Sunday, November 21, 2010

Less than two weeks to go, I've begun excavating the PA speakers. First off, I want to have a look at the bass bins, as this is the element of the system that gets the most abuse. I'm thinking of trying to get out of the habit of calling them subs, as it seems the more I put my head around the mathematics the less deep into true sub territory they go, that said, they are big, heavy, road worn and sound impressive enough that I can probably call them what I like and not meet much argument.

I've knocked this picture onto its side to adhere with my landscape aesthetic preference, so you can correct for gravity in your own mind. Obviously I've been using my speakers as storage for organ guts, which just adds to their charm.

I picked these up in Portland in +/- 2005, a quartet of empty cabinets. The seller claimed that these were the remaining four of a lot of 16 folded W horns built for Carlos Santana's sound company in the 1970s, accompanying him on a couple world tours. I've yet to see photographic evidence to validate that statement, but the notion remains interesting enough to share.

So yesterday I finally got around to making a proper attempt to map these out and calculate volume, that I may stand a little more chance in determining acoustical properties for the safe operation of drivers. Time will tell on the higher mathematics absorption front.

Here's a shot down the gullet, more or less the starting point for the low frequency wave front. The 0.5625 square foot (9x9 inch) throat offers a bit of compression loading on the 15 inch driver. Length of the horn is roughly 7 linear feet, terminating at 5.3281 square feet of mouth.

After assembling this more or less in scale drawing I've determined the volume of sealed enclosure (in blue) to be roughly 3.884 cubic feet.

Depth of horn at the speaker (red) is 9 inches, expanding to 12 inches at the orange split point and further expanding to 16.5 inches at yellow. Outside dimensions are 48x48x18 inches, for what it's worth.

This year I'm only bringing out two of these, one loaded with a McCauley 6242 and another loaded with an unknown Eminence speaker branded Carvin HE-15. Probably high pass at 40hz or so, unless I can determine that these cabinets don't unload until pushed deeper.


valis said...

Very nice story! What's your plan for the PA? Perhaps a Santana synth-noise cover band?

crochambeau said...

Ixnay on the antana-Say, you'll blow my secret project plans! HA

My plan for the PA is to eventually have it set up at all times, only touched by people I trust (operationally speaking), in a place that proves to be a decent venue.

My master plan does NOT include it taking up vast quantities of space in my workshop, which is what it IS doing right now. That said, I'd rather place the burden of storage on myself while I'm still shaking the bugs out of it.

We're in five year plan territory here.