Home Studio Acoustics: Soundproofing Basics

MS-Building-87-Walls

by Pablo Bellinghausen

Most musicians and recordists are aware that recording and rehearsal studios spend a lot of money on installed materials that modify the acoustics inside the recording room. However, this gives rise to one of the most common misconceptions in professional audio.

Acoustic treatment and soundproofing are very different things.

The wall panels, foam tiles, and other products that can be seen on the walls of recording studios are there to make the room sound better, but they do not block much sound from coming in and out of the room. If you just wish to reduce the noise for people next door, you will basically be wasting money by purchasing this sort of product.

Thin acoustic tiles like Auralex Studiofoam absorb reverberation but don’t insulate the room.

There are countless examples of people, often novice producers but sometimes even experienced musicians, who spend a considerable amount of money on covering a whole room with thin foam tiles, only to realise after the fact that this offers next to no isolation. The sound inside the room will be very different due to the lack of echo, but any leakage will at best be dulled slightly.

Conversely, effective soundproofing will render a room even more echoey, since none of the acoustic energy is at that point able to leave the room, and will therefore be reflected back over and over again. A good example of this is the average school gym, which is a large structure of very dense concrete or brick walls.

Balcombe-Grammar-02-rsMost gyms are very reverberant environments, partly due to the thickness and density of the walls, and partly due to the reflective surfaces inside.

If you are interested in acoustic treatment to improve the sound in the room instead of soundproofing it, we suggest you have a look at one of our previous articles:

Home Studio Acoustics: Monitoring Room Treatment

 

Sound Absorbers

Absorbing materials used for acoustic treatment like foam, curtains, or fiberglass, prevent some of the noise from being bounced back into the room. The way they achieve this is actually by mechanically transforming some of the sound energy into small amounts of heat.

But if the noise is being converted into heat, then why doesn’t this attenuate the outgoing sound?

The answer is that the percentage of absorbed energy of most studio-grade acoustic tiles or panels is actually pretty small, particularly at lower frequencies. However, sound bounces back and forth hundreds of times around a room, so a small degree of absorption is enough to noticeably dampen the sound after a few reflections. However, sound only needs to hit a wall once to leave the room, which means by the time the first reflection happens, most of the leakage has already happened.

Sound-Attenuation-B

There are absorbers that dampen enough sound that they actually do indeed prevent most of the sound from ever reaching the outside. They are found in “dead rooms” used for research, called anechoic chambers, but they are very expensive, large, and heavy – and therefore impractical for pretty much any studio environment.

Microsoft-Chamber-2Microsoft’s multi-million dollar anechoic chamber is the quietest room in the world.
Just the door weighs almost 400 kg!

Sound Insulation

Soundproofing is unfortunately difficult and expensive to achieve, in most cases requiring construction work.

Effectively insulating a live room involves creating an airtight environment completely surrounded by dense, high-mass materials. In a way, sound leaks behave like water – even small gaps (for example between walls and floors, or around doors) will cause most of the sound to escape, rendering many expensive installations useless.

Floor-Construction-ExExample of a basic soundproofed floor for a home studio

We will not go into detail here on the best methods to achieve this since that is an area that is best left to a construction specialist. Pro audio retailers will sell some useful materials (like Green Glue, acoustic sealant, mineral wool and high-density rubber or vinyl sheets) but unless these are installed correctly, they will not be effective enough to justify their cost.

 

Acoustic decoupling

There is actually an application where porous, spongy materials like foam are quite effective at reducing sound leakage, and that is the decoupling of impact, or structure-borne noise. Impact noise is vibration that is transmitted directly between two solid surfaces by pushing or hitting the surface, as opposed to airborne noise, in which the air is transmitting the same energy. These vibrations are often made worse if the sound is close to the resonant frequency of one of the components that is in contact with the speaker, like metal beams or speaker stand poles.

For example, footsteps will transmit far more vibration directly through the floor than through the air, and this is why in buildings with poor insulation, even footsteps that feel rather quiet in the room will be easily heard downstairs. In this case, springy materials like carpet will cushion and soften these smaller vibrations effectively.

Loudspeakers will transmit both types of noise, sending vibrations through the air as normal sound, but also pushing and pulling the surface on which they rest. Placing them on mats or platforms designed to decouple them from the surface (which could be a stand, a desk, or the floor itself) can noticeably attenuate structure-borne noise – and improve the sound to boot.

1600-GRAMMA-D
Isolation platforms like the Auralex GreatGRAMMA help decouple speakers from the floor

Loud instruments that create a lot of impact noise (drum kits usually being the worst offenders) can benefit from mats and other absorbers, but to effectively isolate them, the whole airtight structure needs to be separated from the original space by building a “room within a room” that is mechanically decoupled from the original construction.

The easiest way to achieve this – as long as the space is available – is to install a professional premade isolation booth. This kind of product, while not cheap, will include both sound insulation and acoustic treatment as a one-stop solution for a professional-sounding space.

 

ESMONO-BoothIsolation booths such as the Esmono products combine acoustic treatment, insulation, decoupling, and air conditioning for best results.

It is important to align your expectations to what can be achieved depending on budget, time, or space restrictions. If you are unsure, you can always contact your favourite retailer, and they should be able to guide you through the options and suggest the best solution for your needs.

Happy recording!