Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks?

That's right Godzilla! If I compare my two BiB results so far to many elaborate designs, I certainly get close or surpas with relatively little effort. The difference of course is that those designs try to squeeze into as small a volume as possible etc. I bet they do fine for what they are.

As a design routine, the BiB is just a great concept. At some point, it would be great if we could look into incorporating a choke into the BiB design routine. Maybe Scott can explain a little about his strategy for implementation, like in FH3. And how to translate this to a BiB. A longer slanted panel? An obstruction elsewhere? A choke seems like the easiest addition to the classic BiB. I like the curved mouth above here, but it is a bit more complex.
 
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I don't understand the driver position in both your drawings.. It seems to me that it doesn't follow spec for the fe108 in a BIB or even close etc..

Here's a page with a pic of the late Terry Cains inverted fe108 cabs.. If you look through the following pages there's some good info on them there.. Perhaps these would be something to aspire to for an inverted 108 BIB?

http://www.diyaudio.com/forums/full...one-have-those-fostex-craft-handbooks-79.html
 
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Hi Dave,
I remember your inverted BIBs from a few years back. I am looking to improve slightly on the original (at least mine which are upward firing with driver of .2 line length).

In any case, the the drawing on the left maintains the 222cm line length of the original but shifted up to accommodate the driver of approx .5 to .56 line length.

The second drawing uses a line length of 244cm (or less if the opening is not summed) and the driver is in the more "traditional" front placement with the zdriver at approx .4 to .5 line length.

As I said I'm hoping to remedy the lower extension and lower driver position I get when inverting my BIBs and also get back some of the "air" or "openness" of the upward firing placement while maintaining the increase in bass quantity. I'm not sure my changes will have any noticeable effect at all but I believe they are still BIBs and will work as such.

I don't understand the driver position in both your drawings.. It seems to me that it doesn't follow spec for the fe108 in a BIB or even close etc..

Here's a page with a pic of the late Terry Cains inverted fe108 cabs.. If you look through the following pages there's some good info on them there.. Perhaps these would be something to aspire to for an inverted 108 BIB?

http://www.diyaudio.com/forums/full...one-have-those-fostex-craft-handbooks-79.html
 
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I'm not sure why... I've followed the calculator and then made increased the height by 11cm, increasing it's volume specified by the calculator.

An externally hosted image should be here but it was not working when we last tested it.


Specs here:

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Hmm, with no Excel/calculators loaded, this seems way too small for its ~35 Hz 1/4 WL, so no bass to speak of even with [Sm] = vent area [Av].

GM
 
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DaveCan,
A more "normal" take on the inverted BIB using the old recommendation, zdriver at .416 line length.

I have summed the 11cm base with the internal width of the cab (subtracting the width of the divider) to get a mouth of 29cm high. Cut at an angle, a la Terry Cain's, it should increase the mouth area some.

I guess I could also cut out the 11cm at the bottom of the front panel as well and add a leg at the back. 😕

140f0xg.jpg


I don't understand the driver position in both your drawings.. It seems to me that it doesn't follow spec for the fe108 in a BIB or even close etc..

Here's a page with a pic of the late Terry Cains inverted fe108 cabs.. If you look through the following pages there's some good info on them there.. Perhaps these would be something to aspire to for an inverted 108 BIB?

http://www.diyaudio.com/forums/full...one-have-those-fostex-craft-handbooks-79.html
 
DaveCan,
A more "normal" take on the inverted BIB using the old recommendation, zdriver at .416 line length.

I have summed the 11cm base with the internal width of the cab (subtracting the width of the divider) to get a mouth of 29cm high. Cut at an angle, a la Terry Cain's, it should increase the mouth area some.

I guess I could also cut out the 11cm at the bottom of the front panel as well and add a leg at the back. 😕

An externally hosted image should be here but it was not working when we last tested it.



When I made mine I kept all dims as specified by the BIB calculator for the fe108, especially for the Zdriver. Then looking at the TC fe108 iBIB pics I guessed that the front panel was probably 60". So keeping all dims the same and Zdriver location, I increased the front and side panels to 60''.. This now when inverted put the center driver height at 33". I then added a 1'' base to the cab for a final driver height of 34". The only two things I didn't have the same, was I didn't scroll cut the bottom sides of the cab like TC did on his (I probably should have), and my mounting baffle ring wasn't as nice as his.. But they did sound very nice for what they were, and especially when augmented by a subwoofer or two 🙂 To my idea at the time I wasn't needing to reinvent anything really, and basically by just increasing 3 panels to 60" the height for the mouth off the floor near corners was now about where they should be, had the 108 cabs been taller to fire up at the ceiling properly etc.
 
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OK, can't recall if I ever posted any complete [pipe] horn design instructions or just posted bits n' pieces as they seemed appropriate, but the long and short of it is that with one pair of parallel sides it's a parabolic ['fast'] initial expansion that progressively 'slows', so relatively speaking it requires a lot of net volume [Vb] to load down low for a given pathlength.

Note too that it can be viewed as a relatively large cab with a huge flared vent, so theoretically must be designed just like with a T/S designed alignment where a ~0.403 Qts driver is tuned to Fs in a Vb = Vas sized cab, ergo < ~0.403 Qts = smaller/tuned higher and > ~0.403 Qts = larger/tuned lower.

With this in mind, for the BIB calculator to work best overall is to 'juggle' T/S specs as required to get the desired tuning and since historically [including this forum] low Qt horn drivers such as the FE108EZ would be driven with a high output impedance via SET amp and/or BSC filter which in turn increases Qts to at least 0.403, hence my 'too small' comments.

Same thing re: desired [pipe] tuning [Fp], hence with a 77 Hz Fs it calculates a 38.5 Hz Fp, ergo any higher/lower requires shifting Fs to get the ~244 cm path-length down to ~35.3 Hz.

Anyway, the wood's cut, so according to Hornresp, don't expect much below 80-100 Hz unless hard in a corner and even then it's indicating that only a tiny gap of 6 cm^2 [total] is required to get some decent back pressure, so basically a leaky sealed pipe.

Consequently, the driver sims smoothest down at 0.7 with fairly heavy damping from the top to just below the driver, so now too low [again]. I guess if it were mine, I'd use the 0.7 and tilt the cab back a little to create the tiny slit vent. If you cut it out like in the sketches, it will have a large 3rd harmonic suckout in the mid-bass that you may, may not be able to damp out sufficiently without rolling off all of the rest of its gain BW below it and if you do have any significant series resistance it just makes it worse.

GM
 
Hi GM,
Thanks for the detailed explanation... I'm glad I asked as I would have wasted a bunch of time and effort for another, likely, unsatisfactory build. I am still unhappy with my 2x Monacor sp60x MLTLs and never really loved my ff165k BIBS. Right now I am only out the 30€ for the cut wood and will try to find another driver, perhaps Tang Band or Faital, that will work well with these dimensions.

When playing with the values in the calculator and raising the Qts to 0.403 and lowering the Fs to 73 I get a cabinet size of 36.17l as opposed to the 29.95l box I have cut for. Will this difference have such a profound impact on the sound?

Also, I'm not sure why the sims look so bad as my original fe108es bibs, smaller still, not corner loaded and 1.8m from the ceilings still had decent bass, and definitely lower than 80 - 100 Hz. I was just hoping to wring some more bass from them to balance out the rising mids which became irritating over time. When I tried them spaced close to the floor (~ 11cm) I didn't like the sound even though the overall bass was increased.

Of course I have to ask what would an ideal fe108es look like, with a F2 amplifier, corner loaded with 3.10m ceilings? Zdriver preferably up high.

Taking a look at the calculator I noticed that nearly all of the Fostex drivers included have a Qts of less than 0.403, some far less... My ff165k bibs appear to be greatly undersized, with its Qts of 0.2. Perhaps this is part of the reason why I have never been too happy with them, although I seem to recall they were highly touted and a go-to recommendation a few years back? 😕

An externally hosted image should be here but it was not working when we last tested it.



OK, can't recall if I ever posted any complete [pipe] horn design instructions or just posted bits n' pieces as they seemed appropriate, but the long and short of it is that with one pair of parallel sides it's a parabolic ['fast'] initial expansion that progressively 'slows', so relatively speaking it requires a lot of net volume [Vb] to load down low for a given pathlength.

Note too that it can be viewed as a relatively large cab with a huge flared vent, so theoretically must be designed just like with a T/S designed alignment where a ~0.403 Qts driver is tuned to Fs in a Vb = Vas sized cab, ergo < ~0.403 Qts = smaller/tuned higher and > ~0.403 Qts = larger/tuned lower.

With this in mind, for the BIB calculator to work best overall is to 'juggle' T/S specs as required to get the desired tuning and since historically [including this forum] low Qt horn drivers such as the FE108EZ would be driven with a high output impedance via SET amp and/or BSC filter which in turn increases Qts to at least 0.403, hence my 'too small' comments.

Same thing re: desired [pipe] tuning [Fp], hence with a 77 Hz Fs it calculates a 38.5 Hz Fp, ergo any higher/lower requires shifting Fs to get the ~244 cm path-length down to ~35.3 Hz.

Anyway, the wood's cut, so according to Hornresp, don't expect much below 80-100 Hz unless hard in a corner and even then it's indicating that only a tiny gap of 6 cm^2 [total] is required to get some decent back pressure, so basically a leaky sealed pipe.

Consequently, the driver sims smoothest down at 0.7 with fairly heavy damping from the top to just below the driver, so now too low [again]. I guess if it were mine, I'd use the 0.7 and tilt the cab back a little to create the tiny slit vent. If you cut it out like in the sketches, it will have a large 3rd harmonic suckout in the mid-bass that you may, may not be able to damp out sufficiently without rolling off all of the rest of its gain BW below it and if you do have any significant series resistance it just makes it worse.

GM
 
Greets!

You're welcome!

Profound, no. That said, with such a high Fs, low Vas and Qts, significant EQ is required [room gain or some form of baffle step compensation/BSC] to make bass significantly below driver Fs, so stopping at 0.403 isn't going to get the desired bass without massive room gain.

I mean the bass doesn't 'fall off a cliff' in a sim, just rolls off below 80 Hz at ~6 dB/octave down to tuning before it plummets at ~24 dB/octave, but rooms can have a 'profound' effect on bass response, so no clue what you're actually hearing.

Another thing is that the BIB calculator can't factor in 'tight' [low Vas] drivers, which is going to undersize it; after all it takes 'X' amount of net Vb to go down to 'Y' Hz regardless of driver specs, so without simming these types of [horn] drivers and varying Fs, Qts to get the desired results............ 🙁 Of course even if you do, you still may need to use significant EQ if there's not enough room/boundary gain.

All that said; if the F2 is what drives these various speakers it's little wonder that even undersized cabs will have some strong [mid]bass with generally poor response without significant damping and that if you had factored in its 15 ohms of output impedance + a typical 0.5 ohms for wiring/losses, the FE108EZ's ~0.31 Qts rises to a pipe horn filling ~0.922 Qts': mh-audio.nl - Home

So.......re-run the numbers using this Qts and whatever ear height the 0.42 driver location is to set its pathlength and let's see if there's enough net Vb, path-length to get a theoretically room filling bass [in stereo] at least into the mid 40s, and if not, then we'll see what HR 'says' it will take.

Ditto your FF165Ks if interested............ Note that the dual Monacor MLTL would likely need to be a huge [stuffed] Pensil design.

GM
 
Thanks GM!

Here is the updated cab, revised Qts:

o70ock.png


Quite a difference! I kept the 48" height for easier cuts but at this size it may be worth it to raise them up a bit for a longer path length. Not enough to go ceiling loaded though.

As I have the wood already cut as mentioned before, what do you think of the following driver for a fit?

http://www.parts-express.com/pedocs/specs/294-1102-faitalpro-3fe22-16-specifications.pdf

It is reported to sound good and easily available over here in Europe. There are also 4 and 8 ohm versions with varying specs.

Calculated with manufacture specs:

lf6km.png


With Qts pushed up to 0.92:

14sm8u0.png


They also have a cheaper driver, with higher Qts that looks good as well. Neither of these will be used with the F2, instead a chip amp, class D, or the Pass Amp Camp Amp:

FaitalPRO 3FE25 3" Professional Full-Range Woofer 8 Ohm

Greets!

You're welcome!

Profound, no. That said, with such a high Fs, low Vas and Qts, significant EQ is required [room gain or some form of baffle step compensation/BSC] to make bass significantly below driver Fs, so stopping at 0.403 isn't going to get the desired bass without massive room gain.

I mean the bass doesn't 'fall off a cliff' in a sim, just rolls off below 80 Hz at ~6 dB/octave down to tuning before it plummets at ~24 dB/octave, but rooms can have a 'profound' effect on bass response, so no clue what you're actually hearing.

Another thing is that the BIB calculator can't factor in 'tight' [low Vas] drivers, which is going to undersize it; after all it takes 'X' amount of net Vb to go down to 'Y' Hz regardless of driver specs, so without simming these types of [horn] drivers and varying Fs, Qts to get the desired results............ 🙁 Of course even if you do, you still may need to use significant EQ if there's not enough room/boundary gain.

All that said; if the F2 is what drives these various speakers it's little wonder that even undersized cabs will have some strong [mid]bass with generally poor response without significant damping and that if you had factored in its 15 ohms of output impedance + a typical 0.5 ohms for wiring/losses, the FE108EZ's ~0.31 Qts rises to a pipe horn filling ~0.922 Qts': mh-audio.nl - Home

So.......re-run the numbers using this Qts and whatever ear height the 0.42 driver location is to set its pathlength and let's see if there's enough net Vb, path-length to get a theoretically room filling bass [in stereo] at least into the mid 40s, and if not, then we'll see what HR 'says' it will take.

Ditto your FF165Ks if interested............ Note that the dual Monacor MLTL would likely need to be a huge [stuffed] Pensil design.

GM
 
I noticed before that some suggestions of the bib calculator don't sim as well in hornresp and improve when enlarged. I also noticed that if a bib seems really well in hornresp, it usually does so with many and different drivers. Nice to read why, GM.

My current bibs use the Visaton frs 5x, Qts is 0.7. Visaton has loads of. Cheap yet interesting drivers with fairly to absurd high Qts. I would sim a few of those if I were you.
 
Thanks GM!

You're welcome!

Hmm, you were asked to work it out based on a 0.42 driver offset to get it up high in an inverted position as a straight pipe for your high ceiling plus gives more loading in the mid-bass as a bonus, which you can see in the comparison [red is your design].

FWIW, my initial comments about size was based on a guesstimated ~112 L net Vb tuned a little lower, so now you know how much series resistance I assumed [16 ohms]. 😉

Faital Pro 3FE22 comparison between low, high output impedance [red trace]; the 3FE25 would be similar.

GM
 

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  • Faital Pro 3FE22 BIB [0.217 driver offset] comparison between low, high output impedance [giants.PNG
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WOW! The FF165wk with revised 0.922 Qts is a no go!

Yeah, volume wise it's only a couple of cubic feet smaller than one of my cabs, though the tall BIB's footprint is considerably smaller. With a 40 Hz Fs though, you don't need so much added series resistance since the room will normally be loading the pipe pretty good, so typically only needs a few ohms.

Changing it to [Sm] = 1000 cm^2 seems a good compromise and if it turns out to be light in the bass, which would surprise me, then add a BSC filter to flatten it out.

GM
 
OK, I'm confused about a few things. I thought we were still discussing a 48" downward firing BIB... but shouldn't straightening it out and firing at the ceiling be the same, as the line length has not been changed?

The birch ply I can get over here is up to 244cm or maybe 250cm so I can't increase line length any more without folding. The ceilings are 310cm so not much loading, which is why I went to downward firing in the first place.

The grey trace looks to be good. The red is the undersized design using the 0.31 Qts?

The Faitals look to have a similar dip in the mid bass but might not be so bad once stuffed and corner loaded. In another thread I saw they had replaced the FE108es in a commercial design.

http://www.diyaudio.com/forums/full-range/285949-faital-3fe25-3fe22-2.html#post4643957

You're welcome!

Hmm, you were asked to work it out based on a 0.42 driver offset to get it up high in an inverted position as a straight pipe for your high ceiling plus gives more loading in the mid-bass as a bonus, which you can see in the comparison [red is your design].

FWIW, my initial comments about size was based on a guesstimated ~112 L net Vb tuned a little lower, so now you know how much series resistance I assumed [16 ohms]. 😉

Faital Pro 3FE22 comparison between low, high output impedance [red trace]; the 3FE25 would be similar.

GM
 
Don't feel like the Lone Ranger 😉, wanting multiple alignments in a single message tends to do that; so with me doing any responses, sims in little spurts [during TV commercials, phone calls, doing chores, etc, and late at night] combined with failing memory and only HR loaded, I have to keep rereading/checking to hopefully make sure I'm getting it all right.

Regardless, I was working on this request, which I thought was the real goal if it was a realistic one to build:

Of course I have to ask what would an ideal fe108es look like, with a F2 amplifier, corner loaded with 3.10m ceilings? Zdriver preferably up high.

Unfolded, it ideally needs to be longer than 8 ft, but the F2 makes it large enough to handle some pretty significant bass in stereo even if there's not much room gain. For sure it theoretically will freak folks out that a large tweeter can make bass like a really large woofer with the same area [Sd] as the pipe horn's terminus [Sm].

This doesn't mean it will hit high SPLs though since it will only be able to 'cleanly' handle a fraction of a watt down low, but cab efficiency will be high, so a pair theoretically should peak in the 95-100 dB/m range down to at least 40 Hz or a little more if these drivers can be overdriven a bit without making them sound obviously distorted in the critical mids.

In short, the bigger we can make [Sm], the better. Ditto length, so was thinking about a detachable 'top hat' to extend it closer to the ceiling.

No, this is a comparison of the same BIB with the red trace being yours with its default 0.217 driver offset and the gray is at 0.42.

Closed pipes such as a TL, conical horn are basically two octave devices with its first dip at the 3rd harmonic, so if it's tuned to 20 Hz, then the dip is around 80 Hz, etc., ergo as the driver location is shifted away from its closed end, its harmonic structure is changed and the higher it's shifted, the less damping usually required plus the less chance any room modes will aggravate the problem.

GM
 
I noticed before that some suggestions of the bib calculator don't sim as well in hornresp and improve when enlarged. I also noticed that if a bib seems really well in hornresp, it usually does so with many and different drivers. Nice to read why, GM.

My current bibs use the Visaton frs 5x, Qts is 0.7. Visaton has loads of. Cheap yet interesting drivers with fairly to absurd high Qts. I would sim a few of those if I were you.

You're welcome!

Yes, once the horn is big enough to handle a 'worst case' set of driver specs, then any others will at most just need some EQ and why a typical compression driver, which is very under-damped, will work on so many different horn sizes/types.

I've simmed quite a few different Visaton, Monacor, etc., drivers for others, though to date haven't auditioned any of them and just found out that Visaton is now here in the USA, so thanks for the recommendation.

No plans to build any more speakers other than for the drivers I've accumulated that haven't rotted [quite a few unfortunately], though may put new surrounds on the Pioneer B20s and vintage Philips if I last long enough.

GM