SP395 SoundPro Audio Integrator Form7492 Operation Manual
67
Transmission Loss
Transmission Loss is used to measure the amount of sound isolation that a partition provides.
Typically, a noise source is placed on one side of the partition, and the room noise level is
measured in 1/3 octave bands, sometimes at more than one point. Then, the measuring device is
moved to the other side of the partition (presumably in another room) and the same measurement
is taken. Then, the transmission loss (TL) at each 1/3 octave bands is computed, and a formula is
applied to derive a numeric number representing the relative noise reduction of the partition. The
idea is that this number can be used to effectively compute the amount of reduction in sound
level that a partition (wall) will provide in actual use.
There are several ways of measuring transmission loss. One key issue is whether or not the
measurement is being done under laboratory conditions, with carefully controlled room reverb
time and control of sound leaking around the partition, or whether the measurements are being
taken in the field under minimal control characteristics.
Several standards apply here, including ASTM 90, which talks about how to measure the
transmission loss data, ASTM 413 (or ISO 717-1), to define a laboratory measurement, and
ASTM 336, which takes the lab measurement and applies it to field work.
The SP395 calculates laboratory values including STC, RW, and OITC. STC (Sound
Transmission Class) is the ASTM (US) measurement, RW is based on the European standard,
and OITC (Outdoor-Indoor Transmission Class) is based on an A-weighting curve, and is
considered by some to be more modern.
Please note that even if you are doing an “STC” measurement, technically the
measurement is an NIC measurement since it is being done in the field.
The Transmission Loss test screen and control fields.
The Transmission Loss test screen and control fields:
1. Test Function – Identifies Transmission Loss (TL) as the selected function and
measurement screen.
2. Test Standard – Selects a standard used for determining a Transmission Loss value.
Select from Balanced Noise Curves (NCB), Room Criteria Outdoor/Indoor Transmission
Class(OITC) or Sound Transmission Class (STC)
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