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The measurements and calibration of the loudspeaker/room system is done using MLS type signals,
professional WinMLS measuring equipment and high grade measuring microphones. All Genelec loud-
speaker have a design tolerance of +/-2.5 dB over their whole frequency response when measured in
free field (anechoic) conditions. This very tight manufacturing tolerance allows the calibration engineer to
match any Genelec loudspeaker models with any quality Home Theater environment to achieve superior
audio reproduction.
5
Room Construction and Acoustics
Low frequencies have long wavelengths that are omni-directional, so they bounce off all hard surfaces
in the room. The more solidly the room is built, the more the low frequency energy remains in the space.
Here are two basic cases:
•
A solid room offers good sound isolation from the rest of the building; unfortunately, it means that
the low frequency energy in the room should be absorbed to avoid standing waves, room modes
and bass cancellations (different words for the same thing!). A bad example of the reverberation
time in this type of room is shown in the red curve in the right hand graph of Section 5.1.2 Mid
and High Frequency Treatment. Subjectively the bass sounds boomy in some parts of the room
and there are other locations where there is little or no bass.
•
A leaky room allows the low frequency energy to escape from the room and so is equivalent to
improved room absorption. Unfortunately, this means that the low frequency energy travels to
other parts of the building and the mid and high frequencies become relatively lively compared
to the bass. A bad example of the reverberation time in this type of room is shown in the blue
curve in the right hand graph of Section 5.1.2 Mid and High Frequency Treatment.
A solid, isolating structure should be constructed from heavy material such as concrete, bricks or stone.
A single layer of 12 mm (½ inch) sheetrock screwed into wood studs is not a solid structure, however,
three layers of sheetrock on both sides of 4" studs followed by a 6" insulated air gap and another similar
wall starts to be. To get the real benefit of such structures, they have to be constructed with extreme care
and with proper supervision. Genelec recommends the use of a well-qualified room acoustician AND a
contractor with experience designing Home Theaters or similar type rooms, such as music studios.
5.1
Treating the Room for Good Acoustical Performance
5.1.1
Low Frequency Treatment
Sometimes there are customer complaints that the loudspeakers sound bad, however after some investi-
gation it usually turns out to be a lack of low frequency control in the room. Low frequencies are normally
considered to be below about 200 Hz, as this is where the room size starts to dominate the sound quality.
The formula which relates frequency to wavelength is:
c = ƒλ
Where: c is the speed of sound in air (344 m/s)
λ
ƒ is the frequency in Hz
Turning this formula around and applying some values to it gives:
Extending this calculation down to 50 Hz gives a very long wavelength of 6.88 m (25'8") and 20 Hz is a
colossal 17.2 m (56'5") in length.
30
is the wavelength in meters
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