Understanding Room Acoustics 12/10/2020

In wrapping up another semester teaching music acoustics at Webster University, we were able to have a brief discussion about room acoustics. Since we studied how musical instruments produce unique sounds as a source in a room, it was appropriate to talk about how the room can influence and shape the instrument’s sound.

Room acoustics is a broad topic and although we did not have time to cover all aspects, we did address some of the most common “Myths”. These include;

1. Room acoustics is mainly about “Noise Control”.

2. Understanding room acoustics is mainly about taking measurements.

3. Acoustics of a room can be improved by applying acoustic solutions to a percentage of wall space.

4. Improving sound in a room is only necessary for professional environments used for producing or listening to music.

5. “Bass Traps” made of porous material can be used to manage low frequency sound issues.

6. Solutions using materials with a high NRC rating (average absorption) are sufficient for improving the room.

First of all, it was great to hear that the audio students did not perceive the study of room acoustics as a study of “noise control”. We appropriately discussed both the impact of a room on “wanted sound”, music and speech, and on “un-wanted sound” which can be considered noise. It was also noted that the noise can be un-wanted sound from music, speech and other sources and can also be inside and/or outside of the room. Although addressing “un-wanted sound” is important, we mainly focused on the how the room influences the “wanted” good music and speech.

We also investigated the evaluation of a room’s influence on a sound source performed by listening to the room and thru analysis without necessarily taking measurements and/or resorting to applying solutions. Although measurements may be very useful, it is important to analyze the vibration patterns or modes of the room and the locations of both the sound source(s) and the receiver(s) in the room with respect to these vibration patterns. Evaluating the geometry of the room to determine the critical frequencies of music or speech that the room may influence is also a key part of the analysis.

Equally important was a discussion of the relationship between the receipt of direct sound from a source and reflected sound from the source, hitting a surface before being received. This can greatly impact the “clarity” of speech and music in any room.

We concluded with an example to determine the reverb time and total acoustic absorption of a room without taking measurements and how to improve the acoustics with the addition of absorption using a balanced approached for Absorption and Reflected/Diffused sound. We also discussed the importance of balancing across the frequency spectrum and the pros and cons of “bass trap” design and application.

We did not address the room’s influence on noise, including sound transmission and blocking, although it can be very important to analyze and /or measure.

Overall it was a great class and the concepts can be applied to any room that has a sound source(s) and receiver(s) in the room in which the room’s influence needs to be optimized.

If you would like to join the discussion or need specific consultation for your room, please contact me at 314-568-8042 or send me a note at mikeb@sondareacoustics.com

Mike B.