How do I design an aperiodic sub enclosure?

[zobsky]

I happen to have two approx. 0.9 cu.ft MDF boxes I built a long time ago and never got around to using.

I also have a pair of MCM 55-2421 ( http://site.mcminone.com/product.asp...5Fid=55%2D2421 ) 8" subwoofers available and was thinking of building a pair of compact subwoofers with these.

Looking at winisd, the driver is fairly capable of fairly low frequency response in this box when ported.

I've never tried an aperiodic enclosure before (built/enjoyed sealed, ported, TL horn before) and thought this might be a quick & easy project.

Any guidelines / tutorials on how to do this?

Thanks

[rabbitz]

There is a small section on them in the Loudspeaker Design Cookbook and you can buy the Scan-Speak vent from PE.

http://www.partsexpress.com/pe/pshow...number=296-546

[paulspencer]

or you could just use a normal vent but stuff it ...

but

is there really any advantage here to be gained? An aperiodic is when you want to make a sealed box smaller than optimal but avoid the upper peak in response. An 8" driver in a box that size doesn't seem that small to me ...

[zobsky]

Originally posted by paulspencer
or you could just use a normal vent but stuff it ...

but

is there really any advantage here to be gained? An aperiodic is when you want to make a sealed box smaller than optimal but avoid the upper peak in response. An 8" driver in a box that size doesn't seem that small to me ...

point taken, ... by using an aperiodic enclosure, i was hoping to eliminate, to some extent, the boomy "bass reflex" sound, .. while still maintaing reasonable low end extension (the sealed design for this driver in this box doesn't seem to have very much low end extension, though maybe i should play aruond with the design some more)

please post if my idea makes absolutely no sense

[paulspencer]

Aperiodic will give you a higher F3 than a sealed box and sharper roll-off and I don't expect any improvement over a sealed box unless the box is too small for sealed.

"boomy bass reflex sound" ... have you never heard a vented box that was tight, articulate and musical?

[zobsky]

Originally posted by paulspencer

"boomy bass reflex sound" ... have you never heard a vented box that was tight, articulate and musical?

I sure have (my 135 litre sonotube shiva sub..) but nice sounding BRs are more the exception than the rule (for a variety of reasons, mostly marketing related)

I think I'm going to try to port these subs, and abandon the aperiodic idea, for now.

nice job on the basshorn wiki, BTW

[paulspencer]

thanks

actually that driver you have seems like a good bass horn candidate if you have some serious room! I was seriously considering that or a similar driver but shipping was a bit of a killer (was hoping for a cheap experimental attempt at a compact bass horn) ...

[zobsky]

Originally posted by paulspencer
thanks

actually that driver you have seems like a good bass horn candidate if you have some serious room!

I already have one of the drivers in an auto tuba (in which it does very well), ... just considering other options in the spirit of diy, since i have these raw mdf cabinets lying around.

[zobsky]

Originally posted by paulspencer
thanks

actually that driver you have seems like a good bass horn candidate if you have some serious room!

I already have one of the drivers in an auto tuba (in which it does very well), ... just considering other options in the spirit of diy, since i have these raw mdf cabinets lying around.

also considering designing a bass horn, just for the heck of it, . . but need to read up some more (and make more space at home) before i attempt that.

[GM]

Greets!

FYI, aperiodic loading was originally used to 'critically damp' both small format compression drivers and their huge point source driven counterparts. Only much later was it used to critically damp intentionally underdamped sealed and vented alignments to down-size consumer speakers.

When used as originally intended, among other things it allows smaller/shorter vents in alignments that will benefit from it. F3/Qtb goes down and you wind with what is essentially a ~low Q sealed alignment above Fb with gain. Indeed, if a LspCad Pro sim is to be believed, then my 'critically damped' 20 ft^3/~16 Hz Fb EBS 'subs' have a slightly lower GD in the audible passband than an IB. For sure, they have much more gain down low where it counts and even corner loaded only elicits other's observations of 'life-like'/tight/etc. performance.

Note that 'critically damped' is a 'floating target' depending on the app and the designer's performance goals, so no one 'carved in stone' spec. Historically though, once you've damped any audible overhang (boom) from the system, then any additional damping is just reducing acoustic gain for no audible benefit, though with today's incredible measuring gear you will probably find there's still some (considerable?) misalignment WRT a theoretical ideal.

GM