Qt X Sound Masking System
Installation and Operation Guide
page 23
Setting Sound Masking Levels
Target sound masking levels may vary from area to area throughout a facility
based on use. Multiple controller outputs may serve virtual zones of sound
masking making user control and adjustment simplistic. Outputs may be adjusted
independently to compensate for emitter mounting heights and architectural
conditions present. Each virtual zone of Qt X sound masking may serve specific
architectural spaces and include background music and/or paging signals (when
used with supported emitters) by using external audio sources. Best practice
in setting sound masking levels is to use a sound level meter. Typical sound
level targets to create effective / comfortable sound masking for common office
environments are as follows:
Zone Type
Measured dBA SPL
Private Office Zones
38-43 dBA
Open Area Zones
44-48 dBA
Corridors
42-45 dBA
A-weighted sound masking levels in dB SPL as measured 4ft (1.2m) above finished floor using
a calibrated sound pressure level meter. (Class 1 SPL Meter / Microphone recommended)
If no sound level meter is available, the levels above may be achieved in most
environments by setting the Qt X sound masking volumes as follows:
Zone Type
Qt X Zone Setting
Ceiling Height
Private Office Zones
-5 dB to -1 dB
All ceiling heights
Open Area Zones
+1 dB to +4 dB
8 ft (2.4m)
+3 dB to +6 dB
10 ft (3 m)
+5 dB to +8 dB
12 ft (3.7 m)
Corridors
0 dB to +2 dB
All
Note:
Levels based on individual output levels set to 0 dB
In cases where sound masking levels exceed these recommendations,
especially in extremely quiet environments, occupant acceptance will diminish
greatly leading to occupant complaints. This can result in dissatisfaction with
the sound masked environment and a request by staff for eventual lowering of
sound masking levels, ultimately reducing the effectiveness of the system. For
this reason, each zone of a Qt X sound masking system should be calibrated and
adjusted precisely upon installation completion using calibrated measurement
equipment by the qualified installer.
COMMISSION THE SYSTEM
(continued)
Once sound masking levels are optimized for a space, it is always recommended
to that they remain consistent indefinitely as very small changes in level can be
noticed by building occupants as they occur. It is permissible however to adjust
sound masking in small increments over long time spans at specific times of day
using scheduling functionality. Reducing a sound masking levels at night (under
conditions of little to no building occupancy) can be beneficial for security staff to
hear/detect intrusion. Qt X provides daily scheduling functionality which allows
attenuation of the sound masking levels between specific time frames to meet
reduced masking level needs. These schedules include a “ramp duration time”
in which the change in level is to occur, extending the gradual level adjustment
across multiple hours slowly. This slow change in sound masking level helps
to avoid detection of level changes by remaining building occupants. The table
below indicates the recommended ramp duration time based on desired sound
masking attenuation;
15 Minute Ramp Duration
<1 dB attenuation
30 Minute Ramp Duration
1 dB to 1.5 dB attenuation
60 Minute Ramp Duration
2 dB to 2.5 dB attenuation
90 Minute Ramp Duration
3 dB to 4 dB attenuation
120 Minute Ramp Duration
>4 dB attenuation
Effectiveness of a sound masking system is dependent on adequate volume
level. Occupants will typically become accustomed to the sound masking noise.
If a sound masking system is introduced to a location that was previously
occupied, it is necessary to introduce the sound masking to the occupants
gradually. To do this the installer must use the "Soft Start" feature (configurable
in the web interface). This provides an adjustment time period to slowly introduce
the sound masked environment over a period of days/weeks. If the location is
new, or was not previously occupied a Soft Start is not necessary.
Soft Start recommended settings -
Open Office
Set the attenuation to -5 dB over the course of 2 weeks
Private Office
Set the attenuation to -3 dB over the course of 1 week
See the Qt X web interface help <
> for more details on setting sound
masking levels.
