Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 5 - diyAudio
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Old 25th October 2005, 08:55 AM   #41
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Hiya Terry, good to hear from you again!

I've sent an email to the guys at eifl in Japan regarding those Craft Handbooks -just waiting on a reply, so here's hoping that they're back in print, as I understand the basic idea / theory behind this box design is in one or both of these (not sure which, so it looks like I'll have to get both). Perhaps I should get the old slide-rule and graph paper out in readiness, just in case. There is much to be said for the old fashioned way on occasion, I admit.

Without having the Craft Manuals to optimise things, but extrapolating a bit using what I can of Martin's MathCad worksheets, I thought I'd share a few box dimension ideas with you guys for a BIB with the FE168ESigma and the Supravox 165LB. Still work in progress, but this is what I've come up with so far. All assume 3/4" material (because I'm in the UK, and 1" is impossible to find, and, if you did, would be impossible to afford. Modify the dimensions accordingly if you wish to use 1") and I've tried to keep the boxes of a domestically acceptable size.

Sigma first. The driver specs suggest a shorter line-length here, so I'd decrease it by a foot, which will reduce the overall cabinet height by 6", down to 64". A little shorter less than the Fs suggests (that'd be 66 1/2", give or take), but it's a nice round number, and it's still going to be tuned pretty low! If you want to keep the 7" width (already with 3/4" material giving us a little more breathing room), then I'd increase the depth of the cabinet to an external depth of 17 1/4". Take the internal baffle from its starting position to where it terminates, in the internal centre, 7 1/2" from the base and 7 1/2" from the internal face of the front and rear baffles. Driver mounted at 35" from the base. These are still only approximate, but I suspect they should let the Sigma breath better than the original. You could chop the rear down a little too if you wish. If you wanted to do it another way, I'd use external dimensions of 8"x14 1/4"x64", with the internal baffle ending 6" from the base and 6" from the internal walls of the front and rear baffles.

On to the Supravox. Their specifications indicate an Fs of 69Hz, which would mean substantially reducing the height of the cabinet -not in itself a problem, but it would mean the driver would be mounted too low -only around 25" give or take from the base, which isn't anywhere near enough.

Ok, some thoughts. The first thing that struck me is that while the original 1354 Terry used is supposed to have an Fs of circa 50Hz, I recall that it was frequently measured at around 70Hz -very similar to the Supravox in other words. But it still worked well, yes? Therefore, especially considering the considerable excursion of the Supravox, which should hopefully give us a wide safety margin, we should be able to go for the same line length that was used for the little RS driver. That's my take on it anyway. So, I'd try using Terry's original 140" line length and 70" overall cabinet height. Driver positioning remains the same too at 39" from the base. However, I'd use the increased depth of the first idea mooted above for the Sigma mated to the higher cabinet if the 7" width is to be preserved, to end up with external dimensions of 7"x17 1/4"x70". If a wider cabinet is wanted, then mate the width and depth of the second idea for the Sigma mentioned above to the taller cabinet.

If the over-long line-length for the Supravox causes palpiatations, or nervousness, then try a milder version (BIB korma?). Keep the same depth and width of either of the two versions above, but reduce the overall cabinet height to 60", with the driver mounted 31 1/2" from the base.

That's it so far guys. Any comments and / or suggestions will be welcome as always.

Cheers for now
Scott
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Old 26th October 2005, 03:47 PM   #42
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Having finally thrown off (most of) a cold, I've finally been able to roughly complete the new pair of boxes with the original dimensions. Roughly, because 1) The materials I used as an experiment haven't worked as well as I'd like, and 2) I reckon that the larger drivers want a bit more breathing room. It has, however, allowed me to try out the FF165K in the load.

Oh me of little faith. Again. Until I built my first pair, I didn't believe this cabinet design could work, and I was delighted to be proved wrong (always nice to learn something new). Now I didn't think these drivers would work, and I've been proved wrong again ;-) They do work. And how. The limited Xmax doesn't appear to be an issue, and according to my cheap SPL metre, in my room at least the response just isn't rising at all; not with EL34s driving them at any rate. I suspect that SS amps could need some series resistance, but that's going to depend on the room and amplifier. Very little ripple too. They'll nicely complement my ML TQWTs built to Martin's Project 2 design. I'm a happy camper. Oh, the bass-end? These things shake the furniture. You feel the low frequencies in your chest, and there no boom; it sounds almost like dipolar woofers.

My dimensions for the cabinet using the FF165K -this is what I'll be building for them anyway after thinking it over for a while and deciding not to wait for those Craft Manuals:
-Box height: 68", Total line-length: 136", External box width: 8 1/2", External box depth: 16 1/4", Baffle centred at 7" from base and 7" from front and rear internal baffle walls, Driver centre mounted at 36" from the base. Any thoughts on build materials guys? MDF alone isn't optimum, I was thinking of a good ply of some description, but a decent hardwood perhaps, if it can be acquired in the required sizes (I'm in no position to build up panels)?

Cheers for now
Scott

PS: Has anyone else tried placing an acoustic guitar on a stand between a pair of speakers when listening? If you haven't, and there's one in the house, try it. Rather enlightening when listening to John Williams.
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Old 26th October 2005, 05:23 PM   #43
dmason is offline dmason  United States
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Well, there it is again. Audio Alchemy. The Fostex FF165, with its almost nonexistent Xmax, and ...."shakes the furniture." No boom, and "almost like dipole woofers."

This morning there was a package at the door whose origin is Frankfurt, Germany. This could only be the Supravox 165LB, linear Xmax 6mm. It will be VERY interesting to see what happens with these.

Glad you like your new creations, Scott. Which EL34 are you using?
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Old 26th October 2005, 09:53 PM   #44
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I don't know why the FFs work, but they seem to. I haven't really punished them with something like Floyd yet, I admit, but nor have they bottomed out on anything. More excusion would be nice, that's my only slight concern, but thus far it's not been an issue. I look forward with interest to learning how they perform in the load compared to the Sigmas. My bet is they'll beat the Fostex units.

My valve power amp? It's a World Audio Design KAT34 with Svetlana valves. WAD have probably the best output transformers out there, until you get to the suicidally expensive stuff. Their 300b monoblocks look hugely tempting -they were designed by Andy Grove, the bloke behind the latest incarnation of the Ongaku.

Cheers
Scott
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Old 27th October 2005, 12:04 PM   #45
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Hey Dan, hope those Supravox drivers have arrived safely; I'm looking forward to hearing your first impressions when you've had time to get them into the cabinets!

A couple of drivers I completely forgot about that look to be interesting options for the original cabinet: the 5" Fostex FX120 and F120a models. The FX has a 2mm Xmax, Fs 70Hz, 0.45 Qts, 8.4 Qms, 0.47 Qes, and a low 8.21L Vas. Quite cheap too. The F model has a 1.5mm Xmax, 65Hz Fs, 0.44 Qts, 3.1 Qms, 0.51 Qes and another low Vas of 9.876L.
Both specs appear to be quite similar to the RS 40-1354 Terry used for his original pair of pipes, but I bet the quality's better over the rat-shack models! Of the two, the FX120 looks to be my favourite from the specs -it rolls off more smoothly, and seems generally flatter; extremely tempting, expecially as it's very reasonably priced. Either way, both look like nice mid Q types with reasonable excusion for their size. Any thoughts?

Scott
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Old 27th October 2005, 12:54 PM   #46
dmason is offline dmason  United States
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The 165LB are beautiful to behold, better build quality than the 215 IME, and one thing I like is the very heavy driver flange, which would double as a mass loader, for the diaphragm. At first blush they seem quite rolled off, and their 30' FR plots would indicate same, according to the site. FWIW, green, I do not put these in the same sonic league as the Fostex. I plan to let them cook a few days before deciding to proceed further. Not a good feeling about this one.

Scott, have a look at the 5 inch Monacors as well if you would, the two 6- models measure flat, and someone I know here building speakers is really stunned by the performance of the 8 Ohm unit. Says they are incredibly well built, and impressed everyone who heard them recently. Fs/60Hz Qts/~.45. Price is around $20. as opposed to $175 for the Supravox.

www.monacor.com

For the open baffle experimenters, Monacor has apparently released several new models with high Q, and according to the in-house measurements at www.spectrumaudio.de measure very impressively flat, all the way out.
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Old 3rd November 2005, 07:37 PM   #47
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Last offering regarding these pipes, as I think I can now suggest how they are sized, which might be of use to someone.

Total line length, as we all know well enough, is set to 1/2 the wavelength of Fs. Generally. You can play with that -this is probably best followed for drivers circa 50Hz lower, and you're going to get a L-O-N-G pipe indeed.

They are So=0 pipes (we all have exceptions to out rules, and this is mine!), Sm terminates in free space, and is set to approximately 4.25Sd. I say approximately, because there's room for experiment there. That said, based on Martin's explanation of the acoustics, and Terry's suggestion of chopping the back down to increase the mouth area a bit (though I have a hunch that he suggested this more for those running 6"+ drivers in the original pipe, which was designed for the 5 1/4" RS 1354), I wouldn't think going lower would be advisible. Increasing it by perhaps 1/2Sd will probably be OK though. Where the internal baffle ends depends on construction material. It'll terminate in the mid point of the cabinet, the same distance away from the floor.

Driver height appears to be determined by ye olde Voigt pipe equation: D = L + the cube root of So / Sm. It'll usually work out to be around 0.275 of the total line length. Stuffing depends on the room and driver. The point needs a bit, and about 1/4lb or an inch or so of felt on the base would most likely be a good starting point.

And that's it! Easy eh?

At present, my BIBs with FF165Ks in them have now got a few hours on them, and are really starting to open up, though with an Xmax of 0.3mm, I'm tredding easy with Iron Maiden! The new cabinets will be built to the above spec, though I won't be going for a 1/2 wave fs -that'd give a height of around 84", which is I feel a little excessive for a 6 1/2" driver! The FE206E, with its 1.5mm Xmax on the other hand, and a similar Fs would be interesting indeed, though you'd need a big room... I'm currently (no pun intended) using 24AWG magnet wire to good effect with EL34s doing the driving, though I think 30AWG would be more appropriate with an SS amp. I might also try a single pair of Cat5, just to say I've done it! How much series resistance, or how thin a wire you use (or what sort of cap etc) will largely depend on your amp, and what Q the driver you're using is.

Have fun!
Regards to all
Scott
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Old 3rd November 2005, 08:08 PM   #48
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Scott, quick thought on wire. I am a cat 5 user at this point until I make time to cut into my 47 labs length of wire. Anyway, I currently use 1 run of cat 5 in the casing in comes in per side, which is 4 wires per side. (4 twisted pair running though the outer casing) The correct way to do it is to simply seperate the twisted pair on each end and mate the solids and stripes. (this helps eliminiate RF and such, each twisted pair IS actually twisted at a different rate) Strip the ends and there you have it. Pretty easy. I've used this with both tubes and SS with success.

I had tried one twisted pair per speaker and found the sound was much leaner and really didn't gain anything. In fact, lost some of the body and weight.

Just thought I'd share, curious as to your thoughts once you try it out.
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Old 3rd November 2005, 09:49 PM   #49
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Interesting. I'll get back to you on that once I've given it a whirl over the weekend. What amp are you running by the way?

Oh -and correction to the above by the way:
D = L / 2 + the cube root of So / Sm

Cheers
Scott
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Old 5th November 2005, 07:26 AM   #50
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Default terry's BIB plans

Hello all. New to this site and to DIY FR speakers. I've read most of this tread and tried to wrap my head around it but its alot for a newbie. So now I have a question, first are the plans for the BIB pipes (second piture at the single driver site under BIB) available and two could the pioneer B20"s be used even though they are 8 inchers.
I plan on putting them in our living room (14'x16' w/ 8' ceilings) I like the idea of an open pipe and using the ceiling to disipate sound but everything i've read on the B20's says they suffer at the high end and I would rather not use a tweet and crossover, is there an other solution? What would be the most accessable inexpensive driver for these pipes?

Mark
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