What is in this article?:
- Speaker selection is important, but so too is where you place it.
- Speaker placement
How should speakers be placed in a room, and what happens to the sound after it has left the speaker? When setting up a stereo pair of monitors, the first thing to look for is symmetry in the room and symmetry between the speakers and listening position. The distance between your two monitors should be the same as the distance between each one of the monitors and your listening position. This forms an equilateral triangle with 60º corners. Standing behind the left monitor and looking towards your listening position, you should see a similar view as when standing behind the right monitor. If there are different objects or different distances to side or rear walls or other objects (like large screens of your DAW), it will be impossible to achieve a similar response from the monitors. This causes imaging to suffer. The advice is to make sure that you have no reflecting objects between the monitors and your ears, which allows the acoustical audio path to be clean.
Most acoustical phenomena are related to wavelength, i.e. sound pitch. The higher the pitch, the shorter the wavelength and the easier it is to control. The direction where the sound goes from the speaker also depends on the wavelength. That said, it depends, actually, on how large the speaker is in relation to the wavelength. A 20Hz tone has a wavelength of 17m.
At 200Hz, it is still 1.7m. At 2000Hz, it measures 170mm, and at 20000Hz, it will be 17mm. Low frequencies spread all directions, moving as much forward as backward. At mid and higher frequencies, the speaker starts to direct the sound. This can be beneficial as we get more sound to the listener and less to room surfaces.
However, as low frequencies spread in all directions, walls also amplify them. Check this out by standing against a hard wall and talking out in the room. You can hear that your voice gets amplified. This amplification comes from the fact that low frequencies reflect from the hard wall, and the wall becomes a second sound source. When it coincides with the direct signal, the result will be approximately 6dB stronger.
Naturally, the same thing happens when you put a loudspeaker next to a hard wall. If you put the speaker in a corner, then you will have two reflecting surfaces and, thus, a pair of second-sound sources and a boost of 12dB. This can be both good and bad. It is good in the sense that less power is needed for a strong bass reproduction. But, it is bad in the sense that tonal balance will change unless corrected. Here, again, comes the need to adjust the speaker response in the room. It is necessary to correct the room boost in order to get neutral reproduction.
So far, we have talked about stereo only. As you can imagine, these problems become even more complex in a surround sound set up with five or seven speakers and one or two subwoofers. Still, the same guidelines apply: Look for symmetry, and keep the same distance.
There are two approaches to aligning speakers to the room. The frequency response can be adjusted with a few dipswitches controlling the active crossover, with carefully selected frequency ranges.
Or, the second approach is to use a digital signal processor built into the loudspeaker to take care of both the room response measurement and speaker acoustic alignment. This simplifies the whole acoustic calibration so that anyone with a bit of computer literacy is able to acoustically align his own monitors — be it a stereo pair or a much more complex surround system. A well-calibrated and acoustically aligned monitoring system will absolutely make any audio engineer’s life a lot easier, as guesswork can then be eliminated.