Downsize a BIB

[danerius]

Hi everyone.

Quick question? Has anyone tried undersizing a BIBs footprint and not the length? What will generally happen? Im guessing an overdamped bass? Can that be rectified with a lower damping power amp, ie higher impedance?

Reason Im asking is Ive been oogling all the rave over the BOFU and the BIB but doing the math in Zillaspeaks spreadsheet. Its humongeous. The attachments shows my fiddling with the qts value to reach less tank like proportions.

Whats ur opinions on this?

Regards /Bo

 

[jrenkin]

I have seen a few people talking about using smaller BIB boxes than recommended and still sounding great. I built a set using fostex 208 sigma. they are 80 inches tall and 10" x 12", so somewhat smaller than you get for the BOFU and mine are quite imposing. BUT, they sound soooo fine....

I bet you could get away with minor modifications without a problem, maybe around the size of mine, not sure if I would explore much smaller.

I will post a picture in a new thread when I have a moment to take one, they have only been up and running a couple of days and still need to be sanded and finished.

I recommend a cardboard mock-up in full size. See what your wife will put up with and go as big as you can!

 

[GM]

Im guessing an overdamped bass?

Can that be rectified with a lower damping power amp, ie higher impedance?

Greets!

You guessed right!

Yes, and no. It will flatten the response for a better match to the larger cab's tonal balance, but will round off the LF which may/may not be beneficial depending on room loading.

That said, once you drop below ~200"^2 things start getting ugly looking in a quick half space sim, though backed up against a wall, and especially if corner loaded, it will probably still outperform any other typical cab by a wide margin with little/no BSC depending on room loading. Out well away from a wall/corner though and you may be sorely disappointed with only ~134"^2.

Only one way to know for sure though.

GM

 

[danerius]

Thanks GM + jrenkin.

Theyre planned for room corners. See sketchup pic. Im starting to rule out BIBs with a BOFU cuz of the size. Either change driver or enclosure type. My musical taste is more towards rock + pop so the cheap, cheerful and unfatiguing aspect of the BOFU appeals a lot. And Id rather sacrifice some resolution and soundstage and have my speaker play engaging bass instead.

Never liked the sound of bass reflexes or sealed boxes so my other options looks like TLs or Onkens. Regarding taste again. Open baffles, horns, TLs etc have had the most musicality to my ears. Fullrange of course Any suggestions for other drivers?

Living in metric land Im a bit lost on ur figures GM. Is that square inch? Cubic inch? Cubic feet? Regarding room size or?

Regards /Bo

 

[Godzilla]

>>> once you drop below ~200"^2 things start getting ugly looking in a quick half space sim, though backed up against a wall, and especially if corner loaded, it will probably still outperform any other typical cab by a wide margin with little/no BSC depending on room loading.

Thanks for that GM. Can someone generate a frequency response chart for a BIB using the B20 in an 80" x 12" x 12" BIB. I would if i could but i don't have the software to make the chart. That's 144"^2 and with corner loading in the sketch it may work. The B20 is not about perfection, nor is the BIB, so maybe compromises can be made while still producing great sonic value.

danerius, that's a nice sketch. May i use it for the BIB site?

Also, your space seems appropriate for BIBs (and many other tall slim designs). I can envision Fostex 168S in that space too but the price for drivers goes up.

Zilla

 

[GM]

You're welcome!

BIB net base area (Sm) in inches squared (^2): Convert

The Onken is a fairly extreme bass reflex (BR), so if you don't like typical ones.........

Rock/pop historically sounds 'best' with low Fs, medium (low, if tube driven) Qts, high Vas drivers, so what passes for big boxes on this forum is where it's at, especially when Pink Floyd or a few other groups are 'on stage'.

At this point then, it becomes a matter of finding a driver that will fit your space limitations with good output to around 27 Hz when corner loaded in a TL. In rooms I've measured, this equates to around a 38 Hz F3 with a low Qt, but I imagine your home is much better constructed to handle worse Winter conditions, so you'll probably need a somewhat different F3, Qt based on the room's gain curve that will have to be at least reasonably well guessed at before any meaningful driver choices can be considered.

Something that may be worth considering is doubling up B20FUs in an isobaric layout to halve net Vb.

GM

 

[GM]

Thanks for that GM. Can someone generate a frequency response chart for a BIB using the B20 in an 80" x 12" x 12" BIB.

You're welcome!

I don't have any software that will do BIB corner sims, so all I can say is yours looks only marginally better than his slightly smaller one in half space.

GM

 

[danerius]

>>> once you drop below ~200"^2 things start getting ugly looking in a quick half space sim, though backed up against a wall, and especially if corner loaded, it will probably still outperform any other typical cab by a wide margin with little/no BSC depending on room loading.

Thanks for that GM. Can someone generate a frequency response chart for a BIB using the B20 in an 80" x 12" x 12" BIB. I would if i could but i don't have the software to make the chart. That's 144"^2 and with corner loading in the sketch it may work. The B20 is not about perfection, nor is the BIB, so maybe compromises can be made while still producing great sonic value.

danerius, that's a nice sketch. May i use it for the BIB site?

Also, your space seems appropriate for BIBs (and many other tall slim designs). I can envision Fostex 168S in that space too but the price for drivers goes up.

Zilla

Absolutely. Id be honored to have my sketch on Zillaaudio

Ive been thinkin 10" x 12" (to keep the depth/width ratio) and my BIB spreadsheet says 90.5" tall.

Regards /Bo

 

[danerius]

You're welcome!

BIB net base area (Sm) in inches squared (^2): Convert

The Onken is a fairly extreme bass reflex (BR), so if you don't like typical ones.........

Rock/pop historically sounds 'best' with low Fs, medium (low, if tube driven) Qts, high Vas drivers, so what passes for big boxes on this forum is where it's at, especially when Pink Floyd or a few other groups are 'on stage'.

At this point then, it becomes a matter of finding a driver that will fit your space limitations with good output to around 27 Hz when corner loaded in a TL. In rooms I've measured, this equates to around a 38 Hz F3 with a low Qt, but I imagine your home is much better constructed to handle worse Winter conditions, so you'll probably need a somewhat different F3, Qt based on the room's gain curve that will have to be at least reasonably well guessed at before any meaningful driver choices can be considered.

Something that may be worth considering is doubling up B20FUs in an isobaric layout to halve net Vb.

GM

Point taken on Onkens. Apart from cubic feet/meter figures? What else do I need to calculate room Qts? The wall are plenty thick, as u guessed, 45 cm thick outer walls, 18 cm inner with several layers of brick + plaster. Plenty warm during winters, roastin in summer. Theres two flimsy dry walls in the dinner table area but Im gonna brace those.

An isobarik TL may be a very good idea. Im gonna look more into that.

Im a Mac/iPhone guy. Conversion is widget easy once I know what to convert

And Zilla. Ive been sketchin and doin calcs on FE166/FE206. Ive some experience with FE83, FE106Σ and FE207 in the past. They have a sonic signature that favours upper mids. In no way bad but maybe not perfect for me. I havent ruled them out completely though.

Now, Ive never listened to a pair of Bofus but lore suggest theyre more in line with my preferences. Just to give u a bearing of what Im after in my speakers. I once sat down in front of a pair of Lowthers in bass reflex cabs + a mono sub. Even disregarding the timing issues between the docile sub and jittery Lowthers. Not my thing at all. If that helps

Regards /Bo

 

[Godzilla]

The B20 (BOFU) will have you thinking you’re listening in a lounge at a nice pub with a great sound system. A sax sounds like a sax and everything sounds natural (needs a helper tweeter or it sounds dull). Nothing stands out in that peaky way and everything is relaxed… I have Fostex and heard Lowthers and understand your reservations on those drivers (the current 168z is darker sounding than the rest of their line imo). So you will probably enjoy the B20s for years like I have. I can listen to them for hours without fatigue. When I compare them to something else they are less detailed but long term listening, the B20 is really great. What about Changs or Half Changs?

http://homepage.mac.com/tlinespeakers/FH/download/halfChang-map-051107.pdf

 

[GM]

In a sealed up, square/rectangular subterranean basement, room gain begins below its 1st eigenmode and rises at 12 dB/octave with decreasing frequency, so if the room's longest dimension is 30 ft, then 565/30 = ~19 Hz and +12 dB/~9.5 Hz, but most rooms have various losses, so it may initially rise this fast, then start flattening out as the room increasingly becomes an acoustic sieve and worse, rise much more slowly from the beginning if there's large open doorways to act as mid-bass tuned vents to other chambers.

My room for example has a large 'L' shaped entry to two different areas with one a straight shot down a short hall and through another door/room that drops the 1st eigenmode down to around 12 Hz, so no useful room gain at all for me. Corner boundary gain isn't much better due to construction barely sufficient to last through relatively mild Winters. It's only 3-4 dB total at 20 Hz, the lowest I could measure at the time and why I need a very low tuned, low Qt system to a get decent tonal balance and bass without a lot of boost, but the trade-off is dual 15s in ~20 ft^3 cabs/channel to get decent dynamics.

I'm kind of behind the times, I currently don't own a functioning cell phone much less a fancy hand held phone/camera/computer. Heck, not being one to fix what isn't broke, one of my home extension phones is a rotary and the other is a first generation push-button wall phone.

Anyway, if you can, measure an easily portable speaker outside, sitting on hard surface like a driveway, patio or similar and in a room corner to get an idea of what to expect.

GM

 

[holdent]

"Can someone generate a frequency response chart for a BIB using the B20 in an 80" x 12" x 12" BIB. I would if i could but i don't have the software to make the chart. That's 144"^2 and with corner loading in the sketch it may work."

Godzilla here's what I get:

Using the original (fullsize) B20 BIB from the dimensions on your website (Bigger Is Better 'BIB' Cabinet Dimensions - ZillaSpeak) I get:
[IMGHTTPDEAD]http://www.limestone.on.ca/~holdent/images/B20 BIB.gif[/IMGHTTPDEAD]

This is a little bit different from the frequency response you show.

Using the smaller dimensions above with zdriver = L*0.217 or 13.36 inches I get:
[IMGHTTPDEAD]http://www.limestone.on.ca/~holdent/images/B20 BIB small.gif[/IMGHTTPDEAD]

I'm not sure what T/S data was used earlier and this may explain the difference between my result and the one on your website. I used the data published by Parts Express at http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=290-045

 

[danerius]

"Can someone generate a frequency response chart for a BIB using the B20 in an 80" x 12" x 12" BIB. I would if i could but i don't have the software to make the chart. That's 144"^2 and with corner loading in the sketch it may work."

Godzilla here's what I get:

Using the original (fullsize) B20 BIB from the dimensions on your website (Bigger Is Better 'BIB' Cabinet Dimensions - ZillaSpeak) I get:
[IMGDEAD]http://www.limestone.on.ca/~holdent/images/B20 BIB.gif[/IMGDEAD]

This is a little bit different from the frequency response you show.

Using the smaller dimensions above with zdriver = L*0.217 or 13.36 inches I get:
[IMGDEAD]http://www.limestone.on.ca/~holdent/images/B20 BIB small.gif[/IMGDEAD]

I'm not sure what T/S data was used earlier and this may explain the difference between my result and the one on your website. I used the data published by Parts Express at Pioneer B20FU20-51FW 8" Full Range Driver | Parts-Express.com

Wow. Thats quite a difference... Dont know if this helps but heres some parameters for the BOFU. Many, many thanks for doing the sim

Been googling for a european supplier for the BOFU. Shipping from US is quite steep. Anyone knows?

Regards /Bo

 

[GM]

Using the smaller dimensions above with zdriver = L*0.217 or 13.36 inches I get:

Hmm, 13.36"/0.217 = ~61.57" path-length, but for an 80" internal height that I assume GZ means, the sim needs to have a 160" path-length. Regardless, for a given tuning (Fp) with such an acoustically small mouth (Sm) will kill off much of its mid-bass gain which is where you usually need it most and what I meant by 'ugly'.

GM

 

[Godzilla]

>>> but for an 80" internal height that I assume GZ means, the sim needs to have a 160" path-length.

Yes.

 

[jrenkin]

Here is a photo of my newly completed (but not finished) BIBs. They are 80" tall and about 12" x 10" and built close to the specs per the BIB calculator for the main driver, the Fostex 208 sigma. I added a super tweeter, the Fountek CD2.0 for kicks. Probably not needed.

They are quite imposing. Next to them are a pair of Acoustic Zen Adagios for size. The Adagios may be for sale soon

I am going to post my own thread, since I have questions and thoughts on these and don't want to hijack this thread, but a thought for the OP:

If you notice in my pictures the speakers, at over 2 meters tall, come close to the ceiling and that creates a big bass amplification. In my LR, the ceiling over the speakers is an overhang and most of the room is up to 18ft (6 meters) tall and super open. If I stand under the overhang...boom...boom.. too much bass. In a room like yours I would be concerned that a box this big will be overpowering.

I will try to listen to them in a lower ceiling-ed room, but moving them, and everything else is a pain.

I could be wrong and I am getting less bass than I want. I have some digital room correction (very rudimentary) and I do get a low frequency distortion from the woofers, I think due to under damping of the big box and I plan to try to fix it with stuffing above and around the woofer as well as with the DEQ. Anyway that is for the other thread.

I think in your room, you may get plenty of bass with a smaller driver and box. Bigger is better, but you may not like it if it is too big...

 

[jrenkin]

Oh, I forgot to ask, Holdent, what software are you using to create those graphs?

 

[GM]

Godzilla BIB comparison using MJK's original MathCad software - note that I used some older driver measured specs I already had loaded, but for comparison purposes it's good enough to see how a smaller Sm/slower expansion rate affects a simple conical horn's gain BW:

GM

 

[jrenkin]

Godzilla BIB comparison using MJK's original MathCad software - note that I used some older driver measured specs I already had loaded, but for comparison purposes it's good enough to see how a smaller Sm/slower expansion rate affects a simple conical horn's gain BW:

GM

I understand that his software isn't available anymore. Is that correct?

 

[GM]

Not according to his website: MathCad Computer Models : Upgraded Versions

GM