Sealed vs Infinite Baffle

[johngalt47]

In the LDC, Vance makes a distinction between Sealed vs Infinite Baffle speaker systems in the section about Sealed boxes. He uses the alpha generated by a function to determine which it is.

My question is, since, with a given Qtc, Qts is what determines alpha, what difference is there, really, between Sealed and Infinite Baffle?

[billfitzmaurice]

what difference is there, really, between Sealed and Infinite Baffle?

By the classical definition they're the same thing, an enclosure where the front and rear waves never meet. By more recent definition a sealed cab is a relatively small self-contained enclosure, an IB a large enclosure that's part of a larger structure, like a closet, adjoining room, attic or basement. The small sealed enclosure will provide restorative force to the cone, a large volume IB won't, so the driver suspension must be designed accordingly.

[johngalt47]

Is trying to achieve an alpha above 3 a legitmate goal per Vance's instructions?

[johnk...]

Is trying to achieve an alpha above 3 a legitmate goal per Vance's instructions?

This sounds more like you are asking about the difference between a general sealed box, sometimes referred to as an IB enclosure, and an acoustic suspension. Both being sealed boxes, but the acoustic suspension being one which uses a driver with very high compliance so the the box air spring is dominant "spring" in the system. Alpha greater than 3 is usually considered the requirement for an acoustic suspension. That is, the box compliance is at least 3 times less (3 time stiffer) that the driver suspension compliance. Or Vbox is less that Vas/3.

[johngalt47]

Thanks for the responses so far.

My ultimate goal is to figure out if a particular driver is suitable for use in a sealed box and, if so, how big the box needs to be. I'm trying to use the equations in LDC but I can't tell if a particular driver is suitable or not using these equations, except that they "should" have an alpha > 3.

[philiparcario]

here is a free site with some calculators

all of the info
http://www.mh-audio.nl/spk_calc.asp


some sealed box info
http://www.mh-audio.nl/spk_calc.asp#sealed

real fast way is

qts of .2 to .4 vented

.4 to .6 sealed

.6 and up IB that is a general rule of thumb

[johnk...]

Thanks for the responses so far.

My ultimate goal is to figure out if a particular driver is suitable for use in a sealed box and, if so, how big the box needs to be. I'm trying to use the equations in LDC but I can't tell if a particular driver is suitable or not using these equations, except that they "should" have an alpha > 3.

The only real limiting factor for using a driver in a sealed box is that Qts of the driver must be less than the desired Qtc, assuming no electronic equalization is applied. After that it's a matter of whether the box size is and cut of frequency are acceptable. Fc/Fs = Qtc/Qts = sqrt (1 + alpha).

[Jonathan Anspach]

Thanks for the responses so far.

My ultimate goal is to figure out if a particular driver is suitable for use in a sealed box and, if so, how big the box needs to be. I'm trying to use the equations in LDC but I can't tell if a particular driver is suitable or not using these equations, except that they "should" have an alpha > 3.

The old rules mattered more back when equalization and amplifier power were expensive. These days you can use drivers that would not have been deemed suitable in the old days, and EQ them back to flat response (within limits). Don't forget to take their power handling into consideration, though.