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Absorption panels
Look at the data on your absorption panels before you buy. There is a standard for this with several nuances, but for easy practical basic understanding, that is the percentage of that frequency that will be absorbed when it hits that panel.

DIY Guide to Acoustics: Getting Right Tools, Having Right Information

An acoustic measurement is a great tool, and is perfectly acceptable to validate or disprove any suspicions you might have, but it may not necessarily change your course of treatment.

Practically speaking, acoustics is not rocket science.

Not every room needs to be measured to be fixed.

It is my belief that anyone with a bit of gumption and need, can figure out how to treat a room for their church. There are some real dangers that can occur if you are not careful, though, as the average tech person can do a pretty good job by applying some simple tricks.

First of all, not every room needs to be measured to be fixed. This is not an easy statement to make, and likely one that will end being criticized.

A lot of times, I know exactly what I'm going to do, just by hearing it. I usually measure a room to validate my own thoughts. I'll go into more of why you may not need to measure in a bit.

If you are going to measure a room, a couple of small things will quickly help you.

  1. Get a measurement microphone. It doesn't have to be expensive. A simple Google search for “Acoustic Measurement Microphone” will lead you to several options that are affordable and readily available. You will also need a way to get that microphone’s audio feed into your computer. An audio-to-USB device will do the trick. In all likelihood, someone you know will have one (check with the worship band first).
     
  2. Download some measurement software. Again, this doesn’t have to be expensive. REW (Room EQ Wizard) is a great measurement tool, and it’s free! It takes a little work to get set up but it has several graphs that will represent exactly what is going on in your room. It also has a great help guide, which will walk you through everything you need to get the most out of the software.
     
  3. Plan your test of the room in advance. Pick several spots around the room to measure, before you get there. Go in with a game plan!

After you measure a room, it is time to interpret that data. Using REW, the graphs that I look at most are “All SPL,” “Impulse,” and “RT60.” While other graphs are helpful, such as waterfall, the three I just mentioned will provide all the data you need. Again, this looks like a lot, but just take your time and look at the graphs.

All SPL chart

All SPL chart.

Pay attention to the both axis of the graph and what they say. On the left you see dB (intensity) and on the bottom you see Hz (frequency).

The graph above shows the intensity at every frequency from 20 Hz to 20,000 Hz. Pay attention to the high and low points on the graph. Zoom in and measure the differences in intensity from one peak to another.

Do not apply any smoothing at first, so you can see the low end in more detail, but for the midrange and upper frequencies, some smoothing is OK. Take note of anything that jumps out at you.

I also look at the impulse graph below, to see if there are any substantial reflections happening, and how long it is taking to get there.

In this graph, there will be many reflections, but if one or two stand out among the rest, they will be considered problems. Sound travels at approximately one foot per millisecond. So you can gauge about how far away the reflection is by seeing the time delay in the reflection.

Impulse response chart

Impulse response chart.

Finally, the RT60 graph below will show you the reverb time in specific frequency bands. You will likely always have a higher reverb time in the lower frequencies. That is to be expected. But you want to make sure it isn't crazy. For instance seeing 2.5 seconds at 125Hz and .7 seconds at 1,000Hz might be something you want to take note of.

RT60 chart

RT60 chart.

After you interpret the data, it is time to start planning for correction in the room. There are a few types of treatment methods, but the most popular is absorption.

Another great method includes the use of diffusion. This method can be very beneficial, but in most cases, you will see absorption.

A couple items to pay attention to when selecting material:

  1. Look at the data on your absorption panels before you buy. You will see some frequency numbers along with another number that may be anywhere from 0.0 to 1.0. There is a standard for this with several nuances, but for easy practical basic understanding, that is the percentage of that frequency that will be absorbed when it hits that panel.

You may ask the question of why there can be 1.21 at a frequency. Long story short, it's possible, but for starting out, it is good to think of it in that capacity. If you see a 1.21 at a certain frequency, know that it is going to do well at that specific frequency band.

Octave band frequency chart

Octave band frequency chart.

  1. Make sure the product passes the LAR method (looks about right). If it doesn’t seem right, it might not be. Just because numbers are published doesn't mean they are correct. Look across multiple panels to see what vendors are showing. The truth will be evident quickly.
  1. Pay attention to the amount of high-end energy you are absorbing. Overabsorption in the high-end makes a room feel lifeless. It is possible to overabsorb in this capacity.  

As a general rule, I add as much low-end absorption as possible. In most cases, I will offset a panel from the wall, allowing that panel to flex, creating a diaphragmatic absorber. This is a great tool to use, when considering low-end absorption. In addition, low-end tends to build in corners. For this reason, it is good to place treatment in your corners. Remember, there are more than four corners in your room.

I mentioned earlier that sometimes a room didn't need to be measured first and said I’d get back to it later.

Well, it's later.

Everything discussed up to this point falls into this answer.

Let's pretend you have a rectangular shaped room, with windows evenly spaced on each side, with a hard back wall. Intuitively, you might put panels in between each window, and on the back wall.

You might put some panels across the corners or add bass traps to help absorb low-end in the room. You didn't add too many panels, but you did your research, found the right ones, and you placed them in a way that looks visually appealing.

It may not be perfect, but you will have eliminated many reflections and dampened issues that were present in the room.

Intuitively, you have completed 90 percent of what I might personally have done in that room. I may have simply offset the panels from the wall to assist with some diaphragmatic absorption, or added a few helmholtz resonators that are tuned to a specific set of frequencies, but this was a solid round of treatment.

An acoustic measurement is a great tool, and is perfectly acceptable to validate or disprove any suspicions you might have, but it may not necessarily change your course of treatment.

If you have problems at 250 Hz, but you thought it was 200 Hz, does it change your treatment? Thinking back to our absorption coefficients, likely not. Or maybe you have a problem at 8,000 Hz. Does it change your course for correction, if you thought the problem was at 10,000 Hz? Likely not.  

On a final note, there are several acoustic sources out there to learn from. One of my favorite books is “The Audio Expert - Everything You Need to Know About Audio” by Ethan Winer.

There are also several places to research terms and become familiar with common practices online. There are also a lot of poor information sources out there. If something looks different, question it. Be inquisitive and do your research.

I said acoustics isn’t rocket science. It isn’t, but it isn’t relaxing on the beach either.

I firmly believe this is something that any church tech can figure out. It is simply getting the right tools, and the having right information in place to achieve success.

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