Help with crossover design for 18" PA Cabinets

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I'm thinking of making a pair of 3-way cabinets for mobile dj'ing.

The drivers I'm considering (on a budget) are as follows:

Eminence Sigma PRO-18A 18" Cast Frame Driver

Eminence Beta-8A 8" Midrange Driver

Eminence ASD1001S 1" Compression Driver

They will be powered by a QSC 2450 Amp: 500w RMS x 2 into 8 ohms

In photoshop I overlayed the frequency response curves as you'll see in the posted image (sorry about the crappy resolution, best I could do grabbing graphs off the web).

I'm pretty sure these drivers should work well together, please let me know if you think otherwise. I'm sure I could do better with more expensive components, but I'm on a budget.

Do you guys see any problem with these components being used to gether?

Assuming the components work ok together, I really need help designing the crossover. I suppose I could use a premade one from parts express, but I'm worried that they won't level out the sensitivities well.

Would one (or more) of you be so kind as to recommend a design? Assume I know next to nothing about how to design a crossover...but I DO know how to read a basic schematic, and I'm pretty slick with a soldering iron.

Obviously I need the crossover design to not only attenuate at the correct frequencies, but also to level out the sensitivities (as you'll see from the graph the sensitivities of the drivers vary substantially).

It would be super extra nifty if you could also include the exact names of the components, and out of this world spectacular if you could also provide the Parts Express part numbers.

I realize this is no small task, and I would GREATLY appreciate the help. In return, if you need any graphics work done I'd be happy to help you out...I'm very good in photoshop.


  • 18 inch pa graph2.jpg
    18 inch pa graph2.jpg
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sigma 18

There are some problems that occur when trying to apply conventional hifi approach and making a threeway speaker for live or dj sound.The optimum is to be able to dedicate an amp for bass and bass only.The bass consumes the vast majority of the power in a pa setup.By activly filtering out the bass at a line level you will decrese distortion and eliminate heatproblems in the crossover. etc etc etc yada yada yada...
I think you will be more sucessfull making a dual 15 and a horn rather than this configuration.that would make for only one crossover point at a less strained part of the spectrum.
However threeways have been done and and one example is the hurricane from adire audio.That one design crosses the bass at 400hz and the tweeter at 2400.I think selenium have some monster speakers with similar setups on their website.
It would defenitly be alot easier if the sensitivities of the elements are as close as possible.But be prepared to see that the compdriver have quite alot higher sensitivity,witch is ok because you will have to attenuate it anyway.But try to match the mid and lo freq drivers within a db two.
Here is the Hurricane - pretty big indeed:

For me, the typical 15-plus-horn PA speaker sounds horrible. The highs are usually so screeching that any distortion from the amplifier is emphasized, and the bass typically doesn't go much lower than 100Hz. I don't think you can expect a 15" midwoofer to handle strong bass and clear midrange. The solution seems to be to stretch the tweeter/mid horn way down into the midrange, which forces it to do things it is not good at. Add a power amp that is less than awesome and you have a recipe for certain doom.

I like the idea of a 3 way because you let the mid play mids! you can cross the tweeter over much higher, and the woofer much lower.

Of course you need a more complex crossover, which might be tough to do. Starting with that hurricane crossover might make it easier.

I like the idea of using the Aidire 10.1 kit for the high end, but maybe in your case, you could do it with the 8" coaxial driver - although you would be giving up a bit of efficiency.

This is just my two cents since I haven't built any PA systems. I have heard a lot of them though, and they are mostly horrible. I appreciate you trying to get a result that actually sounds good!

I have heard that the bottlehead straight-8 line arrays with a higher power slot-loaded tweeter make good PA speakers. They have fantastic midrange as hi fi speakers, so they should sound great for live sound.


Bass. Equivalent port diametar 5". Vb = 7 cu. ft. Fb = 36 Hz, port lenght 15 ".

Mid. Closed box, Vc = 0.5-0.6 cu. ft.


bass - high pass 12 dB/oct. - at 230-260 Hz -6 dB point. Something like 6,8 mH (ferro)and 60 uF (4x15 uF MKT block 250 V)
mid - low pass 6 dB/oct. - at 450 Hz -3 dB point. 45 uF (3x15 uF MKC block 250 V)
mid - high pass 6 dB/oct. - at 1350-1450 Hz -3 dB point. 1.5 mH (air, 1.6 mm wire or more)
tweeter - low pass 12 dB/oct. - at 4-4.5 kHz -6 dB point. atenuation: paralel - 11 Ohm (2x22 10-15 W each), in order 7.5 Ohm (2x15 10-15 W each) and in order 2.2 uF , paralel 0.39 mH
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