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The manufacturer-rated insertion loss for the first silencer or lined duct section in the path.
From the manufacturer, at the frequency band you care about. Insertion loss varies enormously across the spectrum, so a single headline number is a summary of a curve — and the low-frequency end, which is where fan rumble lives and where it travels furthest through a building, is where silencers do least. A silencer chosen on its best figure will disappoint at its worst one.
The manufacturer-rated insertion loss for the second silencer or lined duct section in the path.
Two elements in series do NOT simply add their ratings. Once the direct path through the duct is treated, the remaining sound arrives by other routes — breaking out through the duct wall before the silencer and back in after it, or travelling through the structure — and those set a floor that no amount of in-duct attenuation gets below. The second element therefore delivers less than its rating, and a third less again.
The manufacturer-rated insertion loss for a third silencer or lined duct section, if present.
Enter 0 if the noise path only has two components.
Estimated total insertion loss
25 dB
This is a simplified additive estimate for first-pass screening only — it does not account for regenerated (self) noise from the silencers/airflow, cross-talk, or flanking paths, and combines losses without full octave-band detail. A complete noise control analysis for a critical space (e.g. a recording studio, courtroom, or hospital) requires a qualified acoustics engineer's multi-octave-band evaluation.
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HVAC Duct Silencer Cumulative Insertion Loss Calculator: 25 dB — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Total system insertion loss (dB) ≈ sum of each component's manufacturer-rated insertion loss, a simplified additive estimating method commonly used for a first-pass HVAC noise control screening per ASHRAE Applications Handbook (Chapter on Noise and Vibration Control) design practice. This does not account for regenerated noise, cross-talk, or flanking, and a full multi-octave-band acoustic analysis by an acoustics engineer is required for critical noise-sensitive spaces.
Inputs used
- Component 1 Rated Insertion Loss (dB)
- 12
- Component 2 Rated Insertion Loss (dB)
- 8
- Component 3 Rated Insertion Loss (dB, 0 if Not Applicable)
- 5
Confidence note: This is a simplified additive estimate for first-pass screening only — it does not account for regenerated (self) noise from the silencers/airflow, cross-talk, or flanking paths, and combines losses without full octave-band detail. A complete noise control analysis for a critical space (e.g. a recording studio, courtroom, or hospital) requires a qualified acoustics engineer's multi-octave-band evaluation.
What this calculation does not cover
- Every silencer in that stack costs static pressure. A packed unit at design velocity typically adds 25 to 125 Pa (a tenth to half an inch w.g.), and three in series can push the fan to a larger wheel or a higher speed — which puts more sound power into the duct at the same time, so attenuation bolted on late in a design partly eats itself. The pressure drop is printed on the same manufacturer's table as the insertion loss, and this total does not touch it.
- Attenuation is not a sound level. Knowing the path removes 25 dB says nothing about where the room ends up: that comes from the fan's sound power, everything else along the path, and the room's own size and absorption — and it is the resulting NC or dBA in the occupied space that a specification is written against. A loud enough source can be 25 dB quieter and still too loud for the room it discharges into.
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This result is a specification — 25 dB — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Total system insertion loss (dB) ≈ sum of each component's manufacturer-rated insertion loss, a simplified additive estimating method commonly used for a first-pass HVAC noise control screening per ASHRAE Applications Handbook (Chapter on Noise and Vibration Control) design practice. This does not account for regenerated noise, cross-talk, or flanking, and a full multi-octave-band acoustic analysis by an acoustics engineer is required for critical noise-sensitive spaces.
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