These terms and definitions are related to Sound Transmission Class and will help provide the
full picture of how sound is measured.
dBa – A-weighted decibels. Measurement of sound as perceived by the human ear. Decibels
relate to all sound possible (that can be perceived by say, a dog). A-weighted decibels are a
scale of measurement for all sound that can be heard by humans, starting with zero as the
lowest threshold of human hearing and going up to 110 dBA for jet fly-over/indoor rock band.
Transmission Loss – How much sound is lost going through a material. When sound
reaches an object, some of the noise vibrations are reflected by it, some are absorbed, and
some travel through it. The amount of sound that does not travel through it, is considered
loss. It is the difference between the sound going into the object and the sound coming out the
other side.
Frequency (Hz) – Sound is vibrations that travel through the air. Frequency is the speed of
the vibrations. Frequency is measured in units of Hertz (Hz). Hertz measure the number of
wave cycles per second. Low frequency sounds, like thunder or a train, would have a lower
Hz. High frequency sounds, like a whistle or a bird chirping, would have a higher Hz.
While STC rating can provide a good indication of how a material or product will perform
against sound in general, it isn’t the whole picture. That’s why it’s good to keep these other
definitions in mind. Certain sounds or noises will affect different people differently. STC rating
is one number that shows general sound resistance, but does not take Hz into account.