My company has finally given me the green light to transform a largish office/meeting room into an acoustically treated foley/sfx/voice/live instrument recording space. The space is located at the ass-end of the building so isolation is not an issue, only acoustic treatment. I posted the plans before over at recording.org and got some great feedback from knightfly (thanks again Steve) and would like to explore my proposed solutions even further before I go ahead and pull the trigger on the materials order.
So, here is the room:
North wall - Bass hangars behind acoustically transparant false wall
South wall - Array of diffusive elements
East wall - a pair of 4'x8' helmholtz resonators stacked either horizontally of vertically
West wall - 2 pairs of 4'x8' helmholtz resonators stacked either horizontally or vertically
I am possibly considering converting the stacked pairs of resonators into single cavities. Another alternative is to make each of the 6 resonators tuned to a specific frequency.
I just finished ripping out the industrial carpet flooring and replacing it with a wood-laminate floor:
And here are the calculated modes (full ceiling height is 12' 4" - acoustic tiles are hung at 8' 6"):
I have been testing my room with ETF (great software!) and have been gratified to see theory and math to very closely predict the results I have been getting:
I have made a fair number of measurements at different locations with different speaker placements and find that the above result is very representative of the frequency response I have been getting. This specific measurement was made with the speaker on the floor (tannoy active reveal) firing into the furthest north-east corner of the room and the microphone (AT4050 in omni mode, no bass cut) at head height in the south-west corner.
So here are my questions:
- Can I assume that the bass hangers will absorb modes below 100 Hz? That 70Hz spike shows up in every measurement I have made in this room and I am quite concerned about it. (I have ruled out a playback or mic resonance by measuring my personal office using the same techniques). I know that once I take care of the fundamentals, that all the harmonics will diminish as well, but this means that those traps have to soak up a lot of energy down in the nether regions and I am at a loss of how exactly to size these hangers and spec their material.
- Should I build broadband resonators or tuned resonators (high Q or low Q)? I might be over estimating the effect that using a wedge shaped air space has on a helmholtz resonator, but I do know that it broadens the curve. Would this be a problem when attempting to tackle the 104 Hz ringing I see? I would still like to keep splayed walls so this could be a big issue in the design if it would be better not to have a broadband helmholtz resonator.
- Should I tune all 6 of the proposed resonators to different frequencies? My intuition says that I should hit low and hard with the tuning and construction, but as I have learned already, acoustics can be quite counter-intuitive .
Scott Petersen