sentences:  Both types are effective, but whereas a resonant absorber needs to be mechanically tuned to resonate in sympathy with the frequencies being absorbed, a porous absorber does not resonate and need not be tuned.Porous absorbers tend to be smaller in size and are easier to design and build as well as less expensive overall than resonant absorbers.However, the deep bass attenuation of a porous absorber is generally inferior, so its usefulness for attenuating lower frequency room resonances is more limited.