PDX Studio : Acoustic Treatment

In this week’s update, we’ll look at the acoustical treatments being applied to the control room and tracking room, including bass traps, absorbers and diffusors (oh my!).

Before digging into the work being done in the studio, I’m going to take a slight digression into soundproofing vs. sound treatment to help explain why we’ve done some of the things I’m highlighting in these blog posts.

SOMETHING IN THE AIR, TONIGHT…

Sound travels through air very easily. That means, if we can seal a space airtight, we will block a lot of sound. This is easily demonstrated by opening and closing a car window or the window to your house. The sound reaching your ear is drastically reduced with the window closed. In fact, most other means of blocking sound are rendered useless if you have air gaps between you and the sound you wish to block. So, we first made sure all of the joints in the studio walls were caulked air-tight and then installed our fancy air-tight doors to seal the openings.

However, even with a window closed, you still hear some sound from the outside. How can this be if there is an airtight seal? Most of the sound is reflected away, but some of it causes the materials around you to vibrate and create new sound waves on your side. Heavier materials are harder to move and transmit less sound than lighter materials.  That is why we tripled up the layers of drywall in the studio. We also installed resilient channel spacers to the studs to reduce the amount of contact between the drywall and the studs to further reduce the amount of transmitted sound.

What I described above is what we mean by soundproofing – the process of preventing sound from moving between two spaces by controlling direct sound traveling through air, and minimizing transmitted sound through materials.

I SAID, CAN WE HAVE THE CHECK, PLEASE!!!

Soundproofing isn’t the end of the acoustic treatment story. Once we’ve controlled sound moving between spaces, we need to control the sound within each space. If sound can’t move through the air around a material, it mostly bounces off of it. Since we now have air-tight rooms, we’ve created a lot of bouncing sound waves! You may have experienced this phenomenon in a restaurant without any acoustic treatment. The sounds of the kitchen, customers and music all crescendo into a mind-numbing din making it hard to focus on any one sound. Since it’s hard to hear conversations, people speak more loudly, adding to the racket. Business may do this on purpose to make the place sound “alive”, or to save money on acoustic treatment. We call these bouncing sound waves reverberation and we can describe how “alive” a room is by measuring the time it takes sounds created in the room to fall off to a certain level.

We use two primary techniques to control reverberation : diffusion and absorption. Diffusors are uneven hard surfaces that reflect sound in multiple directions to reduce resonances, or build-up, between parallel surfaces. Absorbers are soft materials that allow sound to pass through them and reduce the intensity of the sound by absorbing some of the sound energy, converting it into heat. Most soft materials absorb higher frequency sounds and you probably notice how sound behaves differently in rooms with carpeting versus tile floors or a gymnasium versus a movie theatre. Low frequency sounds are harder to absorb because of their longer wavelength and high energy. You may have noticed that you hear the bass sounds of your neighbors TV or stereo much more than the treble. You are hearing the low frequency sounds that were not absorbed by their room.

What I described in this section, controlling reverberation within a room, is often termed acoustic treatment and is the subject of our construction update below!

FIRST BASS

The first thing the team from Brett Acoustics tackled was the bass trap at the rear of the control room.  This special wall configuration creates an air channel where bass frequencies can go to die – surrounded by soft white clouds of sound absorbing fiberglass.  It was done so quickly I only got a couple photos:

SLAT-FUTURE!

One of the most impressive elements of the control room acoustic treatment is the futuristic “Slatfuser” diffusor on the rear wall.  The undulating pattern of wood slats follows a prime number pattern to create an even dispersion of sound.

slatfusor.jpg

THESE WALLS

Before being hidden behind our acoustical fabric covering, the walls were covered with 2″ of 705 mineral wool and another mathematical marvel, the BAD Panel.  The BAD Panel, along with the Slatfuser, were designed with acoustician Peter D’Antonio of RPG Acoustical Systems.  Like the Slatfuser, the BAD Panel uses a mathematical sequence to create a pattern of holes that create a diffusor that allows some sound to move through it to the absorptive mineral wool behind.

IN THE CLOUDS

Rounding out the control room treatments are the acoustical “clouds” in the ceiling.  This is a form of drop-ceiling with fabric covered mineral wool.  In this configuration, sound goes up through the panel, reflects off the hard ceiling, and comes back down through the absorptive material, hitting it twice for maximum effectiveness.

DECISIONS, DECISIONS…

The tracking room receives many of the same acoustical treatments including the BAD Panel wall system and floating clouds.  It also sees the introduction of the Brett Acoustics “Multifusor” system, allowing control over the amount of diffusion v. absorption with reversible wall panels.

multi-diffusemulti-absorb

Well, that’s a wrap for this update.  Stay tuned for more progress!

Related Posts

PDX Studio : Acoustic Treatment (4/30/2019) - Acoustic treatments going in at King's Hill Sound PDX. See what all the diffusion is about!
PDX Studio : Floors & Doors (4/16/2019) - This week, we’ll look at the installation of our soundproof doors from IAC Acoustics and the walnut flooring.
PDX Studio : Building the barricade… (4/9/2019) - We’ve had a pause in updates but work has continued on through the winter albeit a bit slower as the attention of the crew returned to the main house above the studio. We’re in the final stages now and I wanted to catch this thread up with progress since the …
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