3. Which factors can negatively affect the acoustics in your home studio?

Room modes are standing waves, and their potential to interfere is especially strong in the bass range. Modes can be recognised as disruptive booming or droning sounds. Bass instruments may sound imprecise, sometimes insubstantial, sometimes exaggerated, depending on the note you play. Room modes occur whenever half a wavelength or one of its multiples of a sound wave at a certain frequency fits exactly between two limiting surfaces. This phenomenon is called "axial modes" (there are also weaker tangential and oblique modes, which involve not only two but four or all six limiting surfaces, respectively) and it results in stationary cancellations and additions (standing waves).

Take as an example the deepest resonance frequency, with which you will always encounter very strong acoustic pressure directly in front of the walls and in the room's corners and edges. Towards the middle of the room, however, this frequency will almost completely cancel itself. Medium and high frequencies accummulate more and more resonance frequencies, increasing the resonance density so much that distortion ceases to appear. The figure above Shows another problem with modes. Since they are a phenomenon of resonance, they contain a great deal of energy, which takes some time to dissipate. With the lowest modes, the lingering booming and droning noise is easily recognisable.

Modes are especially distinct in small rooms with parallel limiting surfaces.

The worst locations are oblong/cuboid rooms with sides that are whole-number multiples of each other (e.g. 2 : 4 : 8). In rooms of the same relative dimensions, smaller rooms are more critical, as the resonance frequencies are particularly important in the fundamental tone range of music. Regarding room modes, living and basement spaces in contemporary residential buildings are a problem due to their low ceiling height. The typical ceiling height is 246cm; a person of average height's ears when sitting down will be almost exactly at half the room height. This means they'll be sitting in the area of minimum pressure for the deepest resonance frequencies and their odd-numbered multiples. Factory lofts and older tenement buildings are thus not only visually appealing, but also have acoustically beneficial properties.

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).

Typically, the reverberation times of the different frquencies are very uneven in smaller rooms.

Deep frequencies' reverberation is characterized by distinct room modes. Medium and high frequencies are inconsistently reflected or absorbed, depending on the characteristics of the walls and/or furniture. Small rooms therefore often sound droning or tinny. Real reverberation, such as we are familiar with from large auditoriums or churches, for example, does not occur in small rooms. We should therefore more correctly talk of decay time rather than reverberation time.