IB vs sealed in excursion requirements

[tech.knockout]

An IB will generally require more displacement than a sealed box to produce the same spl right?

Software like unibox, etc that can predict excursion (modelling IB as a very large 9999L sealed box) appear to disagree, perhaps they aren't taking something into account?

Whats the rough ballpark figure for extra excursion?

[tinitus]

Originally Posted by tech.knockout

An IB will generally require more displacement than a sealed box to produce the same spl right?

Only if the IB goes deeper, which is usually does and the reason to do it
Br have huge problems below the tuning
Closed doesnt have those problems, and neither does IB, I suppose
But very often IBs are with multiple woofers

[GM]

Qtc tells all, so the lower it is, the higher the F3, ergo the greater the excursion and EQ required to maintain a nominally flat BW to the higher Qtc's F3. Below this point, increased excursion is required due to the IB's weaker acoustic loading, though at some point its air mass loading becomes so great that Qtc starts to drop. WinISD Pro plots this trend.

GM

[tech.knockout]

Well unibox is telling me the sensitivity at very low frequencies say <30hz is higher for IB than for any qtc sealed box.

So what free software out there models the loss in excursion due to less "acoustic loading"? Only upmarket(non free) software like WinISD pro?

[DaveCan]

Lots of good info here http://ibsubwoofers.proboards.com/index.cgi

I read that IB is much more efficient down low etc.. And also for true IB they recommend at least 10X the vas of the driver for volume of space behind it.. Here's the Fact page http://home.comcast.net/~infinitelybaffled/index.html

[Ron E]

Originally Posted by tech.knockout

An IB will generally require more displacement than a sealed box to produce the same spl right?

Sealed box and IB require exactly the same excursion for the same SPL. The only thing making noise in either one is cone movement. Move the cone the same amount, get the same SPL.

IB will usually bottom quicker, but that is because they are more efficient at frequencies below the sealed cutoff. The SPL at bottom at the same frequency will be the same whether sealed or IB, the Sealed will take more power to get there...

[chris661]

Sealed provides damping at lower frequencies.

See attached.

At those same frequencies, the SPL for the huge box is greater, but the midbass is lower (lower Q). Damping (and therefore cone excursion) is what changes the Q of a sealed box. Smaller box means more damping means less SPL at 10Hz, but more higher up.

Chris

[Ron E]

Originally Posted by chris661

Sealed provides damping at lower frequencies.

No, a sealed box provides increased stiffness, which reduces excursion. Below resonance the system is compliance controlled, meaning that changes in stiffness are the dominant factor. The maximum output level (read the original post) is the same for both configurations. Power to get there is different.

Originally Posted by chris661

Damping (and therefore cone excursion) is what changes the Q of a sealed box. Smaller box means more damping means less SPL at 10Hz, but more higher up.

If a sealed box gives damping, why does Q go up?
Note: Q going up means damping goes down (Q = 1/damping ratio)

Damping is dissipation, like a shock absorber. The volume trapped behind the speaker in a sealed box acts like a spring.