CHCC Remodel: New PA, Pt. 2

Last time, I began talking about our new PA. After making the design change from exploded mono to left-right, we had to figure out how to get coverage over the widest section of seating in the middle, while keeping as much sound off the walls as possible. Here again, I was glad we chose the system we did.

At worst, we're down 2-3 dB in the corners of the room, which is a far cry from the 12-18 dB variations we have now.

At worst, we're down 2-3 dB in the corners of the room, which is a far cry from the 12-18 dB variations we have now.

Asymmetrical Boxes For the Win

One of the best features of RoomMatch is how many different modules they have available. It’s not a line array; it’s a progressive directivity array. Each box covers part of the room. Because we wanted wider coverage in the middle than on the sides, we used asymmetric boxes to get some sense of stereo to about 80% of the room, while keeping most of the sound off the walls. 

And because it’s all done mechanically, we limit the effect of phase shifts and smear that tends to happen when you try this in DSP. I don’t know of any other system that can solve problems in coverage the way RoomMatch can. As you can see from the plot, it’s not quite as even as the exploded mono, but I think it’s going to sound very nice.

Each array is made up of mirror-imaged symmetrical and asymmetrical boxes. Here’s the house right one to give you an idea:

  • L26°, R45° x 05°
  • L26°, R60° x 05°
  • L26°, R60° x 05°
  • 120° x 05°
  • 120 x 10°
  • 120 x 20°

The top three boxes are 26° to the left, but 45 or 60° to the right. The last number is the vertical coverage. On the right side, the left and right coverage numbers are flipped. It’s pretty cool what you can do with both symmetrical and asymmetrical boxes in a design.

We'll have more low end to play with than ever before. A lot more.

We'll have more low end to play with than ever before. A lot more.

The Low End

Right now, we have almost no low end in the room. The new system will have four dual 18” subs, flown in the center in a cardioid pattern. As you can see, the coverage is pretty even, with only a little bit of falloff in the back corners—which may be good; bass tends to build up in the corners anyway.

What About Speech?

One common question is how to solve the phase issues that will crop up in the overlap area when it comes to speech. Well, there is no way to solve that. There will be phase issues, but our ears are designed to hear in stereo, so each person’s ears will localize to the closest speaker.

Because this was a concern for me as well, I spoke with a few guys who mix on well designed, well tuned stereo rigs and asked them about speech. Both said it would be fine. And when I think back on my experience at Church on the Move last year, we sat right in the middle and never had any issues hearing the speakers. So I think we’re good. 

Plus, simply pointing the speakers at the seats will increase intelligibility by a factor of about 10.

The Rest of the System

Along with the RoomMatch speakers, we chose the Bose PowerMatch amps to drive them. The amps have a considerable amount of DSP in them and are fully networked. The amps will handle the array correction as well as the settings for the cardioid sub array.  An ESP-880 DSP will act as the overall traffic cop for the audio and do our system shaping. Having spent some time with Control Space Designer, I have to say I’m very impressed with the way Bose does DSP. 

Get Help

I’ve said this before, but when you’re working on a big system like this, get some help. I am not a speaker system design expert. I have a good understanding of what I want, and have good ideas on how to get there. But I still relied on my integrator (CCI) and the manufacturer (Bose) to get us the final designs. I definitely had input into the system and made many suggestions along the way, but it was the guys who really know the engineering that figured out how to implement my ideas into reality. 

How Does It Sound?

Stay tuned. This article posts on June 6, and we’re beginning installation on June 9. You can be sure I’ll have some posts up after the first weekend, and probably after that as we get the system dialed.

Roland

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