HVAC attenuation
Attenuation is how plant noise is kept out of the room, and how two rooms on the same duct are kept out of each other.
Also in this branch
Three different problems share one toolkit. Noise from the plant travels along the supply and return. Noise generated at grilles and dampers is made locally by air moving too fast. And speech passes between rooms through a shared branch — crosstalk, which no amount of wall construction will fix, because the sound never touches the wall.
The measures
| Duct silencer | Selected for the frequencies the plant actually produces, not a nominal length. |
|---|---|
| Acoustic lining | Absorbent lining inside the duct where the run allows it. |
| Plenum | A lined box breaking the direct path, at the plant or at the room. |
| Crosstalk attenuator | In branches serving two rooms that need privacy. |
| Lagging | Where a duct passes over a quiet room and radiates through its own wall. |
| Velocity limits | At grilles and diffusers, so the terminal is not itself the noise source. |
| Flexible connections | At the plant, so vibration does not travel down the duct as structure-borne noise. |
Sizing is arithmetic
Given the plant sound power by octave band, the background noise target in the room, the airflow, the duct dimensions and the pressure available, attenuation can be calculated rather than guessed. Without those numbers it is guesswork with a cost attached — so where plant data is not available, we measure the equipment instead of assuming.
- Collect plant sound data and the room's target.
- Model the duct run — lengths, bends, branches, terminals.
- Calculate the attenuation required per band.
- Select silencers and lining against pressure available.
- Check regenerated noise at the terminals.
- Measure the finished room and report.
Lead with data — sound power, airflow, pressure drop. Numbers before adjectives.
What we need
- Plant sound power data, by octave band.
- The background noise target in each room.
- Airflow rates and duct sizes.
- The pressure the fan can give up.
- Duct layout, including which rooms share a branch.
Tell us the room
Send dimensions and intended use. You get back an indicative acoustic treatment, a systems outline and a budget range.