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

[Nelson Pass]

Originally posted by MJK
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.

[MJK]

There are many ways to design and build a speaker, none of them are the best way. Play to your strengths, personally I stink at building.

[Nelson Pass]

Actually, so do I.

[Scottmoose]

Well, that's three of us... ;-)

[planet10]

I'm not bad at building. I stink at making them pretty. I am good at designing, & my symbiot is really good at building (and he is weak at design )

dave

[doorman]

Dave: "simbiot" -- does that start with a "C"?

[planet10]

Originally posted by doorman
Dave: "simbiot" -- does that start with a "C"?

yes

[GM]

Greets!

Hmm, I believe you mean 'symbiote' since you two have a symbiotic relationship.

GM

[planet10]

Originally posted by GM
I believe you mean 'symbiote' since you two have a symbiotic relationship

i was never a great speller, and i stink at typing...

dave

[GM]

Greets!

Originally posted by Scottmoose
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.

Originally posted by dmason
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