Reverberation Time Optimization for Conference Rooms

By Priya Nair · February 7, 2026

Reverberation Time Optimization for Conference Rooms

Conference rooms fail more often from room acoustics than from microphones, DSP, or loudspeakers. The most common culprit is reverberation time (RT): the amount of time it takes for sound energy to decay in the room. When RT is too long, speech intelligibility drops, far-end listeners on video calls hear a “bathroom” quality, and automatic echo cancellers work harder (sometimes to the point of pumping or mistracking). When RT is too short, the room can feel unnaturally dry and fatiguing, and talkers may feel like they’re “speaking into a pillow.”

This tutorial shows a practical workflow to measure your room’s reverberation, set targets based on room size and use, choose treatments that actually move the numbers, and verify results. You’ll learn how to avoid common measurement traps, how to prioritize mid-band control for speech, and how to keep your fixes from breaking the A/V system (HVAC noise, mic gain, echo cancellation).

Prerequisites / Setup

Measurement tool: Room EQ Wizard (REW) on a laptop (free) or a dedicated analyzer that can compute RT60/T20/T30 and EDT by octave or 1/3-octave bands.
Measurement microphone: Calibrated omni mic (e.g., UMIK-1 USB, or an XLR measurement mic with an interface). Load the calibration file if available.
Signal source: Powered speaker, the installed ceiling speakers (if you can route test signal), or a small portable reference speaker. Pink noise or a swept sine is fine.
SPL meter (optional but useful): To confirm test level and background noise.
Basic room data: Length, width, height; surfaces (glass, drywall, carpet, ceiling tile); occupancy pattern (how many people typically present).
Target use-case: Voice-only conferencing, hybrid meetings, training, or “boardroom” with reinforcement.

Recommended targets (starting point): For speech-centric conference rooms, aim for mid-band RT (500 Hz–2 kHz) around:

Small (up to ~50 m³ / 1,800 ft³): 0.25–0.40 s
Medium (~50–150 m³ / 1,800–5,300 ft³): 0.35–0.55 s
Large (~150–300 m³ / 5,300–10,600 ft³): 0.45–0.70 s

These are practical ranges rather than rigid rules. If the room is primarily for teleconferencing, err toward the lower end. If it’s a training room where in-room sound needs some “support,” stay toward the higher end while maintaining clarity.

Step-by-Step Instructions

Define the RT target for your room’s volume and use

Action: Calculate room volume and pick an RT target band-by-band (at minimum 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz).

Why: RT targets keep you from over-treating (dead room) or under-treating (unintelligible speech). Also, speech intelligibility correlates strongly with the mid-band RT and early reflections; chasing low-frequency RT in a small room can waste budget fast.

Technique: Room volume = L × W × H. Example: 7 m × 5 m × 3 m = 105 m³. A reasonable mid-band target is ~0.45 s (500 Hz–2 kHz). Accept that 125 Hz may remain higher (often 0.6–0.9 s) unless you add thick absorption.

Common pitfalls: Choosing targets based on music rooms; using a single RT value without looking at frequency; ignoring occupancy (people are absorbers at mid/high frequencies).
Measure background noise before you measure reverberation

Action: With HVAC running as normal, measure room noise at the primary seating area for 30 seconds. Note dBA and, if possible, octave bands.

Why: RT calculations rely on observing decay. If background noise is too close to your test signal tail, the decay curve flattens and RT reads artificially short or inconsistent. Also, high HVAC noise forces higher mic gain, increasing the audibility of reverb and reducing far-end clarity.

Specific numbers: Aim for ≤ 35 dBA for premium conference rooms, ≤ 40 dBA acceptable in many offices. If you’re above 45 dBA, fix noise first (diffusers, duct lining, fan speed, door seals) or you’ll fight the room forever.

Common pitfalls: Measuring RT late at night with HVAC off (results won’t match daytime performance); ignoring projector/TV fan noise near the mic.

Troubleshooting: If RT curves look jagged or vary wildly between runs, raise test level by 10 dB (without clipping) and/or move the source farther from boundaries.
Set up your measurement chain and levels (avoid clipping and weak tails)

Action: Place the measurement mic at seated head height (about 1.2 m from the floor), pointed upward if omni, and run a test sweep or noise at a controlled level.

Why: Conference performance is judged at listener positions and at microphones. Measuring at realistic heights gives results that correlate with what users hear and what mics capture.

Specific settings:
- Target test level at the mic: 75–85 dB SPL (C-weighted) for sweeps/noise. This provides enough decay above the noise floor.
- REW sweep: 20 Hz–20 kHz, 256k length if the room is noisy; 128k is often fine.
- Input gain: keep peaks below -6 dBFS to prevent hidden clipping.
Common pitfalls: Driving ceiling speakers too hard and triggering limiters; using a laptop speaker as the source (insufficient level and poor LF extension); placing the mic too close to a tabletop (strong early reflections skew EDT).

Troubleshooting: If you see obvious distortion in the impulse response, reduce source level and re-run. If the RT looks too short at high frequencies, check that the mic calibration file is loaded and that the input isn’t applying noise reduction or AGC.
Capture RT from multiple positions (don’t trust a single point)

Action: Measure at at least 4 positions: near the front, near the back, and two mid-room seats. If the room has a typical “presenter” position, include a measurement 1 m in front of it.

Why: RT in small/medium rooms varies with location due to modal behavior and uneven absorption coverage. Averaging multiple seats gives a result that matches real meeting experiences (“sounds fine here, boomy there”).

Technique: Keep the source location fixed for a set (e.g., at the front where a talker stands). Then repeat with the source at the loudspeaker location if you’re also evaluating reinforcement behavior.

Common pitfalls: Measuring right next to a glass wall or whiteboard and assuming it represents the entire room; moving the source every time (you can’t compare results).

Troubleshooting: If one position shows RT much longer above 1 kHz, look for a local reflection path: glass, uncovered drywall, or a large table surface. That’s often solvable with targeted treatment.
Interpret the RT data the way conference rooms behave (focus on EDT and mid-band)

Action: Review EDT (Early Decay Time) and T20/T30 by octave band. Prioritize 500 Hz, 1 kHz, and 2 kHz performance.

Why: People judge “reverby” mostly from the first ~10 dB of decay (EDT), and speech intelligibility depends heavily on early reflections and mid-band energy. A room can have an acceptable RT60 but still feel splashy if EDT is high due to strong early reflections.

Specific guidance:
- If EDT > RT60 in mid/high bands, suspect strong early reflections (glass, hard ceiling, table bounce).
- For conferencing, aim for EDT roughly equal to or slightly lower than RT60 from 500 Hz–2 kHz.
- Watch 250 Hz: if it is > mid-band by more than ~0.2–0.3 s, the room may sound “muddy,” especially on male voices.
Common pitfalls: Chasing 125 Hz RT in a small room with thin panels (won’t work); ignoring 4 kHz (sibilance clarity) because it “looks fine.”

Troubleshooting: If RT curves are erratic at low frequencies, that’s often modal behavior. Use more positions and average; don’t assume treatment “failed” based on one LF band at one seat.
Calculate how much absorption you need (so you can budget accurately)

Action: Use Sabine as a planning estimate: RT = 0.161 × V / A (SI units), where V is volume (m³) and A is total absorption in sabins (m² equivalent absorption). Solve for A, then estimate additional absorption needed.

Why: This prevents random panel placement. You’ll know whether you need “a few panels” or “a lot of coverage,” and you can prioritize surfaces that deliver the most sabins per dollar and per square meter.

Example: V = 105 m³. Current mid-band RT ~0.75 s. Target RT = 0.45 s.
- Current A ≈ 0.161 × 105 / 0.75 = 22.5 sabins
- Target A ≈ 0.161 × 105 / 0.45 = 37.6 sabins
- Additional absorption needed ≈ 15.1 sabins (mid-band)
Translate to panels: A typical 50 mm (2") fiberglass panel, 1.2 m × 0.6 m (4' × 2'), with an air gap, can deliver roughly 0.7–0.9 sabins at 500 Hz depending on mounting and product. That means you may need on the order of 18–22 panels to make a big mid-band change in this example. (Check manufacturer absorption coefficients for your exact product.)

Common pitfalls: Using Sabine as if it predicts everything perfectly in small rooms; assuming carpet fixes speech (carpet mainly helps above ~1 kHz and does little at 250–500 Hz).
Choose treatments that target the real problem bands (and mount them correctly)

Action: Add absorption where it reduces mid-band RT and early reflections: first reflection points on side walls, rear wall, and (often) the ceiling over the table. Include some thicker treatment if 250 Hz is high.

Why: Conference rooms are speech rooms. You want controlled reflections, not anechoic behavior. Proper placement improves intelligibility more efficiently than covering random wall sections.

Specific techniques and values:
- Wall panels: Use 50 mm (2") panels minimum; 100 mm (4") where you need more 250–500 Hz control. Add a 50–100 mm (2–4") air gap behind panels to improve low-mid absorption.
- Ceiling cloud over table: If the room has a large hard table, a cloud is often the single biggest intelligibility win. Use 50–100 mm thick, cover at least 60–80% of the table footprint, mounted with a 100–300 mm gap to the ceiling if possible.
- Glass/whiteboards: Treat adjacent surfaces (side walls, ceiling) rather than trying to stick panels on glass. Use curtains only if they are heavy and have meaningful fullness (ideally 2:1 fabric fullness), otherwise they underperform.
- Rear wall: In many conference rooms, the rear wall creates strong slapback into table mics. Prioritize absorption here, often 15–25% of rear wall area in panels as a starting move.
Common pitfalls: Thin foam (especially <25 mm) that only affects highs; panels mounted flush with no air gap and then wondering why 250–500 Hz didn’t improve; treating only one wall and creating an unbalanced room (lopsided stereo perception and uneven mic pickup).

Troubleshooting: If the room becomes bright but still “boomy,” you added too much HF-only absorption. Replace some thin materials with thicker broadband panels and add corner/edge thickness where feasible.
Re-measure and validate against conferencing realities (mics, AEC, and talkers)

Action: Repeat the same measurement positions and source setup. Then run two real-world checks: a spoken voice test and a far-end loop test (if you can) through the conferencing system.

Why: The graph is not the meeting. The goal is improved intelligibility and reduced far-end fatigue. Also, treatments can change system gain structure needs and AEC behavior.

Specific checks:
- RT results: Confirm 500 Hz–2 kHz RT moved toward target (e.g., from 0.75 s down to ~0.45–0.55 s). Expect smaller improvements at 125 Hz unless you used thick treatment.
- Clap/impulse check: Listen for “zing” or discrete flutter between parallel hard surfaces. Flutter often persists even if RT improved; it needs targeted treatment or diffusion/angle changes.
- Talk test at normal level: A seated talker at ~1 m from the mic should sound clear with minimal room “halo.”
- AEC behavior: If the system has diagnostics, check for stable echo return loss enhancement (ERLE). Subjectively, far-end should hear less room and fewer “chirps” or pumping artifacts.
Common pitfalls: Changing mic EQ/AGC at the same time as acoustic treatment and not knowing which change helped; judging with the room empty when it’s usually occupied (people shorten RT in the mid/high bands).

Troubleshooting: If far-end still hears excessive room, confirm mic pickup pattern and placement. Ceiling mics in reflective rooms are unforgiving; you may need more ceiling absorption or tighter pickup (beamforming zones, lobes) in addition to RT improvements.

Before and After: Expected Results

In a typical medium conference room with glass and drywall, it’s common to measure:

Before: 500 Hz–2 kHz RT around 0.70–0.95 s, EDT often even higher due to strong early reflections; audible slap off the rear wall; far-end reports “echoey” sound and intelligibility issues.
After (practical target): 500 Hz–2 kHz RT around 0.40–0.60 s, EDT reduced and closer to RT; noticeably improved consonant clarity; less “room wash” into table/ceiling mics; AEC works with fewer artifacts.

Expect improvements to be most dramatic in the speech bands (500 Hz–4 kHz). If you didn’t add thick absorption, low-frequency RT (125–250 Hz) may improve only slightly. That’s normal—and often acceptable—provided mid-band clarity is solid.

Pro Tips for Taking It Further

Design for occupancy: If the room is often full, measure once empty and once with people (or seat cushions/temporary absorbers as a proxy). A full room can shorten 1–4 kHz RT by 0.05–0.20 s.
Control the table reflection: Large glossy tables create a strong early reflection into boundary mics and ceiling mics. A ceiling cloud is usually better than covering the table, but a thin table runner can reduce HF “spit” without changing the room’s overall RT much.
Don’t ignore doors: Leaky doors raise noise floor and reduce usable decay range. Simple perimeter seals and a door sweep can reduce noise and improve measurement stability.
Use scattering selectively: In longer rooms, adding diffusion on the rear wall can reduce slap without making the room too dead. For conferencing, broadband absorption is typically the first move; diffusion is a refinement.
Verify with STI or speech metrics if available: If your tool supports STI/RASTI or you can run speech transmission measurements, use them alongside RT. A room can hit RT targets and still suffer from strong early reflections or poor mic coverage.
Document everything: Save REW files, mic/source positions, SPL levels, HVAC state, and treatment changes. This makes future rooms faster and helps justify decisions to clients or facilities teams.

Wrap-Up

RT optimization in conference rooms is a repeatable process: set realistic targets, measure carefully, treat the surfaces that actually drive mid-band decay and early reflections, then verify with both data and real call behavior. Do it a few times and you’ll start predicting outcomes before you hang the first panel—which is when your work shifts from “trial and error” to engineering.

Practice by measuring a room you know well, making one controlled change (even temporary panels), and re-measuring. The discipline of consistent setup and careful interpretation is what turns RT numbers into meetings that sound effortless.