New Box Idea (Life after BIB's)

[pjanda1]

I'm moving 800ish miles in a couple of weeks and I decided that I probably shouldn't bring the BIB's. I found them a new home, and now I'm laying awake at nights pondering my next box. I've thought about doing an OB setup with helper woofers, but I'm also interested in a resonant enclosure that bridges the gap between the BIB and a vented box. I will of course be using the drivers I sell (Wild Burro BetsyK's), and I'll mention this enclosure to folks, but the point is to get me some new cabinets, not sell drivers.

Design goals:

Bass tuning: I've tried both smaller vented and sealed boxes and the BIB. I've always been happy with the bass extension. However, the sealed and vented boxes needed BSC. The BIBs needed 8 lbs of fill in the horn mouths to keep the bass gain from being overwhelming (in my room). I'd like something that combines a sensible bass rolloff (maybe -6 at 40hz) with 2 or 3 db gain as acoustical baffle step compensation. As they'll be close to a wall in a small room, more is not necessary for me. Toss my BetsyK's specs into a box simulation for 3 cu ft tuned to 42 hz. I'm looking for something like that, but with a couple db gain above flat. I'd also like to get a little more excursion control than the vented boxes give.

Size and shape: I'm not opposed to generously sized, but I'd like to be able to move it more easily. Here again, I'm thinking of something between the BIB and a 3 cu ft vented box. Could 5-6 cu ft do it? I'd like to get a driver height between 30-36". Way up in the air is just weird to me, as is lower than 30 or so inches. I am partial to fairly tall, skinny boxes.

Last goal: A lack of useless arguments. I know some folks might be grumpy as I sell these speakers. I don't want to argue about the specs (I like the folks at the factory, and I'm trusting them). I'm not looking for free advertising. I'm just a guy who doesn't have the mathcad sheets but likes the stuff you can build with them!

So, here is my idea. It's a (well, I think) mass loaded dual mouth BIB. The lines are internal dividers. It's not to scale. As it is mass loaded, I assume you could play with the beginning of the line to get the driver positioning right. I drew in slot vents, but I'd consider anything. I like the dual mouth BVR's, but I'm not sure I can afford the space as I need all the cabinet volume I can get. I'm thinking 5 ft tall. Anyway this could work?

pj

[Godzilla]

>>> As they'll be close to a wall in a small room...

Neat idea for a cabinet design pj. Why not consider something like:

http://homepage.mac.com/tlinespeaker...GabBrynn3D.gif

http://homepage.mac.com/tlinespeaker...alfChang3D.gif

or even something simple like:

http://www.zillaaudio.com/fostex-127e-slotted-box.htm

on a larger scale.

But the boxes that may work best I can't seem to find online at the moment. They were basically voigt pipes with all the workings on the inside and ported out the bottom by a flat slot??? I think Scott designed them? Where did they go?

Godzilla

[pjanda1]

I really like those big vents. However, I think I need all the Vb I can get. Those vents add a great deal of actual enclosure size without contributing to Vb, which is fine if you've got a driver with a lower Qts and Vas and/or are willing to have a giant box (like you'd get with a similarly tuned/designed enclosure for the BetsyK). I'd also like some sort of TL/horn variant (rather than just a vented box with a slot vent), as I'm under the impression that they tend to control driver excursion better. When moving from the vented box to the BIB, I noticed a huge decrease in speaker cone movement which I believe resulted in a cleaner midrange and greater dynamic capabilities.

Now, all of that is based on my rather limited understanding of loudspeaker enclosures, so I'm hoping more folks will chime in!

pj

[tinitus]

Thats a new one
BIG, but rather short line

[pjanda1]

The scale is pretty ugly. I figure you could get a line that is 50-60" long, which based on my guessing, could be long enough given the mass loading.

pj

[tinitus]

You inspired me

[qingcai]

tinitus, what is this?

[tinitus]

Originally posted by qingcai
tinitus, what is this?

OT, I know, but not much else happening
Its a double horn
Wide and flat
Big mouth on both sides
Easy to build

[pjanda1]

I've been playing with horn response. I'm having a hard time getting an MLTL to sim any different from a vented box with the same Vb and port. (I've been comparing designs others have created in Mathcad).

I've been trying to sim a ML-TL with a big taper, like if you unfolded the box I drew. I'm not getting much of anything useful. Either a taper isn't the way to go or I'm not inputing the right stuff.

Aside from those problems, is the folding scheme in my picture viable? I also wonder if it would work to fold a straight TL the same way (imagine the same thing, but with the dividers right down the center of the cab. Would it work like a straight MLTL of the same path length and volume? FWIW, the point of the fold is to get symmetrical ports above and below the driver, if for no other reason than that I like the idea.

pj

[rjbond3rd]

Hi PJ,

I'm sure you already know that the math models of MJK and Horn Resp are totally different and HornResp doesn't do Martin's transmission line / quarterwave stuff. I think HornResp is based on "horn math" like Leach's and Keele's:
http://users.ece.gatech.edu/~mleach/papers.html
http://www.xlrtechs.com/dbkeele.com/papers.htm

You could always do a classic TL (not mass-loaded but definitely tapered) using MJK's classic TL alignment tables. (Martin hints that a tapered TL would be easiest.)
http://www.quarter-wave.com/TLs/TL_Theory.html

Of possible interest:
http://www.randteam.de/AkAbak/Index.html (free to demo, amazing manual!)
http://www.aj-systems.de/indexe.htm (109 Euros but free demo)

EDIT: HornResp is fantastic and well worth using / learning!