A Shed That Rocks – Part 2 – Sound-proofing and Acoustics (a dummies guide)

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It has been months since I posted Part 1 of this brief little guide to building a studio in my garden, the ‘Shed’ is well and truly finished however and now fully operational. I have since been very busy using it for it’s intended purpose of writing tonnes of music and catching up with a lot of work, so this second instalment is well over due!

What I’m going to cover here is how I approached the sound proofing and audio acoustics in my small space. Both subjects are technical, and heavy going so when I started searching around the web I got bombarded with advice, products and technical data, and it all quickly got very confusing.

There is of course some serious science behind sound energy and the developments in materials and processes out there to control it, a lot of which is written in language for men in white coats rather than musicians. There are some simple facts though that helped me get my head around some of the jargon, which can be broken down into laymans terms. So I’m going to try and unpick the basics here for anyone looking to get a better sound in their own shed, or spare room. For the audiophiles who want to dive in deeper I’ll be sprinkling a few links to further reading.

First of all ‘sound proofing’ and ‘acoustic treatment’ are not the same thing. You will be applying both in building any studio space, but the materials you would buy under each banner may have completely different properties. In this context sound-proofing broadly speaking is the process of reducing the amount of sound escaping or entering your room. Acoustics is the science behind how sound waves travel and behave within your room, and there are various techniques and materials that are developed to absorb the energy from the sound waves, make them change direction and diffuse them. All of which contribute towards sound proofing your room.

Why does it matter? Well for two main reasons; firstly and most importantly they affect how accurately sound is transmitted from the source (your monitors/instruments etc.) and presented to your ears and microphones. And secondly – in terms of sound-proofing – how sound will escape from your room to possibly upset your monitoring or neighbours, and how outside sounds can enter your room upsetting any recordings you try to do.

In both areas the aim of the game is to dampen the energy of sound waves to reduce the effects of them travelling through a surface, or bouncing off of it. Manipulating the reflection of sound waves (reverberation) off walls, floors and ceilings plays a big part, and the frequency of the sound determines what materials and processes are most effective.

Fundamentally if you want to stop sound travelling through a surface you need mass – thick walls made of dense materials. However hard thick walls become very reflective, bouncing the sound back and forth at various angles, which distorts the audio you hear. So if you were to set up a studio in an underground bunker for example no one would hear you outside, but it would probably sound terrible inside. Soft materials on the other hand offer absorbent properties to reduce the amount of energy reflected back from them. Higher frequencies are easier to absorb or diffuse than low frequencies, which have a larger wavelength, greater energy and can travel much further.

This ‘Reverberation’ within your room can also cause the unwanted phenomenon of standing waves. At low frequencies standing waves can create the presence of too much bass or none at all, causing you to over/under compensate in the mix. So if you’ve created a new track and played it out somewhere else only to find that the bass is way too loud or nonexistent this could well be the cause.

So as well as processes and products that can be applied to reduce the affects of the above, the shape and dimensions of your room will also make a difference. Parallel surfaces can reflect sound directly back at each other – which is a particular cause of standing waves – where as asymmetrical surfaces can help to deflect such reflections away from your monitoring position.

Here a few links i found useful… Standing Waves … Acoustics

A Room Within a Room…

A commonly used technique to reduce the amount of sound entering or escaping a space is to build a room within a room. By isolating the inside structure from the outside with as little physical contact as possible you can reduce the airborne energy that is transferred from the outside to the inside through vibration – and vice versa. The cavity in the wall is then filled with absorbent material such as fibre-glass insulation slabs, which will also help to keep your outbuilding nice and warm.

Many larger studios will have brick built rooms within them, with deep cavities but as space is of a premium in this build my inside room was created with two layers of acoustic plasterboard separated from the outside wall of my shed by resilient bars. Sandwiched between the two layers of plasterboard is a mineral loaded matting to give my walls extra mass. In the wall cavity itself is a layer of dense mineral wool.

TIP: Many of the top suppliers of acoustic products recommend using their spray adhesive to stick the layer of heavy matting onto your first layer of plasterboard. Don’t bother – it’s quite expensive, not that effective and hazardous to your health. I bought a staple gun for £10, and it was a LOT easier!

The big advantage and disadvantage of a studio in a wooden shed is firstly standing waves at low frequencies are less of an issue as the sound energy can pass through the walls more easily, rather than bounce back as they would in a brick or concrete structure. The disadvantage however is just that – low frequencies can escape to the outside world, and the rumble from planes and helicopters can filter in. It’s a compromise I had to accept early on due to the space and budget I had, but as I said in Part 1 I’m not playing acoustic drums or doing much recording in here.

It’s important to mention condensation at this point in your outbuilding as it’s something you need to address before you insulate it. You and your equipment will generate a lot of heat whilst you’re busy creating. At night when the temperature drops this warm air condenses to form moisture, creating condensation within your wall cavities or in the control room itself. This is very bad for your studio gear and your walls, so some ventilation is essential to allow air to circulate and escape. I created two vents into the cavity on each outside wall, one at the top and one at the bottom to allow the air to flow freely. These were covered with louvre grilles and some fine mesh to stop unwanted critters getting in the walls.

A List Of Things To Do…

So where do you start with a project like this? Well once my shed had been delivered and erected I first set about filling every little crack that moisture or bugs could possibly enter with some flexible sealant. Before insulating the floor and the ceiling I drilled the vents in the top of the walls, and at floor level. Unlike the walls the floor was flat with no cavities to insulate, so I had to fix joists to the floor and laid a new floor on top of it with dense chip board flooring. I then filled the cavities with Cellotex, leaving some gaps for the air to flow.

Planning and installing the electrical circuits came next. I decided not to install lights in my ceiling as I had a relatively shallow cavity for them to sit in, meaning most down lighters would pose a fire hazard. You could use super low profile LED down lighters, but instead I opted for LED strips that could be fixed onto the ceiling in an aluminium channel that looks like coving. For the sockets I had two rings installed, one of which would be dedicated to my electric heating, and the other for my studio gear.

Once my electrician had done the first fix, I insulated the walls with dense mineral wool and screwed the resilient bars onto the joists. Onto the bars I fixed my sandwich of plasterboard and heavy matting. I did the same thing for the door, except I used some thick plywood to panel the inside instead of plaster board, which would be too heavy and easily damaged.

TIP… At every stage of plaster boarding and matting your walls, draw some guide lines marking out where the resilient bars are so you know where to drive your screws.

The ceiling was a bit more tricky; Being made of wood I took into account at the design stage that it would have to be strong enough to hold itself and the plasterboard. However once we had fixed the first layer in place it became apparent immediately that the supporting wooden beam was not going to be strong enough, and over time it would sag. Not wanting to have a supporting post in the middle of the room, I had to take the laborious measure of reinforcing it through the middle with a steel bar.

I had double glazed windows fitted by the shed builders when it was erected, but for extra security and insulation i fitted an extra layer to make them double double glazed with a 60mm cavity in between. Again i wanted to avoid condensation and the glass misting up so before i sealed them in i drilled some small holes in the top of the cavity, and layered some silicon gel patches to absorb any moisture.

I papered the walls with some thermal wallpaper for good measure then the final steps of the build included wiring in the electrical sockets, painting, laying some lino on the floor and rebuilding my desk that I had to dismantle to get through the house.

Moving In! …

The best part of any build is moving in, and turning your room into a useful work space.

Salvaging a load of acoustic foam from my previous studio, I placed it strategically around my monitoring position to stop any unwanted high frequency reverberations off my walls. I managed to squeeze in another desk, some draws and shelving to store all of my cables and the general stuff you accumulate in this business.

For me ergonomics and creativity go hand in hand, and I spent a lot of time placing my keyboards, drum machines and controllers etc. so everything is at my finger tips within easy reach. The result is a warm, comfortable, cosy audio workshop.

Thanks for reading. Head to Part 3, the final part in this series where i wrap up with some hindsight, and a list of things you need to know.

 

 

 

 

 

 

 

 

 

 

 

 

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