Baffle for a BiB?

[mikje]

I'm finishing up a BiB and have a question about mounting the driver. I've noticed that many people mount the driver on a round baffle (or someother shape) and then mount that baffle to the BiB baffle. Is this recommended and, if so, what's the reason for it? Also, should the driver then be offset rather than centered?
Thanks,
Mike

[rjbond3rd]

Hi Mikje, wow what driver are you using?

The supra-baffle (or some people do wings) is optional but the purpose is to move the point of baffle step, to get the driver's forward radiation (off the front of the cone) to match up with what's coming out of the mouth, so that they both sum to a flat response.

Baffle Diffraction Step

Personally, I would say centered myself but whatever sounds best.

By the way, if you can, making the supra-baffle have a slightly convex shape might be better than a flat disk. I haven't tried that but it's on my list

[mikje]

I'm using this TangBand driver:
Tang Band W4-657SH 4" Aluminum Driver
Specifications: Power Handling: 30 watts RMS/60 watts max *VCdia: 1" *Znom: 8 ohms *Re: 6.0 ohms *Frequency range: 65-16,000 Hz *Fs: 65 Hz *SPL: 88 dB 1W/1m *Vas: .22 cu. ft. *Qms: 3.32 *Qes: .43 *Qts: .38 *Xmax: 3 mm *Dimensions: A: 4-15/16", B: 3-3/4", C: 2-7/8".

and here's the info for the BiB:
BIB- Line Length=103.573, Folded Ht= 51.787, Vb=1.313, Sm=43.803, Depth(internal)=7.871, Width(Internal)=5.565, zdriver=22.475, a-b-c=3.935
W X D X H=7.065 X 9.371 X 52.537
Cut List Per Box- Fr/Bk 7 x 52.5, Sides 8 x 52.5, Slant 5.5 x 48.5 Bottom5.5 x 8

I've got everything cut for it and the slants glued to one of the sides. I salvaged some of the wood off an OLD piano I junked a couple of years ago and that's what I'll use for the front panel/baffle. If I decide I need a supra baffle, I'll probably use some more of the paino lumber.

I built some BiBs with a pair of inexpensive MCM $14 drivers. Wow, I'm impressed. I've been using them for over a year, and I still like them quite a bit. I've had these Tang Bands in a couple of different enclosures, but haven't been thrilled with them. I figure a BiB might as well be tried.
Thanks for the info,
Mike

[planet10]

They are also used when the driver is so deep that the back hits the partition before the front hits the baffle.

dave