Sound absorbing materials

Let's start with the concept that every material is in some way sound absorbing.

A small part of sound energy is always absorbed but the substantial difference is how much energy each material can absorb.

It is easy to enter an empty and unfurnished room and feel an annoying echo.

The sound-absorbing materials are used to reduce the excessive "vivacity" of the room and to ensure that the sounds reach our ears directly without bouncing between the walls, making the hearing experience pleasant and relaxing.

Here are some types of sound-absorbing materials:

1. POROUS MATERIALS: the most widespread on the market and the easiest to obtain by processing raw materials. They perform at high / medium frequencies and their porous structure allows the diffused sound in the air to penetrate inside and transform its energy into heat. Among the most important we remember:

⁃ Melamine foam: typically pyramidal in shape, these are the classic sound absorbers that are seen in the rehearsal rooms. Very effective on high / medium frequencies. Their performance varies due to factors such as thickness, position and density.

⁃ Mineral wool: rock or glass, they are mainly used in construction as thermal insulators. They also have sound absorption properties above about 135hz. They are on the market in the form of "broadband" even at large retailers. They belong to the type of "do it yourself" solutions with results that are not always effective.

2. RESONATING DEVICES: they absorb the low frequencies very well and this is why their use should be recommended in combination with porous materials to obtain an accurate listening in an environment. Among the best we find:

Membrana Membrane devices: devices composed of a membrane that resonates with low frequencies and, in contact with an interspace, absorbs them. With medium and high frequencies, on the other hand, they work by reflecting the sound.

⁃ Resonators: more complex than the previous ones, they work on precise resonance frequencies. The frequency on which the resonators act depends on the diameter of the opening, the length of the duct and the volume of the air chamber. Above all they correct the excessive resonances of the room.

3. MYTHS AND LEGENDS: There are materials that tell of incredible acoustic performances. Let's see what they are:

⁃ Egg cartons: present in some DIY test rooms, in reality this material only works on medium frequencies around 1000hz and therefore they are practically null as a sound-absorbing material.

⁃ Cork: popular in the 80s / 90s, this material is beautiful to look at but has no sound-absorbing properties. Moreover, being very expensive, it was soon replaced by other products.

⁃ Wood and chipboard: even these materials do not have sound-absorbing characteristics, however, if properly worked (perforated and milled), they can guarantee excellent performance in acoustics.

⁃ Packaging foam: the porous internal structure and the similarity to the melamine foam can lead off-road. In fact, even this material (present in many recording studios in the 1980s) has no sound-absorbing functions and has disappeared. Today it is used more properly to repair objects from shocks when moving.

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