10/28/2021
Sound Reflection, Reverberation, and Acoustic Solutions
Upon walking into a noisy restaurant, office, schoolroom, sports facility, or any type of room, anyone aware of simple acoustics immediately looks at the floors, walls, and ceiling, probably noticing the hard surfaces and absence of sound-absorbing materials.
Here’s what is happening in that noisy room and how the volume can be lowered with simple acoustic solutions.
When a sound wave strikes a surface such as a floor, wall, or ceiling, the direction of travel is changed by reflection. The reflection of sound waves follows the same physical law as light reflection. The angle of the incidence equals the angle of reflection.
Sound travels about 761 miles per hour in all directions. Quickly, the original sound is reflected from all of the surfaces again and again. At any given moment a listener will not only hear the current direct sound but portions of earlier sounds that are reflected one or more times. Soon sounds are traveling in every possible direction.
The multiple reflections of sound waves have two effects on acoustics:
- Loudness is increased.
- It causes reverberation.
The combination of direct sound and reflected sound results in loudness that is greater than direct sound alone. The loudness of reflected sound depends on room absorption while direct sound depends only on the distance from the source. The overall effect on loudness is determined by absorption present within the room.
Reflected waves will continue ricocheting between room surfaces losing only a fraction of power by absorption at each reflection. The prolongation of sound is called reverberation. The sound will gradually diminish. Reverberation time is the time measured in seconds that a sound average loudness can be heard before it becomes completely inaudible under quiet conditions. The time may vary from a half-second in a very “dead” room to five to ten seconds in an excessively “live” reverberant room.
The maximum reverberation time for clear speech is about two seconds; speech becomes unintelligible at reverberation times of four to ten seconds. Speech intelligibility improves as reverberation time decreases below two seconds, as shown below.
Rooms with various purposes have different optimal reverberation times. MBI Products has been a pioneer in correcting room acoustics, from arenas to classrooms, for over 50 years. Installing acoustical panels or baffles, depending on the space, can make a room more usable for large groups of people or noisy events like concerts. Available in a variety of shapes, sizes, colors, and patterns, MBI acoustical products provide a practical but attractive solution to sound absorption for all types of spaces.
MBI Products recommends obtaining actual sound level measurements from a competent acoustician who uses proper equipment for the most accurate assessment. A thorough professional analysis and evaluation usually lead to better acoustic results and a lower overall cost. Working together with acousticians, MBI develops the best acoustic solutions in the industry today.