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

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#3,182
GM said:


Greets!

Sure, it's what we're here for.......

'zdriver' is normally a fixed value, L*0.217, but is somewhat flexible to keep the driver somewhere around ear height.

'L' is typically a function of Fs, 13560"/Fs/2, which tunes it ~an octave below Fs, but this too is flexible to keep the folded height reasonable when using low Fs drivers.

'Sm' is derived from the net Vb required based on a complex function of the driver's Vas, Qts. Reducing this lowers LF gain BW, which I don't recommend as it limits your tuning flexibility, though some cabs are so large it's unavoidable to either fit in the room and/or keep peace in the family.

An example:

L = 13464.54/2/70 = 96.175"
folded height = 96.175"/2 = 48.09"
Vb = 20*0.29*0.445^1.25 = 2.10804 ft^3
Sm = 2.10804*1728/96.175 = 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
Click to expand...

Thank you GM,
understand a little bit now.
 
#3,183
loninappleton said:

Firefox just snapped my bean and killed my post on this so here goes again:

And a tweak I am using successfully is a pennant-shaped piece of felt as a divider down the mouth to tame boominess.
Click to expand...

Greets!

This is why I write/save responses in an email and then post to the forums.

Have you finalized the material thickness yet? Rigidly attached or just draped over a diagonal brace?

GM
 
#3,185
back again.......with the picture that wouldn't show of my 206s.
They're sounding better all the time but the thomaseliot idea got me thinking about sealing in another driver. Could I attach a small box on each side of the BIB at driver level with a matching 206, but sealed or barely ported. 2 or 3 side by side.......crazy or what.....
 
#3,186
"Greets!

This is why I write/save responses in an email and then post to the forums.

Have you finalized the material thickness yet? Rigidly attached or just draped over a diagonal brace?

GM"



Material is the billiard felt a store owner gave me from remnants.
And yes it's just draped down the mouth suspended from a stick.
🙂 It's a right angle triangle with about 10" at the top tapering to
a-b-c dimension which is 4.5 in IIRC.


What's up with quoting on here? I couldn't find out where to login until
prompted while making a reply. So I couldn't tick the quote box.
 
#3,187
loninappleton said:

Material is the billiard felt a store owner gave me from remnants.

What's up with quoting on here? I couldn't find out where to login until
prompted while making a reply.
Click to expand...

Greets!

Go to the bottom right hand corner of the index page to log in: http://www.diyaudio.com/forums/index.php?

Interesting! I figured it would be too dense, so it must be acting as a diaphramatic absorber of sorts. Does it move around much on low notes?

GM
 
#3,189
edgebc said:
Could I attach a small box on each side of the BIB at driver level with a matching 206, but sealed or barely ported. 2 or 3 side by side.......crazy or what.....
Click to expand...

Sure! You can do whatever you want to, it's your speakers. 😉 Multiple 206s probably wouldn't sound all that good without elaborate XO's and maybe some other EQ though.
 
#3,190
GM said:


Greets!

Go to the bottom right hand corner of the index page to log in: http://www.diyaudio.com/forums/index.php?

Interesting! I figured it would be too dense, so it must be acting as a diaphramatic absorber of sorts. Does it move around much on low notes?

GM
Click to expand...


I have quoting back today. No there is no appreciable movement of
the fabric. I can't speak to any of the dynamics but I've tried to tune the mouth by moving the pennant to different corners etc. It's fun to play with but I can't really hear much difference from moving it around.


What I need is a better listening room where I can put the BIB in a corner. Corner is not part of the setup at this time. And I play at very low levels compared to what I've heard discussed here.
 
#3,192
Fellow pipe-horn builders: you need to aquire the self-titled album by guitarists Rodrigo Y Gabriela; two Mexican Spanish-guitarists living in Dublin. This is one of the very best discs I've heard in a long time -their version of Led Zep's Stairway to Heaven is worth the asking price in itself. Recording quality is first rate, the playing superlative.

A deeply sub-optimal pair, with 126s in an MDF cabinet intended for 167s (currently stuck with Parcelforce as I'm not quite convinced by the £70 import duty HM Customs have seen fit to levy) have just been voted one of the top-sounds at the Owstonfest meet today. I've got the trophy sitting on the mantlepiece at the moment. Not bad for a quick lash-up at 11pm 2 nights back. It was mostly thanks to a friend, who generally dislikes horns, SE amps and FR drivers, who suggested during the lunch-break that we put the aforementioned album on. We ran through most of it & when I happened to glance round after a couple of tracks, I found a group had gathered behind to listen. 😀
 
#3,195
GM said:
OK, with no corner loading or high SPLs combined with a high Fs driver it's definitely acting as a high mass diapramatic absorber. Good to know, thanks!
Click to expand...


Whatever you said. 🙂

You realize of course that I am 60 years old and prob'ly have no hearing left. I'd like to see others with more experience try this tweak to see if it's valid.

I want to make a BIB with FF165 but the nice materials I found for my FE127 have gone dry. That glued up butcherblock shelving is now all knots down at the hardware store.


To try the BIB in a corner I'd have to have a way of mounting my torchier light on top and still have the mouth open. Torchier (indirect up light) is what I have in the audio area for dvd viewing. It would look like a tripod or mosquito legs I suppose.
 
#3,196
No, I didn't know you had 'one foot in the grave and the other on a banana peel', but being 61, where does that leave me? My hearing has really rolled off up high in the last ~5 yrs, but this BW wouldn't be coming out the mouth anyway since it would get lost in any stuffing around the driver, so assuming you don't need stereo hearing aids, you should be able to tell if it's working or not.

Still, I wish others would try it as it worked very well for me in MLTLs and floor loaded pipe variants, but I never built any BIBs per se, so would like to know how it works with higher power and large upward firing mouths.
 
#3,200
Don't try this at home boys and any improbable girls reading this... 1 pair of P10 modified FE126Es in a pair of cabinets intended for Monacors, hense the very roughly screwed on & sealed false baffle. Despite being as sub-optimal as it gets, with the benefit of one of the 2 finest amps I've ever heard feeding them, and on the aforementioned album, these were the boxes that got an award. They went much louder with this music, with far less effort than on other tracks, and even the cone excursion dramatically reduced. Benefits of not needing to plumb the depths, with the high Vb providing additional help. If nothing else, it proves that it's hard to have too large a box (so long as your source material isn't too demanding in the LF regions). And that a good quality amp should not be ignored.

BTW, if anyone's wondering what the baffles are, those are my friend Steve's. Lowther EX4s on top, supported by Goodmans 301s below them, and the woofer vesion of the 301 below that. They filled a 90 x 40ft room with less than 1w.
 

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