DIY acoustics testing, part 5: Interpreting your measurements
Acoustics are huge part of achieving a high quality end result in music production, and the cost of the tools used to improve the acoustics of your home music studio have dropped significantly in recent years.
In this series, we’re going through all of the basics of how to run acoustic tests in a DIY setting.
In previous articles, we’ve taken some acoustic measurements and collected our first set of data points. Now comes the most important part: interpreting this data accurately.
At this point in the process, you should have a bunch of different measurements saved in your Room EQ Wizard (REW) acoustic measurement software. In order to pick the best mix position for our room, we need to interpret these results using some helpful visualization tools that are built into the software. Here’s some specifics on how to do that.
These are a few of the top graphs you can plot with REW, and what they can show you.
The SPL/Phase graph
The SPL/Phase visualization in Room EQ Wizard
What you’re looking at here is a two dimensional plot of the frequency response of your room, shown within the range of human hearing. Frequency moves from left to right, low to high, starting with the lowest frequency humans can hear on the far left (20 Hz) and moving up through the highest frequency humans can hear on the far right (20 kHz).
Amplitude in decibels (dB) is shown up and down along the Y axis of the graph.
With these two variables (frequency and amplitude), we can visualize how much a room is affecting the sonic frequencies you hear within it. In this example, we can see that in the 70-90 Hz area, there’s a pretty significant dip of almost 10 dB from the baseline.
That 70-90 Hz area just happens to be where a lot of the kick drum information lives. So, if you were to mix music inside of this room, it would be easy to mix the kick drum way too loud, as the room would be making you think that the kick drum was sounding much softer than it actually was.
If you’ve ever spent hours on a mix only to get frustrated when your work sounds completely different when you play it back in the car, this kind of acoustic masking by the room you’re working in is the primary reason why this is happening.
This example was taken from an empty room with no acoustic treatment that also had a weird flutter echo. This graph is a good example of what a lot of untreated small rooms look like as a baseline, before we fix them.
What to look for in the SPL/Phase acoustics graph
Here’s a few red flags to look out for when interpreting these kinds of graphs.
Sharp, narrow peaking and cuts (nulls)
Large roll-offs that affect a wide area of the spectrum
Comb filtering in the mid/high frequencies. Comb filtering looks like a comb, with lots of jabby spikes placed close together.
I’ve circled several of these items that are visible in this example:
Common acoustics issues in untreated small rooms.
Solutions for common acoustics issues
Now that we’ve identified some common issues, what to do about them? Well, that depends on where you’re at in your acoustics design process.
In our current example of setting up a small room for the first time, where we’re still finding our ideal acoustic position inside the room before we’ve added any acoustic treatment, we’re really just looking to find the place where these issues are the least bad as the room naturally sounds. Remember all of those micro-measurements I had you take last time?
Here’s where those measurements come into play. Compare your measurements from all of these different points (X, X1, X2, etc) and find the point which has the least amount of spikes, bass roll-off, comb filtering, etc. You’re not looking for perfect right now, just the best option of what you have.
Once you’ve found that point, mark it on the floor (painters tape works great for this). This is the point in your room around which we’ll design all of our acoustic treatment.
How and where to apply acoustic treatment
It’s important to recognize that all of the different acoustic problems I’ve circled in red in the graph above require slightly different acoustic tools to solve.
This is maybe the most common problem I see in DIY room acoustics: assuming that a tool designed to solve one type of acoustic problem (say, bass traps) has any effect at all at solving a different kind of acoustic problem (say, comb filtering).
Effective acoustics design of a room will use not just one, but a range of different solutions to address different problems, as part of a holistic design. All of these solutions are designed to work together as a complete system. If you skip some of them, your entire acoustics design will be much less effective.
Bass traps, for example, will generally only be effective in controlling the bass area, and they won’t do much of anything to help higher frequency issues like comb filtering.
Here’s some notes on potential acoustic treatment solutions (marked in blue) to the different acoustic problems I’ve previously marked in red:
Potential solutions to common small room acoustic problems
The SPL/Phase graph is just one of many helpful tools you can use to help design the acoustics of your space with Room EQ Wizard. Next time, we’ll go over some additional visualizations you can use to help interpret your results further.
