Beyond the egg carton: insulating your rehearsal room and improving room acoustics

This is how you can achieve useful demo recordings and live in perfect harmony with your neighbours - even without the classic egg carton on the wall

When it comes to the rehearsal room, many bands are content with reliable minimum equipment: wall sockets, a few egg cartons on the wall, a computer and a PA so that the singer can somehow drown out the drummer, even on 15 square metres. It is not hard to sufficiently insulate the rehearsal room and improve room acoustics to record a good demo and keep the peace with your neighbours.

What are you particularly interested in with regard to insulating rehearsal rooms and improving rooms acoustics?

Sound absorption and insulation of a rehearsal room

Many musicians confuse sound absorption, insulation and room acoustics. You achieve these three goals with different means which are sometimes the same and sometimes totally different. If your rehearsal room is close to other people's living space, such as a terraced house or the basement in a block of flats, you probably need to look at high-level sound absorption and insulation.

Insulating means that less sound will reach the outside. Sound absorption means that materials 'swallow' certain frequencies.

Windows and doors: polystyrene and mass.

The two most important areas for insulation are windows and doors. You can glue polystyrene in front of the windows. However, remember to ensure sufficient ventilation if you increase the insulation of your room. Do you know the musty smell in many rehearsal rooms? That is often mould. Only regular ventilation or the purchase of a dehumidifier in a DIY store can help to prevent it.

General rule: mass stops sound, especially that of the bass. Depending on your budget, build in a thicker door and glue polystyrene to the edge. When the door is closed, the polystyrene should overlap with the door frame to ensure a high-level insulation.

Due to polystyrene being flammable, please make sure you have good fire prevention and even a small fire extinguisher in your rehearsal room. Everybody must be aware that polystyrene is not the best way but mass is good for sound absorption. And polystyrene panels are affordable for everyone, unlike expensive acoustic panels. Polystyrene is easy to use and another layer of insulation can easily be added which is another advantage.

Practical tip: polystyrene is best cut with a cutter knife or a special insulation knife, otherwise it will break and crumble. There is also glue available which is suitable especially for polystyrene. This is really worth buying, because it sticks to almost any surface.
Costs: the luxury version of the polystyrene panels is 10 cm thick and costs a maximum of EUR 7.00 per square metre.

Walls: mineral wool and plasterboard

A common misconception is that the old cuddly blanket and carpets on the wall noticeably insulate a room. Yes, they attenuate higher frequencies, so everything sounds a bit duller. But the fact is, they only change the sound inwards. They do not, however, prevent the sound from reaching the outside. Especially bass frequencies and the low midrange simply throttle through them.
A 3-layer structure on the wall, on the other hand, has proven to be particularly effective. The important thing about this structure is that the mineral wool lies loosely between two materials. This is done, for example, as follows:

A thick layer of plasterboard is applied to the outer wall which should be as solid as possible.
Then, you put mineral wool on it. Caution: mineral wool produced before the year 2000 could promote cancer and is banned nowadays. Modern mineral wool is harmless. Thus, be sure to use new modern mineral wool.
Two more layers of plasterboard are added on top of the mineral wool. You can also build battens with old roof battens, stuff them with mineral wool and then nail plasterboard on top of them. This creates a larger space in-between the materials.

These layers create an air gap where the insulation wool is placed which ensures a high-level sound absorption. This 3-layer construction, however, must be applied all around the room which also includes the ceiling.

By the way, a room which is sound-proof is automatically thermally insulated.

Practical tip: You can use dowels or glue on a wooden frame made of narrow strips to attach the mineral wool.
Costs: Mineral wool to roll out costs about EUR 4.00 per square metre, depending on thickness and quality.

Now seriously: Are egg cartons good for rehearsal room acoustics?

You may have heard that egg cartons can improve or even cushion the acoustics. Sounds like a quick and cheap solution, right? But does it really work? This is actually just a prevailing myth. Let’s put it this way: egg cartons are better than nothing. Here's the crux of the matter: egg cartons are primarily designed to protect eggs, not to effectively insulate the sound. They can absorb high-frequency noises quite efficiently. But they have little effect on middle and low tones. In terms of fire safety, they are not the safest choice for rehearsal rooms. Egg cartons are made of materials that easily catch fire. This makes them a risky option in any room, especially where you use electronic devices and instruments. Here, too, a distinction is important:

Insulation refers to how well a material blocks sound waves or prevents sound from transmitting from one room to another. Egg cartons are almost ineffective in this regard. They are thin and not dense enough to effectively block sound waves. Egg cartons are lightweight and porous, and thus ineffective at absorbing sound waves. Especially at lower frequencies.
Acoustics: This involves improving the sound quality within a room by reducing echo and reverberation. The textured surface of egg cartons nevertheless have a small impact on high frequencies, since they reduce echo slightly. However, they offer little improvement at middle and low frequencies.

The supreme discipline: the room within the room

The most effective insulation is the 'room within the room'. A room-in-room construction offers total insulation: a disconnected room which is separated as much as possible from the outer layer or the rest of the building. This means you have to separate the walls of your room from the outside walls of the building as much as possible. In technical jargon it sounds like this: between the exciter (sound source) and the vibrating mass (wall), a 'suspension' (air, rubber, mineral wool) must be included in order for the direct frictional connection to be interrupted. It is like a shock absorber for sound because sound basically consists of air blasts. Such a spring-mass system is also used when craftsmen want to reduce impact sound in residential buildings. The floor then 'floats', i.e. is separated from the false ceiling and transmits almost no sound.

You want solely DIY in the rehearsal room? Then, you can usually only get close to a room-in-room.
Building something like this yourself is expensive. Therefore, you have got two options: you ask a befriended craftsperson if he/she could help you to implement this construction. Or you can use your knowledge from this article to at least come close to a room-in-room construction. Some inspirations:

Cover the entire floor with a soft material. This can again be (modern) mineral wool, but it must be crush-resistant. Not every mineral wool is crush-resistant. Then place a strong plate or ready-to-use screed over the entire surface. This results in a 'floating' floor.
Place the drums on a platform of polystyrene which is at least 15 centimetres thick. Then add wooden boards on top of that. The platform must not have any contact to the outer wall.
A suspended ceiling with acoustic suspensions. The suspended ceiling can be made of plasterboard. In the space between the ceiling and the plasterboard you stuff mineral wool again. This is especially effective if you are rehearsing in a basement where people live above it.

If you combine these three steps with the measures for walls and doors described in this article, you have already prevented many dB from escaping to the outside world.

Improving room acoustics

Optimising room acoustics is always about one thing: to reduce reverb and flutter echoes, i.e. avoid sound waves bouncing off smooth surfaces or bouncing back and forth between parallel walls. Because this results in a chaos of different sound sources and provides a very undefined sound.

Clearly: For room acoustics, carpet on the floor is quite helpful. Carpet also helps on the walls but there are also more effective measures available.

Absorbers, for example. These are objects that disperse sound, especially the high frequencies and mid-high range. There are also absorber plates which you can glue to the wall in a layer of about five centimetres thick. However, this option is rather expensive.

What does an absorber do? Imagine sound waves like rays. We want to prevent these rays from bouncing straight off walls, windows or concrete surfaces on their way from the speaker to the ear. Acousticians call these surfaces 'reflection points'. It would be better if the first reflection point did not reflect the sound straight away, but picked it up a little and scattered it. Absorbers do that. This also works with egg cartons. However, not very well and therefore only with a large quantity of them.

The band LENNA has built their own sound absorbers for the rehearsal room:

“You can just buy some wooden slats at the DIY store and use them to build a frame. Then, you put insulation wool into it, pull fabric over it and tack it down well. This is very cost-effective and a few of these DIY absorbers can do a lot in a small room of 20 square metres. And for a powerful bass reproduction, only mass helps. You can put another couch or armchair into the rehearsal room. It helps if there is a lot of stuff in your room and the walls are not completely naked. The only important thing is that there are no smooth concrete walls at which the sound can simply bounce back. It also makes an audible difference to set up the largest pieces of furniture in the rehearsal room in an almost symmetrical way. Otherwise, the hearing is different from every position in the room.”

So an absorber is simply constructed: make a wooden frame, put mineral wool in it, foam on top. You can also stretch so-called pyramid foam over these DIY absorbers.

Or you can also use an old shelf as a frame. Five centimetres of mineral wool and two centimetres of pyramid foam are enough to cover it. This pyramid foam also ensures less reverberation on walls and ceilings.

Positioning absorbers in the room

Okay, you have built absorbers, but where do you put them? That is easy: an absorber should be placed between the first reflection point and the speaker - and you should sit between absorber and speaker. For example, if you were sitting in front of a speaker with a concrete wall behind you, you would hear both the sound of the speaker and the reflection from the wall behind it. This creates an indefinable sound mush.

This is for the following reason: always place or hang the absorber where the sound from the speaker would first hit a smooth surface. This is already very helpful.

Conclusion: small acoustic measures for big improvements

Yes, some of these tips are not that easy to implement by hand. But for completely untreated rooms even small, first steps make a big difference. Once you hear the first improvements, you probably want to carry on optimising. Eventually we grow with the requirements of our applications, right?