Regarding BiBs, ML-TQWP - diyAudio
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Old 28th December 2007, 05:45 AM   #1
fwater is offline fwater  United States
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Default Regarding BiBs, ML-TQWP

I'm a noob to the fullrange / single-driver world but not to speaker building in general. I have spent most of my time lurking and occasionally posting at the PE board where I have found the information, topics, and feedback to be very helpful and interesting. The one thing that bothers me about the PE board is the general undertones of over-reliance on right and wrong, black and white, yes or no calculations and measurements. By no means is this bashing (again, very positive experiences there and I will continue to use the site), but it seems that somehow the magic has been diminished in speaker building by some of the posters. Which is what brings me here...

I am fascinated by the ideas and principles defined by fullrange drivers. My limited exposure to just a few 3" and 4" speakers in open baffles has renewed my excitement for DIY! The results kind of put the magic back into it, now it's time to step up to the plate and start building.

I'm most interested in the BiB design for it's simplicity. I have 4 Tang Band W3-593SF that I want to implement in a bipole BiB. The rear-mounted driver will have a 4" PVC tunnel passing through the center divider and openning into the area just behind the front driver, effectively putting the backwave of both around the same point(?). When calculating the size of the enclosure (via Zilla's speadsheet), would I simply double the Vas when using two drivers, or does it get more complicated? Can the length be reasonably drawn out further than driver Fs?

I'm not locked into this design. I'm open to suggestions for anything that I've overlooked. In fact, I love the visual statement of the Metronomes and I would be floored if anyone was willing to help walk me through the design.

BTW, I'm currently building a set of Half Changs based solely on the discussions and feedback found here, having never heard the BF20. These are for a freind and will soon be gone, so I have to move along and clear out some of my collection of wide-band drivers starting with the W3-593SF. Thanks in advance!
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Old 28th December 2007, 08:23 AM   #2
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Since a bipole works better if it is wider than it is deep, i;d mount the driver's on the BIB s sides (and then rotate such that the sides are now the front & back).

dave
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Old 28th December 2007, 08:42 AM   #3
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Correction: a tunnel for the rear driver in the proposed bipole BiB would be 3". A 4" tube would definitely choke off the 5.5" mouth width as modelled, a 3" tube might also...
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Old 28th December 2007, 11:11 AM   #4
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Since the BIB is specifically intended for corner-loading to smooth its response, going bipole isn't necessarily going to be a good idea as they tend to require the exact opposite & be spaced some distance out from a wall / walls. If you really must, flip it sideways as Dave suggests so at least you won't wreck the horn flare.
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Old 28th December 2007, 11:36 AM   #5
fwater is offline fwater  United States
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Quote:
Originally posted by planet10
Since a bipole works better if it is wider than it is deep, i;d mount the driver's on the BIB s sides (and then rotate such that the sides are now the front & back).

dave
The BiB I'm modelling (W3-593SF with double Vas) is 5.5"W x 8"D x 96"L. Turned sideways, the baskets of the drivers would protrude into the divider at the presribed 21"Z. Could the divider have a small hump to allow for the driver baskets, or is the line too sensitive to deviation at that point? The more I think about the tunnel method for the rear driver, the more it seems like that a tube would present too much of an obstruction in the mouth, so that's out. I've seen a few designs for bipoles in standard TQWPs, maybe that's the route I will have to go (or even ML-TQWP i.e. Metronome)? If it could be done, a BiB would be the best bet for me becuase of ease of assembly and construction time.
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Old 28th December 2007, 12:28 PM   #6
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That would probably be better -remember what I noted above; these cabinets use the room corners & rear walls to complete their expansion. Bipole has opposite requirements.
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Old 28th December 2007, 07:22 PM   #7
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Quote:
Originally posted by Scottmoose
That would probably be better -remember what I noted above; these cabinets use the room corners & rear walls to complete their expansion. Bipole has opposite requirements.
I am now reminded that a BiB pretty much excludes itself from being a bipole. I suppose the main reason for my bipole idea is simply by virtue of having a total of four drivers and wanting to steer away from BSC with a driver of low sensitivity and power handling. I guess there's no reason to not continue with a standard BiB after one more question- how far below Fs can I tune the length? An Fs of 110 Hz and low X-max don't make it a good candidate for low bass, but how about 70 Hz?
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Old 28th December 2007, 08:13 PM   #8
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Don't go past 0.707Fs
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Old 29th December 2007, 08:31 AM   #9
fwater is offline fwater  United States
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Quote:
Originally posted by Scottmoose
Don't go past 0.707Fs
Done. A 75Hz cutoff yeilds 4"W x 6"D x 90"L (45"H) internal dimensions. What about BSC? I'm coming up with approx. 0.75mH and 4ohms. Ideas? Hope to have this built by 01-31. Thanks again.
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Old 29th December 2007, 12:13 PM   #10
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If they're properly positioned in corners, which effectively lowers the step-frequency, they don't require any correction. They provide sufficient gain to counter step-loss by themselves.
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