Lowell EQ1 - Manual (Page 8)

Instruction Sheet
IS-EQ1
Issued: 1-20-14
Lowell Manufacturing Company 100 Integram Drive Pacific, Missouri 63069 U.S.A.
Call: 800-325-9660 Fax: 636-257-6606 Click: www.lowellmfg.com
8
Tuning a Sound Masking System using the EQ1
Sound masking systems are installed to provide speech privacy in modern open-office plans with low partitions
that make up cubicles for the office workers. The concept is that by raising the ambient noise in the open-office
area, workers find it harder to hear and understand what their neighbor in the adjacent cubical is talking about.
Productivity can be increased by reducing distractions. Sound masking speakers are typically installed above
the finished ceiling aiming upward. The masking noise bounces off of the structural ceiling that is above the lay-
in tile finished ceiling and then filters down through the tile to the office area below. The masking sound is
colored by both the material that it bounces off of above the ceiling and by the ceiling tile that it passes through.
It is important to use a 1/3 octave graphic equalizer like the EQ1 to restore the frequency content of the sound
masking noise to a spectrum that has been determined to optimize the speech privacy effect. The curve below
shows the ideal sound masking noise curve to achieve at the listeners position (this is called the NC40 curve).
Sound masking system graphic equalizer adjustment is a fairly simple process. Once the speakers are installed
and all ceiling tiles are put in place so the finished ceiling is completely closed, pink noise (un-equalized) is fed
through the system (
usually the pink noise is generated by a “Masking Noise Generator” that is designed
specifically for sound masking systems). The RTA microphone is placed in a typical cubical at 4' from the
finished floor (the average listeners ear position). The masking sound is turned up until the energy at 160Hz is
roughly 44 dBA. Adjust the sensitivity of the RTA so the 160 Hz band is reading +4dB. Adjust the 63Hz-2kHz
band sliders to achieve the ideal curve shown above.
Desired Results on the RTA Display (NC40 Curve):
63Hz = -7dB, 80Hz = -4dB, 100Hz = -1dB, 125Hz = +2dB, 160Hz = +4dB, 200Hz = +4dB, 250Hz = +3dB, 315Hz = +2dB, 400Hz = +1dB,
500Hz = 0dB, 630Hz = -1dB, 800Hz = -2dB, 1kHz = -3dB, 1.25kHz = -4dB, 1.6kHz = -5dB, 2kHz = -6dB,
The masking noise above 2kHz and below 160Hz should be allowed to roll off smoothly and naturally. The
acceptable levels above 2kHz and below 160Hz can be anywhere in the shaded area of the graph above. The
goal is to make the masking noise sound similar to air handling noise. Any adjustments made above 2kHz and
below 160Hz should be made in an attempt to make the noise more soothing and more like air handling noise.
Desired Frequency Response for Sound Masking Systems