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Fugly SonoMBM Redux - no cuts! no glue!

790 Views 18 Replies 4 Participants Last post by LastButNotLeast, Sep 10, 2019

LastButNotLeast

Discussion Starter · Sep 6, 2019 (Edited)

6

Several years ago, I took a pair of 8" speakers I had sitting around and attached them, dual-opposed, to a concrete tube form:
https://www.avsforum.com/forum/155-...9-sonotube-proof-concept-no-cuts-no-glue.html
At the time, I thought

LastButNotLeast said:
It would be really nice if someone with a bunch of speakers lying around (MoreIsBetter, BassThatHz, tuxedocivic ) would try this with something bigger. I think a pair of the well-regarded Infinity 1262s ($106) in a 12" tube ($9.92) for less than $200 and about an hour of time would kick *ss.

Lo and behold, thanks to
https://www.avsforum.com/forum/155-...4-12-jbl-speaker-29-black-friday-bestbuy.html
I find myself with a couple of well-regarded 12" JBL subs.
So here we go again.
The build is the same. I found a 12" tube that was 11.75" and, instead of feeling cheated, I was overjoyed. The #10 /24 threaded rods are only 3 feet long, so again I needed couplers. Three pillows for stuffing.
I left about 4 inches of rod at the bottom for feet. It probably should have been closer to 2" for better stability, but it's still standing (on carpet protectors

). Again, the materials are undisturbed for disassembly and return.
Having done it before, this one took about an hour to put together and tuck inconspicuously

into a corner:

I still haven't calibrated REW's SPL meter

o), but sweeps at the MLP are flat from 40Hz to 80Hz with very low distortion - the perfect MBM, and it felt that way, too.

Obviously, it could be prettied up by covering the tube and cutting the excess rods, but that's not in the cards for this one.
But it could be in the cards for someone else.

Michael

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Reactions: 1

1 - 19 of 19 Posts

sirjaymz

· #2 · Sep 6, 2019

LastButNotLeast said:
Obviously, it could be prettied up by covering the tube and cutting the excess rods, but that's not in the cards for this one.
But it could be in the cards for someone else.

Michael

You should check out @Nalleh 's build.
https://www.avsforum.com/forum/29-w...franken-atmos-living-room-2.html#post55242312

LastButNotLeast

Discussion Starter · #3 · Sep 6, 2019

I did. Beautiful work which I can admire and never duplicate.

lknhomeaudio

· #4 · Sep 6, 2019

LastButNotLeast said:
I still haven't calibrated REW's SPL meter o), but sweeps at the MLP are flat from 40Hz to 80Hz with very low distortion - the perfect MBM, and it felt that way, too.

Obviously, it could be prettied up by covering the tube and cutting the excess rods, but that's not in the cards for this one.
But it could be in the cards for someone else.

Michael

Why in the world is it falling 23dB in just 7-8 hz?!?!

LastButNotLeast

Discussion Starter · #5 · Sep 6, 2019

YOU are asking ME? That's rich.
Under the circumstances, it falls under DKDC, but I'll give you whatever more information you want.
Michael

lknhomeaudio

· #6 · Sep 7, 2019

LastButNotLeast said:
YOU are asking ME? That's rich.

I'm not sure what you mean by that?

LastButNotLeast

Discussion Starter · #7 · Sep 7, 2019

You have much more experience with these things than I.
I'll have some time Monday night to experiment before I take it apart, so I'll get more measurements.
That corner's going to look empty when it's gone.
Michael

noah katz

· #8 · Sep 7, 2019

lknhomeaudio said:
Why in the world is it falling 23dB in just 7-8 hz?!?!

Room modes, a null in this case.

No doubt a close-mic measurement would be much smoother, as it reflects the speaker's intrinsic response.

lknhomeaudio

· #9 · Sep 7, 2019

noah katz said:
Room modes, a null in this case.

No doubt a close-mic measurement would be much smoother, as it reflects the speaker's intrinsic response.

I suspected that, but the bounce back point is still 12dB down within 10hz. We all know sealed boxes don't do this lol. I'd also like to see a close-mic sweep!

LastButNotLeast

Discussion Starter · #10 · Sep 7, 2019

Happy to oblige. I'll probably do each speaker individually, then both together. Unless the whole thing falls apart.

Michael

Reactions: 1

noah katz

· #11 · Sep 8, 2019

lknhomeaudio said:
I suspected that, but the bounce back point is still 12dB down within 10hz. We all know sealed boxes don't do this lol.

Dunno know what you mean by bounce back point so the following may be off point - nulls are very sharp and deep, and sealed boxes are just as affected by modes.

lknhomeaudio

· #12 · Sep 8, 2019

noah katz said:
Dunno know what you mean by bounce back point so the following may be off point - nulls are very sharp and deep, and sealed boxes are just as affected by modes.

Probably the lack of a better term, for the frequency below the null, where the response comes back up.

Right. The null is very sharp and deep, at 31-32hz. The broad area from 20-27hz should NOT be in the null, yet it is 18-20dB down at less than an octave away. I mean, I guess the entire area could be a null, but I've never seen anything like that with my own systems.

LastButNotLeast

Discussion Starter · #13 · Sep 8, 2019

Yeah, I tend to do that with stuff.

Michael

noah katz

· #14 · Sep 9, 2019

lknhomeaudio said:
Probably the lack of a better term, for the frequency below the null, where the response comes back up.

Right. The null is very sharp and deep, at 31-32hz. The broad area from 20-27hz should NOT be in the null, yet it is 18-20dB down at less than an octave away. I mean, I guess the entire area could be a null, but I've never seen anything like that with my own systems.

Oh, now I see what you mean; for some reason I was disregarding the shelved down area.

It almost looks like a HP filter combined with a room null to give a brick wall filter effect.

LastButNotLeast

Discussion Starter · #15 · Sep 9, 2019

The red line is no eq at all.
Will move the tube to the middle of the room, calibrate SPL (if I remember), and run a bunch of sweeps Tuesday (Monday's out).
Stay tuned (no pun intended).
Michael

lknhomeaudio

· #16 · Sep 9, 2019

noah katz said:
Oh, now I see what you mean; for some reason I was disregarding the shelved down area.

It almost looks like a HP filter combined with a room null to give a brick wall filter effect.

Yes, it has me very confused lol

LastButNotLeast

Discussion Starter · #17 · Sep 10, 2019

2

Don't know if this will help or not, but here it is.
Tube moved to the middle of the family room (which my wife REALLY loves

), mic about a yard (meter) away pointed towards the middle of the tube.
No eq, pure direct, xo = 200.
Red and green are top and bottom, blue is both together in phase, gold is both out of phase.

Michael

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noah katz

· #18 · Sep 10, 2019

Hmm, still puzzling.

What does modeling show for the response?

Any chance you could measure it outdoors or at least near an open door?

Also check what others have measured for the JBL's.

LastButNotLeast

Discussion Starter · #19 · Sep 10, 2019

The family room is wide open to the rest of the house.
As much as I'd love to keep playing, the speaker has been disassembled - my wife is very tolerant of my strange hobbies, but I don't like pushing my luck.
The nine I have in my array (https://www.avsforum.com/forum/155-diy-speakers-subs/3059746-magic-square-subwoofer-array.html) are just fine.
Maybe too may pillows?

Michael

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