Room Acoustics Calculator — Reverberation Time and Room Modes Explained

Recording in a bad room is like trying to photograph through a dirty lens — you can fix some of it in post, but you're always working against the fundamental problem. Understanding your room's acoustic properties is the first step toward either treating it or working around it.

Calculate your room's key acoustic parameters with the room acoustics calculator on CalcHub.

RT60: The Core Acoustic Measurement

RT60 is the time it takes for sound to decay by 60 dB after the source stops. A concert hall might have an RT60 of 2–3 seconds. A good recording studio control room aims for 0.3–0.5 seconds. Your bedroom probably sits somewhere around 0.4–0.8 seconds depending on furnishings.

The Sabine formula (simplified):

RT60 = 0.161 × V ÷ A

Where V is room volume in cubic meters and A is total acoustic absorption (sum of surface areas × their absorption coefficients).

How to Use the Calculator

1. Enter room dimensions (length × width × height in meters or feet)
2. Select wall, floor, and ceiling materials (bare concrete, carpet, wood, acoustic panels, etc.)
3. Get RT60 at multiple frequencies (125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz)
4. See how much additional treatment you need to hit a target RT60

The CalcHub calculator also shows room modes — the resonant frequencies where your room will naturally boom or suck out.

Target RT60 by Room Type

Room Type	Target RT60
Recording studio (tracking room)	0.3–0.5 s
Control room / mixing room	0.2–0.4 s
Home listening room (hi-fi)	0.3–0.5 s
Podcast/voice recording booth	0.2–0.3 s
Live room for drums/full band	0.5–1.0 s
Concert hall	1.5–2.5 s
Cathedral / large reverberant space	3–10 s

Room Modes: The Bass Problem

Every rectangular room has resonant frequencies where bass builds up or cancels depending on your position. These are called room modes (axial, tangential, oblique). They're the reason the bass sounds boomy in one chair and thin in another.

Room mode frequency = c ÷ (2L), where c is the speed of sound (343 m/s) and L is the room dimension.

For a 5-meter room: 343 ÷ (2 × 5) = 34.3 Hz — first axial mode along that dimension. The second mode is 68.6 Hz, third is 102.9 Hz, and so on.

Rooms with dimensions that share common multiples have worse mode stacking. A 4m × 8m room has modes at 43 Hz, 85 Hz, 128 Hz... and the 4m dimension has modes at 86 Hz, 172 Hz... The 86 Hz mode gets reinforced from both dimensions, creating a particularly problematic build-up.

Basic Treatment Strategy

Bass traps in corners: Bass accumulates in corners (where all three room modes converge). Thick absorption material (4"+ of rockwool or rigid fiberglass) in floor-to-ceiling corners addresses low-frequency buildup. Absorption panels: First reflection points on side walls and ceiling reduce flutter echo and high-frequency RT60. Standard 2" acoustic foam or rigid absorption handles frequencies above 500 Hz. Diffusion: Scatters sound instead of absorbing it, maintaining liveliness while reducing comb filtering. Used on rear walls of control rooms.

How do I measure my room's actual RT60?

The simplest method: use a free acoustic measurement app (Room EQ Wizard is excellent and free). Generate a sweep tone from a speaker, record with a calibrated microphone, and the software calculates RT60 from the decay curves. Compare your measured RT60 to the calculator's prediction to validate your material assumptions.

Does room size affect what frequencies are problematic?

Yes. Larger rooms have lower fundamental mode frequencies and mode density increases at higher frequencies (where modes are closer together and less individually problematic). Small rooms — bedrooms, closets — are particularly challenging because modes in the 80–200 Hz range are widely spaced and interact badly. Very small rooms below 3 meters in any dimension should generally be avoided for critical listening or recording without substantial treatment.

Can I record vocals in an untreated room?

For voice-over and podcast work, the most practical solution is close-mic technique combined with a reflection filter (portable isolation shield). This minimizes room influence for speech. For music vocals where the room character is part of the sound, a slightly live room with controlled treatment is often preferable to a dead booth.

Related Calculators

• Speaker Wire Calculator — complete your speaker setup
• Audio File Size Calculator — storage for studio recordings
• Delay Time Calculator — sync reverb to project tempo