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View Full Version : bessel alignment and ported boxes



Beatin'
11-28-2013, 12:21 AM
Is it wise to build a ported box for a sub that is way over sized and tuned below Fs? I've heard you will reach mechanical limits very quickly between the tuning frequency and Fb.

What's the rule with ported boxes? Keep it close to butterworth or don't tune super low?

T3mpest
12-06-2013, 07:05 PM
Is it wise to build a ported box for a sub that is way over sized and tuned below Fs? I've heard you will reach mechanical limits very quickly between the tuning frequency and Fb.

What's the rule with ported boxes? Keep it close to butterworth or don't tune super low?

Generally you don't want to do that. What your describing is an EBS alignment and while they play very low and effeciently, they do bottom fairly easily below tuning. Often your SSF filter will need to be set right at your tuning frequency to prevent overexcursion. It also isn't a very usual alignment for a vehicle due to cabin gain. Any specific design your thinking about or just curiosity?

Beatin'
12-06-2013, 07:43 PM
Any specific design your thinking about or just curiosity?

Curiosity.

Also I'm more interested in excursion above tuning, not below. I've read that huge boxes with sub 25hz tuning will cause the sub to bottom out easily in the 30-40hz range. I figure it's a fact because over size sealed boxes cause the same thing. Don't they?

T3mpest
12-07-2013, 04:43 PM
Curiosity.

Also I'm more interested in excursion above tuning, not below. I've read that huge boxes with sub 25hz tuning will cause the sub to bottom out easily in the 30-40hz range. I figure it's a fact because over size sealed boxes cause the same thing. Don't they?

That's not usually the case, unless your really overpowering it. Hitting xmax on a woofer at 30hz is pretty hard to do unless the susension is very soft and overpowered. Most sealed setups can't hit excursion limits until 20-25hz at the lowest in most cases on near or slightly over rated power. Sealed boxes offer the same excursion vs input plot as a ported box will, except as you get near tuning the excursion drops, so tuned at 20hz it would be identical in most cases until 25hz or so. Play with winisd you'll see what I mean, most subs, unless your talking approaching IB big wont' reach xmax with a 30hz tone near rated power.

The honest MAIN issue on the big box low tuning thing is below tuning, yes your going to get more output as you get low but above tuning in a bigger box, but that's a byproduct of effeceincy of the larger airspace and generally not what destroys woofers, especially with car audio guys not running SSF's in most cases.

Another thing to keep in mind is that most ported boxes in general have maximum excursion around 40hz anwyays. Unless your tuned in the very low 20's or teens.