Isolate Your Own Practice Space or Studio

Isoleer je eigen oefenruimte of studio

By its very nature, music can be a noisy phenomenon which is exactly why any live venue, pub, rehearsal room and recording studio will always need good isolation. For the average musician, playing at full volume in their own home just isn’t an option – there are nagging neighbours to think about. Is it a problem that can be solved once and for all? You’ve heard that some good isolation will keep the noise in and keep your neighbours sweet, but before you start collecting egg boxes, it’s worth learning a little bit about the theory behind sound isolation. Your first lesson: egg boxes make for terrible sound proofing.

Written by Bert Stoltenborg

How Does Isolation Work?

Isolation works as follows: a structure like a wall, ceiling or floor is always joined in some way to another structure so, in the average room, the wall is always joined to the floor and to the ceiling and so on. Sometimes a wall isn’t actually physically bound to the floor, but it’s still held in place by gravity. However when a wall is bound to the floor and ceiling, it will prevent that wall from moving very easily. If a wall is unable to shift or move easily, then sound isolation will be at play, the level of which is determined by the ‘stiffness’ of how the wall is bound to the floor and ceiling. Every structure has what’s called its own ‘resonant frequency’ and, when vibrated at this specific resonant frequency the structure becomes very bad at isolating noise because it means that the whole structure is able to move or vibrate with very little energy. You could compare it to a swing, which is much easier to push when it’s already moving and especially if you time your push well. The swing moves back and forth at a specific frequency or rhythm and, if you try to push the swing randomly and interrupt that frequency you’ll either slow the movement down or stop it completely. The total energy of the motion of the swing has far less energy than the push needed to move the swing.

More Mass

At the right resonant frequency, a soundwave vibrates the structure, and this soundwave moves both sides of the structure i.e. the other side of the wall. That is, unless you have good sound isolation in place. To isolate a structure well, the resonant frequency needs to be kept as low as possible, compared to the frequencies that you want to isolate. You can lower the resonant frequency by increasing the mass of the structure. This is why, when it comes to sound isolation, you always need more mass to make a structure as heavy as possible to the point where you could say that, when frequencies that lie above the resonant frequency hit the wall at just the ‘wrong’ moment, it’s harder to cause any vibration. This is also why most walls and structures are better at isolation at higher frequencies. It’s simply much easier to isolate higher pitched sounds than a kick drum or the low–E of a bass guitar, which can rumble through almost anything. Growling bassists would need a bunker to prevent waking the neighbours when they play.

Lower frequencies transfer the movement of sound waves to the walls, resonating them to the point where the walls can easily bend in response to the wave. This resonance actually has the effect of decreasing the sound isolation of higher frequencies. This is called the Coincidence Effect. By damping or isolating a wall by, for example, converting it into a cavity wall; applying Green Glue between two sheets of plasterboard; or even by sandwiching foil between two glass plates, you can reduce this adverse effect. Above the ‘coincidence’ level, the law of mass starts to work again. However, the Coincidence Effect when isolating music-related noise is less important.

Cavity Walls

When a wall is ‘doubled’, turning it into a cavity wall, the lowest resonant frequency of the structure is increased. This means that, while higher frequencies are better isolated, the noise reduction of lower frequencies is not. When you build a cavity wall, you need to fill the hole in between (the cavity) with mineral wool – also known as rock wool. This prevents standing waves being generated within the cavity and at the same time, the wool ensures that the sound can’t travel as quickly, because it sort of relaxes the sound wave. Basically, the overall resonance is reduced, which is exactly what you want. A loosely filled cavity is optimal because any more filling can stiffen the structure and risks raising its resonant frequency. Creating a wider cavity is definitely an effective way of lowering the resonant frequency and will dramatically improve isolation. By ‘tripling’ the wall and building in two cavities, the resonant frequency gets even higher meaning that the higher frequencies are extremely well isolated while the low frequencies are less well isolated. These so-called ‘triple leaf’ structures are therefore better avoided, especially if you want to reduce music–related noise. The trick instead is to build a cavity wall with one thicker ‘leaf’ because more mass means more isolation. At the same time, you want to make the cavity wider. This will also reduce the resonance and improve isolation. You also want to avoid coupling two walls with a frame or wall ties as this will cause the two walls to function as a single cavity leaf and the whole wall will work like a single wall, often less effectively than when both ‘masses’ are installed as one mass without a cavity, reducing the high frequency isolation. The reason why you use two walls is to dampen these higher frequencies.

Flanking Sound Transfer

When two rooms lie next to each other or one lies above the other, the structure of the walls, ceiling and floor that divide the two rooms will rarely provide enough isolation, causing noise leakage from one to the other. Initially, you need to make the whole structure more insulated, because sound can not only pass through the structure but via all of the other structures from one room to another. This is called flanking sound transfer. While you can help limit noise pollution by using better isolation methods, sooner or later, noise will still get through other parts of the partitioned structure and any further improvements will no longer help. This kind of flanking noise transference can even cause noise pollution in rooms that aren’t adjoining. You often experience this in blocks of flats or terraced houses.

Raising the Floor

To overcome flanking sound transfer, you need to do some raising and distancing. By building walls at a distance from the existing walls and raising the floor, you can build what’s become the legendary box-in-a-box: a completely uncoupled room within a room that doesn’t directly touch any of the floors, walls or ceilings of the room it’s in. The cavity walls of a well built box-in-a-box don’t even touch one another, or are coupled using some kind of springy material. The resonant frequency of the structure also needs to be as low as possible, but it’s not that difficult to achieve this.

If, for example, the floor is set on some kind of elastic material then that material needs to rebound by a certain percentage so it’s able to reach a specific resonant frequency. If you build a floor out of light materials like OSB board, you need to take into account the fact that the situation isn’t all that stable. If the floor is loaded with a few people who are all moving around, or a new piece of equipment or furniture is added to the load, that rebound percentage will no longer be correct. When you have a floor that weighs 20 kilos per square metre and you load it with, let’s say, one musician who weighs 80 kilos, the negative effect on the resonant frequency is far greater than when the floor itself already weighs 400 kilos per square metre. Lighter materials dampen sound less efficiently than heavy materials. A 9mm thick MDF wall will be far worse at isolating sound than a 15cm thick limestone wall and, with the floor, the same rule applies.

Rubber Blocks

It’s also worth remembering that not all elastic materials are exactly the same. Rubber is actually quite stiff, so it doesn’t compress like other materials, but actually deforms when pressure is applied. So if you’re ever advised to lay a rubber mat under a structure that you want to isolate, ignore it. Instead, you need to solve the same problem using rubber blocks or blocks with specific mechanical properties. Then you can accurately calculate how to use them. Certain mineral wools or foam variants bounce back differently, so again, you’ll need to know how to work with it. More wild ideas like mounting the structure on a load of old car tyres or tennis balls are also just asking for trouble. The chance that your box-in-a-box will have any stability to it is pretty much zero.

Normally, the walls and ceilings won’t be subjected to variable loads like the floor, so you can work with a standard construction and work with existing data. However, bear in mind the fact that every element needs to have the same sound isolating properties since the total level of sound isolation will depend on the weakest link in the chain. So you need to take details like ventilation, doors, windows and cable routing into account. And above all, you need to stop collecting egg boxes.

Good to Know

Working in Practice & Noise Level Legislation

Before isolating a room, you need to figure out how much sound isolation is needed, so how much noise you’re making in the room and what the noise level laws are. In a rehearsal space or studio where bands are playing complete with a full drum kit, you’re looking at sound levels that peak somewhere above the 115 dB(A) mark. In buildings in residential areas, sound levels of up to 35dB(A) are permitted from 7am to 7pm and then 25dB(A) between 11pm and 7am. Between 7pm and 11pm, the permitted noise level is 30dB(A). When it comes to music-related noise, there’s an extra 10dB restriction. This is because music is repetitive and recognisable so causes more of a hindrance than ‘normal’ sounds. Therefore, that average ‘band’ noise level of 115dB(A) needs to be reduced by a good 100dBs. Normally, that’s just absolutely impossible, so turning a room in a terraced house into a drum room, rehearsal space or full recording studio will always depend on what’s possible. If you’re building your rehearsal space or studio in a detached, free-standing structure like a shed in a garden, then things get a little bit easier. When it comes to the neighbours, you can legally project up to 40dB(A) onto the back of their house, so that, plus the extra 10dB restriction means that the noise levels need to be reduced by 85dB. If the neighbours’ house happens to be around 20 metres away from the ‘shed’, then we can add another 26dB which means we need a reduction of 56dB.

A concrete floor in a block of flats needs to be at least 30cm thick to provide enough noise isolation, and that’s not even music-related noise, just the normal noises of life. Any thinner, and everyone will know what you’re watching on TV if the volume is turned up just too loud. The walls between houses, flats or any dwellings should actually be built as anchorless cavity walls in order to achieve a reasonable level of sound isolation. When you’re thinking about the kind of structure you’ll need to adequately isolate a studio or rehearsal room, you’ll quickly find out that half-brick walls, tiled roofs and double-glazed windows really won’t cut it. The sound isolation level in an existing building can be measured by setting up a large speaker system in the room you want to turn into your studio or rehearsal room, play some pink noise through it, and take a recording before taking a second recording in any adjoining rooms or spaces outside of the room before using something like an analyzer to compare the recordings and determine how much sound isolation the building currently provides and whether or not it’s enough. If it isn’t enough and you’ve pin-pointed all of the weaker dividing structures like doors, windows, roofs and walls, then you can start figuring out how to improve them.

Isolation Theory In Short

Mass is isolation, more mass provides better isolation.
Because music is mainly made up of lower frequencies, you need a lot of mass to isolate it.
Dual structures can also work, but you need to know what you’re doing, otherwise the isolation will often just deteriorate where it’s needed.
The cavity of a wall needs to be loosely filled with rock wool.
Walls with more than two cavities are best avoided, especially when isolating music.

Building & Rebuilding

Now comes the time to either build or rebuild, but how do you even start, what do you need to watch out for and what can you expect from the results? Say you want to build a rehearsal room and have the space to build a free-standing structure, or have a space that you want to adapt. Even if your neighbours live far enough away and you happen to have very tolerant and understanding housemates, you still need to make sure that you’re sticking to the law by bringing that average 115dB(A) level down to the legal limit. So, from 7am to 7pm, that’s 35dB(A); from 7pm to 11pm that’s 25dB(A) and from 11pm to 7am that’s 30dB(A). Then comes the extra restriction for music, which is another 10dB.

If the neighbours live X metres away, and 20 x LOG(X) = Y, then YdB is the amount of ‘free’ isolation you get. After you’ve calculated that, you can figure out, depending on how late you’re planning to play, how much isolation you’re going to need. In another scenario, you might have a large cellar or shed where you want to build your rehearsal space. If you live above your cellar yourself, then you don’t actually need to meet any noise regulations, but maybe you still want to isolate the space as much as you can. Even if you don’t have the budget for proper isolation, there are other ways you can do it. One of them is to compromise. Maybe you can record the drums and other louder instruments somewhere else and then record the vocals and the rest of the instruments in your cellar or a less drastically isolated bedroom.

Freestanding Structures

Starting with the first scenario: building a detached rehearsal space in a detached building or shed. By now, you should already have a good idea about the level of sound isolation you need to achieve. A single limestone or concrete wall, for example, that’s 100mm thick and is well plastered weighs around 175 to 200 kilos per square metre. A wall like that will reduce the sound pollution caused by average pop music by around 36dB. This means that, if your band will be pushing the 110dB(A) mark inside your DIY rehearsal room, you’ll be able to hear about 74dB(A) of it at a distance of 1 metre from the wall. That’s the theory, but in reality, this is a bit of a stretch, because it also depends on the surface of your structure and the reverberance within the ‘receiving’ room. If the wall is also decked with a frontage, then the isolation will be much better, so you can reduce things down to around 57dB(A). To get there, you’ll need to do the following: make sure that your wall frontage does NOT touch the main wall. So the frontage needs to be uncoupled. Then, you also need to take flanking sound leakage into account. If you have two nicely finished and isolated walls but both are coupled to, for example, the floor or foundations, there is a very big chance that your carefully calculated isolation levels won’t happen. Therefore, if you need to achieve a really high level of sound proofing, then you’re best off designing an entirely uncoupled structure. If you’re starting with heavy walls (remember: more mass = more isolation) then it’s best to set them on their own foundation. This way, the walls are only coupled by the sand in which they’ve been set and, with a normal, fairly dry type of sand foundation, the coupling is relatively ‘small’. A good example of a studio that’s been built like this is Roy’s Kitchen in the Netherlands. Roy has built every room on its own foundation and then built the exterior of the studio around the rooms.

If the walls have to be built on one foundation, you could set the inner walls on some kind of uncoupled material, like Sylomer or a similar equivalent. To do that well, you need to make some calculations. To reach the correct resonant frequency, the Sylomer will need to deflect a certain percentage. If, for example, the roof also rests on the inner walls, then this also needs to be included in the calculations as well as doors and windows and any other potential weak points that are lighter than the rest of the structure and therefore less isolating. You can compensate for this by increasing the cavity between the two sheets of glass in a double-glazed window or inside a door. If these cavities are not filled, so you can actually ‘see’ the cavity within a double-glazed window or door, then this will also count towards the total. The cavity helps lower the resonance frequency and that’s a good thing for the isolation.

Existing Rooms

If you want to install any kind of music room in your cellar or garage, then it’s definitely possible, but will involve a lot of work. One of the ultimate examples of this kind of installation could be found on the now, unfortunately disabled weblog Studiotips.com, which was written by Paul Woodlock about the entire process of converting his garage into a studio. He started by suspending a frame on a specific resilient material before pouring in a concrete floor to create his uncoupled base. Any manufacturer will recommend that their ‘resilient material’ be used to support the entire floor, but in practice, it’s better that the material is used in such a way that it’s better at supporting a lot of weight. To do that, you need to slice it into blocks and then glue those blocks together to create sort of sealed cavities. It’s not just more efficient when it comes to achieving the isolating effect you’re after, but will save you a load of money, simply because you’ll need a lot less material to do it. If you’re planning to build multiple spaces, like a separate live room and a control room, you can build the walls and roof on your suspended floor. You just need to take the extra mass you’re going to set on top of the floor into account when calculating the effect of the material the floor is ‘floating’ on. The benefit of doing things this way is that you get a lot of weight, therefore the increase in dynamic floor load caused by recording artists and/or equipment is much less likely to overcompress the material the floor is floating on. If you’re just planning to sound proof one room, then you can mount some false walls and a false ceiling onto the existing walls and ceiling using some kind of acoustic decoupling nail system. This kind of nail system is specially designed so it can be secured on an existing wall so that a false wall can then be mounted on top without any acoustic coupling taking place. In Alternator Studios in Belgium, the founder built three rehearsal/recording spaces plus a control room in one house and says that when two bands are playing at the same time downstairs, no one can hear a thing upstairs.

In the Attic or the Bedroom

If less isolation is needed or full-on isolation just isn’t possible, then you can work with lighter isolating structures. This kind of approach will work if you, say, want to convert your attic or a bedroom. You can use the same acoustic nail rail system mentioned above and lay flooring made of some kind of sheet material like plywood, OSB or something similar. The walls and ceiling can be treated the same way. The only thing you need to be aware of is the weight on the floor so, before you start, precisely calculate the exact weight of all of the equipment, pieces of furniture and people that are going to be in the room. Also, have a close look at the existing structure. If it’s a terraced house, you’re usually looking at dividing walls with a cavity construction. It’s important to know what kind of walls you’re working with so you can avoid inadvertently creating three-leaf cavity structures, which can actually make the isolation worse.

Good to Know

Thorough Analysis is Crucial

It’s just not possible to know how to build a well isolated room or structure without thorough analysis. How thick do the walls need to be, how wide do the cavities need to be, how can the doors and windows be dimensioned? It all needs to be figured out beforehand. If not, then you won’t get the results that you want and making modifications after the fact can often be more difficult and more expensive than the original job. Just as you can easily do too little, you can also do too much, costing you a lot of money again. In short: a good design will always give you better value. Some people want an immediate quote for how much a renovation will cost, but every situation will be different and you’ll never have a good idea of what you’re in for until you’ve done all of your sums and triple checked them.

Seal the Gaps

In addition to mass and mass-spring-mass systems, if you want to isolate a space, sealing the gaps is also essential. If the false wall you’ve just installed is leaky, then it’ll completely undermine its isolating effect. Every gap, no matter how small, needs to be closed. Sealing the gaps in normal doors and windows can prove quite a challenge to sound proofing. You could make the door heavier, but unless the gaps are sealed, it will have little to no effect on the isolation and, at some point, you might have to invest in some professional window frames to gain the level of isolation you need. You also have to consider details like power sockets and pipes. Any sockets need to be remounted on the false wall and the edges of the housings need to be carefully sealed.

Don’t Forget About Ventilation

In a well sound proofed room you can make a lot of noise without bothering anyone but at some point, the air is going to get stale and it’s also going to get pretty warm in there. As such, including some sort of ventilation system in your design is a must. Of course, this also means making holes in your room where sound can get out. To prevent that, you need to design an isolated ventilation system that affects the overall sound proofing as little as possible.

The Isolating Value of Different Structures

The do-it-yourselfers among us will probably consult the internet when they want to know the sound proofing properties of this or that structure. Just in case you are one of those people, you’ll find some good information on the BBC website, which includes a study conducted by the IRC-NRC. The study includes soundwave data per frequency band but also as single-digit RW and STC data. The values, however, were not intended for calculating sound proofing when it came to live music but normal household noise. Frequencies under 100Hz, where most of the energy of music lies, were not taken into account. Preferably, any calculations need to be made in ⅓ or 1/1 octave bands. Sometimes, you will find available numerical data that’s based on the VROM spectrum of musical sound and household sounds which you can use. Just be aware that they need to be weighted for the surface area of a certain structure and other legislative conditions. So you can’t just state that a structure isolates music by 60dB just because that number is mentioned somewhere. Further from that, there are countless forums and sites you can find on sound proofing and isolation where you can flip through everything you’d ever want to read on the subject, including a lot of nonsense. Unfortunately, the best resource I knew of was Studiotips.com. It included all of the essential info about isolation, absorption and calculation models and software to help figure out the details. In any case, if you’re thinking about embarking on a project, you need to realise that you’ll be working with mass and mass-spring-mass systems with as big a rock wool filled cavity as possible. Difficult structures that feature a lot of cavity sheets/leaves are always best avoided and remember, sound proofing is actually a pretty logical undertaking, so there’s no black magic or religion involved.