Can an Infinite Baffle Sub Perform in Small Enclosure?

10 to 24 cf is not a small enclosure. Most likely the driver will be fine in that size box, but why not get Unibox or WinISD and sim it to find out?

That's small? I'd hate to see large.

Are you talking about the box or the outside area?

Technically they're one and the same.

The ib subs I have seen use a box to mount the drivers and the backs of the drivers are open to the large space.

It's been a while since I've looked into it but when I was researching I was told to shoot for 10x the vas.
Edited by bass addict - 3/3/13 at 3:56pm

The volume of space that designates it as an IB is ~10x driver Vas or more, but most will work well with far less than that.

If you post the T/S specs of the driver someone will be able to give you an answer in minutes.

I'm going to say no. That sub to work optimally as a true IB would need 100cf cab per driver. Otherwise you are just making a really large sealed enclosure.

You might be able to get away with 5x the vas but that's pushing it. At 24 you are .25 the vas and far from optimal.

See graph.

Fi IB3 18 comparo.gif 17k .gif file

In 10cf Qt is 0.92 and 24cf is 0.77. Both will need some EQ, but are not difficult to tame.

I think you need to recheck your calculations, vas is 381 liters or 13.5 cuft, so 24cuft is ~1.78x vas.

A MiniDSP woul probably be cheapest and give you high and low pass filters as well as an EQ required.
without box
with a box

Plenty of threads here on MD use and the three links from HiFiZine are pretty informative.

I don't see why it would not work, you will suffer a little bit of a drop in performance, but I doubt it would be very noticeable. I would think that a 24cft cab should be fine.

I would be interested as to what the gurus here have to say?

People are incorrect. An infinite baffle is an enclosure where the front and rear waves don't meet. That can be a 1/2 cu ft box or a 10,000 cubic foot attic or basement.

Mtg, I was told you needed an enclosure space 10x the vas. 10x the vas is 3810l or app 135 cf.

That was info from TCOTIB.

Via Droid
Edited by bass addict - 3/3/13 at 6:19pm

There's no voodoo involved, just model it like any sealed box. The chart above shows no particular advantage between 10, 24 and 30,000 cu ft, but that's only response. You need to see a maximum SPL chart, which takes driver displacement into account, to see what gives the best overall result.

I was assuming you already had the driver. What is your reasons for choosing the Fi IB3 18? Why not go for a driver that is designed for a sealed situation.

But, to answer your earlier question, a 24 box will work with very little performance drop most anywhere in the response as the above graph shows.

i think part of the problem is that nobody knows because sufficient experimentation has not been performed.

for example, here is the ib in a 4 cubic foot enclosure (not including inductance effects).

the native qts of the driver in that enclosure is 1.24, which creates the hump in the yellow plot. most folks would say that enclosure is too small because the qts is way too high.

but by simply adding a single band of parametric eq, 45hz, q=0.7, gain =-4.0db, the hump is gone and the shape is now that of a qts=0.8 (blue) which most folks would say is a little tight but satisfactory.

i do not know how far you can push this method. i have not seen it addressed either theoretically or empirically.

by making the enclosure too small, low end sensitivity is lost, but if that can be lived with, can simple eq "fix" the high qts or any enclosure that is too small?

What determines SPL is volume displacement: the area of the cone (Sd) times the excursion (Xmax). The type and size of enclosure can affect frequency response and the amount of power required to achieve that, especially at the bottom end. If you put that driver in an IB or a 10CF box the limit on SPL is determined by the driver's capabilitits. In the 10CF box with EQ and some extra power, I could get the same frequency response as the IB.

As you don't have the driver yet, why not choose something that will work in a smaller enclosure?

I can certainly respect you wanting to stick with FI car, but is it worth doing it at the expense of ultimate SQ? I too am a fan of FI, having used them in the past; but there are better drivers to accomplish what you are after, without breaking the bank.

As far as EQ there are a few different options. Mini DSP seems to be popular on here. It's effective and inexpensive; a DIY'ers dream.