DIY Acoustics: A Cautionary Tale

AUTHOR’S NOTE: In the year or so that I have been writing this column for rAVe’s house of worship publication, the majority of the articles have been how to or problem/solution oriented, with an educational and information focus. A number of those have concentrated on room acoustics and acoustic treatment areas (specifically, on intelligibility here and here, new construction room acoustics here and on getting cleaner, brighter and more articulate sound, here). This is because acoustics related problems are one of the major issues that most HOW spaces have to deal with sooner or later.

In the last few months, I have come across an increasing number of articles and blog posts offering advice on acoustic treatment and materials with the DIY reader as a target. Many of these were written by suppliers or sales folks in that market segment. However well meaning their intent, the content of the vast majority of what I have seen is either too general and vague to be of much practical value or — more distressing — offers specific advice on specific solutions without knowledge of the actual space(s). That approach is simply not a good idea at best and at worst, could create more problems than it would purport to solve. I’m not going to mention specific companies or articles because that’s not the point, it’s the idea that advice must be weighted with the facts, not based on theory only.

The Perils of the Vague Idea — One Size Does Not Fit Most!

It was a Thursday a few weeks ago, much like any mid-west winter Thursday — grey, cloudy and COLD! The phone rang, and seeing it was a local house of worship calling, not one of the daily calls with someone trying to sell us computer repair, we picked it up. (Thank you, Caller ID).

The person on the other end said they had reached out to us to try a help them solve an acoustic issue with their sanctuary. On the surface, fine and dandy — we do this all the time.

But then came the “oh-by-the-way” part of the problem: He said that the church had done some of its own ‘acoustical solutions’ work to try and fix the problem, based on various information they found online.

The sources they used, he said, seemed to be supplying information that matched up with their space and conditions, so they followed the advice, bought the materials and put them up as shown in the article’s diagrams. Oooooops!

Warning bells started going off in my head, but I asked: “So what happened, and how can we help you”?

There was this long pause and then: “Well, it’s actually worse now than before we did anything. Can you come and take a look and what would that cost?”

In my head I thought “been there, done that,” but we said “of course,” discussed a service fee and off we went.

What we found when we got there was a room ‘plastered’ with fabric-covered fiberglass panels arranged in a spaced pattern down each wall starting about 3 feet off the carpeted floor. I lost count at 100.

The central cluster sound system was essentially working into a giant mid-band absorber and had no clarity and no definition, but the room had no “echoes,” which was the stated problem they were attempting to solve. And the pews all had thick fabric cushions as well to add to the amount of absorption.

What do you think was the recommended solution and why? The answer is below.

Every Worship Space Has Multiple Acoustic Personalities

One of the primary reasons that general purpose recommendations won’t work is that every worship space can take on any number of different ‘acoustic personalities’ depending on, but not limited to:

  • Various kinds and types of surface finish materials and their response(s) to temperature and humidity
  • Weather — air temperature, humidity and air density
  • Occupancy level and who is occupying the space — for example, adults create a different kind of effect on the acoustics (larger body size more absorption) than children.

Even supposedly “identical spaces” (two rooms built at the same time by the same people using the same materials) are not going to measure exactly the same.

Why?

For instance, the acoustic characteristic of brand A drywall and brand B drywall at precisely the same thickness and rating will NOT be the same due to variations in product formulas, manufacturing processes and so forth.

Even within a brand, a batch to batch difference can often be found — the same applies to every other finish material, surface treatment or acoustical solution that you can think of and a whole bunch you didn’t even consider.

Physics Is Physics — The Aerodynamics Example

Perhaps an easier way to understand this complex set of variables and their significant effects on both perceived and measured room acoustics parameters is to look at a different branch of related physics — aerodynamics.

Both acoustics and aerodynamics incorporate such sub-disciplines/sciences as fluid dynamics (air often behaves as a fluid), atmospheric sciences and the effects of thermodynamic variables such and temperature, humidity, atmospheric pressure (altitude) air-density coefficients and so on.

The Same Plane, Different Conditions

So let’s look at one specific aircraft — say a brand new shiny Boeing 777. That airplane flies in and out of Denver’s airport every day, year round, to different destinations, but that does not matter (except for the weight of the fuel it carries to reach that destination which will vary).

See related  Can You Hear Me Now?

What matters is that aircraft will behave VERY differently depending on the effects of a whole bunch of physics parameters, including air temperature, total weight, humidity, air density, equivalent altitude* and a multitude of other factors. So for the pilots of that plane on any given day, there is no one “setting” that will work for taking off (or landing), even though it’s exactly the same plane in exactly the same location.

[*Actual physical altitude, like Denver’s altitude of approximately 1 mile above sea level is not the real altitude that will have to be factored into the plane’s performance. The real altitude is a complex combination of temperature, humidity and other variables. This is why pilots always check and set their altimeter (altitude reference instrument) to a specific number supplied by the airport for that day, time and set of conditions. That number will change throughout the day and from day to day.]

The complex number of variables that must be considered is why professional pilots MUST use a PILOTS OPERATING HANDBOOK or POH before, during and at the end of every flight. That book will contain tables (or charts) like the one shown below.

If you look at the table you will see data on maximum takeoff weight, range, runway length and speed required for takeoff and landing speed all weighted against a specific set of temperature and humidity conditions and engine type.

For example, the thrust produced by the engines, and thus the distance needed to takeoff is based on a precise set of listed temperature and humidity conditions. If the actual conditions are not exactly the same, pilots must use such tables and the flight management computers to calculate what the actual numbers will be for the actual conditions.

For example, on a nice spring day at 85 degrees the required takeoff distance might say 8,000 feet, but if it were 95 degrees that distance would increase to over 9,500 feet.

Why does this matter? Well I don’t know about you, but when that plane starts down the runway I really, really want it to take off. If the calculations are wrong, it may not be able to do that.

Real World Acoustics

Just like the plane example above, each worship space will vary based on a long list of the potential variables, some of which are mentioned above. The worship space we began this story with had applied a one-size fits all solution, not understanding that they were missing key information needed to properly and effectively address the problem.

And that missing information is really what was needed to determine what was causing the problem and its actual origin. Then the appropriate solution to correct the difficulty, and not have more impact than really necessary.

The leadership was concerned that they had now “solved” their problem, but perhaps they needed a new (and expensive) sound system to deliver their message in the ‘fixed ‘room. There was a distinct undercurrent of, “How are we going to pay for that?” running through the dialog.

Don’t Panic

With no apologies to either Elon Musk or “The Hitchhikers Guide to The Galaxy,” our approach was really quite simple. We told the leadership that although they had apparently solved one problem, they had in so doing created another. They sort of knew this but were not willing to accept the results.

We recommended removing a segment of the panels bit by bit until the problem resurfaced and then finding out what was causing it, where it actually originated and determining a workable solution that DID NOT require a new sound system. Perhaps some re-tuning or adjustment to the system might be helpful but it seemed workable and there was no real reason to replace it IF we could bring back the needed clarity and maintain the echo reduction.

You could almost hear the collective exhale. Now, this would not be a one-day process, we told them. It might take a few days to figure it all out but it could be solved scientifically, and with proper measurement and data collection, corrected once and for all.

The Answer to DIY

I am not saying that any house of worship should not to employ DIY problem-solving. In fact, given real-world budgets and economic realities, it’s probably an inevitable choice. But what I am saying is that just like DIY aerodynamics or brain surgery, you have to know when you’re out of your comfort zone and when it’s time to call in some expertise.

In the case of the house of worship in our parable, the amount of money they ended up spending to find out what the real problem was and solve it was less than a third of what they originally spent on the panels trying to solve it themselves, and they did not need a new sound system — a few aiming tweaks here and there, some level adjustments and EQ and it worked just fine.

So, before you place that order for a truckload of acoustical stuff, spend a few dollars finding out what the actual problem is. In the end, it will most likely be less expensive and produce a better result than guessing a solution and then having to go back and fix the fix.