Can an Infinite Baffle Sub Perform in Small Enclosure? - AVS Forum
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post #1 of 56 Old 03-03-2013, 03:52 PM - Thread Starter
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Pretty simple... Can an infinite baffle design sub perform well in a rather small enclosure.... somewhere between 10 and 24 cubic feet.... Will it be alright, or is that just too much back pressure?
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post #2 of 56 Old 03-03-2013, 04:30 PM
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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?
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post #3 of 56 Old 03-03-2013, 04:31 PM
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Quote:
Originally Posted by Jeremy1998 View Post

somewhere between 10 and 24 cubic feet....
That's small? I'd hate to see large. eek.gif

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post #4 of 56 Old 03-03-2013, 04:41 PM
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Are you talking about the box or the outside area?

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post #5 of 56 Old 03-03-2013, 04:45 PM
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Originally Posted by brian6751 View Post

Are you talking about the box or the outside area?

Technically they're one and the same. smile.gif

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post #6 of 56 Old 03-03-2013, 04:47 PM - Thread Starter
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Well, people talk about infinite baffle subs needing basically your entire attic space to perform properly.... So I wasn't sure... So an 18" infinite baffle sub will do just fine with an enclosure space of anywhere between 10 and 24 cubic feet?
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post #7 of 56 Old 03-03-2013, 04:48 PM
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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.

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post #8 of 56 Old 03-03-2013, 04:50 PM - Thread Starter
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Quote:
Originally Posted by brian6751 View Post

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.
Yeah, I know, but that's not an option for my situation :/ I want to put the subs into basically a normal sealed box, but larger... As I said, between a 10 and 24 cubic foot sealed box.
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post #9 of 56 Old 03-03-2013, 04:51 PM
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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.

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post #10 of 56 Old 03-03-2013, 04:51 PM
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Quote:
Originally Posted by Jeremy1998 View Post

Well, people talk about infinite baffle subs needing basically your entire attic space to perform properly.... So I wasn't sure... So an 18" infinite baffle sub will do just fine with an enclosure space of anywhere between 10 and 24 cubic feet?
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.
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post #11 of 56 Old 03-03-2013, 04:52 PM - Thread Starter
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The subs in question is the Fi IB3 18:http://store.ficaraudio.com/ib318/

Fs: 22.3 Hz | 22.5 Hz
Re: 1.5 Ohms/coil | 2.8 Ohms/coil
Qms: 3.33 | 3.41
Qes: ..81 | .77
Qts: .65 | .62
Mms: 272g | 270g
Sd: 1210cm^2 | 1210cm^2
Vas: 381 l | 381 l
Spl: 89.1dB 1W/1m | 89.4dB 1W/1m
Bl: 8.43 N/A | 11.8 N/A
Xmax: 30mm
Rms: 550W @ 20Hz
Sealed box: Infinite Baffle Only
Ported box: N/A
Sub OD: 18.500”
Cut ID: 16.750”
Mounting depth: 9.500”
Displacement: 0.22cuft
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post #12 of 56 Old 03-03-2013, 04:56 PM
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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.

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post #13 of 56 Old 03-03-2013, 05:08 PM
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Quote:
Originally Posted by Jeremy1998 View Post

The subs in question is the Fi IB3 18:http://store.ficaraudio.com/ib318/

Fs: 22.3 Hz | 22.5 Hz
Re: 1.5 Ohms/coil | 2.8 Ohms/coil
Qms: 3.33 | 3.41
Qes: ..81 | .77
Qts: .65 | .62
Mms: 272g | 270g
Sd: 1210cm^2 | 1210cm^2
Vas: 381 l | 381 l
Spl: 89.1dB 1W/1m | 89.4dB 1W/1m
Bl: 8.43 N/A | 11.8 N/A
Xmax: 30mm
Rms: 550W @ 20Hz
Sealed box: Infinite Baffle Only
Ported box: N/A
Sub OD: 18.500”
Cut ID: 16.750”
Mounting depth: 9.500”
Displacement: 0.22cuft

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.
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File Type: gif Fi IB3 18 comparo.gif (17.2 KB, 35 views)
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post #14 of 56 Old 03-03-2013, 05:15 PM - Thread Starter
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Quote:
Originally Posted by A9X-308 View Post

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.
What kind of equipment would I need to do this? I am very new to this all, so I'm trying to figure it all out.
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post #15 of 56 Old 03-03-2013, 05:20 PM
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Quote:
Originally Posted by bass addict View Post

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.

I think you need to recheck your calculations, vas is 381 liters or 13.5 cuft, so 24cuft is ~1.78x vas.
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post #16 of 56 Old 03-03-2013, 05:27 PM
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Quote:
Originally Posted by Jeremy1998 View Post

What kind of equipment would I need to do this? I am very new to this all, so I'm trying to figure it all out.
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.
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post #17 of 56 Old 03-03-2013, 05:57 PM
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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?

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post #18 of 56 Old 03-03-2013, 06:14 PM
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post #19 of 56 Old 03-03-2013, 06:26 PM
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Quote:
Originally Posted by Jeremy1998 View Post

Well, people talk about infinite baffle subs needing basically your entire attic space to perform properly....
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.

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post #20 of 56 Old 03-03-2013, 06:39 PM - Thread Starter
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Is there any sort of definitive answer here? Because I won't want to waste money on something that work.... But if it will have decent performance down to very low frequencies, I will do it....
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post #21 of 56 Old 03-03-2013, 07:06 PM
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Quote:
Originally Posted by mtg90 View Post

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

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.

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post #22 of 56 Old 03-03-2013, 07:28 PM
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Quote:
Originally Posted by Jeremy1998 View Post

Is there any sort of definitive answer here? Because I won't want to waste money on something that work.... But if it will have decent performance down to very low frequencies, I will do it....
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.

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post #23 of 56 Old 03-03-2013, 07:32 PM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

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.
Well, I don't know a thing about doing these models and stuff. I'm new to the whole audio world, where you guys can precisely calibrate things.
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post #24 of 56 Old 03-03-2013, 07:43 PM
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Quote:
Originally Posted by Jeremy1998 View Post

Well, I don't know a thing about doing these models and stuff. I'm new to the whole audio world, where you guys can precisely calibrate things.
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.

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post #25 of 56 Old 03-03-2013, 08:14 PM
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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?


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post #26 of 56 Old 03-03-2013, 09:36 PM - Thread Starter
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Quote:
Originally Posted by JapanDave View Post

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've just always heard that Infinite Baffle can hit really low notes relatively easily...
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post #27 of 56 Old 03-03-2013, 10:23 PM
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Quote:
Originally Posted by Jeremy1998 View Post

I've just always heard that Infinite Baffle can hit really low notes relatively easily...
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?
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Quote:
Originally Posted by A9X-308 View Post

As you don't have the driver yet, why not choose something that will work in a smaller enclosure?
I suppose that is an option. I chose the IB3 mainly because it's a cheap infinite baffle sub, and it has a good rep... But if something else will serve my application better, I'm fine with that. I would like to keep it within the Fi Car Audio lineup (my own reasons...), so would a pair of the Fi Q 15 or 18's be better? Sealed or ported, and if ported, what tuning? I want to be able to go sub-sonic (like cutoff at 12hz), so what equalizer can I use for that?
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post #29 of 56 Old 03-03-2013, 10:32 PM
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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. smile.gif

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post #30 of 56 Old 03-03-2013, 11:35 PM - Thread Starter
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Originally Posted by bass addict View Post

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. smile.gif
I guess it does not have to be Fi... I just need a pair of 15's or 18's that can hit very low, and also look plain and simple. I also really only need like 500 watts per sub maximum. I will realistically never even power them to that fully.

As for the EQ, can that one truly go down to subsonic frequencies? I've seen alot of DSP's that cut off at 20hz... I really want to maintain the deep subsonic frequencies that shake your body.
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