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View Full Version : IB vs. oversized sealed enclosure(Theory)



Trey803
03-12-2008, 09:02 AM
Ok so IB basically like a sealed box just has an infinite (or as close to infinite as you can make it) amount of internal volume. Would making a sealed box larger than recommended make it more like an IB setup. Would an overly large box pose any problems other than reduced power handling and increased risk of bottoming out. I am mainly wanting to know if it will change the linearity of the frequency response in a negative way.

Some people claim IB produce the best sq....if so wouldn't the best sealed enclosure be the biggest one you could fit. Assuming you are using a subwoofer that can be used in an IB setup

When I say sq I am not talking about of the entire system only of the notes produced by the subwoofer so 20-80 ish hz

DBDRAGGUY
03-12-2008, 09:14 AM
Sound Quality would at best be considered listener subjective. I think IB setups sound like azz. In theory a subwoofer is supposed to blend the the bottom end that can't be covered by the midbass drivers. Which in reality is barely audible. If your going to have a subwoofer, put it in a enclosure and attenuate its output for your desired level of so-called sound quality. In short a subwoofer needs an enclosure to really perform,unless your obsessed with "reproduction of the sound stage" add a little boom to your tunes. It sounds good!

Atimm693
03-12-2008, 09:16 AM
With a big sealed box the top end tends go get a bit sloppy......

Trey803
03-12-2008, 09:20 AM
so in a IB setup.......the top end should also be sloppy right? If so then why do so many claim it to sound so good

Immacomputer
03-12-2008, 12:42 PM
He probably means that it becomes less boosted by the air spring in the enclosure. It doesn't get "sloppy" but more natural sounding.

That doesn't mean that you should always go as large as possible as some people may not like that. Some people want a system that peaks from about 50-100hz (that "fast" and "tight" sound people describe) and that is easy to get when you use a small sealed enclosure.

The larger you go in a sealed enclosure, the lower the alignment goes (approaches Qts when Fc approaches Fs). The resonant frequency of the system will also drop lower as the enclosure size is increased.

So depending on what you want from your setup, you should design the size around that.

PV Audio
03-12-2008, 01:49 PM
An oversized sealed models about 95% same as the IB with the same baffle dimensions. So yep, your theory is correct. :)

Trey803
03-12-2008, 03:33 PM
I think I may try this out! Prolly wont be until Im done with this semester though. I have a good internship lined up for this summer and will be making goooood money and plan on buying a table saw etc.

BrianChia
03-12-2008, 06:13 PM
Sound Quality would at best be considered listener subjective. I think IB setups sound like azz. In theory a subwoofer is supposed to blend the the bottom end that can't be covered by the midbass drivers. Which in reality is barely audible. If your going to have a subwoofer, put it in a enclosure and attenuate its output for your desired level of so-called sound quality. In short a subwoofer needs an enclosure to really perform,unless your obsessed with "reproduction of the sound stage" add a little boom to your tunes. It sounds good!

Sound quality isn't really that subjective. It is how accurate or how close the reproduced sound is to the original recording. Some aspects of this can be quantified and/or measured.

Something can sound great to you (which is subjective) but that doesn't mean the system necessarily has great sound quality.

Trey803
03-13-2008, 02:06 AM
Sound quality isn't really that subjective. It is how accurate or how close the reproduced sound is to the original recording. Some aspects of this can be quantified and/or measured.

Something can sound great to you (which is subjective) but that doesn't mean the system necessarily has great sound quality.

so does IB produce accurate sq?

PV Audio
03-13-2008, 02:55 AM
so does IB produce accurate sq?If and ONLY if the driver is suited for it. Otherwise, it'll just bottom out and sound like ****. :)

Immacomputer
03-13-2008, 03:28 AM
so does IB produce accurate sq?

If the driver is very accurate in its design. All infinite baffle does is remove all loading factors from the cone and it puts the suspension of the driver to the test.

Trey803
03-13-2008, 06:00 AM
would the fi q work in IB

Immacomputer
03-13-2008, 12:52 PM
The 18" and 15" Q would make pretty decent IB drivers but it's really doubtful they would take a full 1000 watts doing so. You could probably reach mechanical power handling around 500-800 watts or maybe even less I bet.

PV Audio
03-13-2008, 12:58 PM
The 18" and 15" Q would make pretty decent IB drivers but it's really doubtful they would take a full 1000 watts doing so. You could probably reach mechanical power handling around 500-800 watts or maybe even less I bet.Bingo. It seems that drivers with a high Cms/BL ratio do pretty well on IB. If only by logical reasoning, the stronger the suspension and the weaker the motor, it would allow the cone to keep in line easier. Don't quote me on that one as fact though, it's just a personal observation. :)

Immacomputer
03-13-2008, 04:21 PM
Don't forget though that a strong motor can be just as helpful at keeping a coil under control as a stiff suspension can.

jdawg
03-13-2008, 04:43 PM
Readin on some home theater forums they say the Q works great but Scott does something to modify them to be optimum in an IB setup.

soydeedo
03-13-2008, 10:33 PM
He probably means that it becomes less boosted by the air spring in the enclosure. It doesn't get "sloppy" but more natural sounding.

Now I can't really back this up, but I think I've heard that same sort of lax sloppiness in boxes that were larger than manufacturer sealed specs. Rather than your proposed lack of higher frequency response explanation, could it be that once you are beyond the volume required for the optimal air spring you are actually making the enclosure so large that back waves collide at odd intervals and create discoloration?

Basically I'm saying it could be that the volume is too large and the waves are allowed further travel, so before they hit back wall of the enclosure they've lost a significant amount of energy compared to normal operation. On the return trip toward the speaker, this wave's timing is off and hits the cone later and with less energy than it would in its intended volume. That would produce slightly audible sloppiness.

The reason IB is OK is because the back wave is pretty much eliminated entirely to the point where any return energy exerted on the cone is negligible.

Now I'm really not that knowledgeable about acoustics so please don't crucify me if this is all way off the mark, but I thought I'd propose this line of reasoning just to help you brainstorm. Let me know if I'm thinking about it all wrong, please. =)

sundownz
03-13-2008, 10:36 PM
I like a 0.5 - 0.6 Qtc sealed box :) Yummy.

DiDan
03-13-2008, 11:48 PM
you just have to fit the box to your sub.
if your sub needs a ported box to sound good, it will not work well IB and the other way around.

regarding only subs meant to be mounted in sealed boxes, they will sound most naturally with a Q alignment of 0.7 +-0.2. the TSP of the sub will tell you what airspace it needs to reach this Q alignment. if it needs 1cu.ft. it will not sound better IB and the other way around of course.

if you put it in less airspace (lower Q alignment) it will produce more ringing and sound more boomy. in a bigger space (higher Q) it will give you more low frequency output and sound more natural but overall output will be limited (due to cone movement and the missing "peak" around 50Hz).

and yes, an (infinitely) big sealed box will be IB.

many types of boxes work well in car, but ported and sealed (IB) are sufficient to meet all needs you might have. its all about building a box that fits your sub AND car (regarding cabin gain!) and about the settings (lowpass and acoustic phase towards the mids) to make it sound good.


DiDan