Loudspeaker Placement

As in the previous post, the environmental effects on the sound of the speakers, the topic of speaker types and their effects on the improvement of the space available for home theater were mentioned, in this post we intend to place the types of speakers, in terms of location. Take the speaker according to the frequency response and conductivity index and finally get a final result of their types.

bookshelf speaker

Fig 1. Small bookshelf loudspeaker (16.5 cm) measured in an anechoic chamber.

Figure 1. shows the measurement of a loudspeaker in an anechoic chamber (free field) which would represent a sort of free standing sound source inside a home theater. The DI is 0 up to 150 Hz showing an omnidirectional loudspeaker performance and becomes progressively more directional as frequency increases due to the violation of the loudspeaker being a point source for higher frequencies with shorter wavelengths.

Flush-mounted and on-wall speakers

Figure 2 (a) illustrates the effect of a flush-mounted in-wall loudspeaker. Compared to the free standing loudspeaker, an increase of the SPL in the low frequency range up to 500 Hz can be observed which is due to the additional sound energy being reflected forward by the wall. This effect shows less influence for frequencies above 500 Hz due to the increased directivity of the loudspeaker and therefore eliminating higher-order cancellations. As mentioned before, correction in terms of loudspeaker equalization is a useful way to address the increased sound pressure levels.

Fig 2. Small bookshelf loudspeaker, in (a) flush-mounted and (b) attached to a wall.

Figure 2. (b) depicts the results of a loudspeaker performance, mounted close to the surface of a wall. Now, besides the increase of the sound pressure levels in the low frequency range one can see a cancellation effect, which occurs with respect to the round-trip distance (78.8 cm) from the loudspeaker to the wall and back. This distance is about one-half wave length of 220 Hz creating a reflection with opposite phase relative to the direct sound and thus causing a dip at this frequency.

Fig 3. frequency response and DI.

Furthermore, a lower sound power output over a wider frequency range after the frequency dip (220 Hz) up to 500 Hz can be observed for the attached on-wall speaker, compared to the flush-mounted installation.

speaker placed in a cavity

Finally, we go to placing the speaker in a cavity inside the wall, in two cases without filling the empty space and filling the empty space around the speaker, and examine their behavior.

Fig 4. Small bookshelf loudspeaker, (a) placed in a cavity and (b) a cavity filled with fiberglass.

In Fig 4. (a) the loudspeaker placement in the cavity produces high quality resonances as well as diffraction effects caused by the edges of the cavity as sound leaves the cavity resulting in constructive and destructive interference.

Fig 5. frequency response and DI.

Figure 2.7 (b) depicts the impact of the cavity filled with fiberglass. The diffraction effect, as seen before in case of the untreated cavity could be addressed and improvements can be seen. Nevertheless, there is still evidence of a decreased performance when compared to the flush-mounted option.

Concolution

In conclusion, the adjacent boundary effects are affecting a wide frequency range and thus are not easy to address. Therefore, care has to be taken in terms of loudspeaker placements.

Eventually, it could be shown that there are just two loudspeaker placements such as free standing and flush mounted which perform quite well leading into a good way to start addressing the room acoustics in a home theater.

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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