Stereo, that's one amazing looking room! How did you select the company/ designer? What were your design goals?
Yes, choice of the acoustic company was a long process. I always take a lot of time before choosing equipment: listen a lot, have a look at the design philosophy. I have to be pleased both rationally and emotionally. It was the same for the speakers: I flied all over the world to hear more than 150 speakers in good condition before choosing Magico. The room and Magico speakers are the only things set for the long term, all upstream components can change quite a lot.
On the room itself, I originally was thinking about Rives (as the most well known name), but a few elements of their room philosophy didn't 100% convinced me, so I investigated further. I decided to go deeper into learning acoustic and spent also significant time reading specialized forums for more experience from others. SMT, a Swedish acoustic company, captured my attention for several reasons:
? I heard of at least 4 cases of Rives rooms in US which were destroyed and rebuilt by SMT
? Their acoustic philosophy made sense to me
? A few audio industry insiders that I trust did tell me that the best room they have ever heard was built by SMT
Of course, choosing a Swedish company with little Asian experience to build a level 3 room in Taiwan sounded like a difficult project. But my interest was excited enough for me to investigate further. So I got on a plane, and flied to Stockholm to meet with Matts Odemalm, SMT owner, and to listen to some of the rooms he built in Sweden. I was convinced by what I heard, and what he told me on his design philosophy , so I decided to go with him.
Small room acoustic is trying to address different phenomenon based on frequencies:
Below around 200Hz, we are in the domain of wave acoustic: sound is omnidirectional, room acoustic is dominated by room mode and resonances at very specific frequencies. To address these resonances, I have used a set of 31 Helmholtz resonators of different sizes, with the objective to get a linear frequency response in the bass and a regular, short decay. The advantage of Helmholtz resonators is that they are very efficient at absorbing a specific frequency and they can get much lower than fiberglass (provided you don't want to use a few meter deep of fiberglass). Additionally, the Q factor (sharpness of the resonance peak of a Helmholtz resonator can be adjusted by adding absorption material in the resonator. In my case, I use a combination of 24 SMT V4 resonator, 3 custom made V6, one 4m3 resonator in a corridor (with a controlled opening) behind my listening position, and 3 large resonators in the ceiling (one of them being large band). See the effect on the decay. This pic is before tuning of the resonators, check my original post for decay after treatment:
Above the transition frequency, we are in the domain of “geometric acoustics”. Here my acoustic treatment is mainly diffusion. All walls and ceiling are treated with 67 diffusers: S-Wings (ceiling), V-wings, flower wings and scattering pillars (walls), transparent wings (front). Basically, 70% of walls and ceiling surface is covered by diffusers. SMT’s new family of wings diffusers are unique in performance – they are the main reason why I chose SMT as project lead for my room. Unlike classical diffusers which require 2-3meter distance to be effective, they work extremely well even when at a distance of only 50cm. In my room, I am sitting 60cm from backwall. Additionally, when used to treat full walls, the small space between the modules also works as a Helmholtz resonator in the 125-250Hz frequency band. Diffusers have low absorption coefficient, around 0.15-0.25, keeping the room lively.
The objective of this extensive treatment with diffusers is to breakup reflections, and to spread out the broadband energy in time. Reflections are delayed by at least 6msec (which is the minimum required ot avoid coloration). Listener experiences a “lawn of reflections”. Leveraging precedence effect, this spreading of energy over time gives to the brain enough time to overcome the masking effect of strong transient: it is like if our brain has an "time integration window", the multiple reflections from diffusers are heard as a single signal with the direct sound. The tones are richer and the listening room acoustic disappears to let the listener hear all subtleties of the recording acoustic.
The periphery of ceiling is treated with variable level of absorption, with the objective to get a constant decay time of 0.35-0.39sec across frequencies