Short answer: Fan noise is specified using sound power level (Lw, dB) measured per AMCA 300, not the easily misread sound pressure at one point. Specifiers should define an acceptable sound power per octave band and a site sound-pressure limit (dB(A)) at the receptor, then select silencers and layout accordingly. Confusing the two is the most common acoustic specification error.
Sound power (Lw) is intrinsic to the fan, independent of distance — what AMCA 300 certifies.
Sound pressure (Lp, dB(A)) is what a person hears at a location, falling with distance and surroundings.
A fan quoted only as "70 dB" is meaningless without stating which one and at what distance.
AMCA 300 (Reverberant Room Method) gives comparable sound-power data across manufacturers — essential for fair specification. Require AMCA-tested values, preferably with the AMCA seal, rather than estimated figures.
Context | Typical site limit (dB(A)) |
Industrial plant boundary | 70–85 (local regulation) |
Commercial/HVAC rooftop | 45–55 at receptor |
Tunnel portal (urban) | Project-specific, often strict |
Over-specifying forces costly silencers that waste energy; under-specifying fails commissioning. Match the limit to the actual receptor.
Inlet/outlet silencers reduce sound but add static pressure — and therefore energy. Specify the minimum attenuation needed, not a blanket maximum, to protect both noise compliance and efficiency.
Sound-power levels per octave band (AMCA 300)
Site sound-pressure limit at the receptor and its distance
Silencer attenuation required (targeted, not maximum)
Fan speed and impeller type influence (lower tip speed = quieter)
Q: What does "70 dB fan" mean?A: On its own, nothing — it must state sound power (Lw) or sound pressure (Lp) and the measurement distance. Always specify sound power per AMCA 300.
Q: Is AMCA 300 the same as AMCA 210?A: No. AMCA 210 governs air-performance testing; AMCA 300 governs sound. Both may be required for a complete fan specification.
Q: Do silencers hurt efficiency?A: They add static resistance, so yes, if oversized. Specify only the attenuation the site actually needs.
Q: Can I specify a quiet fan without a silencer?A: Sometimes — low tip-speed impellers and good isolation help, but most stringent site limits still need silencers.