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Combating Standing Waves With A Studio Subwoofer & Sonarworks Reference 4 Speaker Calibration

Over the Christmas break, I set some time aside to tackle a handful of issues in my studio. I don't usually have a lot of "downtime" so I took this opportunity to really identify and resolve some problems in my studio setup.

Since moving into my new recording studio I have noticed that the performance of my studio monitors hasn't been quite right. I've used a set of active ADAM Audio P22a monitors since 2008. I absolutely adored these monitors in my previous studios but in my new studio these didn't sound good at all. The new studio seemed to be taking away the character of my ADAM P22as, this room made these monitors sound very honkey.

In the article, I explain how I recognised a problem within my monitoring setup, how I tweaked the placement of my monitors to improve the frequency response and how I fixed an artificial sound caused by the Sonarworks Reference correction process by way of a new studio subwoofer.

Studio Monitoring Problems In New Studio

Regular visitors of Pro Tools Expert are probably thinking "Dan, you use Sonarworks, why not use Reference 4 to correct the problems in your monitoring?" The first thing I did when I moved into the studio was run the Sonarworks Measurement application. I found the results quite alarming...

The blue curve displays the frequency response (performance) of my monitors in the studio from the listening position. The green curve displays the corrections made by the Sonarworks Reference software. The correction adds and subtracts areas across the entire frequency response of studio monitors to give playback a flat frequency response, which the Sonarworks software accomplished, however, note the -12db dip between 70Hz - 100Hz on the blue measurement curve followed by a +6db boost in the 100Hz band. If I disabled Sonarworks my monitors sounded very honkey, with Sonarworks engaged everything sounded much better and how I expected my monitors to sound, however, after a couple of weeks of mixing in the new studio I started noticing a weird "flabby sound" in the low end that I had never heard before through my monitors.

This flabby sound was only audible in some styles of hard-hitting full production music. It's difficult to describe this sound, it sounded like a loose kick drum head that needed tightening or a drum mic resting on a drum tom skin. This sound didn't stop me from working with Sonarworks though, nor did it stop me from delivering mixes to my clients however this sound was very irritating, I knew I had to problem solve this issue at some point.

Changing The Height Of The Monitors

Julian inspired me to try this. I dropped the height of the monitors by about 2 inches and remeasured the monitors using Sonarworks. The frequency response appeared to be much better in the low end range:

I suspect the extreme flabby sound I was getting from Sonarworks Reference 4 was the sound of my monitors physically working too hard to boost the 12db 70Hz - 100Hz range to make up (correct) what was being lost in the frequency response due to standing waves caused by the shape and construction of my studio. The flabby sound was reduced but still audible after the height adjustment. I thought... I've gone this far, let's keep investigating...

Take A Load Off

I had a brainwave, what if my monitors didn't need to work so hard? What if I incorporated a subwoofer to handle the bottom end? I've never owned a studio subwoofer in the studio before. If I did, I would have had many noise complaints. Luckily, I now have a soundproof studio so I had no excuse to not get a subwoofer in my monitoring setup.

The Sub

I did a little bit of research and ordered an ADAM Audio Sub8. These are relatively inexpensive subwoofers that have a handful of nice features such as servo pots, remote control and 160 watts (RMS) of pure power.

Truth be told though, I purchased this particular model because it is an ADAM Audio product. A brand of a sub doesn't necessarily need to match a brand a monitor but I chose to match everything up with my existing ADAM monitors because I trust the reliability of ADAM Audio monitors.

Placement Of Sub & Studio Monitors

When setting up any set of studio monitors or subwoofer it is prudent to read the manual. I reread the ADAM P22a manual and studied the setup instructions for the ADAM Sub8. The P22a manual confirmed that I had my Adams setup correctly and the instruction for the sub8 explained that I should avoid having the subwoofer anywhere near a corner or wall as these areas will result in exaggerated low-end. Luckily, I have quite a lot of space below my control surface and between my monitors which meant I had plenty of room to experiment with different locations for the subwoofer. The manual recommended I place the subwoofer vertically in line with the monitor drivers to avoid any phase issues. Internet research informed me to avoid placing the sub in the middle of the room between the main monitors. After some listening tests, the subwoofer sounded most natural to the left (off centre)

The ADAM Audio Sub8 has an adjustable crossover pot that can be set between 50Hz - 150Hz. I applied some common sense here and set the crossover to just above 100Hz with the volume pot set to +6db as this was the area that the Sonarworks measurement showed to be lacking in my monitoring frequency response.

I ran another Sonarworks measurement with the subwoofer, the result showed that the 70Hz - 100Hz cut had been reinforced with the inclusion of the sub and that the correction curve was far less exaggerated than before.

I performed some listening tests using material that used to produce the flabby artefact sound caused by Sonarworks with my ADAM monitors. It had now completely gone from my monitoring. I was over the moon, but I thought to try one more thing. Could I get my monitoring to sound better if I got the Sonarworks correction to work less?

Out Came The Tape Measure

I found a free online speaker placement calculator at No Audio Phile. It's a very simple calculator that you can enter your studio dimensions into which provides monitor placement measurements recommendations with the following measurements for:

  • Space between speakers
  • Head to main wall
  • Speaker from main wall
  • Speaker from side wall

The placement of my monitors was roughly 5cm off compared to the calculator recommendations. I repositioned both the monitors to the recommended positions shown on the calculator, moved the subwoofer inline with the monitors and ran another Sonarworks Measurement...

The results showed the 70Hz to 100Hz problem had all but been completely resolved along with a slight improvement in the 1kHz range. Sonarworks Reference 4 and my monitors now didn't need to work so hard in the low end. Everything sounded fuller compared to the previous monitor position 5cm back. 

Below is a slideshow showing the 4 different measurements. See how each stage improved the physical monitor frequency response which then reduced the amount of Sonarworks correction and, to my ears, improved the overall feel and performance of my studio monitoring.

I am not an acoustics expert, scientist or mathematician. I am, at best, a mere musician who recognised a problem within my studio monitoring setup. I applied some good old-fashioned common sense to work out a solution to my honkey sounding system. To my ears, I feel I have succeeded in getting a monitoring setup that sounds open, flat and completely transparent. Initially, I wasn't sure if a subwoofer was going to work with Sonarworks Reference software but I can happily report that it does, and in my case, works rather well indeed.

If you are not happy with the performance of your monitors then do not hesitate to try different monitor positions, heights and distances from walls. The smallest of movements can often make the biggest of improvements in regards to the sound of your studio monitors.

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