Can an Infinite Baffle Sub Perform in Small Enclosure? - Page 2

You will need the subs first to be able to physically be able to do that, 2 x 18 with 1,000 watts just might not cut it.

The box doesn't change driver max displacement, so what would a chart w/different box sizes show?

IBs don't inherently go any lower with any more ease than any other design. They're usually employed when the builder wants to use through wall/floor/ceiling driver mounting with no actual enclosure, mainly to eliminate sacrificing floor space to cabinetry.

Jeremy, you pose some good questions.

I'm in a unique position. I'm not ready to go into much detail, as I've not completed all my impressions and testing yet. But I own both a capable IB, and high quality small sealed subs. My room has both a quad-set of 18" Fi-IB3-18s, in a manifold IB, and multiple small-sealed subs. I built the IB, and then complemented it's output by purchasing two Seaton SubMersives for filler subs/modal control experimentation, etc.


Bill, I respectfully disagree.

I'd suggest that's not entirely true. One chief theoretical advantage of the IB approach, is the ease at which it can delve into the bottom octaves. Yes, the same frequency response can be attained with either a sealed or IB design. However, without the acoustic suspension air-spring, the drive signal is utilized with a greater level of effectiveness, with less being disapated in heat and potentially negative effects associated with compression. Additionally, the quality that many IB enthusiasts claim is inherent to a properly executed IB, may include both the lack of compression and be the lessening of latent energy re-encountering the driver via reflections and pressure.

Those two characteristics, in my opinion, very much differentiate the two approaches; small sealed, and IB. There's a third as well, the way we power each type .. and that advantage goes to the small sealed.


Now having multiple small-sealed certainly can facilitate a much easier path to one's acoustic goals for a multi-seat HT or music listening space. Trying to overcome the room's dominance and influence in the bass octaves, is clearly benefited from multiple sub sources, carefully positioned, EQ'd, and aligned in time.


Jeremy a little review;
Within the sealed alignment, there are two sub-sets; IB and small-sealed ... clearly the acoustic back pressure or air spring is the primary mechanism differentiating them. Small sealed, properly executed, utilizes that air spring in essence to facilitate a variable limiter keeping the huge excursions in check. Thus you can have massive amounts of power on tap both above and below the "knee" of the response curve, .. so big inherent advantage their IMO.

Heat is a by product of current flow. Typically, a driver can take enormous amounts of power, but they're limited with regard to dissipating the heat. This creates compression effects, which onsets at relatively modest power levels, but doesn't become a big problem until higher levels. A driver changes electricity into acoustic pressure, ....any deviation toward more heat is bad, an can be problematic in conveying realistic dynamics and accurately tracking the material.

For example, whether it's the subs or the mains, if any section enters into compression, noticeable spectral shifts occur, robbing the playback of adequate dynamic realism. This may not be as nasty as clipping, or over-loading of other types, but it really detracts from realism.

Also, inherent to a small sealed is the native response shape prior to EQ. Just like the Fi IB3-18 in a smaller box. Typically, a small sealed has a somewhat smooth, yet peaked, or mounded in the middle and un-extended frequency response before equalization. This is due to the low efficiency, up against the air spring ... as frequency lowers .. the box fights back. However, one can EQ back in the response shape desired to attain a smooth, extended response in room, as long as the driver has enough magnetic motor strength.

This works very well, and is the fundamental principle behind essentially all small-sealed designs. But, it costs amplifier power, thus more heat. If excessive, the heat can easily rob the driver of efficiency in the form of compression, so even more power is added. Although it sounds quite detrimental (and certainly can be), all small sealed subs work this way and many of them just fine with few noticable issues.


Now, with an IB sub, the drivers aren't thermally limited .. like the sealed. The IB approach is excursion limited. The lack of acoustic loading on the back-wave side of the drivers, allows for fantastic bottom octave efficiency and native extension without EQ. This allows for far fewer negative effects of compression, and allows for superb dynamic delineation of transient detail. Now the trade-off is typically, you need more drivers for equitable output in an IB, vs that of a small sealed approach. This is because of the power limitations of the IB excursion limited design. In the lower frequencies, you will not encounter thermal issues with an IB. The limiting factor will be running out of throw (excursion) down in the bottom octaves.


Those are the theoretical differences, which favor the IB. Greater accuracy in tracking signal transients, due to both a lower level of compression, and lessening the smearing effects of latent acoustic energy influencing the output. The IB's potential disadvantages are within the realm of placement, and adapting to room's acoustic needs. Realistically, the small sealed has advantages in placement flexibility, which is huge.

Also, in my opinion, the manner in which one can power a small sealed has disticnt advantages. This is what call the IB power conundrum. If the IB design runs without a high pass filter (which is the whole point in the first place), then the power available is limited above the knee. The 18" Fi's encounter their excursion limits about 300 watts or so @10hz. So operating with no hi-pass, you're limited to a modest amount of power. Now, they'll play much louder with tons of impact with an hi-pass and much more power. However, that negates the wonderful, natural extension of an IB in the first place. This is why there's more drivers needed with an IB system as compared to a typical small sealed .... The IB power conundrum.

The sealed approach on the other hand, has all it's power availed to the driver, .. both above and below the knee. This is because the vari-limiter imposed by the air-spring. This is best case use of power, which is significant in use, .. because spectrally much is required from 25hz-35hz. So, either high-pass and pour the power to them, .. or multiply the drivers 2x or 4x.


Wrapping up, both design's inherent problems, have clear workarounds ... with the exception of the latent energy issue of the small-sealed. How much of an issue is it? I don't know, but it is a clear theoretical advantage to the properly executed IB.


Both approaches are fine. My IB sounds different than my SubMersives, .. they're both great. Any differences pale in comparism to the real hurdle one faces; the acoustic distortions of the room.

Good luck, and I hope this helps

If by 'ease' you mean being able to cut a hole in the ceiling/floor/wall, install a baffle and attach a driver, rather than build an enclosure, I agree, assuming the driver specs are amenable. How effectively it can delve into the bottom octaves is, as always, determined by the driver specs and enclosure, even if said enclosure is an attic, basement or adjoining room. And just as with every other alignment one can't assume that just because it's an IB that the results will be better than other options.

No, that's not what I meant

IBs do inherently go lower with more ease, .... and I can't explain it with any more detail, but no problem.

Jeremy,
Consider IB just an infinitely large sealed box. For equal SPL from the same driver at "deep subsonic frequencies", an "IB" (large box) requires less power than a small sealed box.

Since you don't actually have an IB option, I'd choose a driver designed for a relatively small box coupled with more amp power than an IB would require. There is nothing to be gained by putting a large box (IB) driver in a small box.

The driver he linked to shows a 62.5 cu ft box gives a .7 Q, so it's hardly a small box driver. If xmax is actually 30mm it's OK to 500w to 20Hz in that size box., and If he goes to 10,000 cu ft it's still OK.

I asked a similar question back in September. Among the responses I had one from Thomas-W, one of the IB sub gurus. He gave the impression that the motors in the Fi IB subs just aren't designed for use in large sealed (I was asking 2.5x VAS, about 900 Liters or 32 cu ft).

http://www.avsforum.com/t/1431180/infinite-baffle-vs-large-sealed

I can't say how the motors are designed. What I can say is that all of the rest of the specs indicate that it gives a 0.7 Q in 62.5 cu ft. and it's not displacement limited to less than Pe.

I didn't say it was a small box driver...and Jeremy is asking about a box 1/4 the size. I did suggest a driver designed for a smaller box and using a little more power than the same driver needs for the same ULF SPL in an IB.

Actually, most of the people I know (including me) who have built an IB subwoofer, HAVE done so because it will go low easily and cleanly.

IB is inherently superior to all other subwoofer designs.

And there is the real answer. ThomasW has forgotten more about IB subs than everyone in this thread knows combined.

Like all alignments IBs are a compromise. They're easy to make and can go low. But they lack the extension of an LLT, or the sensitivity of a BP or horn. One can make the argument that a full size horn is inherently superior to all other designs, as it goes as low as any other alignment with higher sensitivity and lower distortion than any other alignment. But they're very large and not an easy build, so by no means are they 'easy'. Speak for yourself.

Agreed. Or as people who don't uses terms developed by internet kiddies, EBT (Extended Bass Shelf).
EBSs are like IB, but with a giant enclosure you need to build, the possibility of port noise, the rapid loss of extension below their tuned frequency and that wonderful box coloration/distortion that everyone loves.
I actually can recreate the sound of any box subwoofer on my IB. I simply record the output (including all the distortion and "box coloration") of a standard sub with a quality microphone. Then I play it back on my IB. The IB reproduces it all perfectly. Unfortunately the same cannot be done in reverse..... box subs can't reproduce the sound of an IB. Because they are inferior.

Yep, properly designed and built, waveguides and horns can do wonderful things. As you pointed out, it takes someone like Danley/JBL/Bose to do it right though. PhD level stuff.

I manage with my mere M.Eng. No Wolowitz jokes, please.

Don't worry, that's how we always roll around here.


I don't think good and cheap are synonymous with each other.

If you are looking at running only a pair of drivers, LLT/sonotube would be something I'd recommend looking into.

Some of us are sick of seeing the wool pulled over other's eyes, and must shout it from the rooftops.

My IB subwoofer's cost about $1500 (4 Ficar IB3s and a pro amp) and lay waste to any subwoofer in the world, save a IB
that is built with Thigpen rotary drivers (look 'em up). They are cleaner, deeper and louder... BETTER than any other type of
sub you can build.

I wouldn't. A giant, hard to build box that adds nothing but coloration and port noise. Blech.

Perhaps better than any other type of sub that you can build. Some of us can do a sub capable of this response, should we be so inclined:



That's a $150 Dayton DVC fifteen. Just one. And it's a 1 watt chart.

And what are it's dimensions?

Bigger than a house, no doubt.

Bill is just shooting at the easy target S_rangeBrew is making of himself with his absolutist statements.

Lets face it - there is no shortage of absolutists on forums.
Edited by WVSyd - 3/7/13 at 8:31am

S_rangeBrew,

You can make a similar point perhaps in a different manner.

Like many DIY subwoofer approaches, a quad 18" IB, properly executed, is a revelation. With a mere 225 watts per driver, one can easily achieve a clean, sustained 125dB@1m@20hz(25'x13'x8' room), for ~$1200. Yes, all told, a $1500 IB system (drivers, material, amp, EQ) can absolutely lay waste to equally priced commercial offerings, but other DIY approaches can also offer extraordinary bang-for-the-buck.

Like essentially every aspect of DIY subwoofing, it's all about design compromises, fitting within one's targeted goals. Many trade off the deeply extended native response of the IB for that of the transfer function and headroom of a horn loaded subwoofer.

I agree, an IB system is outstanding.

Bringing it down a notch, I'll nominate the Dayton RSS460HO. Seems like a good driver for under $300....and I'd go large sealed for the lowest native extension with the least power. Haven't looked at subs in years so others may have better options.