General Considerations about Room Modes

oom modes are acoustical interferences inside a room, either constructive or destructive, resulting in narrow-band peaks or dips in the measured frequency response of the room.

The audible consequences for listeners in a home theater may be excessive reinforced sounds in case of constructive interference or entirely missing in the perception of the listener when sound interferes destructively. This can be observed by moving around a room while perceiving a change of the sound level at the frequency of the resonance.

Room modes

There are three types of room modes:

Room ModesInvolved surfacesEnergetic Ranking
AxialOne pair of parallel surfaces1
TangentialTwo pair of parallel surfaces2
ObliqueAll surfaces are involved3

The energetic ranking can be explained by the number of surfaces involved. Energy is lost at every surface interaction which makes the axial modes the most energetic ones.

The following equation can be used to to identify the type of room modes with respect to the room dimensions:

f: frequency of the mode

n: mode order

l: dimension of the room

c: speed of sound

Olive showed that 30 % of the subjective sound quality judgements are due to the performance in the lower frequency ranges. In home cinemas, one aims to deliver a good sound quality at all listening spots in the audience area. However, this can be a high demanding objective as will be shown in this chapter. Seat-to-seat variations in sound level inside the listening area are mostly due to room resonances.

how a standing wave is formed between two parallel room boundaries?

Figure 1 depicts how a standing wave is formed between two parallel room boundaries:

Figure 1: Standing wave between two parallel surfaces.

As is generally known, there are room dimensions which are often recommended by professionals like Bolt, Boner, Louden, Sepmeyer, Volkmann.

However, according to Linkwitz, Fazenda et al. it seems that “the acoustical performance of rooms cannot be generalized on the basis of their dimensional ratios”, and thus are irrelevant in sound reproduction. Therefore, other considerations have to be taken into account to address room modes in home theaters.

What has been said so far and what we will discuss in the future, will pave the way for creating a home theater of the highest quality. The audio products offered in Saba Smart systems, which include Dali speakers, Yamaha amplifiers and inakustik cables with their great variety and high quality, make it possible to implement any type of equipment according to the relevant needs.

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