Why not much on Pioneer B20 MLTL?

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Thanks Scottmoose. I will try to build that one.

Has anbody tried building it yet?

What about the slot port at the bottom, does it need to be shorter? That length is based on how it sims up as a bass reflex in WinISD and I see that the port is usually shorter in an MLTL from designs I have looked at.
No-one's built one to the best of my knowledge, which is a pity, as it'd be well worth it IMO. Ironically enough, WinISD's prediction for a reflex is also a pretty good approximation of this MLTL, which doesn't often happen.


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I posted a bunch of them some years ago on the old FR forum and AFAIK no one built any, they were more interested in putting them in little boxes, and no one's asked about them here until you AFAIK.

FWIW, here's the one I wanted built:

L = 50.75"
CSA = 127.372"^2 ( prefer 28.5" W x 4.47" D)
zdriver = 19.3"
zport = 4" dia. x 2" long near/at the bottom for T/S max flat

All dims i.d. and approximate, minimal stuffing and add more down at/in the vent if too 'boomy'. Driver mass loaded against the back panel.



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That looks nice GM. You would have a pretty wide, but not very deep box with that. You wouldn't necessarily need BSC with that up against the wall. I think if I have the time and money, I will try both.

This is what I am working with for a room. The pony wall is 29 inches deep and 46 inches tall. The roof is 80 inches from the floor.


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I like! Especially the minimal damping bit. And with that kind of aspect ratio, this is another 2001 style Monolith, if painted black. I didn't know you'd done those / that Greg. Loads of gain, little damping, no BSC -can't go wrong. :)

If you're feeling insane of course... welcome to my nightmare. I think you're g... (sorry, don't know what came over me). Something I did for fun recently: 2 B20s per channel (lower one rolled off above ~500Hz) with perfect 1:4:9 external dimensions (3/4in material assumed) 8in x 32in x 72in (DxWxH). Vent 4in diameter x 1in long, 3in up from internal bottom. See attached FR. Nobody would ever be insane enough to build a pair, but I couldn't resist it. :D

Name your poison, Gentlemen:


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Actually, in most rooms a 30" wide baffle is the point where a T/S max flat is 'flat enough' when well away from the walls and why I prefer them, so usually have to be rolled off if near one. Neither will probably work 'best' as is, but mine is a bit more tunable unless you convert the other's slot port to an adjustable vent.

Yeah, the B20 got a lot of 'air play' for awhile and I posted about my crude OB experiments with a B20 and its woofer variant (-54F), with a small square piezo horn nestled in the lee of the two. Pretty impressive, all things considered, but never got a chance to fine tune it or work it into a pipe design. Then recently I shifted to my still-born B20 BIB/tapped horn Monolith with these drivers. I'm starting to wonder if the foam's going to rot before I get to build something with them.

Interesting! What movie is the video from?

FWIW, here's one B20 tapped horn I simmed:



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davidallancole said:
Do you guys have in suggestions for bracing?

Some 0.75" x ~2" plywood strips glued on edge run ~2/3 the length of the pipe on the front and rear panels should be sufficient, just stagger them at some golden or acoustic ratio, and if it were me I'd put the back panel ones on its rear if they're not going to be visible.

Really, placing one riser centered at ~28.5*0.618 = ~17.625" from each end yields two ~down the middle with a 6.75" gap and if one is notched out to put the driver at ~30*0.618 = ~18.53" - 0.75" = 17.78" should suffice when combined with the driver threaded mounting rods tying the front/rear together and give us a nice driver/baffle off-set to average out standing waves, i.e. mirror image baffles.

Man do you guys subscribe to "bigger is better"!!! How about trying more WAF-friendly dims of:

L=28" with a cross-sectional area of 9.5 x 14 in

Driver - 5" down from the top

Stuffing density = 0.25 lbs/ft3
(entire cab stuffed for a total of 0.539 lbs)

Port = Parts Express 260-404 Port Tube 3" ID x 4-1/2" L
located 4 in up from the bottom.

Using MJ King's MathCad worksheet:

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

When I model the in-room SPL response of either, the curves are different but there's no clear winner. Both go as deep and are equally as sensitive. Its really a case of what you'd like your peaks & nulls to look like from 200 Hz to 1 KHz. Most of the differences there are probably attributable to the different heights the B20 is up from the floor.

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

The blue curve is for GM's, the red dotted curve is my suggestion. Both cabs are placed within 1 in of the back wall. Both perform better away from the wall but I doubt anyone would want to pull GM's "B20 Monolith" too far away from a wall!
It looks like various different sizes will work but all will probably need tuned to work properly in my given situation. I want to keep it against the wall because floor space is at a premium down there. If I were to guess, I would say the opposite fronts of the pony walls are ~8-9 feet apart, so having them against the wall would help tremendously for me. Would I just need to make a high pass filter that will cut down the peak on the low end for yours GM, or will I need a notch filter to bring it down. This would help with excursion of the driver I would think on the low end, having to reduce the signal to the speaker to get flatter bass I mean.

Holdent, have you tried the MLTL you have shown or did you just whip that up now? I noticed that what you said for the width and depth is getting close to the golden ratio. Does it help the sound any to keep the width/depth measurements close or on the golden ratio?

I should probably get MJKs sheets and fool around with one. I would like to build it ~48 inches tall so that it makes it easier for cutting the panels out of a 4x8 sheet. Anybody see a problem with that?
Ouch. I can feel that one thundering Greg -graph's from Hornresp, right? Typical isn't it -I just get the hang of Akabak and David goes and adds a tapped horn facility... ;)

That video of Christopher Lee as you've never seen him before? It's from The Return of Captain Invincible -Name Your Poison was written (no surprise here huh?) by Richard O'Brian.

Yes, we like our big boxes. :) More tuning potential than a small box, reduces / eliminates baffle-step issues for all practical purposes & generally they sound better than a small box even if they look the same on a graph.

If the big box booms too much BTW, just damp the port down a bit. Simple & effective.
Thanks for the info guys. I will try the wide baffled one first and see how it sounds against the wall. If it is to boomy, I will add some stuffing to the port to tame it like Scottmoose said. I will probably build some of the others at a later date as well just to see what its like having the narrow baffle.

Thanks for all your help guys. I will post build picks in here in teh future when I get them made.
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