IB vs. oversized sealed enclosure(Theory)

[jdawg 5,000+ posts]

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 10+ year member]

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 Pro Seller]

I like a 0.5 - 0.6 Qtc sealed box //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Yummy.

 

[DiDan 10+ year member]

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