This month I'm spending two days a week in a more formal setting learning about architectural acoustics. It's just for a brief period and is hopefully giving me a sense of what working in acoustics is all about. It's no surprise that like many people I know in the tech/music/electronics crossover world, I'm interested in the whole picture. Not simply wondering about the DAW, or the microphone, or the song for that matter that you might be recording, but also the room - what's on the walls, how is the shape of the space you're in becoming literally part of your instrument? Or, why does it seem sometimes like I can hear the music from the outdoor concert "better" when I'm further away? Or, why do those cheap baffles I helped a friend install years ago, not actually work at all, but we thought we heard a difference.
While designing recording studios, listening rooms and performance halls, or even taking into account the effects of psychoacoustics in these spaces, is certainly part of architectural acoustics, a lot of what goes on (especially in residential acoustics) seems to be more in the arena of noise abatement - controlling, restricting, and decoupling unwanted noises. And though this might seem somewhat less interesting (it's possible it is, like I said I'm totally new to this) there are certainly many interesting factors that go into the design process in residential acoustics. In addition to the architectural considerations like aesthetics, design and construction feasibility, looking at use cases for a space and weighing cost vs. efficacy, architectural acousticians look at things like sound transmission classes, vibration analysis, air flow, reflections and absorptions and resonances to name a few, and figure out how all of these things affect and become effected by the architectural considerations.
Like most engineering this involves lots of modeling - physical, numerical, even aural, but mostly just numerical, which means spreadsheets. Lots of spreadsheets. MATLAB is big in this world (and I'm excited to start learning it), but when you're down and dirty there's always google docs!
One of the more important factors in understanding a room's acoustics is looking at it's reverberant qualities: how sounds linger after whatever's making the sound, stops. And which frequencies in particular linger, and for how long. This boils down into what is known as RT-60 - how long it takes for the reflections of the direct sound to drop by 60db. There are papers on papers about which algorithms best model this acoustic principal and in what situations the Sabine, Eyring, or Fitzroy equations are better suited. All of these equations look at the volume and surface areas in a room and what the absorptive properties are of these surfaces at a range of frequencies (125Hz-4KHz for Sabine). So far I've only managed to eek out a sheet for the RT-60 of the Sabine equation in my free time, but feel free to take a peek at it and play around with it.
Hopefully more reflections, comments on my month to come. I'm still hoping to roll the NYC impulse responses from earlier this month into some Web Audio API concoction and loop all of these things together, that's the idea, right?
Soon :)