7 x RE Audio XXX 18" subs, Infinite Baffle Sub, Ultimate IB build - Page 6

No s**t? Awesome. Even with the monsters I'm working on, I'd still like to make a pair of line arrays someday. Cool stuff.

if possible, you should really try to get a few sealed subs and put them in the areas you are hoping to install the drivers in your wall. I've seen what you want to do a few different times at other peoples HT's and the results were not very good. Thats not to say it won't work, it could be awesome in you room but don't just blindly build, you may regret it in the end. If you can get your hands on a few subs, you could at the very least get a real good idea of what some of the different configs of your wall could sound like.

I know I fought it at first but now I am a proud basshead, just don't tell anyone outside the DIY section

Ummmmm, with 4 LMS Ultra's and 4 XXX 18's you're in the rare category of Supreme Bassheads, I am honored to be in your presence

if i recall, one of the jbl guys suggested that placing drivers at 1/4 room dimensions is a way to minimize many room modes.

might at least be worth raising as an option with your consultant.



slides 40-41. this wouldn't cancel the front wall/back wall modes, but not a bad start.

multsubs2.pdf 815k .pdf file

by the way, a pic of a xxx, then mj buys one just for fun and beast signs up for two more just because...you guys are awesome. :-)

as a sidebar, can somebody tell me how to unblock a member? i couldn't find it in the control panel.
Edited by LTD02 - 10/19/12 at 5:51am

This may be opening up a whole 'nother can of worms, but...

Any thoughts on setting up an IB double bass array? I'd think the drivers you already have could work well that way. The implementation will be more complicated, but there'd be no more concerns about room modes.

"Any thoughts on setting up an IB double bass array?"

a great question.

there was a guy in germany who tried that. he set up front subs at 1/4 dimensions on the front wall and the same on the back wall.

it did not work as expected.

apparently, when the wavelength gets very long relative to the room, air behaves more like an incompressible fluid and the speed of sound increases by a factor of 4-5x. that throws off the "pitch and catch" theory of how dba's should operate.

i forget the member's name who tested this.

JapanDave, that will only put me at 4 total RE's, but I also run quad 15" jbl's for midbass duty

Speaker pron is not addictive....Said no one ever

That's consistent with essentially everything I've seen, .... in that employing an approach like you've shown (a quad array,.. each LF source toward each corner of the baffle wall) is as close to a "not miss" as one could attain. Is it true in practice? I've not done it, but it seems like acoustic sources on each side of both the L-R, and vertical centerline approximates the ideal. Selective mode cancellation, and the benefits associated with energizing each lobe of acoustic polarity, can largely be realized in in the axis involved. Then, the implementing of the small-sealed toward the rear of the HT, addresses the front to back axis.

If any problematic modal or SBIR issues exist, there's a certain degree of flexibility inherent to the portable small sealed balancing "subs".

This is the approach I've taken with my IB. It's a dual, dual opposed (quad 18) attic manifold. I bought some balancing subs to further explore smoothing in the frequency domain, and fully integrating them with my mains. I'm just beginning to optimize again, experimenting and making purchases.

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LTD, as always great posts

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LTD, I remember the previous, comprehensive discussion of this, ... however; wondering, .... if this is related to the subjective characteristic of "room lock", that's oft associated with superb, highly adept low bass reproduction.

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"LTD, I remember the previous, comprehensive discussion of this"

yeah, that one was a real bloodbath, but i learned a lot so it was worth it.

anyway, i'm not familiar with the term "room lock", but it sure does sound like the point where the room transitions to a pressure vessel--peaks and dips from modes are no longer present and the rolloff that you typically see with sealed subs in 2pi space goes away--occurs at approximately the point where the long dimension of the room is 1/2 wavelength.

do you own a set of those speaks in your avatar?

are you sure that you want to go dual opposed? i know it gives a little better performance in theory, but dual forward facing like 'not's build just looks so much more badass...

I've been reading audio related material since the 70s. Everything from Audio, Stereophile, TAS, Speaker Builder, Mix, everything. In the pre-internet days (doesn't seem that long ago) I easily spent $75-$100 a week on reading material at the news-stand. Anyway, I recall seeing many mentions of the term "room lock" used in context with superlative bass control in a listening room. I'd not given it much thought, however I'd always felt it was some subjective metric of the ratio of room cubes, to the system's capability in the bottom octaves.

Upon reading the above mentioned blood-bath thread (great ride for sure, all good), and now your comments above wrt the variable viscosity characteristics encountered below the PVG transition at the first mode (1, 0, 0), I'm curious if this incompressible transition influenced the term chosen for superb control and adeptness at bass reproduction. Merely thinking aloud here, contemplating that it sure makes sense that even without full knowledge of the viscosity behaviour, assigning the term "room lock" decades ago, is certainly an appropriate descriptor,...no?



No I don't own them, merely a fan.

In a studio, in the sweet spot, I heard the model below these once, and the experience was so incredibly superior to anything I'd ever heard it was hard to fully comprehend. JBL did, and still does, perform a phenomenal amount of relevant R&D. I'm constantly amazed at the work they've done. The more I read and learn about their past, the industry giants involved there, the more I'm simply blown away. So, having the monitor as my pic, is in some small way paying homage to these innovators.

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I'm anything but an expert on diy subs. As I understand it, the beauty of the LMS5400 is the big ass motor, and the manner in which it can play well with the smallest of boxes. I wouldn't go crazy on bracing either, but that's me. I'd think a well constructed double wall thickness of 3/4" (~19mm x2), with modest bracing would serve you well. But the quality diy crowd in here is all about subs, someone will hook you up.

If it were me, I'd build four identical boxes, just big enough for the driver. With that much total displacement capability (eight of the finest high excursion 18s on the planet) you'll be golden, and largely operate well away from the rgged edge.


Best of luck Dave, in all yor current projects.

Just go with your original plan of dual opposed. This will help to keep the cabinets from moving and make sure that most of the energy from the excursion goes into the room instead of wasted by pushing the cabinet around.

Even though no one has been able to document this liquid air/room dimension-dependent phenomenon (except maybe to reference a Star Trek episode).

Rooms don't transition to a pressure vessel. That's a physical impossibility.

The longest dimension = 1/2 the wavelength of this imagined transition theory is not borne out in any posted measurements.

System roll off does not go away.

But hey, don't let any of the data, facts or common sense get in the way.

I have to agree. It would chew if after all that work and heavy lifting there was a better solution. Theories about in-room low end tend to get shredded by reality.

woah man...now just hold on a minute. May be intervention time, im starting to get a little concerned....

Hey Bosso,
I don't understand. Are you saying you've seen no measured evidence of the influence of the longest room dimension, correlating alteration of the native roll off?

That's not consistent with what I've seen.

True

Theory gives one a solid starting position from which to begin, but that's all. Without verification via measurements one is flying blind. Empirical evidence trumps all. The boundary impedances are so deeply complex in their interaction, they can't be entirely accounted for in modeling, thus absolutely warrant verification.



Conversely, taking the boundary impedances away (ie, pro-audio large spaces/outdoor sims), modeling LF behavior, even multi sources/multi locations, holds up quite well.

Dave, have you hooked them up free-air yet to see them move?

Just set the speaker on the ground and hook it up just like it was installed. Might need to stabilize the frame with something when you get it moving a decent amount.

+1

Free air testing is important, especially so within the IB realm.

Ideally, you hook them up exactly in the specific electrical load/amp channel config that you'll implement in the baffle wall. Then, with test tones (or even known LFE/RB scenes/effects with bass management etc, in full effect), slowly raising drive level while closely examing excursion behavior, volume settings, and clip indications. Performing these test in free air allows one to really get a feel for the ragged edge of the drivers stroke, without of course being exposed to the crushing SPLs that come with the post baffle wall/fully mounted testing.

In my opinion, with an IB, much can be gained from this and is equally or more important in this alignment than small sealed, vented, etc. Plus, it just looks bad-ass seeing big drivers pumping to and fro, .... Freud would likely offer insight

Good luck

As Ricci has noted on these drivers, they will definitely make some noise before major damage is done. I would just very slowly raise the volume and be ready to back off when needed. I have never reached maximum excurdion with mine, as I am more worried about my clone amp than I am about the drivers.