Creating a system you love shouldn't be difficult. The Acoustic Frontiers blog is here to help.
David Beck came to us wanting help with the acoustic design of his home theater. He specifically requested that the majority of the acoustic treatments be 'DIY-able' to save cost.
Acoustic Frontiers provided the following services: acoustic treatment design, baffle wall design, low frequency optimization (limited engagement), design of custom slat diffusers and bass traps, supply of engineered absorbers and diffusers from Auralex, Vicoustic and Acoustics First, provision of Sony 55ES projector.
We started out by determining the placement of the LCR speakers. We asked David to take measurements of his JTR Noesis speakers so we could understand their lateral off axis performance. It was apparent that the JTR Noesis speakers have very narrow dispersion, and so need to be toed in towards the seating area to prevent drop off in the high frequencies across the room. We designed a baffle wall with angled side wings to toe in the left and right slightly towards the center of the room.
Now that the speaker and listener positions were fixed the next task was to determine the acoustic treatment. We created an acoustical model of the room to determine predicted reverberation times (T60) across the mid and high frequencies without any treatment. The carpeting and chairs used in the room meant that we did not want to use too much purely absorptive treatment, otherwise the high frequencies would be excessively dead. From here we used ray tracing from each speaker location to the listener together with the speaker off axis performance data to understand the level and spectral balance of the early reflections relative to the direct sound. From this we determined the psychoacoustic effect [how listeners would perceive the sound] of each reflection. This analysis gave us the information we needed to design a suitable acoustic treatment scheme for the early reflection points in the room. We decided to specify two types of slat diffusers / absorbers at the side wall reflection points, cotton absorbers on the back wall LCR reflection points and kraft paper wrapped fiberglass absorbers on the ceiling.
Outside of the early reflection points we specified a combination of diffusers from Auralex, Acoustics First and Vicoustic. Most of these diffusers are hollow and so they provide an absorption peak in the upper modal range (150-300Hz). You can see the test data from a similar product that we use made by RPG, the Harmonix K. If you notice on the design we placed these up in the wall / ceiling corners...this was done because most room modes have a pressure peak in this location so it is a particularly effective place to put absorption. Secondly there is often a double bounce reflection from the upper wall / ceiling area which many people (and designers) miss in their acoustic treatment schemes.
Once the acoustic treatment scheme was completed we reran the reverberation time study and found a predicted steady 0.4s decay time from 250-4000Hz, right on point in our opinion for a larger home theater using narrow dispersion speakers. David did all the build out, and you'll see from the photos below that it looks great. All the acoustic treatments will be covered with a fabric stretch, so you won't see any of it!
Acoustic Frontiers designed the baffle wall to provide an optimal acoustical environment for the speakers and subwoofers. We included slots in the baffle wall and left the corners open to allow for large bass traps that were positioned behind the wall.
David's Theater, "The Savoy" was named AVS Forum Home Theater of The Month in June 2014. Here are some post-calibration measurements, showing the flatness of the frequency response and the absence of modal ringing.
The below extracted from e-mail correspondence with David:
"Hope all is well. Just checking in to see how you are doing and to tell you that I'm really enjoying my theater. It sounds amazing and people are in awe when they come over to watch a movie or see a demo or two."
"Don't know if you have read much of the feedback from the AVS Forum Get-To-Gether (GTG) that I held. Everyone was very impressed with the acoustics. Also had Jim Salk tell me that it's the best theater he's ever heard/experienced. Don't know if you know Jim but that's quite the compliment!"
We created a video explaining the home theater and acoustic treatment design process for The Savoy that aired at the AVS GTG (get together). Check it out!
If you still want to read more, check out the threads on AVS.
Nyal Mellor, Founder, Acoustic Frontiers
Nyal Mellor
Author