A while back we asked you to submit your studio design and build stories. Well, community member Artur Rakhmatulin has submitted his story, it took a lot longer than expected. In part 1 of a 3 part series, Artur walked us through the options, his study, and the theory behind his chosen design. In part 2, we look at the structure, the detail design and implementation of the floor, ceiling, interior walls, and the layered back wall. Over to you Artur...

Room Within A Room

The concept of my studio was based on a room inside another room approach, and in my case, a room in a heated basement.

The structure of the chamber was a cuboid with inner and outer walls, made ceiling and floor. The process of creating the main structure of the room was divided into the following steps...

• Installation of ceiling and floor wood beams for back wall layered bass trap;
• Installation of ceiling and floor wood beams for outer and inner walls;
• Installation of timber struts between ceiling and floor wood beams for stability;
• Placement of spanbond layer for exterior walls wood struts for isolation;
• Installation of 10 mm gypsum plasterboard as outer walls.

The materials that I used during this process were the following...

Isolation To The Existing Structure

In order to minimise acoustic transmission, all screw connections between 120x50 mm wood beams and basement floor and ceiling were made through rubber gaskets.

For me, the main task of creating the main structure was to make all construction slightly movable so thick waves of low frequencies will lose some energy by moving the overall room and not just perforated panels. I had an idea of using damping dowels, but it added the necessity of modelling the whole physics, so I gave it a second thought and went with a simple combination of thin screws and wood dowels.

Another thing I kept in mind was that the room and studio monitors should be decoupled. I needed to ensure minimal interconnections through the floor between the speakers stands and overall structure and by lifting wood beams I created detached points of contact between surfaces. As I understood the process behind this approach, by decoupling the room and the speakers I minimised the room resonances that could occur with speaker hitting the resonant frequency and transmitting the vibrations. The option I went with was plain and straightforward - every connection between surfaces and materials were made with rubber gaskets. In my mind, I had a concept of creating multiple points of energy loss so that it would add to the overall absorption of the room. Then I spent some time figuring out what rubber I should use.

I chose the thickness and density of rubber and spacing between gaskets experimentally so that the wood rails would have some motion but the overall structure would have enough stability not to bury its creator under the rubble. If the rubber was too dense then there would be no compression of rubber, it’s stiffness will transmit vibrations. On the other hand, if the rubber was too soft then there would be a lot of compression, and the weight-driven increase in density would transmit vibrations.

As the studio was situated in the corner of a basement, the gap between basement walls and studio walls were around 15-20 cm.

I see it as an additional absorption element as it changes the medium one more time before a sound reaches the massive concrete walls. Again, I understand that it prevents the transmission between the surfaces. Also, I wanted to leave enough space for air to travel between the walls, reducing the humidity and spreading the heated air across the basement. The only thing I didn’t want for sure was some black mould spreading in the corner of the room.

There were heat radiators in the basement and it wasn’t an option to remove them, on the contrary, they were used to warm up the outer walls of the studio and to shift back the point of freezing, helping to reach the comfortable temperature in the studio more easily. Certainly, there were no physical connections between the heat radiators and any element of the studio.

Interior Walls

After the main structure of the studio was created, I moved onto the inner space which I divided into the following sections:

• Layered back wall
• Side walls
• Front wall

One of the main things to do was to perforate plywood according to technical project. To speed up the process, I stacked several plywood panels and perforated them with the drill. In my area, I didn’t have an option to purchase pre-perforated wood because in order to get it I needed to order an industrial amount which in my case wasn’t an option.

Although whilst searching the market I did find different sorts of perforated plasterboard panels and perforated plywood with different parameters than those I had calculated during my research. So after a brief analysis, I chose to go with my parameters as the whole concept of the room was based on my calculations.

It was another point when I needed to choose from two paths - to go with perfectly prepared and standardised industrial material or go with a self-made approach, based on the knowledge that I had gained during several months of reading.

And the moment I started comparing two ways I realised that there was only one path. What’s the point of doing something if I don’t trust my own judgment?

That said, having done it I must confess that I will never drill another hole in my life. It took me several weeks to drill over 100,000 holes, some spare drill bits and a lot of nerves.

When doing monotonous work, it’s important to split work into even parts and take regular breaks. After you reach a condition when you are becoming angry after a minor failure then it’s time to leave your work as it is and switch to something else at least for several hours.
This approach helped me survive the drilling trial and saved me from madness.

After all the perforated plywood panels had been prepared, mineral wool and spanbond were delivered and stacked in the basement, I took some time to equip the building area with necessary safety measures. For myself, I used protective goggles, air-purifying respirator, safety gloves and protective clothing. All the above was necessary to keep dust, particles and other debris from harming the nearby premises and people involved in the building process.

Layered Back Wall

Due to the height of the ceiling, I found it expedient to create a large layered bass trap as the back wall. The structure of a back wall was a layered sandwich made of mineral wool and perforated plywood one after another in order to get different resonant frequencies as shown in part 1. A 50mm air gap between every layer of plywood and porous absorber was preserved to increase absorption efficiency.

Perforated plywood featured the following indexes (from outer to inner walls):

• Hole diameter - 7 mm, Spacing - 120 mm;
• Hole diameter - 3 mm, Spacing - 40 mm;
• Hole diameter - 5 mm, Spacing - 30 mm;
• Hole diameter - 10 mm, Spacing - 30 mm.

For inexpediency, I didn’t use spanbond between the inner layers of the back wall, but I did use it with the wall that was inside the room. The depth of the back wall was nearly a meter of differentiated layers of propagation media, and that was when the proper material logistics showed themselves. The materials were placed where they were easily accessible, and it saved me a lot of energy during the building process.

Stacking layers of mineral wool on top of each other was rather an easy job but I found out that it was much better to build up mineral wool horizontally. When I put batts of mineral wool together horizontally they were stuck between the wood bars and perforated plywood panels so it was a natural mounting.

After each building step, I used an industrial vacuum cleaner not only to get rid of small particles and dust but to preserve the overall general sanitary condition of the area. Although mineral wool is relatively safe for health, especially when isolated, long-term exposure to this material can cause lung disease similar to asbestosis.

As you can see in the image above a cavity between two wood bars hasn’t been filled with mineral wool in order to preserve air gap between mineral wool and perforated plywood that would be mounted afterwards. As this is a massive bass trap, alternating different types of propagation media increases the low frequencies absorption capabilities.

To understand the influence of air gap I spent time comparing the graphs I got during the modelling process and reading through the knowledge sources. A few of them clearly stated that the larger the air gap you have, the more effective actual absorption is. At some point, I found out that an absorber consisting of 50% of mineral wool and 50% of air had the same absorption as 100% mineral wool absorber did. I didn't want to experiment so I chose to leave a 50 mm air gap in every element of the room.

To get even pieces of spanbond while cutting I placed a table inside the construction, and then with a straight metal strip and a knife, I prepared enough spanbond sheets for each part of my work. This table was also used to cut mineral wool panels where they were smaller than full-sized mineral wool panels.

It was important to keep perforated plywood panels from touching the floor or the ceiling. During the building process, I totally understood what I needed to control when I was constructing the room. The knowledge I gained earlier helped me highlight the areas I needed to pay particular attention to. In fact, even when I didn’t know the exact solution for the particular task I usually came up with my own solution that was based on the overall principles of sound absorption.

Side Walls

After the back wall had been created, I started building inner walls using the same approach, only this time it was one layer of perforated plywood and mineral wool. Unlike the layers of back wall, this time air gap was between the mineral wool layer and gypsum plasterboard wall.

The idea behind this approach was to let plasterboard vibrate freely without the applied pressure of mineral wool weight. I saw gypsum plasterboard as a big membrane between the room and basement walls. For me, it was needed in order to increase the efficiency of low-frequency absorption.

The plywood strongly reflects high-frequency sounds so I planned to cover most of the surface area with acoustic foam. After some time I saw the absorption process as the low pass filter that gradually reduces the frequency until it comes to the lowest range of frequency response of the speaker (which in my case was 32 Hz). So the first frequencies that got absorbed were the high frequencies, then the mids and at the end were the lows. As the low frequency carries a lot of energy it needs to hit a lot of mass in order to be neutralised effectively. To get an even frequency response, for inner walls I used perforated plywood with the broad range of absorption.

The index of perforated plywood was the following:

• Hole diameter - 10 mm,
• Spacing - 30 mm.

The image above shows the section of the wall from exterior to interior. I used vertical wood struts as the backbone of the wall so there would be a mounting surface for plywood and gypsum plasterboard. Natural mounting of mineral wool between the two surfaces found its place here as well with the mineral wool mats fixed between the vertical wood struts.
In fact, it wasn’t hard to mount mineral wool sheets between the struts as the wall depth was the same as the thickness of eight sheets of mineral wool stacked together as you can see in these images...

Again, careful calculations and preservation of dimensions during the initial building process left me with a predictable result.

An Interim Listening Test

After several days of work, I found out that the building process of the inner walls was coming to an end. There were only front corners that needed to be done and after that, I could begin creating the ceiling. Though inners walls were not finished and in front of the room there were places with exposed mineral wool and spanbond, I brought down my old KRK speakers to the room and placed them where I expected to put the speaker stands to see the progress of my activities and I hoped to hear at least some minor results.

I heard separated bass as the speakers were too far away from each other, I heard flutter echo as the ceiling and the floor were not treated but I also heard the thing that inspired me a lot - I heard the stereo field, or it’s better to say I saw it.

During that listening test, I felt the same as I felt during my tour to the studio - sounds floating in the air, precisely situated in the space between the monitors. For me, it was like looking several pages ahead and knowing that I would get stunning results.

At that moment, although there was a long road to go to get to the final point, in terms of feelings it was like having a look into the future when the studio would be finished and I would be able to reach my target destination. I was a little tired of monotonous work but after that point, I increased my efforts to finish the project as after that day I saw the end result more clearly in my head.

The Ceiling

The next important but difficult part of studio creation process was the building of a ceiling – it has to be safe and efficient. The cap construction had to hold the weight of several dozens of mineral wool mats and several perforated plywood panels, but it also shouldn’t interfere with the acoustic treatment.

In order to achieve this, the ceiling construction was based on the frame made with 70x50 mm wood rails with lap joint connection between them. This wood frame was also connected to inner walls and ceiling.

I didn’t go with an additional gypsum plasterboard ceiling because after the waves propagate through the perforated plywood, mineral wool panels and air gap, they hit basement ceiling. I’ve wanted to leave as much space for the ceiling absorption as possible and gypsum plasterboard with additional air gap and mounting would’ve have used a lot of it.

To ensure the mounting reliability of centre wood rail to the ceiling, I pulled metal wire through the wood rail and in order to reduce transmitted vibration wire was wrapped in rubber in points of coupling.

To speed up the construction process I went with coarse woodworking so the frame was not polished but the joint connections were cut carefully. After the frame was set in place I began mounting spanbond and perforated plywood panels filling the resulting cavity with mineral wool. As it was a very low gap between the basement ceiling and wood frame (~35 cm) there were no other options.

I approached the process of creating ceiling sections by two perforated panels at a time, otherwise, it would be impossible for me to reach far corners of ceiling sections.

It was interesting to see how differently I reacted to different work conditions. The same job that I did at 90 degrees became more time consuming and jumpy the moment I began doing it at 180 degrees. Also, that was the time when I intensively used protection equipment - falling wood and mineral wool particles could damage my eyes.

Frequent rests during the process made it quite calm and without haste. Although, there was a tricky moment when I was putting mineral wool batts between the perforated plywood and the basement ceiling. The height between those two surfaces was very low for me to stack mineral wool panels comfortably and I had the feeling of a person stuck in a very small space. But it’s funny that when I was layering the acoustic material in quite uncomfortable conditions, the only thing I had in mind was that I needed to do it the best possible way I can. Because right at that moment I was bringing my dream to life.

At that moment I was driven by my desire to obtain a necessary tool for my future aural adventures. No matter how unpleasant the work looked to me, I understood that it was one of the last barriers between me and my goal. As I find it, our deepest wishes and desires can make us do nearly impossible things.

With each step, I was driving myself towards the end of that interesting experience. The final touches I made to the ceiling were matching plywood panels with angled front walls and adding an air duct. After that, I began cleaning up the space and started preparing the room for the final massive event in the building process - the creation of a floating floor.

The Floor

After all the messy work with walls and ceiling was done, I cleaned up the floor area and began creating floor structure.

The floor was fully isolated from the main studio structure, the contact between floor structure and basement floor was made through rubber gaskets, so basically it was a floating floor.

I used a parquet flooring as it was both practical and esthetical. In order to get it working in the acoustic absorption field I used mineral wool and formed a very gentle arc so that the floor moves down 1–2 mm when you step on it (it’s like playing ball on the carpet – it doesn’t bounce well). To ensure the isolation of the room from humidity and possible water leaks the basement floor was first covered with several layers of hydro-protection materials and a generous amount of polyethene.

Another step for me to take that day was spreading the cable canals under the floor so that any connection between the equipment would be conducted safely without me flipping over them or ripping audio jacks from the sockets. In order to ensure the simplicity of drawing the cable through the cable canals, I put several metal broaches inside every channel.

Even if I’ll put some cables inside the tubes I will still have an opportunity to add another cable sometime later. Of course, I remembered that it was not a good idea to place cable canals for audio and data transmission in parallel to electricity cables. So to avoid the necessity of buying ultra shielded cables in the future I located power cable canals at different places of the room.

For me, the room was dead enough so I chose not to place any soft material on the floor. Nevertheless, it’s the easiest thing that can be done any time I want - I’ll just put everything away for a while, lay a carpet and then bring everything in.

Summary - The Studio Construction

The overall height of the studio with ceiling and floor comes up to 2,2 m, but I felt comfortable with it as I have a height of 1,78 m. Concluding the information written above, I’d like to consolidate the studio construction principles. This table contains the generalised schematics for main absorption mechanisms of the studio.

In fact, the whole studio consists of massive blocks of mineral wool placed behind perforated plywood panels. The configuration of holes in the plywood and amounts of mineral wool needed for the target absorption were calculated by me during the research phase so all work was straight and predictable. Some minor questions were raised during the building process but with only the basic knowledge and understanding I got from the books I found I could easily solve them.

In terms of building complexity, the process was not very hard and didn’t contain any high specialised qualifications. The only thing I paid attention to where the dimensions and sizes precision of building materials and acoustic treatments. During the finishing phase, I found out that I had overestimated the amount of mineral wool needed for treatment. It was not critical as half of that spare amount was used on additional absorption and the other half was used for several house needs. Nevertheless, work tidiness always saved me some money and time.

Part 3

In the last of this 3 part series, we will be looking at the additional treatment including broadband porous absorbers, doors, air conditioning, ventilation, power supply, lighting, studio equipment, and speaker stands.