Acoustics is a field that fascinates me. Both my dissertations on both my degrees were on acoustics. You might be thinking, “How come you didn’t get into that industry?”. Oh well, it’s a niche market and I wanted to have options.

My fascination with acoustics stems from my need to be able to work with music in a space that is balanced and whatever I create in there, translates well pretty much everywhere. As it was becoming increasingly difficult for me to work on any music in my study -which of course was minimally treated- I eventually decided to build a critical listening room (aka control room), that would allow me to work with some comfort, and I guess gain also some experience while doing that.

After clearing out piles of old stuff, I finally gained access to a space measuring 3.1m x 3.4m x 3.0m (L, W, H). If you've made it this far reading, you might be thinking, "Wow, those dimensions are far from ideal", and you're absolutely right; on a Bolt chart, they're practically off the charts!

To make matters worse, the materials in the room didn't help either. The two walls were solid concrete, part of the house's foundation, and even the floor was made of the same unyielding material. Moreover, I had to build a new wall to separate the studio from the staircase leading to the ground floor, and of course, adding a door was essential, but I'll delve into that part a little later.

The next logical step was to adjust my expectations. Here's how I prioritized my requirements:

1. Create a room that sounds better than my current study, even though it's only lightly treated for acoustics.

2. Seize this opportunity to learn valuable lessons from the entire design and construction process.

3. Keep the costs as low as possible since the return on this investment is bound to be uncertain.

In essence, my main goal was to achieve a level of comfort slightly higher than what I had at the moment while gaining valuable experience throughout the entire project. I saw it as a win-win situation, where I could improve my music-making environment and enhance my skills simultaneously.

Moving on to the next step, the flooring phase turned out to be one of the easier parts of the construction process. I decided to go with a laminate floor, which made the task relatively straightforward. Before laying down the flooring, I diligently swept the floor multiple times to ensure there was no trace of dust or debris. Once the floor was properly prepped, I covered it with a layer of soft viscoelastic material. That material didn’t play any role in the acoustics other than providing a soft foundation for the laminate floor. With that done, I completed the installation of the laminate floor.

At this point, the room began to take shape. It did have a slightly industrial vibe due to the raw concrete walls on two sides, but despite that, it represented a significant step forward in my project.

With the studio space finally in good shape, the next logical course of action was to conduct some measurements to assess the acoustic conditions of the "raw" room. These measurements would provide essential data to calculate the required amount of absorption and aid in the overall studio design.

To proceed with the measurements, I utilized my monitors, placing them on their stands. Employing a measuring microphone and a combination of REW (Room EQ Wizard) and Python for analysis, I gathered valuable data from the measurements. This data would serve as a crucial foundation for determining the optimal acoustic treatment needed to achieve the best possible sound quality within the studio space.

With all the essential data at my disposal, the next crucial step was to conceptualize the actual design of the room. The design process was divided into two main parts:

1. The diffuse field

2. The modal region

Starting with the easier part (a), I needed to determine the optimal reverberation time (RT60) suitable for the size of my room.

Referring to a paper by AES/EBU, with a volume of 31m³ and a surface area of about 60m², they recommended an optimal RT60 of 160ms. Moreover, they also mentioned an overall, minimum RT60 of 200ms. Therefore, my design objectives aimed at achieving an RT60 value anywhere within the range of 160 to 200ms. Striking the right balance in this range would be vital for creating a well-balanced and acoustically pleasing environment in my studio.

Indeed, treating the diffuse field was one of the more straightforward aspects of the design. I decided to go with simple porous materials like light, low-density, rock wool. Fortunately, this material had extensive documentation regarding its acoustic performance, making it easy to estimate the quantity required for my studio. I had to get this right beforehand because that would essentially define the performance of the absorbers for the modal region.

You wouldn’t want the total surface area of your treatment to exceed the surface area of your room, right? You understand what I am talking about, yes? 😛

The near-perfect cube shape of the room presented a significant challenge as it allowed at least two modes to almost coexist within the same "pitch" range. Despite being a weakness from the outset, this characteristic turned out to be advantageous in my design process. It allowed me to tackle two issues with a single solution, killing two birds with one stone, so to speak. Since the axial modes were closely spaced, I could efficiently treat all three modes with just one absorber, without the need for a broad bandwidth. This was a cost-effective and practical approach.

With the acoustic treatment for the modal region sorted, the next puzzle to solve was how to ensure the room had an excellent stereo image. Achieving a well-defined stereo image was crucial for accurate sound perception, especially during the mixing and mastering stages of music production. So, while addressing the modal issues, I simultaneously strategized on creating an optimal layout and placement of monitors and other acoustic elements for my design.

Our ability to echolocate relies on interpreting level and phase differences, and in the context of studio design, first reflections can be problematic. Ideally, I would have loved to implement a Reflection-Free Zone (RFZ) design, as it would provide optimal acoustic conditions. However, due to the limited size of the space, a complete RFZ was not feasible.

Nonetheless, I knew that the next best alternative was to create a design that effectively addressed the first three reflections. By strategically slanting walls and placing absorption and diffusion panels, I could significantly reduce the impact of these reflections. This approach would help me achieve a more controlled and accurate listening environment, reducing any unwanted coloration or comb filtering caused by early reflections. While it might not be a full RFZ, this design would still greatly enhance the overall acoustic performance of the studio and contribute to better mixing and monitoring capabilities.

Before proceeding with the design though, I had to figure out where my listening and monitor positions would be.

I opted for the monitors to be 7/10nths and the listening position 2/3rds from the front wall. The idea behind these positions was to have an even modal response (as much as it can be).

As mentioned earlier, my goal was to lead the first 3 reflections around me in order to enhance my stereo image. Doing so was easy thanks to Python. Using ray-tracing techniques I was able to generate a geometry that would take as little space as possible and the 3 first reflections would miss my listening position. Well, I ended up creating an RFZ in the shape of a sphere with an 80cm diameter. Considering the 3.1 meters of width, I’d say that I am ok with that.

At this point, the problem became an optimization problem. I had to balance performance, cost, and complexity. Not an easy task. I am not going to say too much about this process but I went through countless iterations for the LF absorbers and about 3 or 4 iterations for the design.

Both of these designs were rejected eventually.

One major challenge was the complexity and cost of construction. The initial 4-pair slanted wall design (RFZ-ish) proved impractical due to effort, material cost, and time constraints, leading to its abandonment. Instead, a more efficient 2-pair slanted walls design was adopted, yielding similar results.

Another critical challenge was deciding where to place the bulky LF absorbers. To maximize space, I utilized the entire ceiling as an absorber for the modes on the vertical axis, the left wall (concrete) for the modes on the horizontal/width axis, and the entire front side for the modes on the horizontal/length axis.

The front wall of the studio consists of 2 slanted walls with additional space behind them, serving dual purposes. The space serves to conceal ventilation pipes for the studio and a fireplace located on the back side of the wall. Moreover, this area is utilized to extend the low-end performance of the perforated (Helmholtz) absorbers.

In the photo provided, you can observe that the perforated panel is constructed using OSB plywood. On the back side of the panel, a layer of porous material is placed, covered with fabric to prevent stray fibers from circulating in the air.

The ceiling was designed in a similar fashion as the front wall. The ceiling was treated with plasterboard that was (painstakingly) perforated. The depth (air gap above) and perforation were designed in such a way that the whole surface will work as an absorber, but at the same time, while still retaining the desired level of absorption. I want to control the modal region, not eradicate it.

The top of the ceiling was covered in fabric, and above the fabric, a layer of porous material was placed. This design decision contributed to the effective absorption of sound energy in the studio space. It's worth noting that the building's original ceiling was composed of styrofoam, which was used as thermal insulation. While I didn't remove or alter the styrofoam, it was carefully considered and factored into the overall design process.

This was the point where things got complicated. Building the last element of my studio before starting the "cosmetic" work presented a challenge: taming the modes on the horizontal/width axis. Considering complexity and cost, treating only one wall out of the two made sense. This meant devising a different approach compared to the front wall and ceiling treatments.

I wanted to avoid the look of a perforated side wall, and the laborious process of drilling holes drove me to a brilliant idea – a limb membrane type of absorber. I used an aluminum frame for building plasterboard walls as my absorber frame, and the plasterboard as my mass for the limb membrane, creating practically a limb membrane absorber in the size of the whole wall. However, during performance measurements, I noticed slight over-absorption around 120Hz. Though tempted to go with it due to the clustered modes, I feared it might render everything thin and dull.

To address this, I calculated that adding a second layer of plasterboard would shift the resonant frequency down an octave (around 60Hz), which seemed promising. After putting up the first layer, the result was disappointing – indeed thin and dull due to excessive absorption. Implementing my contingency plan, I added a second layer, leading to a much-improved final result. 

Success.

To enhance the behavior of first reflections and optimize my stereo image, I incorporated diffusion into the studio design. I built a skyline-type diffuser, tuned to work in a range of 2kHz to 8kHz. The diffuser was placed precisely at the room's center. Its unique feature was diffusing in both horizontal and vertical planes, “breaking” any first reflections and diffusing them in multiple directions.

For the second part of the diffusion, I utilized a QRD diffuser, significantly larger, placed on the back wall. This diffuser was tuned to diffuse frequencies between 800Hz and 4kHz, and it was designed to work specifically on the horizontal plane.

The results were remarkable. The stereo image saw significant improvement as a result of these diffusion additions. Additionally, the annoying flutter echo between the two side walls nearly disappeared, further enhancing the overall sound quality and ensuring a well-controlled acoustic environment for my creative work.

Fortunately, I didn't require excessive absorption to treat the diffuse field. For the front wall, I incorporated a few porous absorbers covered in black fabric. Additionally, I hung four panels on the side walls to enhance the treatment. These panels effectively eliminated the flutter echo, achieving the desired results.

As a result of this treatment, the RT60 (reverberation time) for frequencies from 1kHz and onwards fell within the target range. The studio's acoustics were significantly improved, offering a well-balanced and controlled environment for my music production and listening experience.

The following audio samples were generated from the measurements that I took during the construction of the studio. For each stage, 2 measurements were taken. One for each monitor and the listening position. These IRs were compiled in a stereo file and then with the help of a convolution reverb, I was able to "simulate" the acoustic characteristics of the room. Note that what you hear is the raw room. There's no any other processing. After finishing the construction of the studio some corrective EQ was was applied to the monitor singal route, to further smooth out any "rough peaks" in my frequency response.