The idea behind the slot is to create a somewhat "variable" length so as to spread the ripple out and get a flatter response. It is small compared to the terminus, and you should not need to adjust length. Essentially the equivalent can be done by adjusting the height of the terminus from the floor.
dave
dave
Almost; AFAIK the iBIBk started here with a driver offset more optimized for floor loading and with an empirically arrived at K-slot, so in this case one designs based on desired driver/floor height [and if I didn't post earlier in either thread, max offset is L*0.56]: http://www.diyaudio.com/forums/full-range/94994-fostex-126e-127e.html#post1116979
GM
GM
iBIBk is a regular BIB flipped to use the floor to terminate the horn since the box is too short to use the ceiling. The k-slot was added to create a “diffusion” of the BIB’s ripple, to smooth it out. It is all theoretical, we never built one, but at least a few have been built.
If you do the k-SLot by drilling holes to create the shape you can slowly increase its size till things are good.
dave
If you do the k-SLot by drilling holes to create the shape you can slowly increase its size till things are good.
dave
Thanks, GM and Dave. I've been thinking through a BIB build for Fostex FF105WK, either in an unfolded ceiling-firing version or a floor-loaded folded version. Assuming the mouth-to-boundary distance formula that GM provided in the BIB megathread applies equally to ceiling and floor loaded versions, and with a driver offset of L * 0.416, for an iBIB or iBIBk I'd get:
* Mouth-to-floor distance = 2.275"
* Driver height = 40" or a little more, which is pretty ideal for the room, which is:
* 221"L x 93"W x 98"H / 18.4' x 7.75' x 8.16'
Speakers would be in corners of the the short wall, firing down the length of the room.
I would make the height adjustable to dial in that mouth-to-boundary distance. Seems like I could also build it initially without a Kslot and then cut one and adjust it later. I'm pretty good with a freehand jigsaw, so that's probably how I'd go.
Instinct tells me the unfolded ceiling firing version would sound fantastic, but compared to a folded version it would require twice the wood, double the cost, and be much more difficult to make the long rip cuts on my dinky little table saw. So again, trying to figure out what would work best with my resources and skills.
* Mouth-to-floor distance = 2.275"
* Driver height = 40" or a little more, which is pretty ideal for the room, which is:
* 221"L x 93"W x 98"H / 18.4' x 7.75' x 8.16'
Speakers would be in corners of the the short wall, firing down the length of the room.
I would make the height adjustable to dial in that mouth-to-boundary distance. Seems like I could also build it initially without a Kslot and then cut one and adjust it later. I'm pretty good with a freehand jigsaw, so that's probably how I'd go.
Instinct tells me the unfolded ceiling firing version would sound fantastic, but compared to a folded version it would require twice the wood, double the cost, and be much more difficult to make the long rip cuts on my dinky little table saw. So again, trying to figure out what would work best with my resources and skills.
So, in this and other threads I've seen allusions but not specific information pertaining to three questions I have about iBIB and iBIBk.
* Is L*0.56 the ideal Zdriver for iBIB? Would L*0.416 be OK, or is that only for BIB?
* Is the forumula for determining mouth-to-floor distance of an iBIB the same as determining mouth-to-ceiling for BIB? e.g. Ec = Rp*0.613, where Rp = pipe/terminus radius
* Would the above two calculations be the same for iBIBk?
Thanks,
Jeff
Thank you, Dave. So unless L*0.56 is more optimal for floor loading, I'm going with L*0.416 because it will result in an ideal driver listening height.
This will be an iBIB for FF105WK with a truncated pyramid suprabaffle, subject to adding a Kslot if ripple needs smoothing.
OK, so I calculated what would be the driver height using L*0.56 and realized that the driver will be placed at a little more than halfway along the line from the closed end.
In a folded iBIB, that means you'd have to place the driver on the opposite side of the cabinet as is customary, i.e. on the same side of the fold as the mouth (as in attached pic). Is that correct? And would it still hold true for iBIBk?
In a folded iBIB, that means you'd have to place the driver on the opposite side of the cabinet as is customary, i.e. on the same side of the fold as the mouth (as in attached pic). Is that correct? And would it still hold true for iBIBk?
Attachments
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BIB driver position
Hi there j: If I recall, the driver position for a BIB used in GM's posted calculation is
Z=(about) 22% down from the pointed end, clearly on the front side... terminus being on the back side for upward exit. Given my advanced age, I may have recalled this incorrectly, however, I, will check on my other computer for the GM calculation equations. ...regards, Michael
Hi there j: If I recall, the driver position for a BIB used in GM's posted calculation is
Z=(about) 22% down from the pointed end, clearly on the front side... terminus being on the back side for upward exit. Given my advanced age, I may have recalled this incorrectly, however, I, will check on my other computer for the GM calculation equations. ...regards, Michael
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Correct, yes, though again 0.561 is just the lowest I recommend, so 0.217, 0.349, 0.442 are options based on some of MJK's postings.
GM
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I resemble that remark!
Close enough, 21.7%. BIB math example:
Fs = 70 Hz
Vas = 0.29 ft^3
Qts = 0.445
Vb = 20*Vas*Qts^1.25
L = 13464.54/2/70 = 96.175"
folded height = 96.175"/2 = 48.088"
Vb = 20*0.29*0.445^1.25 = 2.10804 ft^3
Sm = 2.10804*1728/48.088 = 75.751"^2
depth = SQRT((75.751*SQRT(2)) = 10.35"
width = 75.751/10.35 = 7.319"
zdriver = 96.175*0.217 = 20.87"
a-b-c = 10.35/2 = 5.175"
GM
Greets!
Hmm, can't recall for sure, but based on the post above it's just a BIB with a L*0.217 driver offset: BIB Calculator | Speaker Projects by Zilla
Hmm, can't recall for sure, but based on the post above it's just a BIB with a L*0.217 driver offset: BIB Calculator | Speaker Projects by Zilla
You're welcome!
Thanks, couldn't remember and didn't feel like picking through the thread.
Hmm, wonder why I used the 0.217 zdriver unless it was strictly a woofer app........
Regardless, not knowing the driver/app, guess I'll fall back on this post for now: iBIBk developement thread.
Thanks, couldn't remember and didn't feel like picking through the thread.
Hmm, wonder why I used the 0.217 zdriver unless it was strictly a woofer app........
Regardless, not knowing the driver/app, guess I'll fall back on this post for now: iBIBk developement thread.