This is the beginning of a report covering tests we conducted with diffusion in four different churches. Each church sanctuary (and one gym) had numerous problems very audible to the ear. We haven't had the time to report on all of the details at this time, but hope to make a full report in the near future. Below you'll find photos, descriptions, and audio files in mp3 format. We hope this introductory information helps you learn a little.

We used SMAART Pro as our acoustical measurement system, along with another program we were testing out. A Toshiba portable laptop, Digigram VxPocket V2 sound card, Earthworks M30 mic, and Tannoy powered test speaker were used to complete the test system.

Various sound stimulus were played into the room via a Yamaha SM 12 IV monitor speaker powered by a QSC amplifier. Sound stimulus was off prerecorded CD's as well as an Alesis D4 16-bit digital drum module. The stimulus were then recorded via an Earthworks M30 mic plugged into a Presonus Digimax digital pre amp. The recording was done on an Alesis Masterlink set at 16 bit/44.1kHz.

While we could have used a better stimulus speaker, better CD material, and a higher sampling rate, our goal was not perfection, but simply for an audio recording of what our ears heard. The recordings have some noise on them; some of this is hiss from the pre-amp (in some cases we were unable to play the stimulus sounds at a high enough SPL for the record mic to pick them up with a lower gain setting), and some of the noise was from HVAC systems and road and building-use noise. The audio files have been converted from .wav to mp3. They have been edited for length and to take out dead space only; no other editing has been done to them. What you hear in the mp3 files is what we heard with our own ears in each room. Sure, the recordings contain some hiss from the gain stage on the pre amp turned all of the way up, but beyond that, what's contained in these audio files is what we heard. In all reality, the recordings don't contain as much information as we heard with our ears. That is, we heard a bigger difference with our ears than what was recorded. So, if you like the difference you hear with the recordings, you would really like the difference heard live in the room!

Most of the RDU's used required a special saw to cut them as well as other specialized tools to work with them properly. They were designed and built specifically for these church tests, and therefore have a number of special features.

The measurements and recordings were completed by Blake Engel & Robert Yoder.

Prince of Peace Lutheran Church

This was a gym we worked in, 46 feet wide and 75.5 feet long with a peaked suspended ceiling of about 28 feet. The walls are all concrete block, the floor tile on concrete. Recently, they installed dozens of 4x8 foot sections of what appears to be 1-inch thick foamboard covered with a thin carpet material. This was done to help with the acoustics of the room. As you can see in the photos below, the panels are flat and are mounted against the wall. Because the panels are thin and because of the mounting method (flat against the wall), they only help to absorb frequencies from about 3,400Hz and up. Since the fundamental frequencies of speech are much lower than this, the panels have very little effect in controlling speech in the room. A simple handclap in the room showed multiple flutter echoes and other strong reflections.

Acoustical measurements were taken and different sound stimuli were recorded. Then we placed RDU's (Random Diffusion Units) around the room at roughly 18" intervals. We used a combination of 8", 10", 12" and 16" RDU's. The acoustical measurements and recording of sound stimuli were repeated.

There were two changes that stood out amongst all of them; first, the flutter echoes were not audible anymore. Second, the frequency response of the room changed. Yes, it changed! No longer was the room muddy sounding, but crisp and clean. Listen to the audio samples below to hear for yourself.

While we don't have all of the information ready to present at this time, there's one comment we can make about the acoustics--the average RT60 didn't change after the RDU's were placed in the room. If RDU's were installed in this space, some additional absorption would need to be added in a very small quantity to dull the very high frequencies that are much more clear after the RDU's are in place. Not much would be needed though, just a small amount. This is the beauty of diffusion; it allows you to actually TUNE the room as needed.

This room doesn't have a sound reinforcement system installed in it; the room is used with portable dividing walls for Sunday school classes and other such events.

This was an average church, but with a not-so-average ceiling. The sanctuary is 45 feet wide, 100 feet long, has side walls about 10 feet tall with a peak that's nearly 55 feet. The side walls are brick, the floor in the isles and platform is carpet covered concrete, and the back wall is glass on the lower portion, but 3/8" plywood mounted on 16" center 2x10 studs (as far as we could tell) above that point. The roof is wood on laminated beams.

Initially, we found standing waves between the side walls and a slap echo off the rear wall. Acoustical measurements were taken and different sound stimuli were recorded. There was quite a bit of activity at 60Hz, which, after several hours of investigation, led us to the rear wall. Originally the room was planned to have a balcony. That wasn't done, so a wall was built where the front edge of the balcony would have been (this dead space is now used for the youth). After finding some keys that were recently found (they had been missing), we were able to determine the construction of the wall, which when we looked up some information in a few reference books, found that the resonant frequency of such a wall built of 2x10's and 2/8" plywood was just about 60Hz, hence what we were observing in the measurements. That "solved", we then placed the RDU's around the room. First we only covered the side walls--and, as expected, the echo off the rear wall became more apparent, but not quite as much as we had expected. Then we covered the lower (glass) portion of the back wall (since we had no way to place the units high on the back wall). While we heard a difference, we didn't hear as much of a difference as we expected or would have liked to. Part of the reason was because we were unable to treat enough of the back wall, but another part of the problem was something we hadn't realized. Not until talking with Joe De Buglio of JdB Sound, Acoustics did we learn that the other portion of our problem had been the roof itself. We had played with a digital measuring device at the church and had found that we could actually hear the pulses it sent out to make the measurement (very similar to what bats do). This very directional sound source showed us the angle of reflection off the wood ceiling was putting quite a bit of sound into the congregational seating area, from about 3 feet outside the isle to the side wall. Thus, another issue that needed solving. Having never dealt with a room that had such a high peak compared to the width of the room, we never thought to question if reflections off the steep roof were causing problems. In this case, they are.

Finally, we made our audio recordings and then listened to the before and after. Again, the difference wasn't nearly as great as the church gym we had visited the day before, but there was a difference. Below you can hear the before and after. Note the audio quality and frequency response. Listen to the clarity of the upper mid and high frequencies--is there a difference?

Comments made by church members were not all that positive. While I agree it was tough to hear the difference (especially when you're not able to hear the before and after and especially when the difference isn't nearly as obvious as the church gym), there was a difference. If we had RDU's that were 15 feet long, we could have better treated the rear wall. If we had realized the ceiling was an issue, while we couldn't have changed that temporarily, at least we would have known better. Both younger and older people listened to our before and after recordings via a monitor speaker in the church sanctuary. Some noticed a difference, others didn't at all. One older woman (we know she was older since she had beautiful gray hair--and she even said she was older!) said she heard a huge difference and couldn't understand why others didn't hear it.

While these details make it sound as though this was a failure, we don't think so at all. The rear wall of the room was larger than we realized (and we were unable to treat it properly), and the roof issue had not been expected, seen, or understood while we were there.

The sound system in this room is a left-right system with the speakers mounted on a laminated beam just above the flat side wall on either side (see the lower photo, below). Coverage and intelligibility of the system isn't ideal, nor is it the proper design for a church like this.

This sanctuary measured 49 feet wide, 56 feet long, and had a peak at 23 feet. The side walls were about 16 feet tall. The walls and ceiling were drywall, the floor spancrete covered with industrial carpet. There are several sections of 2" thick tectum panels on the upper wall portions. At one time, the room was used 90-degrees from how it is today. Thus, the tectum was on the rear wall at that time. Based on how they're mounted, they're doing a little absorbing of high frequencies, but not much else because they're mounted flat and against the wall.

The main problems in this room are the reflections off the rear walls, standing waves between the side walls, and simply an overall muddy sound to the room. As in the two previous churches, measurements and recordings were done, then RDU's were placed in the room and the process repeated again. The rear wall wasn't covered with RDU's besides on floor level, so there was still a noticeable echo off the back wall. Again, the frequency response of the room changed (before vs. after), and there was a nice improvement. It would have been more noticeable if we had been able to treat more of the back wall.

An interesting thing was happening with the rear sliding door that broke a rear room off of the back of the sanctuary. The moveable door partition reflected some frequencies, but allowed much of the mid and low frequencies to pass right through; these were then reflected off the exterior wall and reflected back into the sanctuary. This resulted in echoes returning later than you might expect for a room this size.

The sound reinforcement system in this room was recently upgraded from a single-speaker system (using a 3-way studio monitor speaker of which only the 12" woofer worked). The new system utilizes three speakers to cover the center, left, and right sections. More information on this system can be found in our "projects" page of this web site.

The sanctuary is 56 feet wide, 99 feet long, has side walls about 28 feet high with a center roof peak of 33 to 35 feet. The walls are all a hard, stucco-like substance on concrete block. The rear wall is wood paneling covered with fabric covered panels of some sort. Originally, the rear 20 feet of the room had a wall that went from floor to ceiling which created a hallway along the back of the sanctuary (since the sanctuary connects two portions of the building). Behind this hallway section is a classroom area nearly the full width of the sanctuary (about 40 feet wide) but only 20 feet deep with a 10 to 12 foot flat panel ceiling. This area has movable partition doors that can open and close the room from the sanctuary. The rear floor area is flat, the platform (front) area has a flat floor, but the congregation seating area is raked (sloped) very gently. The congregational seating area is all hard tile on the floor; the rest of the floor in the room is carpeted.

There's a very noticeable flutter echo between the side walls, and of course, standing waves. There's a slight echo off the rear wall, but it's masked by the standing waves between the side walls. When standing in the congregational seating area, you mainly hear the flutter echo between the side walls. When standing at the front or rear of the room, on the flat floor, you hear not only a flutter echo between the side walls, but a very interesting echo off the ceiling. The height and angle of the roof and the large, flat surface it is results in a very strong slap echo, then a flutter echo with just a simple hand clap.

Once again, we took our initial acoustical measurements and recorded several audio stimulus sounds before bringing in the RDU's. We were afraid we didn't have enough units to treat the room, but ended up with just enough. The problem was not with quantity, but length. The height of the side walls called to use RDU's that were at least 10 feet tall, but ours were only 4 feet and 6 feet. Also, we were unable to cover the back wall at all. The change we heard put a smile on our face. This room was a great example in many respects. The flutter echo we originally heard was almost inaudible now. One great example was the answer to the question "do we have to treat the wall from floor to ceiling, and can be start the treatment 8 feet off the ground so no one damages the treatment?". As stated, after the RDU's were in place, when standing, the flutter echo was almost inaudible. If you sat in the pew, it was even better. If you crouched down so your ears were only a couple feet off the ground, just above the tops of the pews, you didn't hear it at all. However, if you stood on a pew and stretched your neck, the flutter was just as apparent as it had been before the RDU's had been brought in. This was a great example showing how treating the area where your ears are (on the vertical plane) is most important. (Sadly, while we talked about doing it, we didn't record any sound stimuli at different heights to show this point audibly.)

The church organist had arrived at the church earlier in the day, and we had spoken with him a little (since he was curious what we were all doing!). Our luck was great when he again passed through the sanctuary after the RDU's were in place and we got a chance to talk with him for a couple minutes again. We asked if he could spare a few minutes to play something on the organ to see if he could hear a difference. As he walked toward the front of the sanctuary and we continued to talk (from the rear of the sanctuary), he suddenly exclaimed he heard the improvement already, that normally you couldn't have a conversation from the front of the room to the back, even half that distance was very difficult (from the middle to the front or back). This made our day; he heard a difference and was impressed. Now the real test came--would he like the sound of the room for music; for the pipe organ? He played a few dozen measures of a prelude from the previous Sunday, and suddenly stopped--at first, he didn't know what to say. His smile on his face told a lot; he then went on to explain how much more clear, defined, and crisp the sound was. He stated that normally he presses a key and it seems as though the sound takes a split second to get to him and it's muffled and distorted. Now, he said as soon as he pressed the key, he heard the pipe and it was more clear and crisp than anything he had heard in that room before. As if these comments were not good enough for us, he asked if we had increased the reverberation time of the room! It took all we had to hold back our excitement as we explained that the average RT60 hadn't changed at all; all we had done was reduce the audible echoes and reflections in the room! When he left the room, both Robert and I said (almost in unison) "we should have recorded the organ being played with and without the RDU's!"

The sound reinforcement system in this room was put in nearly 10 years ago. As I (Blake) have been told, there's been numerous problems with it since day one as well. Over the last several years, the church has had us (All Church Sound) make minor changes and adjustments (like adding an EQ for the house speakers, and a digital delay for the rear classroom speakers). We've held a number of church-specific training events to train their operators here as well. The speaker cluster, while it blends in aesthetically, isn't ideal. The speakers are hung upside down (the horn is on the top), and the three trap boxes are hung with chain--right against each other. The horn in the side speakers are aimed at the side wall about 3/4 of the way back (where the original wall for the hallway had been). This leaves the front corners of the seating area not covered with sound from the system at all, and allows plenty of comb filtering in the rear half of the room, plust all of the sound spilled onto the side walls, which only makes things worse. This was not an inexpensive system at all. It was designed and installed with good intentions, but no real grasp of acoustics or church sound reinforcement needs.

Notice the "roof" over the pulpit in the photo below; this was a sound reflector to help the sound of whoever was at the pulpit to be heard in the congregation.