X12 driver ideas + questions

The reference horn is the one they presumably took polars and other measurements on.

Assuming we are all talking about constant directivity horns (pretty much every modern one...).
You choose a horn based on the compression driver's exit (1", 2", 1.4"), and the dispersion angle needed. Sound quality then comes into play. A good driver can be ruined by a crap sounding horn and a bad driver made acceptable by an excellent one. To further complicate matters, some people use adapters to fit smaller drivers on larger horns and vice versa. This is the case on the X12. What compression driver you go for depends on your budget and the wanted xover point - (mass generalization) 1" comps can't go low, 2" comps can't go high, and 1.4" comps can be awkward. But it is all application specific really.

In the case of the passive crossover, I am not sure what calculation you did to get that impedance.

As a failsafe, I have posted this excellent introduction to the art of passive crossover design. Keep in mind there are several other approaches, these are discussed on the site linked (see 'articles') but there's lots of opinion involved at the high end of passive crossover design, so google is your friend.
http://sound.westhost.com/lr-passive.htm

Personally, I would Bi-amp these, since you use reflex subs, and the xover you buy will probably do 3-way stereo, it is well worth the benefits. And smallhigh quality amps for the comps are easily found for good money.

EDIT for quick advice:

There are a whole load of horn + comp combos, state your budget and your dispersion angle.

Cheaper drivers (unless you are heavily constrained) are a false economy in the long run.

Best cheap 1" I can think of is the Celestion CDX-1745


Edited by Deadbeat - 21 August 2008 at 3:48pm

Try to do some extra reading tonight on passives, it's a very useful section of audio to be knowledgeable (well, mandatory in some cases)

Take manufacturer's notes pertaining to the 'throw' of anything with a bag of salt.

I forgot one thing in my paragraph.

When you pick a horn, you also keep in mind your wanted xover. Basic horn theory stipulates that you have to have sufficient mouth size and length to get to a certain cutoff. Which is why you can't cross, for example, B&C ME10s low at all.

Also think of the dispersion vs spl. Replace the comp with a lightbulb and the horn with panels of that exact dispersion. The energy has to cover that specific section of a sphere. The smaller the section, the smaller the dispersion of the panels and the more concentrated the light is. This concentration allows manufacturers to claim 'long throw' status through some hidden means.

The linked article is actually about passive crossover design.

It may have looked like I was avoiding the question...

that calculation would be correct for 3 8ohm drivers all run across an amplifier in parallel,

however when you design a passive crossover, it's good practice to take impedance measurements on your drivers, this is explained in the article, along with more stuff.

Happy reading!

That Celestion driver sounds good - good price.  Regarding dispersion - I don't know really.  I read through that article on horns and it was pretty interesting but I'm still not sure how to match a horn to a driver, the main point I took from it was that you have to have the horn extend right out to flat with the front baffle to avoid reflected waves from the mouth which cause honkiness. 

Seeing as the X12's cone drivers are flush mounted, should I be going for a wide-angle dispersion with the top horn?  That would seem logical.  The idea is that people are standing fairly close/next to the speakers.

Also will that 75w/110dB sensitive celestion driver be loud enough to go with, say, two P-Audio SN12-MB's (200w/100dB)?


Edited by Phil.2008 - 29 August 2008 at 10:44am

True. A rough guide is that at 1200hz, a lot of 12" drivers will have their dispersion angles at around 90 degrees, which is why that's a sort of 'magic number'.

Manufacturers should provide polars of their horns as well as beamwidth charts, check them out on the spec sheets.
You want the directionality of the loudspeaker at HF to be as uniform as possible.

I would recommend the 18sound XT series as a good bunch of horns, note the mouth termination and elliptical shape, etc.

PS

try experimenting with an MTM positioning of the drivers, horn in the middle, drivers on either side.