Clarity, EDT and ITDG

This text delves into how ITDG (Initial Time Delay Gap), EDT (Early Decay), critical distance, radiation coverage, and speaker directivity all influence the perception of space and sound clarity within a real room, focusing on aspects relevant to living rooms and home theaters.

Understanding ITDG

ITDG refers to the time difference between the arrival of the direct sound from a source (speaker, instrument, voice, etc.) and the arrival of the first significant reflections of that sound bouncing off the walls, ceiling, and floor.

ITDG and the Perception of Clarity

A room’s ITDG plays a crucial role in how clear the sound feels. Here’s the impact:

Note: range and value can vary from one author or research to another and about preferences.

Critical Distance and Radiation Coverage

Relationship to ITDG and Directivity

Early Decay Time (EDT) and its Impact

EDT is the time it takes for the sound level in a room to decrease by 60 dB after the source has stopped emitting sound. This decay is primarily caused by the absorption of sound by the room’s surfaces (walls, ceiling, floor, furniture, acoustics, etc.).

The Relationship Between EDT and ITDG

While ITDG is influenced by the room’s shape, size, and the placement of sound sources and listeners, the absorption characteristics of the room (reflected in the EDT) also play a significant role:

Optimizing for Clarity: Balancing ITDG and EDT

When aiming for good acoustics in a living room or home theater, it’s important to consider both ITDG and EDT:

Optimizing Your Room’s Acoustics

When optimizing ITDG and sound clarity in your living room or home theater, consider these points:

When aiming for optimal Initial Time Delay Gap (ITDG) and sound clarity in your living room or home theater, consider these key factors:

In most cases, proper acoustic treatment combined with speakers that offer constant directivity with a coverage adapted to your listening distance, oriented to the central listening position, will provide the more effective solution.

Constant Directivity

While constant directivity speakers (those that radiate sound uniformly across frequencies) can offer some advantages:

Consistent ITDG: Constant directivity speakers can help maintain a more consistent ITDG across the listening area, regardless of the frequency content of the sound. This can be beneficial for achieving a more uniform and predictable sound experience.

C20 and C50 Integration Times Explained:

In the context of EDT measurement using the exponential sine sweep method, C20 and C50 represent different integration times used when calculating the decay curve. These integration times essentially filter the measured data to focus on specific frequency ranges:

By analyzing the decay curve using both C20 and C50 integration times, acoustic professionals can gain a more comprehensive understanding of the room’s absorption properties at different frequencies, which ultimately influences both ITDG and overall sound clarity.


By understanding ITDG, critical distance, radiation coverage, and speaker directivity, you can achieve a more comprehensive approach to optimizing the acoustics in your living room or home theater. By considering these factors alongside the previously mentioned techniques, you can create a space with clear, well-balanced sound that enhances your listening experience.