Build of Loudspeaker Enclosures

Banf National Park, AL Canada (Photo by Yuichi)
This experiment is to simulate sound intensity (SPL) distribution in the room space considering reflection from the ceiling.

A white dot indicates a speaker position (Height Z=1m), A black dot indicates a listening (mic.) position (Z=1m). Room size is set as (X=4.5m, Y=3.7m and Z=Ceiling=2.6m=Solid)

Above curve is the frequency response at the mic position
in case we apply relatively flat sound source. Since mic
position is very close to the
sound source, response curve
is almost flat. After we confirm this, we move mic position to the listening position. Then, we find out better position by moving mic front or back or up or down.
The tool I used is TOA's Speaker System Design Software. This tool gives us simulation capability of sound intensity in the room. We can first define room size, then set speaker(s) position and ceiling material whether it is absorbent or solid in the setting window.

The system shows 2D sound intensity pattern. Red shows high intensity and blue shows low. Then, we can set or move the listening (=mic) position by the mouse. Then frequency curve at the mic position is shown. Therefore, we can find out best position. In this case, ceiling factor is only considered.
Intensity displays are both for sound pressure level and sound energy level depending upon our needs.
Mic position = Listening pos,
Freq = 1KHz
Speaker = 1
Ceiling = Solid
Mic position = Listening pos,
Freq = 1KHz, Speaker = 1
Ceiling = Absorbent

(Frequency curve is improved dramatically.)
Mic position = Center,
Freq = 1KHz, Speaker = 2
Ceiling = Solid

(The interference between two
speakers is outstanding.)
Mic position = Shifted to left a bit
Freq = 1KHz
Speaker = 2
Ceiling = Absorbent

Freq = 1KHz, Speaker = 2
Ceiling = Solid
(This is the Energy distribution in
the same parameters.)
Freq = 5KHz, Speaker = 2
Ceiling = Solid

(Intensity is below as expected in high frequency domain)
The sound reflection effect from the ceiling is not negligible to the frequency response at the listening position. The reflection effects from walls, floor and back wall in the listening room are not counted in this simulation. So, the intensity pattern and frequency response including all factors are very delicate. However, this will give us one of the ideas to find out better listening position in the room.

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