From bruce@ashbysolutions.com Mon Aug 05 12:17:14 2002
Subject:Re: speaker cabinet design (was Opinion of Motion Sound KBRM)

Hi Charlie,

>Let me get this conversation straight. Given 2 well designed cabinets of identical type, one with a well designed 10" speaker and the other a well designed 15" inch speaker, and you believe the 10" will produce better bass? Do you really believe this, or are you trying to justify your choice of amplification? I thought my Leslie simulator sounded great - until I bought a 147. Play through a well designed cabinet with a good quality 15" and you'll change your mind. Of course, in the end, its all relative - isn't it? Any sound technicians out there that can respond to this on a truly analytical plane?

Yeah, let me try ...

For two PERFECTLY designed cabinets, one with a 10" woofer and the other with a 15" woofer, using identical amplification, the 15" cabinet will most likely give deeper bass. This is just plain physics in action: it is generally easier to keep a large mass moving at slow speeds than a small one, because that larger mass tends towards the slower oscillation.

The difference between "perfectly designed" and "well designed," however, can be significant. Perfectly designed is, "Give me the exact size cabinet I'm looking for, made out of a very dense, stiff material." All speakers have a parameter called "VAS," the minimum cabinet volume the speaker is looking for. Unless the VAS is met, the response of the speaker falls off at low frequencies, usually at a steep rate. Although the value varies all over the place, the VAS of a 15" speaker is generally larger than that of a 10" speaker.

What is "well designed," anyway? Probably it is a combination of big-enough, stiff-enough, light-enough, and small-enough that allows the speaker to work reasonably well, while still being carried around to gigs. The problem is that big-enough and light/small-enough tend to be opposites. Many 15" speakers need 10-15 cubic feet of air to push against to work well; a similar 10" speaker might get by with 3-4 cubic feet. Unless cabinet size is unlimited, a smaller woofer may actually result in a better speaker cabinet design, even if it's frequency response is slightly less deep. The smaller speaker may, however, be a little less efficient, since it's "piston" isn't as large -- requiring a bigger amplifier.

Then there's transient response: the ability of a speaker to quickly change speed or direction to catch thumps and such -- like kick drum or B-3 percussion, f'rinstance. Here, physics works the other way; it's easier to get a smaller object to change direction, because it has less momentum to fight. This is why my bass player uses 6 10's, instead of 2 15's.

If you want a terrific example of a small speaker that performs like a big one, take a look at Bob Carver's Sunfire subwoofer, a 10" speaker in a 12" cube, that outperforms many 18" subs!

Regards,

-BW

--
Bruce Wahler
Design Consultant
Ashby Solutions™ http://consult.ashbysolutions.com
CloneWheel Support Group and HiNote moderator
978.386.7389 voice/fax
bruce@ashbysolutions.com