Question

Which of the following is a technique used to reduce echoes in large spaces in architectural acoustics?

• A. Installing reflective surfaces
• B. Using sound-absorbing materials
• C. Increasing the volume of the space
• D. Removing all barriers

Hint:

\textbf{Echoes} are distinct, delayed reflections of sound. Excessive echoes and reverberation reduce sound clarity.
\textbf{To reduce echoes/reverberation:}
Use \textbf{sound-absorbing materials} on surfaces (walls, ceiling, floor) to reduce reflected sound energy.
Use \textbf{sound-diffusing surfaces} to scatter reflections.
Optimize room shape and geometry to avoid problematic reflections (e.g., flutter echoes between parallel hard surfaces).
Reflective surfaces increase echoes. Increasing volume without adding absorption increases reverberation time.

Answer 1

The Correct Option is B

Echoes are distinct repetitions of a sound that occur when reflected sound waves reach the listener with a sufficient time delay after the direct sound. In large spaces with hard, reflective surfaces, echoes and excessive reverberation (multiple blended reflections) can impair speech intelligibility and sound quality. Techniques to reduce echoes and control reverberation in architectural acoustics:
Using sound-absorbing materials (Option b): This is a primary method. Sound-absorbing materials (e.g., acoustic panels, carpets, curtains, upholstered furniture, porous ceiling tiles) convert sound energy into heat when sound waves strike them, reducing the amount of sound reflected back into the space. This shortens reverberation time and minimizes distinct echoes.
Diffusing surfaces: Using irregularly shaped or textured surfaces (diffusers) to scatter sound reflections in many directions, rather than reflecting them specularly (like a mirror). This helps to create a more uniform sound field and can reduce the perception of strong, discrete echoes.
Optimizing room shape and geometry: Avoiding large, flat, parallel reflective surfaces that can cause flutter echoes or strong focused reflections. Using non-parallel walls, angled ceilings, or curved surfaces can help.
Breaking up large surfaces: Introducing barriers or elements that break the path of sound waves. Let's evaluate the options:
(a) Installing reflective surfaces: This would \textit{increase} echoes and reverberation by reflecting more sound energy, which is the opposite of what is needed for echo reduction. (Reflective surfaces are sometimes used strategically to direct sound towards specific areas, e.g., reflectors above a stage, but not for general echo reduction in a reverberant space).
(b) Using sound-absorbing materials: This is a fundamental technique for reducing echoes and reverberation by absorbing sound energy.
(c) Increasing the volume of the space: For a given amount of absorption, a larger room volume generally leads to a longer reverberation time (Sabine's formula: $RT_{60} \approx 0.161 V/A$, where $V$ is volume and $A$ is total absorption). So, increasing volume without adding more absorption would likely worsen echo/reverberation problems.
(d) Removing all barriers: Removing barriers (like partitions) might increase the effective volume and change reflection paths, but it's not a general technique for echo reduction. Barriers, if designed as diffusers or absorbers, can actually help. Therefore, using sound-absorbing materials is a key technique to reduce echoes in large spaces. \[ \boxed{\text{Using sound-absorbing materials}} \]