RT60 Reverberation Time | Measuring & Optimizing Soundproof Room Acoustics

Built a soundproof room but notice “too much echo” or “muddy sound”?

The cause is RT60 (reverberation time) not being optimized to ideal values.

RT60 is the critical metric for quantifying acoustic environment in soundproof rooms. This guide details RT60 measurement methods, optimal values, and improvement techniques.

RT60 (Reverberation Time): Understanding the Basics

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First, let’s establish fundamental concepts:

RT60 Definition

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RT60 = Time required for sound to decay 60dB

Sound source generated
  ↓
Maximum volume (0dB)
  ↓
60dB attenuation
  ↓
Measurement complete (time = RT60)

Examples

• RT60 = 0.3 seconds: Sound decays quickly (heavy absorption)
• RT60 = 0.5 seconds: Good balance (professional grade)
• RT60 = 1.0 seconds: Excessive echo (insufficient absorption)

Why RT60 Matters

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Optimal RT60 by Use

• Podcast/streaming: 0.2–0.4 seconds
• Vocal recording: 0.3–0.5 seconds
• Music production: 0.4–0.6 seconds
• Movie/gaming: 0.5–0.8 seconds

RT60 Measurement Methods

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Here are three measurement approaches:

Method ①: Smartphone App (Basic)

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Required Items

• Smartphone
• Free app like “Room Acoustics”
• Audio source with white noise generation

Measurement Procedure

1. Install app
2. Select measurement mode
3. Play white noise
4. Stop audio (app auto-measures)
5. Read RT60

Accuracy

• ★★☆☆☆ (Reference value only)
• Sufficient for trend analysis
• Unsuitable for precise values

Cost

• Free–¥1,000

Method ②: Frequency Analysis Tool (Intermediate)

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Required Items

• PC + external audio interface
• REW (Real Room EQ Wizard) free software
• Microphone (¥3K–¥10K)
• Speaker

Measurement Procedure

1. Install & launch REW
2. Connect mic and speaker
3. Generate measurement signal
4. Receive via mic for measurement
5. Graph RT60

Accuracy

• ★★★☆☆ (Quite accurate)
• Frequency-specific RT60 available
• Optimal for DIY

Cost

• Software: Free
• Microphone: ¥3,000–10,000
• Audio interface: ¥10,000–30,000
• Total: ¥13,000–40,000

Method ③: Professional Measurement (High Precision)

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Providers

• Acoustic consultants
• Architectural firms
• Soundproofing companies

Measurement Contents

• Multi-frequency RT60 measurement
• Detailed spatial analysis
• Improvement recommendations report

Accuracy

• ★★★★★ (Highest precision)
• Frequency-specific detailed data
• Professional improvement advice

Cost

• ¥50,000–150,000

REW Measurement Method (Detailed Guide)

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Best cost-performance measurement using REW software:

Equipment Selection Guide

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Microphone Choice

Recommended: BEHRINGER ECM8000

• Best cost-performance
• Flat frequency response
• Standard measurement microphone

Audio Interface Choice

Recommended: Behringer UMC202HD

• Sufficient performance
• Reasonable price
• Simple setup

REW Setup

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STEP 1: Software Installation

1. Visit www.roomeqwizard.com
2. Download REW
3. Execute installation
4. Launch

STEP 2: Audio Device Configuration

1. Preferences → Audio Device
2. Output: Select audio interface
3. Input: Select mic input
4. Latency calibration

STEP 3: Speaker & Microphone Placement

【Measurement Setup】

Speaker (connected to audio interface)
        ↓
    ┌────────┐
    │ Test   │
    │ Room   │
    │        │
    └────────┘
        ↑
   Microphone (height: 1.2m)

Critical Points

• Microphone height: 1.2m (ear level)
• Speaker distance: 1–2m
• Multiple room locations measured (5+ recommended)

Actual Measurement Procedure

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STEP 1: Calibration

1. Preferences → Calibration
2. Enter mic sensitivity (first time only)
3. Set reference SPL

STEP 2: Measurement Signal Generation

1. Measurements → New Measurement
2. Set SPL (85dB recommended)
3. Click “Generate”
4. Play measurement signal from speaker

STEP 3: RT60 Measurement

1. REW automatically measures RT60
2. Plots on graph
3. Frequency-specific RT60 displayed

STEP 4: Record Results

• Overall RT60
• Frequency-specific RT60 (125Hz, 250Hz, 500Hz, 1k, 2kHz, etc.)
• Save graph as image

Reading Measurement Results

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RT60 Graph Interpretation

RT60 (seconds)
1.0 ┌────────────────┐
    │  ×: Current    │
0.8 │  −: Ideal range│
    │    ×           │
0.6 │  ────────────  │
    │ ×              │
0.4 │ ────────────  │
    │   × ×         │
0.2 │              │
    └────────────────┘
     125 250 500 1k 2k 4k 8k
         Frequency (Hz)

Reading Key Points

• Lower frequencies naturally having longer RT60 is normal
• 1kHz region values most important
• Significant frequency-specific variations warrant improvement

Optimal RT60 Values

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Target RT60 by application:

Application-Specific Optimal RT60

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Podcast/Streaming

Recommendation: Overall 0.2–0.35 seconds

Vocal/Singing Recording

Recommendation: Overall 0.3–0.5 seconds

Music Production/DAW

Recommendation: Overall 0.4–0.6 seconds

Movie/Gaming

RT60 Adjustment Methods

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Post-measurement optimization:

① Too Long RT60 (Increase Absorption)

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Strategies

Implementation Procedure

1. Measure current RT60
2. Calculate target gap
3. Estimate required absorption material
4. Add incrementally
5. Re-measure at each stage

Calculation Formula

Added material area = (RT60 difference / 0.1 sec) × Current material area

Example: Reduce 0.6 sec RT60 to 0.3 sec
(0.6 - 0.3) / 0.1 = 3× absorption needed

② Too Short RT60 (Reduce Absorption)

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Strategies

Implementation Procedure

1. Partially remove absorption panels
2. Make rear walls reflective
3. Re-measure for verification

③ Frequency-Specific Differences

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When Bass Too Long

• Add bass traps (corner treatment)
• Use large absorption materials

When Treble Too Long

• Add treble absorption (thin panels)

Practical Example: Podcast Box Optimization

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Concrete example:

Initial Measurement

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Results

Frequency | Current RT60 | Target
----------|-------------|----------
125Hz     | 0.8 sec     | 0.3 sec
500Hz     | 0.5 sec     | 0.25 sec
1kHz      | 0.4 sec     | 0.25 sec
4kHz      | 0.3 sec     | 0.2 sec

Assessment

• Bass too long (bass emphasis)
• Treble acceptable
• Overall absorption insufficient

Improvement Plan

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STEP 1: Add Absorption

• Side panels (50mm × 4㎡)
• Ceiling (50mm × 2㎡)

STEP 2: Re-measure

Frequency | After Improvement | Target
----------|-------------------|----------
125Hz     | 0.6 sec          | 0.3 sec
500Hz     | 0.35 sec         | 0.25 sec
1kHz      | 0.3 sec          | 0.25 sec
4kHz      | 0.25 sec         | 0.2 sec

Assessment

• Improving (bass still long)
• Mid-treble targets met

STEP 3: Bass Treatment

• Add bass traps at corners

STEP 4: Final Measurement

Frequency | Final Value | Target
----------|-------------|----------
125Hz     | 0.3 sec     | 0.3 sec ✓
500Hz     | 0.25 sec    | 0.25 sec ✓
1kHz      | 0.25 sec    | 0.25 sec ✓
4kHz      | 0.2 sec     | 0.2 sec ✓

Result

• All frequencies meet targets
• Ideal box achieved

Measurement Precautions

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Accuracy points:

Prepare Measurement Environment

• Minimize external noise (quiet time)
• 1-hour pre-measurement ventilation/temperature stabilization
• Multiple location measurements (use average)
• Humidity ~50% ideal

Verify Measurement Equipment

• Microphone sensitivity accuracy (calibration)
• Cable integrity check
• Audio interface level setting (prevent clipping)

Record Results

• Save all measurement data
• Graphically archive images
• Record before/after comparisons

RT60 Measurement: Final Verification

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Beyond numbers, practical verification important:

Listening Test

• Does voice sound natural?
• No echo present?
• Bass not muddy?
• Treble not harsh?

A/B Test

• Compare pre/post-improvement recordings
• Experiential difference important

RT60 Measurement Equipment Recommended Kits

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Complete equipment sets:

¥30,000 Course (Entry)

¥50,000 Course (Recommended)

Summary: RT60 Measurement “Determines Soundproof Room Completeness”

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Key Takeaways

• ✓ RT60 quantifies soundproof room acoustic environment
• ✓ Application-specific optimal values exist
• ✓ REW enables accurate measurement for ~¥30K
• ✓ Gradual improvement effective
• ✓ Frequency-specific tuning important

Measure → Improve Cycle

1. Initial measurement (baseline)
2. Target value setting
3. Gradual improvement
4. Re-measurement
5. Fine-tuning

Proper RT60 management creates completely professional acoustic environments.

Achieve professional-level performance through data-driven improvements!