Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 366 - diyAudio
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Old 19th October 2007, 10:44 AM   #3651
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It all depends.

Assuming you use the T/S parameter based calculation GM came up with to establish the ~optimum Vb, then this enclosure is not going to require 5ft^3 volume. It wants 22.6209 cubic feet. Per cabinet. The relatively high Vas & middling Q of the Hemp Acoustics driver mean it needs a lot of volume. Using a 60in tall box, with a 26in Zdriver, this means internal WxD dimensions of 21.5in x 30.375in. Fc is 36Hz, should be usable to 30Hz (before room-gain). A baby box 60in x 10in x 14in just isn't going to work I'm afraid -it's flat not big enough.

Something smaller than the ~ideal is possible, but it depends just how big you can go. This is assuming the HA parameters are accurate of course -they're far too pat to be believable.Qt is incorrect for the other claimed figures for a start.
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Old 19th October 2007, 02:04 PM   #3652
pebbles is offline pebbles  Australia
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Scott, thanks for the link re BSC, that was very helpful. Unfortunately I have been informed that the 168 ez's I ordered are out of stock; a 2-3 week wait....Damm. However I have emailed a few OS distributors who may be quicker.
Interestingly there are a pair of used Lowther PM6a's with new fabric surrounds on EBay down here and I reckon they could be had for about the same price as the Fostex. I cant find much info(any) specification wise so I have no idea what size BIB they would need nor do I have any idea whether they would be suited to one at all. What sort of boxes would suit these ? Regards, Andrew
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Old 19th October 2007, 02:39 PM   #3653
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I'd be very wary about 2nd hand Lowthers, especially if, as you say, they've had a new surround fitted. If the factory did it, they'll be fine, but if someone else (a possible monkey) has been fooling with them, I'd suggest avoiding. Lowthers need TLC, although if you got them for peanuts (sorry) you could always send them back to Lowther, either for a service, or, better yet, an upgrade for new units, at a much reduced price. Lowthers will work in most things if you design it right, so your call.
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Old 19th October 2007, 02:52 PM   #3654
pjanda1 is offline pjanda1  United States
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Default Re: ok..scott

Quote:
Originally posted by Nanook
so to keep with my "why not mdf" responses, and Baltic Birch is available in 60" X 60" chunks here...
Surely there are some furniture and marine grade plys in 4x8 up there. Most of them would cost an arm down here, but it should be cheaper for you. It would be kind of a PITA, but you could probably edge glue the birch ply to make it work. It would probably be easier than more ambitious back horn designs.

I'd be curious to see a model of a short BIB. I wonder if you'd lose enough low freq. extension that the Mileva would start to look more ideal.

pj
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Old 19th October 2007, 03:49 PM   #3655
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It looks just like the model of a regular BIB for the same driver -the cut-off frequency is just a bit higher (how much so depending on the line length), that's all. A 120in line with a Vb appropriate to the driver will give an Fc of ~36Hz.
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Old 19th October 2007, 06:23 PM   #3656
Nanook is offline Nanook  Canada
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Default furniture grade ply...

I am very partial to Baltic Birch. Availability is 5' X 5" sheets, that's it.



Scott, I guess I didn't notice your spreadsheet does one column or the other (metric vs imperial) , not both simultaneously, that's where I got the 5 cu ft number, but the volume is 608 litres or so which is 37077 cu. inches.

using GM's 140 " tall dimension results in a 27.37" X 19.36" enclosure. with z=30.38", so a pretty huge enclosure...guess I'll be looking for a different driver
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Old 19th October 2007, 06:57 PM   #3657
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Nanook... if you want a shorter cabinet you can look at the Half Chang using either the Fostex 206e, 207e or Pioneer B20 (plus a helper tweeter). This cabinet is about 50 inches tall and uses an 8 inch driver like the hemp you wanted to use.

My BIBs are about 65 inches tall using the Fostex 165k. Im sure the 168S will also work in this shorter than optimal cabinet too. I have the older 168 and it worked great. Just less extension into the lower depths i suppose (without having listened to both speakers - but the charts suggest less extension).
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Old 19th October 2007, 07:15 PM   #3658
GM is offline GM  United States
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Default Re: furniture grade ply...

Quote:
Originally posted by Nanook
...guess I'll be looking for a different driver
What's your max dims?
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Old 19th October 2007, 08:13 PM   #3659
Nanook is offline Nanook  Canada
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Default scottmoose, godzilla and GM

thanks for the encouragement. (and help)

50" tall is max outside dimension, due to the sheet size of Baltic Birch availble here. I really don't want to use anything else, but would consider other marine grade plywood that is voidless. Almost all "choice grade" wood products are exported to the good old USof A, rather than sold to the Canadian market

My intent was to try a BiB, because of the longevity of the thread and the apparent good results many have had. I already have the Hemp Acoustics FR8c drivers, so I figured a quick and easy build would be good.

These speakers are an experiment for one of my kids' boyfriends, who has an idea of what quality is about. I can get other drivers, I just want to make sure that it is to his taste before commtting any real money on drivers. As he uses his system for both HT and music, I'm hoping to get him into something that is good (but reasonable priced). He's not against spending money , but would like a known quantity. Currently using a mass market HT reciever (which he's willing to change if need be). Currently using some no-name or HT included non-0descript speakers. He'll also need a cenmtre channnel as well. TV is a DLP projector, so shielding may not be an issue.

so that's really the issue.

He did hear the planet10 Fonkens when I had them here, and really enjoyed them, but the HT reciever will most likely sound pretty bad (or rather the Fonkens would sound bad being driven by the reciever). I'm not sure how much or to quality point he'd be willing to go, but he did say he'd be willing to buy a different reciever or amp. He has heard good 2 channel at my place . I'm usually not this carefull, but this guy could end up marrying my daughter (and long term familia peace would be a good thing).
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Old 19th October 2007, 08:53 PM   #3660
GM is offline GM  United States
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Default Re: scottmoose, godzilla and GM

You're welcome!

Looks like a BIB isn't 'in the cards'.......

Hmm, BB ply is 60" square, so if getting closer to the edge is OK, this MLTL may work, though like any MLTL there's the issue of blending a smaller CC to them if he doesn't set them to 'small' and XO to a sub when used for HT:

L = 57.5"
CSA = ~113"^2 (recommend 13.5" W x 8.375" D)
zdriver = 20.875"
zport = 45"
port = 4" dia. x 0.75"
density = 0.2 lbs/ft^3 down to the port

If 'boomy' in-room, either more damping and/or a longer vent can be used to roll it off.

GM
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File Type: gif hemp acoustics fr8c t-s max flat mltl.gif (6.7 KB, 494 views)
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