Sean
Ex Member
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I have two Electro-Voice EVX-180B cone drivers, and two JBL 2441 2" compression drivers, which I originally intended to use in a two-way system as per Steve D's original imperial project. I have a couple of questions about this, though:
The mouth of the HF horn built by Steve and a few others, at least from the posted photos, appears to be as wide as the imperial cabinet itself. This presumably allows a very low cutoff for the HF horn, but I'm curious as to what effect this has on HF rolloff? What about efficiency? I'm guessing that this profile is tractrix adjusted for area since the upper and lower faces of the horn are not parallel? 40 degree dispersion, or something else?
The 2441 specs indicate that it plays to 18khz. Do I need to add a driver to take the reponse to 20k? Or is this unnecessary? Probably for my hearing, but maybe kids would hear a difference?
Next, highest recommended crossover for the EVX-180B is 500Hz, and the lowest recommended crossover for the 2441 is 500 Hz. I don't know what the actual response will be, but I'm guessing that if I'm forced to cross over at 500, I'm too close to the limits on both drivers, and should add a midrange driver to the system? In that case, I was looking at the JBL pro drivers - specifically the 2012H 10" cone driver. The only reasonable way I can see of integrating this into the imperial cabinet is to place the EVX on one side of the baffle, and the 2012H on the other. This raises a couple of concerns:
1) What will this do to soundstaging? Not a huge issue with PA cabs I know - but in reading Steve's original imperial thread - I don't want the "head in a vise" problem. (incidentally, how close can you listen to these cabs? Near field?) Of course, I'm not going to be running full range (Behringer DCX2496/DEQ2496 combo), but still, there is an effect created by having the mid and high sources at different locations - how significant is this?
2) Will the imperial cab function properly with the LF driver on one side of the baffle, or do I need to change the way that the rear chamber opens into the horn with this arrangement? Since the mid driver would have its own small sealed enclosure, taking volume out of the LF rear chamber, I would need to do this carefully so I don't totally screw up the throat geometry in a way that negatively impacts the LF driver. Thoughts?
3) The thought crossed my mind that it would be cool to horn-load the 2012H as well, so that I have a three way cab with all drivers in horns. I couldn't figure out a way to do this in the available space on one side of the imperial cabinet that didn't make it look like a carpentry nightmare, so I shelved that idea, but still wonder if there's a better way?
I think my understanding of efficiency is severely limited. The efficiency specs given on the driver spec sheets will allow me to calculate SPL in free air or OB, correct? How do I determine what effect the horn lens has on SPL? How do I determine how many drivers I need for a balanced system? (in this case, I was curious because an imperial with an 18" and a 10" looks kind of funny, but with two 10", looks much more intimidating, and then I realized that I have absolutely no idea what I actually need to get comparable SPLs). How do I figure out the total combined SPL of the system across the entire frequency range?
Finally, as I had originally intended to build one of these with the two EVX's in it, I scaled the plan by 18/15 - quite a massive cabinet. If I go down to only one LF driver, does the horn cutoff actually change (i.e. should go back to original dimensions), or does this only affect SPL?
Sorry for all the questions, but I'd like to get this nailed down before I start spending money and making sawdust.
-Sean
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