Resonance absorbers, also known as tuned traps, pressure absorbers or narrowband absorbers, are devices that are frequency-dependent. This is because of the desired resonance of a particular material at a specific wavelength. There are several types of resonance absorbers, such as the Jaumann absorber, the Salsbury screen, the Dallenbach layer, the circuit analog absorbers, and the crossed grating absorbers.
Resonance absorbers involve either a mechanical or an acoustic oscillation system. This system is commonly a membrane absorber featuring a solid plate with a tight air space on the rear end. Within membrane absorbers, the absorption achieves its maximum value when reaching a specific resonance frequency. Membrane absorbers are capable of falling to lower values at both higher frequencies and lower frequencies as well.
Users can control this maximum value of absorption by choosing a specific material to fill the air space. It’s worth mentioning that sound engineers often fill the space with porous material in order to broaden the absorption over the range of the frequency. This material can be either a porous board or blanket made of mineral fibre or glass fibre. It’s worth mentioning that the value of absorption depends entirely on the flow resistance of the particular material and not on the depth of the airspace, the open area, the perforation diameter, and other physical dimensions of the sound absorptive treatment.
Resonant absorbers zero in on specific problems with bass frequencies while ignoring everything in the mid/upper range. On the other hand, porous absorption provides great broadband coverage and lacks bass absorption. Also, resonant absorbers operate best when placed against a wall because the pressure tends to be higher and the sound waves are more likely to collide. On the other side, porous traps work better when spaced of the wall so they require much more space than resonance absorbers.