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fundamental frequncy cabinet design

#101
Cirk said:
Yup, I know I'm probably get beaten over the head for this, but please indulge my curiousity. I'm looking to build a cab (or biamped cab set) that will respond down to a fundamental drop A (about 25hz IIRC) without dropoff. Light enough and small enough for reasonable transport and able to fit through an average sized door. Loud enough for a medium sized gig. Watts are pretty cheap these days, so efficiency is somewhat negotiable.
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It isn't possible. The smallest cabs that can do 50Hz without drop-off and are loud enough for a medium sized gigs are the very best 1x12" cabs you can buy. To go an octave lower without loss of sensitivity requires a cab eight times the internal volume. You also need to quadruple the volume displacement of the drivers. So you need a ported cab tuned down to 25Hz or thereabouts, with drivers with 2000cc of volume displacement (so two very high excursion 18"s or high excursion 21"s) in a box the size of two large 4x12" cabs. I don't think something like that fits the "small enough for reasonable transport" criterium. Sorry.

On the plus side, it's neither useful nor desirable but I understand the appeal on paper...
 
#102
alexclaber said:
To go an octave lower without loss of sensitivity requires a cab eight times the internal volume. You also need to quadruple the volume displacement of the drivers.
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Yup!

Bringing the same analysis to bear on the efficiency side of the tradeoff relationship, if we want to keep the box size the same and instead trade off efficiency, going down one octave deeper will cost 9 dB, thus requiring eight times the amplifier power to get back up to where we were in SPL. Woofers that can handle that kind of power aren't cheap.

Loud bottom octave energy is the most expensive commodity in sound production or reproduction.

If practicality is a consideration, my first suggestion would be "move the goal posts" and do a really good job at the first overtone of that low A, which would be 54 Hz. My second suggestion would be, add a suitable subwoofer to an existing cab, biamplified.
 
#103
+1. Even in the pro audio world, there are very few systems that can truly reproduce those lows at a useable volume. Those systems costs many tens of thousands just for the speakers. Wonderful feats of engineering but nothing I would want to drag to the local watering hole.
 
#104
Duke, that's what i'm thinking might work. Biamping with a subwoofer cabinet, maybe designing one for a TC 5400. It's all hypothetical at this point. I'm the kind of person who makes sure it will work well before shelling out hard earned cash.

Thanks so much to all who have replied, this has been a great discussion. This is exactly how design progress happens. Say i do build a sub cab and the sound man hates me - ok, then we have a nice subwoofer for FOH. At the very least, something killer to add to my home theater. My PS3 would rock.
 
#107
SVS that I linked earlier has an interesting cut-away at CES

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#108
Cirk said:
Not sure. I'm going to do some cabinet modeling work aimed at different responses, then decide what, if anything would be practical.
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I think you'd find it useful to combine your modeling efforts with at least a few real world trials, if possible.

Modeling will help you understand how the low end extension versus loudness versus cabinet size relationship is interlocked; how one value must be compromised to enhance the other two.

But, if at all possible, a little time spent playing through one or two cabinets with real, known, accurate response data would help you evaluate how much low end extension you really want. The overall cost, both in real dollars and basic inconveniences of increased size and weight, may well make it apparent that extreme low end is just not worth it.

I once built a 12 cubic foot vented cab with an Eminence Kilomax 18 in it, just to see how it would work in real life. I'm pretty sure it modeled close to flat down to about 30Hz. At volume, you could actually see the walls of my house flexing back and forth close to half an inch. But it still didn't seem terribly loud, just kind of added a low presence that wasn't really all that impressive. Paired up, biamped, with a typical 210, you couldn't really get a whole lot of balanced volume out of the system; powered it with a Crest CA9 (1800w bridged@8 ohms)for the sub and the power section of an old Sunn Concert Bass (~200 watts@4 ohms) head for the 210, tried both a Yamaha PB-1 and an ADA MB-1 on the front end. The Crest would hit clipping before the Sunn was even breaking a sweat.

While I still had this system, I then got a pair of Acme B2s and a QSC PLX2402. Did a side by side comparison. The Acmes do have less low end. But the extra low end that the 12 cubic foot 118 had really wasn't even useful, not musical. It was just kind of like a pressure applied to your head.

I've still got the Acmes. I sold the Kilomax driver on eBay. I now use the 12 cubic foot cabinet for storage of hardwood scraps.
 

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