PA speakers

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Dark Fader

New member
Before I get flamed out, I know this is not a RECORDING topic. But it's close.
I want to build some PA speakers, and I'm cusious to see if any of you have ever done such a thing as that, or something similar and can give me some pointers.
I'm planning on ordering the drivers and parts from Parts Express (www.partsexpress.com) and I'm thinking of going with a 12 inch woofer and horn-driven tweeter. Perhaps adding a transmission line (I think that's what it's called) to the woofer for more lows... I think the drivers have a max RMS somewhere near 150-175 watts... more than I'll need, and a frequency response of something like 40hz-20khz. All that for about $200... much better than buying a stock speaker, IMHO. The specs seem nice, but that says nothing of linearity or transient response. So, if anyone has any suggestions/comments, please post them.
Also, the speakers may rock, but my fatal flaw may end up being my amp. Currently, all i have is an Onkyo home audio amp (TX-15).... Which is lame to run high-end speakers off of a low-end amp, but has anyone tried this? Is it a *bad thing*? Thanks all, in advance!

Matt Good, or pedalboy, or dark fader, or whatever.
www.mp3.com/pedalboy/ if you're bored.
 
No, i'm not working from plans... (or any formal plans... The cabinet design is going to be the appropriate dimensions and all, but I'm not working from any pre-set plans.) I am using the following:

270-065 MOTOROLA KSN1142A HORN DRIVER with
270-092 HORN LENS 7-11/16" x 6-1/8" x 4
290-382 12" PRO WOOFER

also, each speaker will have two six-inch double-flared ports.
 
Dark Fader,

I checked out these components. They are pretty low-end drivers and I wouldn't expect to get anything close to "high-end" performance out of them.

You're talking about a ported design, but I strongly recommend against it for this particular woofer. The high Qts=0.59 will yield a very low f3=24Hz, but the damping will be extremely poor, and the box will need to be huge (450l). The effective radiation in a large room at those low frequencies will minimal for a 12" driver anyway. A closed box (260l) makes much more sense for this driver, yielding an f3=43Hz. Still, the box is quite large, and I wouldn't expect a whole lot of sound considering the efficiency is only 92 dB/W/m and Xmax is only 3.8mm. All in all, it looks as if this is not a well designed driver.

The Motorola compression driver is also not a very good quality unit. Peizo speakers have terrible levels of distortion, not to mention they are difficult loads for an amplifier to drive. The 30kHz spec they give is meaningless since any horn you connect it to will likely acoustically filter out signals above 20kHz. Also, all 1-3/8" throat horns beam very sharply above 15kHz, so unless you're directly on axis you won't hear the extreme highs anyway.

If this is your first attempt at speaker building, something like the Selenium coax driver 264-390 might be an excellent choice. The crossover is already designed (this is one of the most complicated aspects of speaker design) and built in, so all you need to do is design and build the cabinets. You can get a respectable f3=42Hz from a 117l ported box with and efficiency of 96dB/W/m.

Now if you really want to get into truly hi-end sound reinforcement on a small budget, I posted a design a few weeks back in this thread https://homerecording.com/bbs/showthread.php?threadid=34845. For your purposes I would redesign it as a ported system with an f3=42 Hz in a 120l ported box (actually 4x30l ported chambers). The drivers and crossover components would cost about $350. This design is essentially 4 Alesis M1 studio monitors stacked in a vertical array giving 95dB/W/m efficiency and about 250W max power handling. The sound quality of this system will be beyond that of probably any small 2-way PA speaker you have ever heard. :cool:

barefoot
 
Hey barefoot, if you want to modify a design to use 2 drivers instead of one do you just double the box volume? put each in a seperate chamber? or is there some formula for calculating the required volume for two (identical) drivers in the same chamber?
 
vox said:
Hey barefoot, if you want to modify a design to use 2 drivers instead of one do you just double the box volume? put each in a seperate chamber? or is there some formula for calculating the required volume for two (identical) drivers in the same chamber?
Click to expand...

Yes, for a two driver single chamber the volume doubles. The port size, however, also changes but is not so straightforward. If you use two chambers, each one is identical to a single speaker box, so you don't need to calculate anything new. Having the two drivers in one chamber has a slight advantage with respect standing wave excitation, but generally multi-chamber boxes are more solid and well behaved. I always go with separate chambers if I can.

WinISD is a nice freeware speaker box calculator http://www.linearteam.dk/. It doesn't model box losses or damping material, but it gives a quick rough estimate and has a large library of drivers already programmed in. Fs, Qts, and Vas are the critical parameters. Qes (electrical damping) and Pe (max power rating) are needed for determining the minimum port area.

The Loudspeaker Design Cookbook is a must have http://www.audioxpress.com/bksprods/bookindexl.htm.

barefoot
 
Hey barefoot, thanks a TON!
That Selenium thing looks like a monster. Unfortunately, it will essentially double the total cost of my project. Hmm...... I'll take a look at your post, too, cuz they seem like they might be similar in price. What kind of commercial speakers would either of these compare to, just so i can get an idea of how much I'd save or whatever. Cuz it seems like for that much I could buy some similar JBLs or something.....
Also, i'm intruiged as to how you deduced that the original driver was of low quality... If this whole PA speaker thing gets too expensive, I might take a look at what I do for studio monitors, and if i could figure out what was good and what wasn't i could save myself about 90 posts here. Like how do you judge transiet response and stuff from just those statistics they give you?
You've been a huge help already, thanks!

dark fader
 
Dark Fader, If you post your email addy I might have some plans for you. I have a few cad drawings that might help you.

Troy
 
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