Back in January, I wrote an article covering acoustic room treatment. Today, I’d like to offer you a part two to that article that covers studio soundproofing. These topics can often become confused so let me quickly define them for you so you know what it is you need. Acoustic room treatment is the act of using diffusion and diffraction to create a neutral monitoring space with a flat frequency spectrum. Studio soundproofing is the act of stopping sound from leaking in and/or out of a studio space.
I’d highly recommend that if you haven’t checked it out already, you read the article on acoustic treatment. These two topics go hand in hand and having a sound knowledge of both will really help when you’re trying to implement either. Now, let’s jump into today’s topic of studio soundproofing!
Noise Floor & SPL Readings
When it comes to soundproofing your studio space, everything is relative. Without some standard measurements as a base to work from, you have no way to determine if what you have done is effective. As such, we must begin by taking some SPL readings in both the studio space and the areas around it. If you’re lucky enough to have a studio that’s in the middle of nowhere, you’re not going to be too worried about sound leaking out. However, you will still have to deal with some degree of sound leaking in. This is why it is important to take measurements both inside and outside of the studio space.
The best way to do this is to load up a song you love and know well and crank your audio interface to the loudest you’re ever likely to be working at. You need to make this sound obnoxiously loud so that there is no risk of under doing the soundproofing. Equally, flicking your system into mono means an equal distribution of sound throughout the room. This is handy for the purpose of taking measurements. Grab your trusty SPL meter and take a reading of the level in your studio space. Move around the room and try to find the loudest position in the room. Your listening position is likely to be a pretty good place to get a useful reading. Now that’s done, mute the desk and stay as still as you possibly can. Take a reading of the ambience in the room. This will be your noise floor reading and tells us how much ambient noise is already in the room.
A quick side note on noise floor and machine rooms. The ideal setting for any studio control room is a noise floor of 20dB. Ideally, this should never exceed 25dB. The reason for this is that too much ambient noise effects our ability to hear the subtleties of the audio we are working on. Imagine trying to mix a track whilst somebody talked to you? It’d be impossible due to all the extra noise. If you’ve taken your noise floor reading and it’s too high, it’s likely that machine noise is the root of your problem. Noisey fans in computers and A/C units are the common culprits. Building a dedicated machine room or machine isolation cabinet is your best bet for reducing the noise floor. Many recording studios house the machine that you record onto in a separate room to the control room. This is to completely remove that unwanted ambient noise. After all, you only need the screen to see your DAW.
Now we’ve got our control room readings, it’s time to crank the music back up and go outside of the room. Take readings from as many different sides of the studio as you can. This includes the floor above and below if you’re in a multi-storey building. If it’s a home studio, politely ask your neighbours if you can take some readings from inside their house/apartment. This shows you’re being considerate whilst allowing you to properly protect from the excess noise that they might make. With all of these measurements taken, you should have established which areas of the room leak the most sound and how much reduction you’ll need to make everybody happy.
As a good rule, you want the measurements you are taking outside of the studio space to be below 55dBA. This would be sufficiently quiet enough to negate any complaints that you may get. However, you may find that only soundproofing down to 55dBA does not create sufficient studio soundproofing against noises coming into your studio space. That is where it can be a little trickier and generally more costly. If your noise floor readings were sufficiently low enough already, then you won’t have as much of a problem dealing with sound coming in. However, if your studio is in a busy area and your noise floor is already over 25dB then you’ll be needing to do a lot of work.
Studio Soundproofing Practises
Now that you’ve taken some measurements and you know how much reduction is needed, it’s time to implement soundproofing techniques. There are a variety of ways that you can go about this. My suggestion to you is to try and make use of elements of all of them. The more variety in your approach, the more effective it’ll be in a wide range of circumstances.
Mass & STC Numbers
The first and most simple action you can take to improve soundproofing is improving mass. Objects of a higher density will do a better job at stopping sound from passing through them. If you’ve got a particular wall in your studio that is leaking more sound than the others, consider building a second wall in front of it made from a much denser material. But how do I find out how dense a material is I hear you cry? This is where STC numbers come in handy.
Typical studio soundproofing materials will have a sound transmission class rating which roughly translates to the number of decibels of reduction that they will provide. For example, the standard house brick that has been rendered on both sides will yield an STC rating of roughly 45. This means that it will provide roughly 45dB of reduction. Obviously, these figures are subject to the specifics of your actual design and will be reflected differently when subjected to different frequency ranges. However, they provide you with a rough idea of the reduction you can expect. This means that if you’re reading 80dBA outside your studio with the speakers turned up loud, building a rendered block construct around the room should lower the external level to an acceptable 35dBA.
Dampening & Absorption
Dampening is another great way to reduce unwanted sound leakage. This is most commonly done through materials that absorb sound energy and convert it to heat energy. This dissipates the sound in a safe and simple way. It’s also one of the easiest techniques to apply in a space where building a whole new wall is totally unrealistic. Materials such as Green Glue can be used to absorb and dissipate this sound energy. By simply covering a sheet of plasterboard with Green Glue and mounting it to your walls, you create a layer of dampening as well as adding some mass. Given that most plasterboard is only 1/2″ thick, this means you’re loosing only 1″ of your rooms footprint. Green Glue can add around 10 STC to the materials you mount it with. For what this can offer in terms of studio soundproofing, it’s probably the best option for most of you.
Decoupling & Rooms Inside Rooms
Decoupling is probably the most expensive but most effective way to go about studio soundproofing. The idea here is that we eliminate sound transmission between materials by disjointing everything from the things around it. This creates cavities of air where sound gets trapped and uses materials that effectively dissipate vibrations. There are two ways that this practice can be most effective.
Firstly, by building your studio with a floating floor. We can do this by using rubber feet to support a second-floor structure a few inches above the actual floor of the building. This eliminates transmissions into the surrounding rooms as the sound energy can’t travel through from the speakers and directly into the floor/walls. The other thing that can be done is to build air cavities into the wall structures of your studio space. Stagger the studs, use double layers of plasterboard and leave a cavity that you fill with fibreglass. This makes use of the same separation techniques that a floating floor offers but also implements elements of mass and absorption.
Cinema screens use this technique to ensure that no leakage occurs between each screening room. There is usually three double layers of plasterboard built with staggered studs and two fibreglass filed cavities. This provides in excess of 80dB of reduction! If it works for a cinema, it’ll surely work for your home studio setup.
Now for those of you who aren’t very DIY inclined, there are some prefabricated options on the market. Many companies make what are known as sound isolation enclosures that are effectively a prebuilt room that you can place in an existing room. This can be something as simple as a small vocal booth all the way up to a room big enough for an entire band. Custom built designs fit for purpose mean that they can offer incredible levels of studio soundproofing through a combination of all of the practices that I have mentioned. However, they are normally far more costly than the DIY option. It’s up to you whether you prefer to spend money or time.
Studio soundproofing is just as important as acoustic treatment. The two go hand in hand but must be approached and treated as separate things. If you’re doing any mixing or mastering, you need to be able to hear the entire track clearly and without interruptions. Make sure to start off by taking some accurate readings of the noise levels. This should be done both inside and outside your studio space. These will provide you with details on how much soundproofing you’ll need to do in order to create a suitable studio space. Machine rooms can be very handy for reducing the noise floor of your studio. If that’s a big problem for you (perhaps because of an old PC), consider placing it in another room. Utilise mass, absorption, dampening and decoupling to maximise soundproofing and build the best studio soundproofing that you. It’s one of those things that you can’t really over-do.