Of all the principles that govern sound isolation, mass is the most fundamental. The relationship between a structure’s mass and its ability to resist sound transmission is not a rule of thumb — it is a physical law, and understanding it prevents the most common and costly soundproofing errors.
The Mass Law describes how the sound transmission loss of a partition increases with its surface mass and with frequency. For every doubling of a wall’s mass — adding a second layer of the same material — transmission loss increases by approximately 6 dB. For every doubling of frequency, transmission loss also increases by approximately 6 dB. This means that heavy structures attenuate sound more effectively than light ones, and that all structures attenuate higher frequencies better than lower ones.
The practical consequences are significant. A standard timber stud wall with a single layer of 12.5mm plasterboard on each face has a surface mass of approximately 25 kg/m². Adding a second layer of plasterboard to each face doubles this figure and adds roughly 6 dB of transmission loss. Adding a third layer adds a further 3 to 4 dB — diminishing returns set in, but the principle holds.
Low frequencies are the most difficult to attenuate for this reason. A 50 Hz bass note has a wavelength of approximately 7 metres. Stopping it requires either enormous mass — far beyond what domestic construction typically provides — or decoupling strategies that prevent the vibration from transferring through the structure in the first place.
This is why thin acoustic foam, acoustic wallpaper, and mass-loaded vinyl applied to light partitions fail to achieve meaningful bass isolation. They add some mass, but not nearly enough to produce significant low-frequency attenuation. The Mass Law is not negotiable — and marketing materials that imply otherwise are not to be trusted.
For meaningful broadband sound isolation, mass must be a deliberate part of the structural design, not an afterthought applied to an existing light partition.