffle's smaller BSC filter's component values and greater dynamic headroom loss Vs a larger one's. I would think that the difference wouldn't be subtle even with 'top drawer' ($$$) components. Since I don't like giving up any dynamic headroom for any reason other than sheer lack of $$$ and/or space, I do whatever it takes to avoid the issue as much as practical, but I can see why folks with small rooms, sitting fairly close to their speakers would find narrow baffles and maybe some BSC acceptable if they have adequate amp power.

Specific to the Abby, if the baffle has a 11.5" diameter, then its effective radiation diameter is ~11.5+((11.5/2)*0.613) = ~15" plus whatever % area the main baffle contributes to its effective diameter, so its F3 will be somewhere below ~13560"/pi/15" = ~287 Hz. NP's Abby measurements show a baffle step corner below this frequency and no high Q peaks/dips in the midbass/mids response due to eigenmodes, so there's at least one measurement 'proof' that the 'small' curved round baffle is more than just a 'pretty face'.

GM
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Old 21st December 2005, 12:08 AM   #9
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Well, there you have it. Thanks for that Greg. I didn't think I could see any significant response problems on NPs Abby measurements over circa 250Hz; nice to have some confirmation that I'm not going blind. It will, however, take me some time to digest all of the implications of that post -I can't recall the last time I read one without learning something or it forcing me to spend even more time with the literature. Fine with me though. As I say, I don't pretend to be an expert, and I stayed firmly on the fence when these things cropped up a few months back, but there was a certain amount of... friction that emerged. This is the thread I was thinking of: Circular Baffle for Voigt Pipes?
Not having any hard facts to make any decisions by, I didn't really pursue matters other than having a suspicion that there could be something in it, but I'd do without until I learned some more. Thanks for clearing some of that up!

I assume that's why several of your MLTL designs (the MLTL48 for the Jordans, say) are wider than they are deep? I built a pair of MJKs MLTLs with FE207Es a few months back with 6" extensions on each side (the internal line was unchanged as I kept the original side-walls) to try out the effects of wide-baffles and came away impressed. Bit too large for my room in terms of their width, but instructive -BSC requirements were negligable to the point of not required, and I did like the overall presentation, which did sound like it had some of the benefits of dipoles.

Cheers
Scott
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Old 21st December 2005, 03:02 AM   #10
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What a banquet of info I just sat down to. Very much appreciated, Scott and GM.

Yes, the 98 cent foam strip mod does sound like a more 'civilized' way of dealing with the whizzer cone (cheaper than I remembered, too! ;)

I make elegant sense out of what GM says re the baffle, though off the top of my head I don't know the precise practical steps in making it, as he said, big enough to blend into the room's boundary gain; I'll research that in the morning.

Here's an off the wall question, if you'll excuse the worthless pun, since we're loading the ceiling with this box: I wonder how significant a change in the quantity and quality of bass is produced by changes in the distance between the top of the box and the ceiling, both on account of shorter/taller box dimensions and of lower/higher ceilings?
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