>>> FWIW, you could always add a chamber, with the driver in it, as a pod-like addition to the side, & tap in at the appropriate distance along the line. I'm not sure how much difference it would make though, as you'll still be activating the line-harmonics with the fundamental, and it's one more complicating factor.
Sometimes simpler designs are more rewarding. There is an elegance to the BIBs simplicity (once all the complicated math has been figured out). Tall and slim with the opening 'hidden' at the top provides a beautiful looking column. Sonically, it is a very good choice for getting a dynamic full sound from full/wide range drivers.
Sometimes simpler designs are more rewarding. There is an elegance to the BIBs simplicity (once all the complicated math has been figured out). Tall and slim with the opening 'hidden' at the top provides a beautiful looking column. Sonically, it is a very good choice for getting a dynamic full sound from full/wide range drivers.
Scottmoose said:
My concern actually is that the sides start flopping. With the 1:1.41 ratio, I think it is more probable than front/mid/back baffle resonance.
Gastón
GM said:
The bracing in ScottMoose's rendering is exactly the sort of thing I was thinking of doing when I built mine. GM's post (from way back in the thread) convinced me to try going without (except for a brace from side to side across the mouth). I can't say I'm disappointed, but I'm still thinking about adding something when I take them down to finish.
pj
pebbles said:
Greets!
You're welcome!
The easiest way is to add a veneer of rigid material such as sheet metal to keep the material thickness increase to a minimum or use the nearest thickness no void grade plywood if a specific minimum thickness is desired. Or just use additional bracing to increase their rigidity to keep the various costs down.
Well, as I noted, with the exception of a rigid driver baffle and mouth with a lossy material base if there's no air gap to the floor, it depends on a number of variables, and if in doubt then as a general rule of speaker design assume it can't be too rigid, only a point of diminishing returns. You can always add damping to fine tune it.
As for mouth bracing, best to assume that any BIB will have a large enough one to benefit from it on at least a subjective level just like any undersized horn. Yes, internal is fine if not so big in diameter to audibly affect the tonal balance, though how many dowels will be required will depend on their diameter, so if during playback you can feel them vibrate, more in line to mimic a solid plank will ideally be required.
That said, reducing the mouth area at this point can sometimes be very beneficial, especially if it's a wedge shaped loading plug covered in felt or similar to damp the pipe's higher harmonics.
GM
BIBsnBraces
Hi GM, not sure if I understand this; is the benefit from the damping of higher harmonics by the absorbant material on the plug or is there also a benefit from increasing the impedance of the mouth of the horn by ( I assume) the volume and shape of the plug? What sort of dimensions would be ballpark? Thanks, Andrew
GM said:
Hi GM, not sure if I understand this; is the benefit from the damping of higher harmonics by the absorbant material on the plug or is there also a benefit from increasing the impedance of the mouth of the horn by ( I assume) the volume and shape of the plug? What sort of dimensions would be ballpark? Thanks, Andrew
once again i must say thank you to gm! 
last week i went and cut 2" blocks of wood and flipped the speakers up on top of them, with a bit of bluetack to keep them from sliding, and the difference is enormous. i may be dreaming but it sounds as if i lost a tiny bit of low frequency extension but the lf that are there are MUCH fuller without losing any clarity. the bibs are no longer lean and are much easier to listen to for longer periods of time. the drivers are a little lower than optimal but i can live with that for the gains it has brought.
so... thanks again gm!
last week i went and cut 2" blocks of wood and flipped the speakers up on top of them, with a bit of bluetack to keep them from sliding, and the difference is enormous. i may be dreaming but it sounds as if i lost a tiny bit of low frequency extension but the lf that are there are MUCH fuller without losing any clarity. the bibs are no longer lean and are much easier to listen to for longer periods of time. the drivers are a little lower than optimal but i can live with that for the gains it has brought.
so... thanks again gm!
GM said:
Chosing driver
I need some help choosing a driver for my coming BIB project.
Our living room is 50 m2 (650 square feet) and shaped like an 'L'.
The speakers will be placed in the top of the 'L' in the cornes, 4 meters from each other. The primary listening position will be 3-4 meters from the speakers, but I would like sound in the entire room.
They will be used for music primarily, but if possible they should also handle some HT with an additional sub .
Based on the many comments in this thread I have been looking at the Fostex FF165K, but then I saw that Cain & Cain's Abby only uses the FF165K for nearfield and the FE167E for bigger rooms.
So now I don't know which driver to chose. Please help?
By the way. I'm a bass player, and I like to listen to other bass players, so the speakers should handle the bass well.
Thanks
Lars
I need some help choosing a driver for my coming BIB project.
Our living room is 50 m2 (650 square feet) and shaped like an 'L'.
The speakers will be placed in the top of the 'L' in the cornes, 4 meters from each other. The primary listening position will be 3-4 meters from the speakers, but I would like sound in the entire room.
They will be used for music primarily, but if possible they should also handle some HT with an additional sub .
Based on the many comments in this thread I have been looking at the Fostex FF165K, but then I saw that Cain & Cain's Abby only uses the FF165K for nearfield and the FE167E for bigger rooms.
So now I don't know which driver to chose. Please help?
By the way. I'm a bass player, and I like to listen to other bass players, so the speakers should handle the bass well.
Thanks
Lars
giantstairs said:
Greets!
You're welcome!
Actually, floor loading will in theory lower Fp, but change the roll-off slope to a steeper one, hence the illusion of a higher Fp.
BTW, did you try any spacings other than the 2"?
GM
GeWa said:
Greets!
Using the 'search this thread' window at the bottom of the page for 'b3s' yielded some posts: http://www.diyaudio.com/forums/sear...esults&searchid=1163437303&sortby=&sortorder=
GM
Re: Chosing driver
Greets!
The Abby has very limited LF output, hence the need for different drivers for different listening positions. Corner loaded BIBs OTOH should work fine with lower Qts drivers. Indeed, the FE208ES with super tweeter is considered by some to be the 'ne plus ultra' of the Fostex BIBs and should have no trouble filling your room.
Using the math here yielded this sim and assuming your ceiling height is ~ 2.75 m, then it should fill in the dip and flatten it out to at least 30 Hz:
GM
Lars Timm said:
Greets!
The Abby has very limited LF output, hence the need for different drivers for different listening positions. Corner loaded BIBs OTOH should work fine with lower Qts drivers. Indeed, the FE208ES with super tweeter is considered by some to be the 'ne plus ultra' of the Fostex BIBs and should have no trouble filling your room.
Using the math here yielded this sim and assuming your ceiling height is ~ 2.75 m, then it should fill in the dip and flatten it out to at least 30 Hz:
GM
Attachments
Re: Chosing driver
Greets!
Well, that wasn't my intent if you're referring to the parallel bracing, though it's common practice in bass-horn design and Scott/Dave use it extensively in theirs, so nothing wrong with it. I was almost always in a severe time constraint to get cabs built though and I learned early on that I often didn't need all that big a brace to stiffen a panel considerably, so would just use 0.75" x at least 1.5" wide ply or hardwood wood scraps glued on edge, though where it would be visible I'd use one that spanned the full distance.
WRT dividing it into two differently tuned pipes, this will require two radically different lengths, so to get the same gain BW as a single pipe will mean the total length will have to be longer since the acoustic length will be an average of the two. This has been done before, but are no trivial pursuit to design with a single driver otherwise they would be common in prosound apps, though Tom Danley is trying to make them so with his version of tapped horns.
Your version will require designing two separate horns fed from a common filter chamber and use a separate program to sum the results unless you can 'do the math' and know how to modify and/or add to MJK's existing BLH WS, so won't be a BIB. Then again, IIRC T.D. said Akabak could sim his DTS 20, so might be able to do it, but that's a steeper learning curve than this 'ol' boy' has time for unfortunately.
GM
Variac said:
Greets!
Well, that wasn't my intent if you're referring to the parallel bracing, though it's common practice in bass-horn design and Scott/Dave use it extensively in theirs, so nothing wrong with it. I was almost always in a severe time constraint to get cabs built though and I learned early on that I often didn't need all that big a brace to stiffen a panel considerably, so would just use 0.75" x at least 1.5" wide ply or hardwood wood scraps glued on edge, though where it would be visible I'd use one that spanned the full distance.
WRT dividing it into two differently tuned pipes, this will require two radically different lengths, so to get the same gain BW as a single pipe will mean the total length will have to be longer since the acoustic length will be an average of the two. This has been done before, but are no trivial pursuit to design with a single driver otherwise they would be common in prosound apps, though Tom Danley is trying to make them so with his version of tapped horns.
Your version will require designing two separate horns fed from a common filter chamber and use a separate program to sum the results unless you can 'do the math' and know how to modify and/or add to MJK's existing BLH WS, so won't be a BIB. Then again, IIRC T.D. said Akabak could sim his DTS 20, so might be able to do it, but that's a steeper learning curve than this 'ol' boy' has time for unfortunately.
GM
Re: BIBsnBraces
Greets!
Right, the mass loading of the 'vent' also rolls off the higher harmonics somewhat. I'm sure there's some math to define the optimum shape for a given horn flare or wall angle, but I don't know it and don't recall ever seeing it, at least defined as such anyway. My experiments were limited to simple 45 deg angle pyramids using scrap plywood filled with used oil dry (aka kitty litter). Base area was 2x mouth area IIRC and I just lowered the pipe down over it till whoever traded for them liked their in-room response as they rarely liked them at the working gap for my room/position/preference.
GM
pebbles said:
Greets!
Right, the mass loading of the 'vent' also rolls off the higher harmonics somewhat. I'm sure there's some math to define the optimum shape for a given horn flare or wall angle, but I don't know it and don't recall ever seeing it, at least defined as such anyway. My experiments were limited to simple 45 deg angle pyramids using scrap plywood filled with used oil dry (aka kitty litter). Base area was 2x mouth area IIRC and I just lowered the pipe down over it till whoever traded for them liked their in-room response as they rarely liked them at the working gap for my room/position/preference.
GM
Re: Re: Chosing driver
A metronome has similar profile to Abby, with considerably better bass potential.
dave
GM said:
A metronome has similar profile to Abby, with considerably better bass potential.
dave
Re: Re: Chosing driver
Thanks for the answer GM.
I just want to clarify, so I'm sure what you mean.
Are you saying that I can chose either the FF165K, FE167E or FE208ES
Or that I should forget the smaller ones and just go for the 208?
The reason I was hooked on the 165/167 was that they where a great deal cheaper than the 208 and don't require an extra tweeter.
My ceiling hight is only 2.4 meters.
Thanks again
GM said:
Thanks for the answer GM.
I just want to clarify, so I'm sure what you mean.
Are you saying that I can chose either the FF165K, FE167E or FE208ES
Or that I should forget the smaller ones and just go for the 208?
The reason I was hooked on the 165/167 was that they where a great deal cheaper than the 208 and don't require an extra tweeter.
My ceiling hight is only 2.4 meters.
Thanks again
Re: Re: BIBsnBraces
The idea is interesting to smooth the ripple in an upfiring BIB too, by avoiding the reflection from the ceiling...
I was thinking in a Karlson-like opening at the terminus, plus a little one in the back to still have the same area, with the widest side pointing to the back...
Gastón
GM said:
The idea is interesting to smooth the ripple in an upfiring BIB too, by avoiding the reflection from the ceiling...
I was thinking in a Karlson-like opening at the terminus, plus a little one in the back to still have the same area, with the widest side pointing to the back...
Gastón
Attachments
Greets!
Hmm, the ~2.75 m is in error since I thought I divided a standard 96" room height by 39.37" = ~2.44 m.
Anyway, none of these drivers have much audibly low distortion excursion, so even combined with corner loading there's only a few watts at most available, which requires a lot of efficiency to fill a room considerably larger than my relatively large double car garage, so while the small ones might be OK at the listening position, I'm even less sure about filling the rest of the room around the corner.
I guess build what you want and XO to a sub system if you're not pleased with its low distortion SPL output.
GM
Hmm, the ~2.75 m is in error since I thought I divided a standard 96" room height by 39.37" = ~2.44 m.
Anyway, none of these drivers have much audibly low distortion excursion, so even combined with corner loading there's only a few watts at most available, which requires a lot of efficiency to fill a room considerably larger than my relatively large double car garage, so while the small ones might be OK at the listening position, I'm even less sure about filling the rest of the room around the corner.
I guess build what you want and XO to a sub system if you're not pleased with its low distortion SPL output.
GM
If you can afford the drivers I wouldn't muck about -just go straight to the FE208ESigma with a suitable supertweeter. The FT17 is the budget option; the T90a or higher if you're feeling rich & indulgent (if you don't indulge yourself in this life nobody else is likely to, and as you can't take it with you, enjoy it while you can.) As Greg says, if you're not sold on its LF ability, XO to a sub. A TOP tapped horn would be my choice, probably with a driver from the Beyma range, and is in keeping with the overall theme.