Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 230 - diyAudio
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Old 2nd February 2007, 04:52 PM   #2291
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Drool.

Can you imagine one with maple front, internal and rear baffles with purpleheart sides, built & polished up by the local tame cabinet-maker?

Thanks for the info as ever Greg. BTW -is anyone else having the same problem I am in accessing the old Full Range Forum database? The search page, even for items I know are there, simply doesn't find anything at all.
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Old 2nd February 2007, 07:15 PM   #2292
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Thanks again everyone who contributed to my (rather nice to have) dilemma.

GM - I don't really understand the bit about the reason to have a suprabaffle. Can you explain the bit about equaling out the baffle step ... in a way that I might actually catch up with what you mean. Sorry to ask, but I would rather ask and feel a fool for a minute, than not ask and feel a fool forever!
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Old 2nd February 2007, 07:49 PM   #2293
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I'm not GM, but as he's not at the time of typing on the forum, I'll do my best to explain it as simply as possible & Greg can correct / add to it.

Baffle-step is the point at which bass begins to drop away due to the speaker starting to behave in an omni-directional fashion and less energy is being directed forward. (technically the transitional point between 2 pi hemispherical radiation and 4 pi spherical radiation. Wince.) The loss is typically 6db below this point of baffle-step diffraction. Now, the point at which this occurs depends on the width of the baffle to which the driveunit is attached. The narrower the baffle, the higher in frequency the baffle-step point, the wider, the lower the baffle-step point. The F3 point (-3db ) occurs at approximately 11,600 / baffle width in cm (or if you prefer Imperial, 4566 / baffle width in inches).

So, when you add a suprabaffle, as well as other possible unrelated benefits, you are in fact providing the driver with a wider baffle, and lowering the point at which baffle-step will occur. If the suprabaffle is wide enough, it will lower the baffle-step frequency to a point where the horn will supply the gain lost from baffle-step and flatten the frequency response without needing any other form of correction, from a circuit, active Eq or whatever.
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Old 2nd February 2007, 08:04 PM   #2294
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Scott, I think that was a pretty good summary.

Further advantages can be achieved (at the expense of material and most significantly fabrication labour) by extending the thickness of the supra baffle to "wrap around" the sides of the enclosure and profiling with a chamfer or radius edge.

Also, shapes other than round (i.e. square, elliptical, star-burst) are worth experimenting with.
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Old 2nd February 2007, 08:17 PM   #2295
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Ahhhh. I think I get the bafle step concept now! Thanks for that Scott (and Chris).

So to recap, Dmason quoted a measurement of 13" for the 168. If I take a profile (roughly a continuation of the outside edge of the driver cage/surround) and extend that curve out to meet the edges of a 13" Dia circle (1" thick), I am getting pretty close the right dimensions?

All well and good me understanding it - now I,ve got to go into some poor unsuspecting cabinetmaker/joiners workshop and try explaining it to them!
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Old 2nd February 2007, 08:34 PM   #2296
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Quote:
Originally posted by Martin Prothero
All well and good me understanding it - now I,ve got to go into some poor unsuspecting cabinetmaker/joiners workshop and try explaining it to them!
Hi, Martin. I realize the English and we Yanks are two people separated by a common language. Woodworking is one of those places where the jargon is different.

If I were going to explain it to someone here, I'd ask them to face-turn a round blank so that it matches a convex profile like you would draw, starting with the outer dimension of your driver.

Hope that helps.
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Old 2nd February 2007, 08:51 PM   #2297
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Teehe. Thanks for the tips! Thank god we share the same humour.
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Old 2nd February 2007, 09:33 PM   #2298
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Quote:
Originally posted by Martin Prothero
I think I get the bafle step concept now! Thanks for that Scott (and Chris).
Page 1 & Page 17 of the Frugel-Horn plans have more info on supraBaffles.

dave
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Old 2nd February 2007, 10:09 PM   #2299
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erm...moment please..."polite cough"...would that GM be that GM from ~Hotlanta?

"friends of mine
have moved to NewYork city
now, NewYork's fine
but it ain't Doraville"

One and the same- and still alive & kicking?
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Old 5th February 2007, 02:48 AM   #2300
GM is offline GM  United States
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What's up dude? Long time no hear! I'm still alive, but don't 'kick' so good/much anymore.

Sadly (IMO), this 'bit of country in the city' is no more. This old 'redneck' is now part of a small minority in a thriving multi-ethnic 'village' where English is rapidly becoming the 3rd language.

GM

PS: FYI we're quoting lyrics from Atlanta Rythm Section's hit 'Doraville'.
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