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XF212 for PA?

Posted: Tue Oct 08, 2019 3:53 pm
by CSConrad
I'm thinking of making a simple 3-way PA with a 21" Eighteen Sound subwoofer in a simple TL aligned box, crossing over at 80 or 100hz to a pair of BMS coaxial 12" speakers in a crossfire cabinet. I might have to modify the design to un-slant them. It's for an install. Obviously, they'd be made with the full back panel. I may or may not vent them, depending on the low-frequency response of the box once it's built.

Will this design work well with coaxials? Is the idea too nuts? The BMS Coaxials are 80 degree coverage, and I want to spread that out to 120 degrees or so. I've thought of just putting one on top of the other without splaying them and dealing with the 80 degree coverage, but this is for an install so perhaps this design will sound better and make more sense.

I've also thought that the slant might not hurt, if I hang the cabinet high and upside down. I'm still pondering that one!

Re: XF212 for PA?

Posted: Tue Oct 08, 2019 4:28 pm
by Bruce Weldy
CSConrad wrote:
Tue Oct 08, 2019 3:53 pm
Will this design work well with coaxials? Is the idea too nuts?
The quick answer is NO and YES. :mrgreen:

That cab is not designed for that kind of use. The proper cabs would be OT12s, OT8s, or DR series. Even SLA Pros would work and be the easier of the boxes to build. There is also the Simplexx line. You could use a coaxial driver in the Simplexx 12. But you could only use one box per side. The high frequency exit points would be be too far apart to try and stack them.

Re: XF212 for PA?

Posted: Tue Oct 08, 2019 4:49 pm
by CSConrad
I've crossfired radial horns before, with excellent results, from a distance. (Three 60x40 horns, with the middle one forward and the outside ones angled 25 degrees in each, to give a 90x60 output), and those drivers were far farther apart than the two 1" drivers would be in the coaxials.

I would also cut the top (the bottom using it upside down!) so was to give a clear path for the sound. But I'd do that if I was to use it as a guitar cabinet too.

The OT12 isn't at all the sort of sound I'm looking for. What I'm looking is 1) not that loud, and 2) far closer to a really big studio monitor than a typical horn-loaded PA system. I'm even considering NOT porting the subs - I'll try it both ways - to keep the bass as tight as possible. The subs I'm looking at will handle 3600 watts each, so efficiency is hardly a concern. The BMS coaxials, with the mylar diaphragms, are clinically good - Altec 604 series good, with higher power capacity. I just want to angle it out more, as a point source.

Perhaps just stack-and-splay is the better alternative.

CSC

Re: XF212 for PA?

Posted: Tue Oct 08, 2019 4:50 pm
by jimbo7
What you just described is taking the engine out of a motorcycle. You just made a bicycle.

Re: XF212 for PA?

Posted: Tue Oct 08, 2019 5:32 pm
by Bill Fitzmaurice
You should post a diagram of the room where the install will go and what the system will be used for so we can recommend which of our cabs would work best. Since this appears to be for pro-sound it should be posted in the pro-sound setup section.

Re: XF212 for PA?

Posted: Wed Oct 09, 2019 12:46 pm
by CSConrad
The room will be about 40' wide across the front, with 24' of that taken by a thrust stage extending about 8' into the room, and 4 to 6 feet behind the proscenium. The room will be 60' deep, trapezoidal, 70' wide at the rear. Seating will be in three levels, with roughly 100 seats at each level. The room will have some massive bass traps built in, by installing two rows of booths that will be stuffed with fiberglass, and the exposed rear of those booths will be pegboard covered with carpet. The ceiling will not be parallel to the floor, and the rear wall will consist of convex panels so as not to be parallel to the front. Flooring will be cork, but the room will have a reflective ceiling, side walls and rear wall. The front of the room will be absorbent, with raw cork, curtains, and acoustical panels. Basically LEDE. I want the room to be good enough that an unaccompanied violin or piano can be heard anywhere in the room, and as the furthest seat will only be about 50' from the stage that shouldn't be a problem.

The subs will be two Eighteen Sound 21NLW4000 drivers or the RCF equivalent, in either ported or sealed cabinets. I prefer the punchiness of a sealed box, but low frequency extension down to the lowest notes of a piano is important to me. Quite frankly, I'm going with 21" subs as much for the visual as the aural impact. Because this combination can handle and will be powered with roughly 6.28KW (two Macro-Tech 3600VZ amps in bridge), efficiency is not much of a concern. Clean 25hz reproduction is.

The mids/highs will be a pair of BMS 12C382 coaxial speakers. I'll cross at roughly 80 and 1200 hz, respectively. I'll use three sets of these (LCR). The center speakers shall be used only for vocals so they won't need subs. (Those will be powered by Crown Macro-Tech 36x12 amps). (Yep, I'm cheap so I'm buying used amps!)

Just to give a better idea what type of sound reproduction I'm looking for, my primary vocal mics will be Neumann KMS 104s and 104 Plus's, with Neumann TLMs for the baby grand and similar large diaphragm condensers for strings. For more electric music, I've got the AKG D112 (kick drum), AKG D40s (toms), a bunch of good pencil condensers (overhead/hi-hat) Shure Beta 58As (I've got these wireless), Sennheiser E935's, E906's, E609's, etc. I'll also have a set of AKG C518's for horns. The speakers can't reproduce better sound than the mics pick up! (I've got a pile of old SM57's and 58's for those who just HAVE to have them.)

Monitors will be Turbosound Flashline powered monitors. They are cheap and very cost effective. I'll be running 4 monitor feeds to the stage through White Instruments EQ.

My only issue is in how to best arrange the six co-axials so as to cover the width of the room. I may be overthinking this. It is possible that the 80 degree coverage angle of the coaxials will be fine if they are simply stacked one on top of each other, aimed downward a little. They'll go down to 52 hz in a box as little as 1.25 cubic feet, vented, or 3db down at 100hz sealed (which would require a 100hz xover frequency instead of 80hz.)

My initial thought was to splay them, with the pivot point being at the diaphragm of the HF driver. However, Leland Crooks recommended that cross-firing may give less issues with comb filtering, and I'm certainly open to that idea.

The room will be for R&B, jazz, blues, gospel, roots, country, singer/songwriter, chamber music, etc. Not for heavy rock and roll or funk, although it might see SOME of that. There's a comedy club nextdoor so even with treatment there's a limit as to how loud I want to get. It's a listening room environment, with food and beverage service. However, there will be several rooms between the comedy club and the listening room.

Re: XF212 for PA?

Posted: Thu Oct 10, 2019 7:19 pm
by Strange Kevin
Hi CsConrad,
Welcome to the Forum.

I gotta say, I'm a little confused, you mentioned the OTOP 12 would be way overkill then described the room as holding 300 people or more... in a room that big you could get away with 2 OTops on each side at least.

Have you purchased your drivers already?
Coaxial drivers are great and solve a few phase issues that you get with more a traditional setup, but putting two of them right next to each other will reintroduce most of the problems they were designed to fix.

If you're really set on not building any horns, I might suggest looking at the TLAH Pro. They're simple to build and have the wide dispersion you are looking for. You may still need a center fill with a stage that wide.

As far as impressive looking and sounding subs, you can't get much more impressive than the T60s.
They are physically Masive, play incredibly low, and sound Fantastic! Not to mention cheaper to build and power than an inefficient 21.

Re: XF212 for PA?

Posted: Thu Oct 10, 2019 9:28 pm
by CoronaOperator
+1 on the T60 for clean 25hz. No direct radiator (even sealed) will ever sound as good as a folded front loaded horn.

I totally agree with Strange Kevin that 2 coaxials together will totally create all the problems and introduce new ones that co-axials were meant to fix.

If 1 box isn't wide enough for you then you are using the wrong design, co-axials don't sum nicely when splayed. https://youtu.be/Iuv6hY6zsd0?t=281 This is what happens to the wave fronts when the 2 sources are more that 1/4 wavelength apart (all your upper mids and high end). Why would you want to create an interference pattern using a box that was designed to eliminate them :noob: ?

Re: XF212 for PA?

Posted: Fri Oct 11, 2019 1:00 pm
by CSConrad
Yes, sadly, there doesn't seem to be any way to sum two of the coaxial 12's.

I'm not concerned about efficiency. I'll have the two subs built-in over the stage, dead center. Horns have all sorts of problems that I don't need. I also have more old Crown power amps than I can possibly use, so that's not my issue.

My next choice is to use a pair of light 15's from 80hz - ??? per side, with a BMS coaxial compression driver, crossed in as low as I can get it. Now I'm looking for a wave-guide or horn that will allow this driver to go down to 300/400 hz.

My primary concern is with coherence in the vocal bandwidth.

http://www.bmsspeakers.com/fileadmin/bm ... driver.pdf

Re: XF212 for PA?

Posted: Fri Oct 11, 2019 1:12 pm
by Bruce Weldy
CSConrad wrote:
Fri Oct 11, 2019 1:00 pm
Yes, sadly, there doesn't seem to be any way to sum two of the coaxial 12's.

I'm not concerned about efficiency. I'll have the two subs built-in over the stage, dead center. Horns have all sorts of problems that I don't need. I also have more old Crown power amps than I can possibly use, so that's not my issue.

My next choice is to use a pair of light 15's from 80hz - ??? per side, with a BMS coaxial compression driver, crossed in as low as I can get it. Now I'm looking for a wave-guide or horn that will allow this driver to go down to 300/400 hz.

My primary concern is with coherence in the vocal bandwidth.

http://www.bmsspeakers.com/fileadmin/bm ... driver.pdf
Sorry, but what you are wanting to do does not fit anything that Bill has designed. Seems as though you have chosen components first and are now looking for an enclosure. There's really nothing here to do what you want to do.

Although there are several choices here that will most likely do everything you need to do for WAY less money that those drivers cost.

Re: XF212 for PA?

Posted: Sat Oct 12, 2019 10:46 am
by CSConrad
Actually, I wanted to consider co-axials first, and then picked out the best co-axial for use 80hz and above.

Sadly, doesn't look like I can get away with multiple coaxials. I also considered trying to use a "zone" type system, but it's not appropriate for the architecture.

I want to have all the midrange coming from one source - a coaxial accomplishes that well. There are intelligibility issues that arise when you use different drivers in the vocal region. So that leaves two options: an array of small speakers (6"-8") from say 300-3KHZ, or a compression driver capable of going down to 300hz. BMS makes the 4508ND coax planar wave guide capable of 300hz, but at over $800 each, putting a pair of those in each box along with two matching 12" speakers takes this over the price of an off-the-shelf solution. Will it be so good as to justify that price? Doubtful. The RCF TTL6a, for example, is pretty damned good. If I used off the shelf, I would go with a pair of those.

The SLA may be the best choice. I'm rather intrigued with what the low-end of these boxes might be. I'm thinking I could put some planar wave guides with compression drivers in along with four 8" speakers, and run the 8" cones from 100hz-3khz, and the wave drivers over 3khz. The 21" subs should go as high as 100, but I might have to go four-way if the SLA's won't go low enough.

Re: XF212 for PA?

Posted: Sun Oct 13, 2019 1:14 am
by Charles Jenkinson
What is your background; your experience / interest in audio and acoustics?

Re: XF212 for PA?

Posted: Thu Oct 17, 2019 8:49 pm
by CSConrad
I've designed systems before, worked for touring bands and sound/lighting companies and remote recording companies, did some producing but not much. Built a small recording studio, largest room I ever mixed in was 30,000, the smallest ones were probably under 100... can honestly say I've worked at all levels.

Re: XF212 for PA?

Posted: Fri Oct 18, 2019 1:26 am
by Charles Jenkinson
That's interesting. You've worked in a nice industry. I "fell back on" mechanical engineering as a career, I suppose by virtue of having done a degree in it and being reasonably satisfied that that is therefore what I should do for a job. Don't know if I could do anything else now - too much to learn wherever I look. I really wanted to do a sound engineering degree but it just didn't seem there was the opportunity when I was thinking about it in the early 90's.

Have you read any reviews of PA system performance with respect to the designs on this website?

Of course, I appreciate that to read them here may be a bit like asking for an honest appraisal from a football supporter of their team, to a cynical type - Confirmation bias has a strong pull, but then that is about belief and not objectivity. There are however many here who have and do work in your industry who's ethos is to constantly review equipment and setup to optimise sound, particularly in the PA arena.

Re: XF212 for PA?

Posted: Tue Oct 29, 2019 12:34 pm
by CSConrad
I'm looking at a room that's wider than it is deep, so horns are not the best choice. I don't believe there's a "best cabinet," any more than there's a best sized suit. The cabinet must fit the room (and, sadly, the budget. We can't all afford new Meyer or L'Acoustics...)

Because the room design I'm trying to fit is unusual, I'm having to be a bit creative... hence my failed attempt to find a way to merge two coaxials!