First reflections must arrive within 30 ms to avoid being heard as echoes

Evidence

These results have important implications for studios, concert halls and sound reinforcement systems. In essence, it is important to ensure that the first reflections arrive at the audience earlier than 30 ms to avoid them being perceived as echoes. In fact, it seems that our preference is for a delay gap of less than 20 ms if the sound of the hall is to be classed as “intimate.” In sound reinforcement systems, the output of the speakers will often be delayed with respect to their acoustic sound but, because of this effect, we perceive the sound as coming from the acoustic source unless the level of sound from the speakers is very high. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 749

These results have important implications for studios, concert halls and sound reinforcement systems. In essence, it is important to ensure that the first reflections arrive at the audience earlier than 30 ms to avoid them Direction towards earlier sound Trading region Figure 2. — David Howard, Jamie Angus, coustics and Psychoacoustics, 742

Categorization

• XREF: Connects to concert hall acoustic design and the precedence effect commonly covered in soundscape/silence literature like The Soundscape. — connects to: Echoes too fast to be heard still color sound and can impart pitch; Early reflections must be suppressed about 15 dB to stay inaudible; Early reflection delay below 30 ms avoids echoes while adding spaciousness (+1 more)
• SHARE: An audio engineer friend would care that 20 ms sets the intimacy boundary for hall reverberation.
• corroborated: 4 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 749; David Howard, Jamie Angus, coustics and Psychoacoustics, 742

Broader Connections

• Early reflection delay below 30 ms avoids echoes while adding spaciousness #corroborates (0.92)
• Echoes arise only when reflected sound exceeds a 30-millisecond delay #corroborates (0.88)
• Early reflections must be suppressed about 15 dB to stay inaudible #expands (0.82)