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DIY PA Speaker Project

DIY PA Speaker Project

My good friend Dave is always thinking of ways to make his gear dollar go as far as possible and coming up with some great projects! This PA Speaker Project is quite ambitious, and yet, could yield the DIY musician with a great set of perfectly tuned PA speakers for that small coffee house gig!

The PA Speaker Project Concept

Dave asks me, "Would something this size be too unwieldy?" Then goes on to explain...

This is a 3 cu. ft. box that's tuned for 40 Hz, for a 12" and a horn.

The PA Speaker Project Comes To Life

So, because we've had a few dialogs like this in the past, I let him know they look great and I ask a few questions:

Looks nice!
12" speakers for the vocal mid-range, huh?

I had some huge 1981 Sunn cabinets with 2x12 and a horn. I'm glad they're somewhere else and not my house. They were huge! Sounded great, tho...

PA Speaker Design Questions

  1. When you say tuned for 40 Hz... How does that translate to practical application? Would that be set for bass? ...or is that the effective bottom end?

    I think of speakers as having a "range" ...like 40-18k Hz...

  2. Oh... One more thing...
    After loading the box with drivers, determine the weight distribution... Then add a sturdy "stand mount" to the bottom.

PA Speaker Design Answers

  1. When a box is 'tuned' thru a port or ports, what that means is that the free-air resonance of the woofer is slightly suppressed, evening out the freq. response down there. Otherwise, you'll get a big response peak at that resonance. Then the port acts as a device to bring the rear radiation of the cone into phase with the front and emit it, thus reinforcing the bass above that tuning frequency. So you tune the box to the F.A.R. (free-air resonance) of the driver.

    Below that port tuning frequency, though, the driver is effectively 'unloaded', so it's not a good idea to put anything below that frequency thru the system. If you wanted to DI the bass thru a PA system, it'd be better to bi-amp your PA and put everything below 200 Hz thru a subwoofer, or at least have cabs that will go down to the lowest freq. that you plan to blow thru them.

    So in this speaker system, you'd use a woofer with a freq. response typically about 40 Hz to 3 KHz. The horn (in rectangular slot at top) would kick in about 2.5 KHz, and go on up to perhaps 18-20 KHz. You'd then have a usable frequency response in this speaker system of 40 Hz to whatever the upper limit of the horn is. BTW, 40 Hz is low 'E' on a 4-string bass, so you could probably run bass guitar thru this box, but I wouldn't put the kick-drum thru it at high power levels.

    Clear as mud?

    PA Speaker Project Cost Estimates

    A set of DIY speakers like this could be built for probably way less than $300, using some woofers that Parts Express sells (400W!) for about $80 each. They have lower-powered ones of roughly the same freq. response for even less money. The horns could be molded ABS lenses with threaded-in piezo drivers; very economical and tough/trouble-free.

    3/4" Birch Plywood isn't too expensive, and it wouldn't take even two sheets, maybe only one, to build a pair of these. Add some 12" grills and some handles & jack trays, paint them with DIY truck bedliner, or just flat black enamel...and voila.

  2. It's easy enough to find the center of gravity with the drivers loaded, and then put the stand socket smack-dab on it.

Hint of a Floor Monitor Project

Then, some little 10" floor monitors with piezo tweeters...

Get your drivers (speakers) at Parts Express

 
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© 2014 DIY Musician    . . .    M. Scott Worthington - Austin, TX