Resolving Flutter Echos In Your Studio

Flutter echoes occur between parallel limiting surfaces when sound is percussively stimulated, for example when you clap your hands. The short acoustic pulse is thrown back by a “hard” wall and travels to the opposite wall only to be reflected towards the first wall once more. This is repeated in rapid succession until the sound energy has been fully absorbed. The closer these parralel walls are, the faster the reflections follow one another and the stronger are the resulting distortions. They manifest as metallic “boing” noises and are generated by the repeating sound pulses stimulating the higher-frequency room modes. If, in addition, the mode density is low in the medium frequency range, the stimulated modes result in distortions to the sound. The room’s own deep resonance frequency will most likely not be stimulated, however, as this would require continuous stimulation. Flutter echoes are therefore a phenomenon prevalent in the medium frequency ranges. They become a nuisance mainly if the room has already been well dampened acoustically in other ways, i.e. when the decay time of the room overall is shorter than for the flutter echo by itself.

This, too, is a problem of small rooms in particular. Since the reflections need to pass through relatively little space, they rapidly encounter the next limiting surface and are reflected once more. With every reflection, the reflected sound loses some of its energy and thus decays after few reflections. This does not allow for a dense or diffuse sound field with even sound distribution to be generated. The sound receives a metallic tinge in such cases, which can be traced back to the time-delayed overlap of the direct sound with the few reflections (comb filter effect).