I’m sure 99% of newbies doesn’t know the importance of this element. They probably thing the most importance element of acoustic treatment is acoustic panels. That’s wrong! The most importance element is bass traps. If you have money to only buy bass traps or acoustic panels, you should go for bass traps. And this is why…
what is a bass trap
First of all, lets clear out the purposes of bass traps and acoustic panels. In short and sweet,
Acoustic panels are to handle the mid and high range frequencies
Bass traps are to handle the low-end frequencies
But why did I say, “If you have money to only buy bass traps or acoustic panels, you should go for bass traps”. And this is why,
Bass traps have ability to control not only the low frequencies but little amount of mid and high range. And also function as a diffuser.
May be bass traps are the most non-attractive part, but the most valuable part of acoustic treatment and a must.
So finally, bass traps take care of low frequencies and makes the sound clearer inside your home studio.
Types of Bass Traps
There are two types of bass traps:
- Porous Absorbers (velocity absorbers)
- Resonant Absorbers (pressure absorbers)
Porous absorber are built with dense materials like mineral wool, fiber glass. Unless we call these absorbers bass traps, it doesn’t trap anything at all. Porous absorbers only absorbs the bass energy and convert it into heat energy.
How does this process happen?
Actually, Sound is movement of air particles. And you have definite learnt that sound doesn’t travel in vacuum. It needs a medium.
These air molecules hits inside these tiny pores in these material as they pass through it and stops movement of particles. So, when air molecules rub inside these tiny pores it generates heat.
And this is how bass energy to heat energy happens.
Porous absorber are also called velocity absorber because it perform action on velocity component of a sound wave.
where to place bass traps
First of all, you must know the relationship between pressure and velocity.
In a sound wave, the place where the velocity is high is the place where the pressure is zero and the place where the pressure is high is the place where the velocity is zero.
Imagine, when you throw a ball towards a wall, when the ball touches the wall it doesn’t move. So, the velocity at that moment is zero but the pressure is maximum.
So, a sound wave acts the same. On the surface of the wall the pressure is max, and velocity is min.
You might have notice bass traps are always mounted in corners. Yeah that’s the place to mount bass traps. The reason for that is usually corners are where bass energy builds up.
As porous absorbers are velocity absorbers, to get the maximum efficiency of bass traps we should place them where the velocity is maximum. But you know now on the reflecting surface the velocity is zero. So, you should place them far form the wall. And this is where ¼ wavelength rule get used. As shown in the above picture, where the ¼ of the length of the sound from the wall is where the velocity is maximum and also that’s the place, we should mount our bass traps.
By placing bass traps like this we can get the full efficiency of porous absorbers to absorbs low frequencies with the use of ¼ wavelength rule.
Resonant absorber are pressure absorbers. So, these absorbers act on pressure components of the sound wave. The reflective surface is the point where pressure is high as we studied earlier. But not as porous absorbers, resonant absorbers are much default to mount. If you don’t place them in the right position you don’t get the proper use of it. And it will be waste of time and money.
If you are a newbie or trying to build a regular home studio with a low budget, I recommend going for only porous absorbers.
There are two kind of resonant absorbers:
- Helmholtz resonators (absorbs bass frequencies through air cavities)
- Diaphragmatic Absorbers (cancel bass frequencies by a membrane or vibrating panel)
In a pro studio, these both two types of absorbers (Porous and Diaphragmatic) used.
Resonant absorbers can absorb very low bass frequencies than Porous absorbers. So, these two types of absorbers work great together.
If you are building a home studio, skip these absorbers.
Mounting the Bass Traps
In a room, there are two types of corners, dihedral and trihedral.
When we are mounting the bass traps, the first priority goes to the trihedral corners because they have 3 surfaces. And after goes to dihedral corners.