Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 131 - diyAudio
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Old 6th September 2006, 02:39 PM   #1301
MuaDibb is offline MuaDibb  United States
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For the smaller driver BIB's is it possible to load the floor in front of the speaker rather than behind? Or is the wall behind the speaker necessary to complete the horn action.
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Old 6th September 2006, 04:35 PM   #1302
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Yes. It completes the 1/4 space or 1/8 space loading.
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Old 6th September 2006, 10:13 PM   #1303
Empee is offline Empee  Netherlands
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Hello!


You guys seem to know very much about the BiB
(I'm a wee dazed of what I read in this 131-page thread....)

As you may or may not know, I've posted a thread asking for
possible designs for a Philips AD3800/AM driver.

Now, this is a dual-cone ("whizzer") type of driver,
and I was wondering if a BiB would be a good way to go.

But with a needed baffle opening of 183mm (that's slightly
over 7"), I cannot stick to the original TC' dimensions.

Can I just widen the whole lot and make an 8" internal BiB?

And with an Fs of 72Hz, what linelength should it be?



ooooh, I wish I had more background in this (or knew how
to calculate this sort af things)


Can anybody help me on this one?



regards

Empee
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Old 7th September 2006, 09:12 AM   #1304
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What's their Vas? In fact, what's their T/S parameters in general?
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Old 7th September 2006, 01:53 PM   #1305
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My apologies. I've just done a quick glance around the 'net. We're looking at classic jobs from the 1960s right? Are yours the 800ohm version by any chance? That means no T/S parameters (unless you can measure them yourself?).

I can give you a decent line length and Zdriver, however, with Vb we're in the realms of guesswork I'm afraid, not knowing the driver's Vas or Q. Anyway, I'd use a 105in line with a Zdriver of 21in. Beyond that, take a shot in the dark. I'd go for a hefty Vb as it's better to be too large than too small, so Sl=200in^2 might get you somewhere.

Got one other idea up my sleve. Not something I'd usually advise, but could be worth exploring at least. Back shortly.

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Old 7th September 2006, 02:56 PM   #1306
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We don't want to tune the driver too low, so roughly, using Martin King's alignment tables, you could try a TQWT with So=Sd, Sl=3Sd, internal length of 75in, driver at 0.377 line length (from So). That's about as far as we can go with the tables though without any driver parameters; I'm wary about shooting in the dark.

Finally, you could try (I can't believe I'm saying this) a Voigt pipe. I don't like these cabinets at all, but unless someone can provide a set of parameters, we're just guessing anyway, so it's unlikely to be worse than anything else you could build.

A few years back, I seem to remember that Herb Jeschke actually built a pair of 8 foot tall VPs for a pair of big old Philips 800 ohm drivers. Going by memory, they were 96in tall or thereabouts, with a base that was 12.5in wide x 12.5in deep (internal). St (driver position, or more accurately the cross-section of the pipe at the driver-centre, which was usually taked to = driver surface area) was usually approximately 0.47 line length. I beleive the formula was St = L / 2 + (cube root of So / Sl). Vent area was also normally taken to roughly equal to the cone area of the driver a la the original, pre T/S alignment, bass reflex patent (Greg, put me straight on these if I'm wrong).

Best
Scott
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Old 7th September 2006, 03:25 PM   #1307
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Greets!

FWIW, back in pre-T/S days many DIYers used Altec's nomographs to build cabs based on only the driver's frame size and published Fs, which I SWAGed to ~8*Sd for Am (aka Sm) when L = 1/2 WL of Fs (BIB tuning) in a At (aka So) = 0 conical pipe firing into a corner.

I only built a few because it was assumed that a large driver had to be used to keep from overdriving them due to TT 'rumble' (we were mostly clueless about line level filters), ergo too big even back when 2 ft^3 was considered bookshelf sized, but the cavernous, pipe organ like room excitation was, er, exciting, especially to young adult females! Maybe size really does matter, my speakers have always been big, with a low Fb (for the times), and never had any speaker size related SAF issues.

I seriously doubt that they would measure well whether outdoors or in-room by today's standards, but driven with a tube p-p amp that has bass control (adjustable DF) and with a bit of mouth/corner damping as required, any 'boominess'/obvious tonal imbalance could be smoothed over, so EQ is your 'friend' down below ~100 Hz.

GM
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Old 7th September 2006, 03:53 PM   #1308
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I do like a big speaker... ;-) Thanks for that, Greg! Are those Altec formulas up on the web anywhere, or still lurking around in print? I'd like to look into them at some point, for interest's sake.

Regards
Scott
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Old 7th September 2006, 07:38 PM   #1309
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AD3800

http://www.hupse.nl/radio/speakers/AD3800.htm

I've not had a set of 3800s, but the AD2800 http://www.hupse.nl/radio/speakers/AD2800.htm i've had had the same lattice basket (unlike the link) and cone, but with a smaller motor, and i do have numbers for those. Here is the average of 4 fairly closely matched units.

Fs 80.86
Re 3.78
Qms 6.67
Qes 2.73
Qts 1.93
Vas 32.83
Cone mass 7.65
Sd 213.82
dB 90.18
comp cm/dyne 5.08E-07
BL 2.33

Measured with low V. Higher V will give lower Fs, Qt, and larger Vas.

dave
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Old 7th September 2006, 07:45 PM   #1310
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Nice one Dave. From that, I'd say that Qt, even accounting for a high voltage driver and larger magnet will likely still be too high for a BIB. I think the highest we've done was by Greg -one for the B200, which is up at around 0.7 I believe (off the top of my head). Terminus is a monster 350in^2.

An open ended, untapered pipe like a big Alpha might be about the best box option at present. Fudging around the data, I plugged some info into Greg's Alpha TL spreadsheet. Assuming a Qt of about 0.8, a Vas of about 40 litres, and tuning the box to 50Hz (too low, but it's non-resonant, so it shouldn't damage things) you could try one ~54in long, 264in^2 CSA, 0.6lbs ft^3 of fibreglass damping. Alternatively 64in long, 193in^2 CSA, 1.3lbs ft^3 of Dacron. Best I can suggest really.
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