ROOM CASE STUDY

Room Treatment Report
Frank Oesterheld, CTS
GIK Acoustics

The Goal: The goal was simple: the take a bad room and turn it into a good one using a combination of good positioning and acoustic treatment. When I say, “bad”, I really mean “almost as bad as you can get”. As you can see by the dimensions listed above, the space is nearly square and while all the glass isn’t necessarily a bad thing from a low-end standpoint, it’s definitely a problem in the mid range and high end.

The Procedure: I took all the treatment out of my room then shot it for a baseline reading. After that I added acoustic treatment one area at a time, using well-established best practices and commercially available panels from GIK Acoustics. All panels utilized mineral wool with densities ranging from 48kg/m3-70kg/m3 depending on the thickness of the panel.

Room Shot 1:
No treatment. Note the 25dB null at 70Hz, the 14dB null at 100Hz, the resonance at 280Hz, and the 14dB trough from 700Hz to Decay times are too long across the board.

Room Shot 2:
Add GIK 244’s floor-to-ceiling in the back corners. The goal was to begin to stabilize the low end response in the room and to improve decay times in a general way.
All of the dips from 150Hz are improved by 2-4dB each. There is some smoothing in the 700Hz-1Khz trough and in the highs. Note the improvement in decay time.

Room Shot 3:
Add GIK 244’s floor to ceiling in the front corners and two GIK 242’s on the front wall to further soften the sub 250Hz range and to reduce decay times some more.
Got 1dB reduction in the 70Hz null and some more reduction in the 150-700Hz range. There is a good bit of smoothing from 1.2Khz to 4Khz. 6Khz to 20Khz is nearly flat. More broad improvement in decay time, but there is specific reduction at 80Hz.

Room Shot 4:
Add five Monster Bass traps to the back wall. Moved the listening position back 12”; moved the speakers 7” further apart. The point on this step was to take a serious bite out of the sub 200Hz issues. I also suspected that covering much of that glass would result in a good bit of high end smoothing. The move back was a calculated risk to see if I could move out of (or partially out of) the 70-80Hz modal issues; it paid off.
This one took 8dB off the 70Hz peak, took 2dB off the 80Hz peak, evened out the low midrange more and evened out the 700Hz-1Khz valley. Unfortunately there’s a new dip at 1.7Khz. Testing indicated that this was comb filtering caused by the console. The highs are still pretty even. There is more improvement in decay time especially at 40Hz and 80Hz.

Room Shot 5 (PLEASE NOTE THE CHANGE OF SCALE):
Add four GIK 244’s at the first and second reflection points, two GIK 244’s above the mix position and two 242’s just ahead of the firs reflection point. Moved the listening position back 6” more. I knew that moving back had produced a dramatic reduction in the 70-80Hz problems, so I decided to try moving back a bit more to see if I could reduce it further.
Huge improvement. The 44Hz peak was reduced by 2dB or so; the dips in the 50-100Hz range have improved by 6-8dB each. The biggest change is the radical smoothing from 100Hz-3.4Khz, though there is still some comb filtering from reflections off the console and a 15Khz dip to work on. Though decay times are still much more even than they were to start with, the move back into the room results in a longer decay time at 80Hz. 40Hz is still better than the first three waterfall plots.

End Result: The room is within 10dB of flat from 50Hz to 22Khz at 1/12 octave smoothing. The highest peak (80hz) is 85dB and the lowest dip (15Khz) is at 75dB. The rest of the room is within 8dB and the majority of it is within 6dB of flat. Note the stead reduction in decay time between 40Hz and 200Hz throughout the process, with the exception of the last waterfall dispay (note the 80Hz area). While the move back 18” into the room reaped a significant benefit in terms of frequency response, there was a trade off with respect to decay time.

Frank Oesterheld, CTS
GIK Acoustics
Room Design/Customer Support
www.gikacoustics.com