Introduction

The Aim

The aim of the studio was to be able to both rehearse and eventually record a five-piece rock band inside the space. Thus it needed to serve as a dual purpose room. For this reason, I chose a single room design  instead of the more classical Live Room + Control Room setup as this would have taken away valuable rehearsal space.

The Existing Garage

The existing building was a large double garage, built on an isolated concrete slab. It was constructed from a single skin of blockwork, clad in wood and tiled. The front right hand corner had been made into a wood storage shed (as seen below), thus creating a cut-out into the available space .

The Design Plan

After a significant amount of time spent researching soundproofing solutions, one principle that kept coming up was the idea of a room within a room. This allows for extremely high levels of acoustic isolation by creating a Mass - Air - Mass system, with the air gap aiming to reduce the transference of resonance between the inner mass (the inner wall) and the outer mass (the outer wall), thus minimising the escape of sound. 

I won't go into much detail about the physics of acoustics throughout this site as there is already plenty of information out there (this article by Sound on Sound is a great place to start). Having said this, the fundamental requirements for acoustic isolation can be summarised simply as follows:

• Mass
• Airtight construction
• Minimise flanking paths (i.e. physical connections between the inner and outer rooms)

 The ideal way to achieve this would have been by creating a completely isolated inner skin using as dense a material as possible. Although an inner skin of blockwork would have been perfect in terms of mass, it would have been very difficult to isolate the two skins as they would have both sat on the same concrete slab. This, compounded with the difficulty of blockwork construction (for a complete construction novice), resulted in the choice of stud walls lined with plasterboard skin.

To maximise acoustic isolation, I decided to use two layers of acoustic grade plasterboard, with a compound called Green Glue sandwiched in between. This product creates a "constrained mass damping" layer, increasing the acoustic isolation by minimising the transmission of sound vibration between the two layers. It does this by transforming some of the incident sound energy into heat.

Thus the plan became to create a free standing inner stud-wall structure, isolated from the concrete slab by using some form of neoprene blocks, and complete with self supporting roof rafters that would need to bear the weight of two layers of acoustic grade plasterboard. The depth of the stud walls would be filled with insulation in order to minimise resonance in the air gap between the inner and outer structures.

In order to help visualise this construction (and being an engineer), I created "to scale" 3D CAD plans  of the existing garage, as seen here:

Building a Workbench

 After I had decided to use stud wall, it became clear that there would be a large amount of timber involved in the construction. Thus, it became necessary to build a workbench that could be used to hold a mitre saw, to speed up the process of cutting the pieces of timber. The tools that were used in this project are all detailed under the Tools tab, and will be discussed in a subsequent post, but for anyone embarking on a similar project, a Mitre saw is a must have as it allows for fast, precise, repeatable cuts - crucial for stud wall construction.

The bench was constructed out of off-cuts of 2by4 (more on UK wood sizes here) that were readily available and followed the design found here. The end result is shown below: this bench lasted the entire project and proved invaluable at every stage.

Purchasing Tools

 As I only had limited basic tools available for the build, the first step was to purchase the required equipment. Although this was done in stages (as and when they were required) throughout the project - the initial purchases involved the below, which were essential to get started with. A full list of tools can be found under the Tools page.

The initial purchases included the following:

• PPE - including gloves, mask, eye protection, ear defenders.
• Mitre saw - invaluable for fast, repeated cuts of timber 
• SDS hammer drill - required for drilling into masonry blockwork
• Toolbelt - vital to working faster and/or at heights, an absolute must!
• Wood screws - mostly 5x80mm for joining 2by4 timbers
• Set square - for efficient framing
• Clamps - for holding pieces together while framing
• Wet and dry shop vac - used everyday to keep dust/sawdust levels in the garage manageable
• Spirit level set - crucial for making things true/plumb/square
• Angle grinder - for cutting hardier materials (masonry, metal etc)

Strengthening the Existing Structure

As part of the build, significant effort was put into reinforcing the existing building shell. Because of my plan to add a false roof to the underside of the timber rafters, I had to be sure the rafters, (and the walls!) would take the additional weight. In order to best explain this, here's a closeup of the rafter structure where the roof meets the wall just above the window:

Windows Pt 1 - Exterior Windows

 The next step in soundproofing the garage was to address one of the major weaknesses - the window. As any soundproofing article will tell you, ideally the room should have no windows at all as this will inevitably be more soundproof - but a closed box with no natural light doesn't make for a very comfortable and productive atmosphere, so for me, the one existing window was essential.

 Fortunately, the garage already had double glazed windows, so this provided some level of acoustic isolation, but this was nowhere near enough. These windows also opened, which meant that they weren't sealed completely. Here is a picture of the existing window from the outside:

Although there is lots of information online on soundproofing windows, in general these refer to internal windows between the control room and live room. As I was dealing with an external window, I had to come up with a slightly different construction strategy. 

Load Calculations

 Checking the load capacity of the existing rafters

The main worry I had about the studio build as a whole was on how to ensure that the existing ceiling framework would be able to bear the additional "double plasterboard skin" false ceiling that I was going to install on it. Clearly, it was pretty imperative for this not to collapse under the additional weight...

Being an engineer, I wanted to do some calculations myself, rather than calling in a professional structural engineer which would have been very costly. Helpfully, I was told about a piece of software called The Timber Beam Calculator, which does all the calculations for you, instead of having to spend hours researching/remembering all the various formulas. 

The calculator that I used was the "Ceiling Joist Calculator". Here I inputted the clear span, the joist spacing, the timber grade (C16 or C24, normally printed on the wood itself), and the specific dead load that represented the plasterboard that would be hanging from the ceiling. I won't tell you what my values were as each situation is different, and I wouldn't want someone to just copy mine! However, the process for the calculations is described below.

Rafter Collars

 Parts of this article are fairly specific to my exact building, but if you have a similar blockwork construction, or similar rafter arrangement then this will be very useful for you

As part of maximising the internal space in the room, I decided that we would need to cut back one of the block walls at the back of the room, pictured below, just to the right of the red cannister. Although the space loss seems minimal, I was reasoning that by the time we had built our internal room around the protruding wall, leaving the ~30cm air gap that we planned for, we would lose quite a lot of valuable space. 

Stud Frame

 Now we come to the first stage of actually constructing the inner room. All the steps so far have been alterations to the existing garage shell - and although the removal of the purlin hadn't been completed yet, I decided to start on the framework at this stage to avoid delaying the build any further. 

To do this, I opted to make the framework in 2.4m sections (of 2by4), so that I could manoeuvre them around by myself, and also so that I could move them out of the way if necessary. Then I also needed some smaller sections to fill gaps of less than 2.4m. Because of the heavy load expected on the stud wall (due to the double layer plasterboard ceiling), I chose to have my studs at 40cm centres, i.e. the centres of the studs were 40 cm apart from each other.

To begin with, I made a simple box shape from lengths of 2by4 , and then used a mock up of a rafter joint (circled in red in the image below) to work out the height that the upright studs would need to be in order to give a 5cm air gap between the top of the rafter and the future outer room ceiling. As 2by4 is almost 5cm in thickness, I used a piece of 2by4 fixed on top of the rafter segment to represent 5cm air gap as you can see in the circle. After several attempts at designing the correct mock rafter piece (you can see the one in the image it labelled 'E', but the final one was 'J'...), I finally worked out that my upright stud height should be 175.5cm:

Power

 From fairly early on in the project, I knew that having sufficient power to the studio was going to be a major requirement. Given how much musical equipment we were planning on installing (amps, desk, pedals, monitors, pa, etc.), it was crucial to have sufficient electrical sockets to be able to plug things in in every corner of the studio. I also wanted sufficient lighting, and an electrical connection for the ventilation system, which will be discussed in detail further on.

After getting hold of an electrician (Charlie) to come and give us a quote, he explained that there would need to be two sessions or "Fixes". In the first fix, he would come and install all the necessary wiring, as well as the new circuit breakers and connect us up to the main house. The second fix would then be to install all the actual electrical sockets and lights - once the inner room was completely plaster boarded. He quoted us for three days work - one day first fix and two days second fix (this would later be condensed to one day with an assistant).

On the first visit, I gave Charlie the following plan to lay out my requirements:

Ventilation: Acoustic Baffle Boxes Pt 1 - The Theory

 One of the key aspects of my studio plan was trying to achieve a room that was as airtight as possible, in order to maximise the acoustic isolation. This meant sealing up any gaps or cracks in all of the different wall layers. The issue with having an air tight room, however, is pretty obvious - the people inside still need to breathe! 

Given that I was designing the room to accommodate a five-person band, potentially in the summer heat, there needed to be fairly significant ventilation. Therefore, I planned to use a powerful extractor fan on an air outtake, and a passive air intake.

 Clearly, I didn't want to just cut a large hole all the way through my air-tight layers, effectively compromising all my soundproofing efforts. This is where the acoustic baffle boxes came in: these would force the air to pass down a piece of flexible ducting, snaking through a series of wooden baffles. The direct path for sound to follow from entrance to exit would therefore be blocked by the baffles, and at each reflection the sound leaving the ducting would lose intensity due to rockwool insulation filling the box. A heavy plasterboard lining would also minimise the amount of sound leaking into/out of the box. The diagram below shows the concept:

Ventilation: Acoustic Baffle Boxes Pt 2 - The Build

 Now that I've discussed the theory behind the design and the locations of the two baffle boxes, onto how I actually built them. In this article I am mostly talking about the bigger box (the one that would go outside the studio), but both boxes were very similar design. To begin with, I halved some lengths of 2by4 to make pieces of 2by2 using a mitre saw and a guide (you could also just buy 2by2, but I had lots of 2by4 left over). I then used this to make the frame of the box, before covering the sides with pieces of 11mm plywood as you can see below:

Cutting the Wall and Installing Some Steel

 As I mentioned previously, the only piece of "Building" work that I had no intention of doing myself was the cutting down of part of the back wall, and the installation of some heavy steelwork to replace the existing purlin. This was the original back wall:

Strapping in New Rafters

 Now that the steelwork had been installed, I was finally free to begin the extra roof-work that would be needed to support the outer room plasterboard roof. This involved adding a whole new layer of rafter collars below the recently added Flitch Beam, to which I would then attach the plasterboard. 

Here is a reminder of the plan - the upper rafter collars are marked in black, and the lower collars that I am talking about here are marked in red. The yellow line then represents the connection between the two: a 2by4 timber noggin reinforced with a steel restraint strap.

Additional Roofwork

 Although the majority of the roof-work from which I would hang the external room plasterboard ceiling was now complete, there were still some problematic areas that required attention. These mostly involved the end sections of the garage, where I would need something to fix plasterboard onto on the far walls. 

Additionally, there was the front section of the garage where I had to install a new timber board into the wall in order to be able to use Joist Hangers to hang the required rafters in this section. Here is a picture of me doing just that:

Plasterboarding Pt 1 - The Outer Room Ceiling

 Now we come to perhaps the most time-consuming task of the project: installing the acoustic plasterboard. Overall, (with lots of help from my dad) we installed 85 "Siniat GTEC dB" 4ft by 8ft sheets, each weighing 32.5kg - a total of around 2.8 Tonnes of plasterboard!

 This would be done in two phases: initially I would install a double layer on the outer room ceiling framework that I have been discussing. This was Part 1; later on down the line in Part 2, I would build the entire inner room walls and ceilings - more on this later.

The General Process

The key to the plasterboard installation was the purchase of a plasterboard crane, pictured below:

Scrim Tape and Jointing Compound

 After I had installed the two plasterboard skins of the outer room ceiling, I next had to seal the gaps between the individual boards, ensuring there was one smooth and airtight surface. To do this, I used scrim tape and plasterboard jointing compound. Essentially, the tape is a self-adhesive porous material that gives strength to the compound when it sets, and the compound is a powder that you mix with water before applying it over the plasterboard joints.

This was a process that I found quite challenging, so I will spend some time describing the tips that I found to make it easier. Here's a picture of my very first attempt at applying the compound - as you can see, not a very neat result at all!

The Ventilation System

 Although I have talked before about the baffle boxes, and how they prevent noise from coming through the ventilation holes, I haven't yet explained how the entire ventilation system works, so I will do so now. Please note that pictures in this article were taken at varying stages during the project, but I thought it would be useful to put them all together in one section.

Essentially, the plan was to have a passive air intake, (a hole through the wall connected to a baffle box), and an active air outtake, using a powerful extractor fan. I have already gone through the calculations needed to spec the fan, so I will now describe the exact layout of all the components and how they interact together. To make this easier for myself, I drew diagrams of both intake and outtake to ensure I purchased all the correct parts. Let's start with the passive intake:

Passive Air Intake

Assembling the Stud Walls

 At this point of the build, the outer room was basically complete. I had finished hanging the plasterboard that formed the outer room ceiling, so now it was time to finally begin on the inner room - the actual studio space. The first thing to do was to join up all the individual pieces of stud framework that I had already built - this would form the wall structure of the inner room.

Here are the frames for the stud wall lined up in position:

Acoustic Isolation Frame Mounts

In order to achieve maximum acoustic isolation, I had decided to try and decouple the inner room of the studio as far as possible from the outer room. This meant using a resilient layer of EPDM rubber underneath the sole plates of the stud sections, as I have mentioned before. As a reminder, here's a picture of the resilient layer underneath a horse shoe section of frame that I was about to flip upside down into position. The black tape in position is the damp proof course: