Acoustic Study - Room Acoustics (RT60) and HVAC Noise (NC / NR)

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Input Data

Enter your project data

Room type

Sets the target reverberation time and the target NC (both can be overridden below).

Room length (m)

Inside dimension

Room width (m)

Inside dimension

Room height (m)

Clear height (to the ceiling that is acoustically effective)

Floor finish

Base finish of the whole floor - other materials on part of it: '+ Add area' below

Ceiling finish

Base finish of the whole ceiling

Wall finish

Base finish of all walls - windows, doors and panels: '+ Add area' below

Number of people (-)

People present during use (each adds absorption)

Furniture

Equivalent absorption of furniture, as a share of the floor area

Target reverberation time (0 = by room type) (s)

Leave 0 to use the target of the room type

HVAC noise calculation

Supply air path from the fan to the outlets in this room

Target NC (0 = by room type) (-)

Leave 0 to use the NC of the room type

Fan sound power

Catalog: enter the discharge (outlet) sound power per octave from the manufacturer

Fan air flow (m³/h)

Air flow through the fan

Fan total pressure (Pa)

Total pressure rise of the fan (for the sound power estimate)

Fan type

Sets the shape of the estimated spectrum

Ducts run

Sets the recommended maximum duct velocities

Outlet type

Supply outlets in this room

Number of outlets in the room (-)

Identical outlets sharing the room air flow

Outlet neck width / diameter (mm)

Neck (connection) size - diameter for circular diffusers and disc valves

Outlet neck height (mm)

Rectangular outlets only (slot: slot width × length of the plenum spigot)

Outlet catalog NC (0 = estimate) (-)

NC of one outlet at its air flow from the catalog - 0: estimated from the neck velocity

Listener distance to the nearest outlet (m)

Typically the height from the outlet to the ear (seated 1.2 m)

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Calculation Results

Calculated instantly from your inputs

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Room acoustics and HVAC noise

Two things decide how a room sounds: how long the sound lingers (reverberation time) and how loud the background noise is (mostly the HVAC system). A long reverberation makes speech hard to understand in classrooms, meeting rooms and mosques, while churches need some for music. HVAC noise travels from the fan through the ducts and is joined by the noise of the air leaving the diffusers; silencers, lined ducts and low velocities keep it below the NC target of the room.

Key Points:

RT60: time for the sound to decay by 60 dB after the source stops
Sabine for ordinary rooms, Eyring when the room is very absorbent (ᾱ > 0.3)
Absorbent ceiling is the most effective single measure in most rooms
NC rating: the lowest NC curve that no octave band exceeds
Low-frequency fan noise needs long silencers or lining - elbows help little
Outlet noise rises with about the 6th power of velocity: keep neck velocities low
Use manufacturer octave-band data for the fan, silencer and outlets in the final study

Calculation Steps:

Enter all required parameters
Click "Update Calculation"
Review results and analysis

Formula Variables:

T Reverberation time (decay of 60 dB) (s)

V Room volume (m³)

A Equivalent absorption area (m²)

ᾱ Mean absorption coefficient (-)

Lw Sound power level (dB)

Lp Sound pressure level (dB)

R Room constant (m²)

Q Directivity factor (-)