PART 1: INTRODUCTION


What is room acoustic treatment?

Acoustic treatment is used to reduce the frequency-dependent reverberation times of your room (RT60) and thus to correct the frequency response.
Often terms such as "room acoustics" and "soundproofing" are used interchangeably by laymen and suppliers of acoustic panels.
That's wrong !!!

To address your individual problems, and to have no misconceptions about the result, it is important to understand the difference between room acoustics and soundproofing:

Room acoustics is airborne sound attenuation resp. diffusion and "ONLY" improves the acoustics within your room.
It uses sound-absorbing or diffusing materials that are positioned at specific points in your room.
Room acoustic treatment doesn't make sure your neighbors will not notice your nocturnal sessions

Soundproofing, on the other hand, is structure-borne sound insulation and is usually a very expensive construction project in which a room is built inside your room.
For this purpose, double layer drywalls are being constructed, which are filled with insulating wool and bitumen foil. These drywall layers must be completely decoupled from each other and from the original room walls. To decouple the floor, several layers of insulating wool and mass loaded vinyl or rubber mats are layered under the floor.
However, since this thread is only about room acoustics, I will not discuss the subject of soundproofing here.


Why do you need an acoustic room treatment?

When recording, producing or mixing in your home studio, it is important that ...

• Your signal can be recorded as dry as possible and without unwanted sound coloration of the room.
• You can hear everything in your production or in your mix.

If we want to treat the acoustics of our room, we basically have to deal with two parameters:
Reflections and Frequency Response!



Reflections:

For example, when an acoustic signal is reproduced by a loudspeaker in the room, the mechanical energy of the loudspeaker diaphragm is transmitted to the air and the mechanical energy is converted into sound energy.
The sound spreads in all directions in your room, reaches your ear directly (direct sound), reaches walls, is reflected off the walls and thrown back, hits other walls, is thrown back and so on ...
The result is that the reflections hit your ear with a time delay to the direct sound.

If you are in a very large room, for example in a church, and the speaker is close to you, the time difference between direct sound and reflection is quite high.
This means that your brain perceives the direct sound and the reflections as two or more separate events and interprets the reflections as echo or reverberation.

However, if you are in a small room, for example in your bedroom, the delay between direct sound and reflections is shorter.
Your brain can not distinguish between direct sound and early reflections and interprets both as a single event.
This can lead to several problems:

• First, the frequency response and the perception of the impulse (smearing of transients) change due to interference between direct sound and early reflections.
• Second, the spatial perception of the signal is affected. Phantom sound sources between two speakers are not clearly localized or even shifted.

Frequency Response:

Reflecting and superimposing sound waves in your room emphasizes some frequency ranges and underemphasizes others.
It is important to understand that the frequency response of the room differs at every point in the room based on reflections and pressure.

To illustrate this, just do the following experiment:
Open a tone generator in your DAW, set a sine wave to 100 Hz and play the sound through your speakers. The sound should be played relatively loud.
Now move slowly through your room and pay attention to where the sound in the room is perceived louder or softer by you.

The biggest challenges in the acoustic treatment of a room are its own resonances, the so-called room modes.
Room modes are (by definition) frequencies below 300 Hz whose wavelength or quotients (/2) and multiples (*2, *4, *6, ...) of this wavelength correspond exactly to the length, width or height of the room.

If the room has a length of 5m, a width of 3m and a height of 2.5m - then the possible room modes are

• for the length: 34,3 Hz, 68.6 Hz, 137.2 Hz, 274.4 Hz
• for the width): 57.15 Hz, 114.3 Hz, 228.6 Hz
• for the height: 66.1 Hz, 137.2 Hz, 264.4 Hz

However, these axial modes are not all possible room modes. Diagonal room modes (tangential, oblique) are also possible.

THE PROBLEM: To absorb a frequency, it needs absorbing mass!

The lower the frequency, the more energy has to be absorbed. Accordingly, it requires more mass, the smaller the room is.
The sound wave length of 34.3 Hz is 10 meters! Although it depends on the absorption material and its gas flow resistivity,
but as a rule of thumb we can say:

It takes 1/4 of the wavelength of pure absorbent material to completely damp this frequency.
This means that a 2.5 meters thick absorber is in a room with a total length of 5 meters.
This is completely unrealistic and can be solved much more efficiently. I will return to this topic later.

I just wanted to make it clear that pyramid foam or 5 cm thick Rockwool absorbers will not solve your problem.
It's quite the opposite!

PART 2 ->

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Last edited: Oct 1, 2019