I'm planning on embarking on my first journey into PA loudspeaker design. I fully understand that this is not the most economical way to make good sound for PA purposes but I've been designing Hifi loudspeakers for over 10 years and I'm ready for a new kind of project.
The best thing I've learned in my foray into Hifi loudspeaker design is that attention to what is happening off-axis makes all of the difference in the world. However, I'm having a hard time understanding dispersion goals of point source PA boxes.
The target location is a pretty small church with a room that is approximately 70' wide by 120' deep by only 10' high to the bottom of the rafter. The room is currently setup with a pair of MR 825 JBL's with 15" woofers and 1" tweeter. Due to ceiling height limitations and interference with lighting, the speakers are turned on their side. The horn patterns are 100x80 so basically we are getting an 80 degree (if we are lucky) wide pattern right now that does not provide adequate coverage on the sides. Note that the speakers are placed only about 3-4 feet apart dead center. There is some room between rafters to move the speakers up but that may cause problems depending on frequency. Like a 3 way low frequency driver could recess into the rafters but I don't think the bottom of a 2 way will work pushed up.
Since we can't really move speakers back further due to feedback concerns, I was hoping to move the speakers further apart and come up with a nice wide dispersion design.
So most people who design hifi speakers would never use a 15" driver crossed over at 2kHz as beaming will happen well before the crossover point. In PA speakers, is this often done just to save cost or is the beaming meant to meet the dispersion characteristics of the tweeter?
If I went the route of a 3 way design with something like a 6.5" mid, the dispersion characteristics might be much closer to a wide horn.
I'm confident that I can meet the SPL goals and design a good 3 way system. I'll probably vertically align the mid and tweeter and place the woofer adjacent to the mid/tweeter. What I'm not confident on is that the dispersion will meet the intended goals unless I can go really wide or add multiple boxes per side. How wide of a pattern can I get from a compression driver? How will this effect the response and output of the compression driver? Please excuse my ignorance, I've never designed speakers with compression drivers so I'm just learning how to effectively use them.
The best thing I've learned in my foray into Hifi loudspeaker design is that attention to what is happening off-axis makes all of the difference in the world. However, I'm having a hard time understanding dispersion goals of point source PA boxes.
The target location is a pretty small church with a room that is approximately 70' wide by 120' deep by only 10' high to the bottom of the rafter. The room is currently setup with a pair of MR 825 JBL's with 15" woofers and 1" tweeter. Due to ceiling height limitations and interference with lighting, the speakers are turned on their side. The horn patterns are 100x80 so basically we are getting an 80 degree (if we are lucky) wide pattern right now that does not provide adequate coverage on the sides. Note that the speakers are placed only about 3-4 feet apart dead center. There is some room between rafters to move the speakers up but that may cause problems depending on frequency. Like a 3 way low frequency driver could recess into the rafters but I don't think the bottom of a 2 way will work pushed up.
Since we can't really move speakers back further due to feedback concerns, I was hoping to move the speakers further apart and come up with a nice wide dispersion design.
So most people who design hifi speakers would never use a 15" driver crossed over at 2kHz as beaming will happen well before the crossover point. In PA speakers, is this often done just to save cost or is the beaming meant to meet the dispersion characteristics of the tweeter?
If I went the route of a 3 way design with something like a 6.5" mid, the dispersion characteristics might be much closer to a wide horn.
I'm confident that I can meet the SPL goals and design a good 3 way system. I'll probably vertically align the mid and tweeter and place the woofer adjacent to the mid/tweeter. What I'm not confident on is that the dispersion will meet the intended goals unless I can go really wide or add multiple boxes per side. How wide of a pattern can I get from a compression driver? How will this effect the response and output of the compression driver? Please excuse my ignorance, I've never designed speakers with compression drivers so I'm just learning how to effectively use them.
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So this coming weekend we are going to move the existing speakers to a wider position and rotate 90 degrees. It might be hard to tell in the photo, but the current location also interferes with lighting and tall people on the platform. We do have a 15" JBL EON subwoofer in play right now but the room is crying for multiple subs as the modes are very bad.
Delays are a good idea but I don't know if I can sell it because it being a church and all, they like having people who think it is too loud sit in the back
The left to right coverage is the bigger issue right now....That is a pretty small room that you should have no problem covering with a pair of speakers, I'd suggest placing them far L and R outside the screens at the wall/ceiling angled in and down some.
The 15+1 PA speaker is a horrible compromise that still sells well to knuckle draggers that think bigger is better or budget buyers that sacrifice everything else to get some kind of fullrange sound.
You can do better, but I don't know if you really have room for a conventional 3-way box, have you considered trying to build a unity horn or synergy horn.. both creations of Tom Danley.
The 15+1 PA speaker is a horrible compromise that still sells well to knuckle draggers that think bigger is better or budget buyers that sacrifice everything else to get some kind of fullrange sound.
You can do better, but I don't know if you really have room for a conventional 3-way box, have you considered trying to build a unity horn or synergy horn.. both creations of Tom Danley.
I'm now looking at the Danley Labs designs. I've heard the name but wasn't really on my radar for home usage. However, these make lots of sense to me based on my current knowledge of how acoustics work in a real room.... After all, my hifi mains were someone else DIY design (Linkwitz LX521) because I can't best them yet
BTW, you mention near wall placement. In hifi this is typically a big no no due to psychoacoustic studies on early reflections. Is this just something that you don't worry about in live sound? This is for stereo mixing so I'd love to get to have an opportunity to produce decent imaging....
I believe there is a unity horn thread somewhere on this forum, it may be buried a little now.
Home audio shares little with PA despite using much of the same equipment. The top priorities in PA are going to be coverage, inteligibility and sufficient SPL before everything else, stereo imaging rarely comes into it because only a select few listeners would benefit from it and live instruments are mostly mono sources anyway. To this end speaker pattern control or directivity should be a top priority in design, if you can keep most of the energy off the boundaries the system will deliver better results, but you also want SPLs to be somewhat consistent for all listeners so the idea is to position the speakers so they're not completely blasting those in front. In your case options are limited due to the existence of those projector screens so hanging them near the wall is an option that needs to be explored, this boundary loading will enhance bass output but that can corrected with EQ.
You should try to put an eminence beta 10 cbmra on each cab (they have closed back), then with try with a DSP or a mdification of you JBL passive filter try to cover the 500Hz-1.5K range with it.
Then hear the magic happen
PS : Every 15" start to be unpleasantly narrow in dispersion at 1052Hz.
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Live sound has many more difficulties to overcome before you can start worrying about how good the stereo image is. Consider, for a moment, the people sat right next to one of the speakers - they're going to get 99.99999...% of their sound from the speaker they're nearest to, so the idea of a stereo image doesn't really apply to them.
We've already said a 15"+1" cabinet is a bad joke. Sure, you might get some 80Hz kick from the 15", but the midrange suffers horribly.
Lets start from the top. Fill in the blanks.
Budget?
Maximum cabinet size?
Maximum cabinet weight?
Do you have an amplifier available?
Do you have any signal processing available?
Do you have a measurement setup?
Now, this bit is very very important: if you are planning on hanging the speakers, DO NOT DIY THEM, unless you're willing to make lots of cabinets and send them off for strength testing by the proper authorities. Putting them on stands is fine, because nobody will ever be underneath them. Hanging them from a ceiling (which needs to be done with proper certification etc) is a different ball game, and if you mess up you could kill someone.
With that out the way, a 10-12" 2-way cabinet, even with a 1" HF unit, will do a better job than your current setup. Put them on stands out past the screens and it'll be fine.
Chris
Thanks for the considerations. The whole point in engaging this project is to learn more about PA speaker design. I'm not generally looking for the direct solution here but to better grasp the optimal dispersion characteristics of a PA system. I've given the use case to try to determine if wide dispersion is desirable (assuming they would not be wall mounted) and how to best achieve uniform wide dispersion with a compression driver. I have done literally hundreds of speaker measurements and many speaker designs from the ground up. I enjoy the design part but hoped to gain some insights on what makes a great PA speaker as it applies to my use case. It sounds like uniform dispersion over a desired coverage range, ability to reproduce adequate SPL and obviously a good response. I've started looking at CLFs of various speakers and this is helping me understand horn dispersion a little better. This is really the requirements gathering and research phase. Once I clearly understand the objectives I'll start designing something..... If there are unconventional design recommendations, I'm also interested in learning how others have solved dispersion issues for conventional PA systems (reading the Danley Labs patent was very interesting to me)
PA Systems is probably a good read for you.
If you are a bit more specific about what the system is used for (just speech <-> hardcore house parties) and what the strong and weak points of the current system are, then others can advice you more specific.
In any case I would go for separate subs and tops instead of full range speakers as placement is key and different from hifi / small rooms / low volume systems. Drivers closer then 1/4 wavelenght to each other or walls, or more then 2 wavelenghts apart; 100hz = 3.43 meter. Most made mistake in PA is placing subs left/right under tops closer then 15 meters apart.
// not for improving the sound, but the looks of he room, I would move all light about foot up.
If you are a bit more specific about what the system is used for (just speech <-> hardcore house parties) and what the strong and weak points of the current system are, then others can advice you more specific.
In any case I would go for separate subs and tops instead of full range speakers as placement is key and different from hifi / small rooms / low volume systems. Drivers closer then 1/4 wavelenght to each other or walls, or more then 2 wavelenghts apart; 100hz = 3.43 meter. Most made mistake in PA is placing subs left/right under tops closer then 15 meters apart.
// not for improving the sound, but the looks of he room, I would move all light about foot up.
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