Or first case study is a small—about 290 seats—A-frame style church. Typical of many small churches built in the early to mid sixties, this building has Glu-Lam beams on 12 foot centers, brick side and end walls, a wooden, tongue-and-groove ceiling and interior partitions of drywall on wood studs. The main part of the sanctuary is 60 x 45 feet, with a 18 x 30 foot platform and there’s a small balcony of 24 x 20 feet. The seating is in upholstered pews and the floors are carpeted.

The service is traditional, but, the congregation realizes that they need to have the capability to have more contemporary services down the road. The budget isn’t large, but after a string of poor PA systems the church is ready to do it right. They do however insist that they don’t want a “speaker in the middle” as they don’t want to block the view of the stained-glass window behind the pulpit.

The room is not bad acoustically, certainly the local string quartet isn’t breaking down the doors to play there, but the acoustics are benign and live enough that the congregation can hear themselves for singing.

The first issue to deal with is the view of the stained-glass window. If you look at the long section drawing, you’ll see a dashed sightline from the standing figure to the top of the stained-glass window. Anything above this line will not block the view of the stained-glass window for anyone on the main floor.

Now that we have the window issue solved, we can get on with selecting the loudspeakers. We built a simple EASE model for our investigations. If you have EASE, you can open the model and follow our train of thought in selecting the loudspeaker system.

As a first try, we’ll select the ST-STX4/64. We placed it 28 feet up, centered and hanging from the third Glu-Lam beam and pointed 23 degrees down, aimed at the last row of seats. Its predicted Direct SPL coverage is very good for the back half of the room, + or – 2dB. You can see this on the “DSPL@1-4kHz, Main Only” EASE maps.

I’ll mention now, that this two octave average from 1kHz to 4khz, is where we generally “start looking” at loudspeaker coverage. It’s in the frequency range where most pro-sound loudspeakers have good pattern control and covers the very important intelligibility bands.Of course, we want to look at the full range of frequencies eventually, so let’s start on the lower end of the spectrum and have a look at the 200-500 Hz range, any of the “DSPL@200-500Hz, Main Only” maps will show this. As you can see, at lower frequencies, our coverage is good over the entire room, the main floor is + or – 2dB and even including the balcony, we’re still + or – 3dB. So below 500 Hz, our single ST-STX4/64 is all we need.

Note also that the loudest spot isn’t right under the loudspeaker, this is the benefit of the “doublet-source” woofer array in the ST-STX4, a single 15” woofer wouldn’t have this kind of control.

Now we’ll look at the higher frequencies. The “DSPL@5-10kHz, Main Only” EASE maps show the predicted coverage of our ST-STX4/64 averaged over the 5kHz to 10kHz range. As you can see, the back of the room is still fine, but we’ve lost the front half—we’re shooting over their heads.

Now some of you may be thinking, just point the main loudspeaker down more, in fact, some may have a protractor out on the drawing and thinking that a single 40 degree vertical ought to just cover. Lets look at the EASE mapping if we aim the loudspeaker so that -6dB on the polar is just at the back row. The mapping DSPL@1-4kHz, Main Only, tilted down.bmp shows the coverage of this aiming.

As we’ve seen, our single ST-STX4/64 covers very nicely below 500Hz, so we need additional coverage just from 500Hz and up. If you have a look at DSPL@1-4kHz, Main and DF Only.bmp you’ll see the coverage of the main loudspeaker, aimed again at the 23 degrees down with the addition of an STX2M/94 as a downfill. The STX2M/94 is aimed down by 55 degrees. As you can see our coverage is now very even front to back and side to side on the main floor, but a bit weak in the balcony.

If the balcony is seldom used this may be fine, but lets add a second STX2M/94 as a delay on the seventh Glu-Lam beam, the 28 foot trim height matches the main ST-STX4/64, and it’s aimed down by 25 degrees and delayed 55ms.

All of the other EASE mappings represent the full system and you can see that coverage remains very even at all frequencies.

A handy mapping function of EASE 4.1 is the distribution chart, available in the View Mapping control window. Have a look at “Distribution, DSPL, 1-4kHz.bmp” to see this chart for the full system over the main floor and balcony seating areas. As you can see, our system is + or - 2.5dB over more than 96% of the seating areas with an absolute maximum deviation of + or – 4dB.

While the rooms acoustics aren’t bad, it never hurts to plot intelligibility. EASES’ predicted %Alcons is mapped in “Intelligibility .bmp” This is for an empty room, (always best to predict for the worst case) and as you can see, intelligibility is good everywhere.

Let’s discuss some options for this room. If the system were to be fully self-powered, then the STX2M/94s could be replaced with the PN121/9s and the coverage would remain the same. To reduce cost and maintain the same coverage, a system with the TRX151T/6 as the main, a TRX121T/9 as the down fill and a TRX121/9 for the delay would be the “Budget Solution.”