> G'day folks! I am currently building a couple of subs for a small PA 
system.
 > I'm going for a ported design and I'm wondering how critical port 
 > dimensions are.  I've seen a lot of cheaper commercial designs that just 
 > have a rectangular "hole" at one end of the baffle, very few seem to use a 
 > round port of a specific length as in HI-FI stuff.  Is this because it 
 > doesn't matter or they don't care?  I'm using a single RCF L 15P 530 in 
   Hello David,     Port demensions are one of the most important parts of 
loudspeaker design and building. Ports are intended to make a speaker as 
efficient as possible by utilizing the air movement from the rear of the 
moving loudspeaker. The rear of the speaker generates the same amount of 
moving air/sound, as does the front. Some argue that it actually generates 
slightly more...but I am unconvinced. I believe it just dissipates the moving 
air more due to the build and angle. 
   Ports like you mentioned, just drilled or sawed in at no particular 
measurement, aren't much more than an air leak. Whereas ports of calculated 
diameters and lengths, properly sealed to the enclosure and "flared" at 
either 
end to cut down on air turbulence noises, are actually tuned to and enhance 
certain frequencies in the bass range. This makes the ported speaker far more 
efficient (but less accurate) than a sealed loudspeaker. The ported speaker 
requires far less power to drive than a sealed enclosure. And, the ported 
enclosure will give you deeper and higher amount of bass reproduction than a 
sealed OR haphazardly ported loudspeaker.
   There are numerous books, computer programs and actual designs for the 
speakers you are considering. I would take a look at a few. If really 
interested I would purchase: The Loudspeaker Design Cookbook by Vance 
Dickensen. I believe it is up to the 5th or 6th edition. It runs around $30 
and is really fascinating reading for anyone interested in any type of audio, 
whether building a loudspeaker system or not. 
   I bought the book a few years ago and blame it and the author for getting 
me started designing and building systems that have kept me awake at night 
trying to squeeze every last db of sound out of then. It is a great hobby. 
But 
even if not interested in building a system, just the understanding of the 
principles set up and explained in the book assist you greatly in setting up 
all kinds of sound systems in not so perfect surroundings.
Cheers, John
www.grump@netzone.com
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