Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks?

The one and only
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MJK said:
Actually the MathCad worksheets account for the damping provided by Dacron fiber. You can define the amount and location of fiber in the line. Calculated results correlate very well with measurements.

I also like to experiment and try a lot of things to see how they effect the response, but I choose to do it analytically and only build one speaker design.

I stand corrected. I build lots of speakers because I'm not that
smart.

:cool:
 
Greets!

Scottmoose said:
That internal baffle particularly interests me for example. Terry's original is 14" deep, yes? Subtract 1 1/2" for the front and rear walls to give us 12 1/2". Now, unless I'm confusing things here (I'm not at my best at the moment, so if I make a stupid error do let me know), I understand that it finishes 5 1/2" from the base, and 5 1/2" from the rear wall. But half of 12 1/2" is not 5 1/2", so surely the expansion of this taper is not constant?


He apparently used 5/4 wood (1" thick finished) and implies as much with his ~1-3/8" wide diagonal glue line statement since the diagonal of a 1" x 1" right triangle is ~1.4142", or a tiny fraction more, so the dims are correct and the 'ballooning' due to the lack of angle boards in the corners have no audible effect in the cab's gain BW defined by the driver's effective HF mass corner.

.......he also suggested the best bet would be a higher Q driver like the FF165K -I assume he's referiing to its 10.92 Qes, because Qts is down at 0.2 which is the lowest of all the Fostex 6" drivers.

Well, he's referring to the higher Qms ;), so yeah, if you're using a high output impedance amp or lots of series R which raises the effective Qes and lowers Qms.

dmason said:
Thanks, Greg, that makes all the sense in the world, and explains the balanced sound we are getting using a 168Sig in one of these. The 168 measures real ratty from 5KHz up, but, after the requisite thousand hour cook time, it is truly a music maker.

You're welcome, but it's only part of the story as MJK notes since the room dominates the LF BW. At the time TC posted, it was negatively critiqued by him IIRC (can't find the archives) since TC stated it was based on a 1/2 WL, but I had recently done a 40-1354 BLH design for someone and noted that TC's design was pretty decent for a corner loaded one, so if his ceiling is rigid/well damped enough to reflect low frequencies fairly efficiently and he designed it with the proper gap to finish the expansion.......... Unfortunately, the pic in his article shows too much gap, but there will still be some loading at the lowest frequencies.

Another thing to consider is that he noted driving it with a high output impedance amp (1.8, 3.8, or 8.7 ohms selection) through a tiny 30 gauge wire (further increasing the effective impedance), so the FR would be considerably different even without considering the room's effect.

Bottom line, he shared a design that satisfied his stated performance goals with a specific driver, but he had the misfortune to get it published at a time when folks finally had a simming program to give them a clue as to how the bare driver would perform in a horn in half space, and because it doesn't sim well enough by some folk's standards it gets dismissed as an untenable design, even though the sim clearly shows that it meets his stated goal before the room is factored in.

Indeed, he initially left the drawing vague, with a note that he was just suggesting a general direction to begin experimentation, but folks wanted details, so reluctantly added the desired info only to be ~trashed for his efforts.

GM
 
Trashed perhaps by the legion of theoreticians, some notable witch hunters at Audio Salem, but absolutely not by those whom have actually built them, such as Scottmoose, and myself. More drivers are on the way to explore further. Again, I was completely amazed at how well the driver which shouldn't, could. Scottmoose is working the numbers for the Supravox 165LB which should arrive later in the week, let us see what happens with a driver far more suitable in this case.
 
Curses! I wondered if someone would notice that typo! Sorry about that! I meant Qms in the original post when talking about the FF165K. (Note, however the cunning disclaimer elsewhere in the post that mentioned I wasn't feeling bright at the time ;) )
So, he used 1" material for the original design. Now that is interesting; it certainly means that the internal volume of most of the replicas is somewhat out, as I imagine that 99.99% will have been constructed from 3/4" material, though I doubt the difference will be huge. Thanks for clearing that up; I wondered what was going on there; why it didn't occur to me that Terry had used 1" wood, not 3/4" I can't imagine (the eyes were open, the mouth / hands moved, but Mr Brain had clearly long since departed). It'll also mean that some routing around the basket and magnet structures if the original 7" external width was maintained would be necessary if the Fostex units were used, correct? I see what you mean about the Sigma needing more room to breath if this is the case. I wonder... Cheers for that anyway; that's cleared up the question of the dimensions that was driving me nuts, and Martin seems to have figured out now why they can perform well, given the right room and placement.
I'll get back with some dimensions that I would use for the Supravox based on their posed material -they'd probably be a better load for the Sigma too.

Cheers for now
Scott
 
"All out of whack." --Not surprising given their acknowledgement of the Anglo market is to maintain their site ...en Francais, seulement.

Okay, meaning....comparitively better, as in compared to the results with the 168sigma, whose results were completely contraindicated by parameters. one1speed had the same reaction I did. :bigeyes:
 
I'm trying like he** to follow this thread, just so much going on right now, not much time for the forums. Yes, the 168 works well in this cab. I tried other drivers as well, like the elusive 4" RS 103. While that worked and sounded nice, it was pretty lean. The 168 has real bass. Sounds quite balanced. Like I stated earlier, I'd change the dimensions a bit if building for this driver. It seems to like to breathe a bit.

TC did note that his plans were for internal dimensions, as I recall. (been a while since I've visited them) And, that his plans were for experimentation. Very cool, I thought. He mentioned to me, the thought of chopping the back at an angle. Pretty cool. Yet to try. But at this point, I'm on to other things. However, this is a design I would like to come back to and build correctly out of a more suitable material, not MDF, as I did.

A cool design that's really easy to plug other drivers into. I had chatted with one fella who was had built them for vintage 8" x 12" Isophons and was very happy. Those have a pretty high Q, but TC said to go for it. Pretty amazing little design.

Back to what is at hand here...
 
By little, I meant simple with regards to the build. I like the idea of throwing an idea out there that has had some thought and allowing others to run with it. Yeah, little was a poor choice.

Anyway, I've got a pait of the same drivers just sitting. At this point, no time to mess with them. Let me know if someone may be interested in them...
 
Indeed dave it was me with the Isophon version. I have drivers to get them back into action, but unfortunately my latest amp is valve and doesn't have the facility to drive a 4ohm load. I finally got my Tannoys sounding satisfactory.
The reason I liked the Isophons in them was because they had that vintage sound, but with incredably low and detailed bass. I was for ever looking out of the window to see what lorry was pulling up outside.

A design point that I applied to the BIB pipes was to mass load them. This cuts the bass quite a bit, but keeps it very clean right down to the bottom of its frequency range. One to consider if you can lose a little bass.


Shoog
 
Hiyall,

Nice to see the thread. Thanks GM especially, DMason and Scottmoose for trying the design.

Credit has to go to Fostex. Acousticians, all of them better than we (save for GM). They sim alright, only on paper with pencils and leave far less to chance than we imagine. Few here will know of their math accumen combined with their creativity.

I have revisited the design in various configs and drivers sometimes with amazing results. Once in a while I get to hear a BIB with fe168 I built hooked to a Nakamichi amp, stunning.

Ya'll be good.

TC
 
It's funny, a lot of good audio stuff comes out of Japan (DIY, audiophile, and mass market). But I see very little discussion of theory except in a vague handwavy way. I don't read any Japanese so maybe it's just that only the marketing speak gets translated to English. Does anybody's experience differ?