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

I don't think there's any question that the Ultras would be the better setup and would be awesome in an IB setup. I didn't model but make the statement based on past experience with the Ultra. If you didn't have the ultras already there could be a discussion about whether they would be worth the higher price of admission over the FiCar but since you already have the Ultras this seems like a real no brainer

The LMS-Ultra isn't the most ideal driver for IB use but it can be used for such. I would highly recommend a rather small amplifier for the job or you'll be bottoming out like crazy.

400-600w per driver looks good.





You would stand to get a lot more output if used in small, high powered sealed enclosures.

the lms will model better but they cost 4x the price. about 2db difference @ 10hz

Hey Dave,

Without question, if you want a IB alignment, and you already have the LMS drivers, go for it.

Why not?

The LMS are more tolerant to a less than theoretical ideal 10x VAS,so any needed boosting to regain whatever is rolled off due to the backspace volume, you;ve got all the motor strength needed to do so. The modestly motored Fi IB3-18s, do roll off a bit too soon in use, even in full infinite back space loading.

The LMS would have lower distortion numbers, audible, I don't know, ... probably somewhat. Just size your amplification prudently, as to not damage the LMS drivers. As you likely know, the IB requires dramatically less power as the octaves plunge. So essentially zero compression with those robust motors, very responsive.

I'd do it.

Not sure I understand this comment. As output is determined by displacement, unchanged in IB vs small sealed, I can only gather you are talking about higher frequencies that are power limited? Why would someone want to pursue such a non-flat frequency response?

Bigus,

The IB being excursion limited, and the small sealed being thermally limited, the approach to powering associated with each is quite unique.

It's a typical IB power conundrum. With a sealed you have an acoustic limiter, and you can have more power on tap above the knee, without concern below the knee. With the IB, you power according to excursion capability, with the sealed you power more according to thermal capability.

You could easily hit Xmech with the IB, yet still be way under the thermal limitations. This is good and allows a very low compression, highly responsive system. But typically you make up for the lower power handling with additional drivers. With a small sealed you have all the power availed to the driver both above and below the knee. This is due to the back-pressure associated with the lowest frequencies, inherently limiting the driver. This must be overcome with a strongly EQ'd response, boosting the power needed below the knee to overcome the incredible pressure involved with the excursions encountered with the deepest frequencies. Thus, properly designed, the thermal limits are encountered prior to the physical limits. Exactly opposite of the IB, whereby the physical limits of excursion are easily encountered at quite modest power levels.

Bigus, I'm aware that most or all of that is merely review for you, however many may not fully grasp the relative considerations associated with the two sub-sets.


"Why would someone want to pursue such a non-flat frequency response?"

Will you elaborate? Both systems can be shaped to reproduce whatever essentially whatever response needed. The IB possessing a more linear power transfer perhaps, absent whatever compression effects occur. Audible? Depends on how over-engineered the subwoofer system is relative to playback level.


Interesting nonetheless.

Thanks

[quote name="FOH"[/I]
Will you elaborate? Both systems can be shaped to reproduce whatever essentially whatever response needed.[/quote]
Sure. Speaking sealed, as that is the context of this thread, maximum spl is a direct function of available displacement, doesn't matter if that is small sealed or ib. You can see that in the red line in the graphs above. Since displacement rises as frequency drips for a given spl, the desired low frequency knee sets the limit on maximum flat spl for the sub.

Say you want to be flat to 15hz. You look at your available displacement with your chosen drivers, and know you can generate xxx DB. Lets say 100db. Doesn't matter if you put that driver in a little box with gobs of power it an ib with relatively little power. X displacement buys 100db at 15hz. Now you figure out how much power it will require in the enclosure size you want for full excursion at 15hz. Big box, little power, small box gobs. You want flat response, right? So you apply the correct eq for the enclosure size (linkwitz transform). Lots of eq on the small enclosure, little or perhaps none on the ib.

Say your calculations showed you needed 100watts for the ib, and 1000watts for the small box. Does that now mean you have 10x more power on hand for higher frequencies in the small box? Not really, because the LT circuit is going to be applying lots of boost down low (or alternatively viewed as lots of cut up high, same thing). If the ib is drawing 100 watts at 100hz, guess hoe much the little box is going to be drawing at 100hz? That's right, about the same 100hz.

But you could play the little box a lot louder up high if you wanted since you have the extra power on hand, right? Well, how would you do that? If you turn the volume up enough to draw more than 100watts at 100hz, the low frequencies are going to clip the amp. Or if you oversized the amp, you will over excurt the driver. The only way to avoid this behavior is to eq the system non flat, so that spl gradually rolls off with frequency. Not exactly what you wanted. The only possible solution is to use limiting so that the response is flat at low volumes and low frequencies become progressively more limited as volume increases. Very few would do that, nor should they want to... the whole purpose of a sub system like this is so that the sub sub gets loud as you turn up the volume, not relatively softer.

Which is why I asked who would want to pursue such a non flat frequency response. Who cares if by having more power on the lms you could theoretically hit higher spl at midbass frequencies? You can't actually do that without designing a non flat system.

In other words, the whole purpose of the big box is that you don't need the big power (and all the baggage that entails). The fact that you then don't have the big power is in no way limiting compared to the alternative.

That's a strong wall to support 400lbs of high excursion. Lot's of bracing to keep it steady.
Yes it would be 2-ch of 8-ohm 2350w per side.
You don't need a small amp, the FP14k is fine, then there will be no clipping just don't bottom out the subs, keep the gain low until you've seen what 10hz does at max volume.

Re: strong wall - If you put them in a pair of dual opposed manifolds, most of the vibration cancels out, no?

"I am sick of having to worry about blowing a driver due to a sub 10hz signal."

put a high pass filter on at 10hz. worries gone.

if you have the space to do it, you can get about 8 of these for one lms-ultra:
http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-455

10x more sensitive, so 1/10th the amp will get the same results.

This is pretty easy to accomplish and it doesn't require $1k drivers to do so. Especially not 6-8 of them.

This is not a bad idea. Again, the LMS-Ultra is a very nice driver however unsuited for IB use. I would consider using something else unless you plan to use them in small sealed or PR enclosures.

While you are able to accomplish what you are aiming for, it is slightly unrealistic to persue. Even the guy with the most capable system on this DIY, Notnyt, with 8 LMS and his own power plant to run them high passes his system at 7hz. A) movies, even summed dont have response that is 0dbfs at 5hz, two with Not's system cranked, he said by 5 hz he couldnt even tell there was content anymore. wanna make it flat still? a rotary sub sounds like a good plan.

Dave, just go ahead and do this. You can wire 4 drivers per side for a 4 ohm load to better utilize your clone. Notynt is flat at 120db down to 10Hz with his 8 sealed Ultras. Throwing 8 LMS-U's in an IB sounds like uncharted territory around these parts, but I can't envision anything negative coming about by giving it a shot.

Besides... We all know what these are capable of in sealed applications, so if you don't like your IB setup, just beef up your amplification and switch it around again.

Again. Very easy. Just put them in 3-4cuft sealed boxes, don't use a HPF or too much power. No more than 2,000w per driver is ideal.


Yeah but Notnyt has an awesome looking system though he is overpowering the LMS-Ultras in too large of a net enclosure space. The Xmax is not controlled and continues to rise rapidly with lower frequency. He says he doesn't notice the deep bass ~5hz anyway and prefers being able to just go loud everywhere else ...which is fine. Using a rotary system is completely not needed to get loud output down to 5hz.


IB will not use up the excursion efficiently and will be severely excursion limited down low.

LMS-U drivers are not ideal for IB use. Make two or four sealed cabs, use 1-2kw per driver. Don't high pass. I don't see why that is so difficult to grasp.

One does not use a Ferrari to do the job of a Bulldozer.

I just like Ferrari's...

Never said it would be ideal or efficient. I let the idea of owning 8 LMS-U's cloud my commonsense judgement.

Sorry Dave. Listen to these guys and go for the bulldozer.

Want a big bass pump that will get you do 5hz with redicluous excursion. 4 RE XXX18's and you should be good to go, do an IB setup with two facing the other two in a manifold type design and call it a day. They move some serious air and are technically the happiest in super large boxes or IB setups.

Everyone loves a Ferrari. That doesn't mean hitching a trailer to one is a good idea.


This would be much MUCH more ideal. Great idea, Beast.

I disagree wholeheartedly. IB will use excursion extremely efficiently (that's kind of its' "thing" actually). Whether or not that's how you want the excursion to be utilized is something entirely different though. Fortunately that can and should be controlled via EQ (actually that's true for any setup). I fail to see what advantage a smaller enclosure would have over the IB other than acting as a high pass that may or may not be desirable.

Oh, and that's a really poor analogy Although the LMS would be overkill it's certainly capable of doing the job of IB specific drivers, a Ferrari isn't really capable of doing the job of a Bulldozer though

Actually, you just made my point. A Ferrari is nice and overkill but not suited for all jobs. You could pull a trailer with one. *shudders* But there are other vehicles suited for doing things like that and could do it better than the Ferrari. Ugh....audio/car analogies get awkward quickly.

And no, sorry. Read post #15 and #18. He wants extension to 5hz and useful output and doesn't want them to self destruct down low. That will be tougher when you will require a high pass filter just to not explode the drivers. Kind of defeats the purpose and a real waste of a bunch of LMS drivers.

I'm not saying he can't do it. There are just better options. This is DIY however. Do what you want. I'm out.

Meh, still disagree. Your analogy and subsequent explanation make it sound like the IB specific drivers would be better in an IB than the LMS which just isn't the case. The LMS might not be *much* better in an IB than the IB specific drivers but that's irrelevant as he already has the LMS drivers. Obviously in a conventional alignment the LMS would really have an advantage over an IB specific driver but I digress.

I'm confused. The fact that he wants extension to 5hz is an argument for IB over small sealed not against? Unless, as Bigus points out, he doesn't want it to be flat to 5hz which I doubt is the case. The only advantage a smaller enclosure would provide would be a built in acoustic high pass filter but that would need to be undone via EQ to achieve flat to 5hz. This doesn't provide any additional protection to the driver it only requires sending more power to the driver for the same output at any given frequency.

Although there may be more efficient options from a $/performance perspective I don't believe they'll actually out perform an equivalent number of LMS in the same IB.

I agree with Scott. I would never IB 5400's personally. Dave already crushed one by slamming it too hard as have a lot of others. An IB (free-air) only makes it that much easier to bottom them out or damage one. Efficiency and distortion aren't the problems with these drivers it is the danger of damaging one. Due to the strong motor on the 5400 it gains a lot less than other drivers by increases in box volume. They can work in IB but it would be my last choice of alignment for them since you will need to severely restrict the available power going to them or risk mechanical damage. Either that or high pass at which point why not just go vented in the 15Hz range? 5400's are the wrong tool for an IB. My two cents.

Interesting. Seems I've underestimated the potential for damage.