Standing Waves Experiment.

Standing Waves


For me to understand what a standing wave is I spent some time reading over The Ultimate Live Sound Operator's Handbook By Bill Gibson. I took the following information straight out of the book : 


Modes are reflections that set up a pattern between surfaces in an acoustic space. Modes are also known as standing waves.Standing waves are vibrations that stay stall of certain wavelength and frequency which occur on a medium of certain size. If a sound wave reflects along the same path from which it came, it will reflect again once it reaches its originating surface, then back again, and so on.

There are 3 types of standing wave; Axial, Tangential and Oblique. 


We used the Axial modes to calculate the standing waves of the room 11:

The following are the equations used to calculate standing waves:

Hz = 1120 (ft) ÷2

Frequency = Speed of Sound (Ft) ÷ Lenght of Room x 2

The above equation is the fundamental frequency

Extension = Multiply the result of the equation by 1, 2, 3, 4, 5, and up as far as 300 Hz

With the help of a laser, we measured Room 11 to figure out the standing waves and here are the results :

Room Width : 5.766

Hz : 30 / 60 / 90 / 120 / 150 / 181 / 211

Room Length A: 7.310

Hz: 23, 47, 70, 94, 117, 141, 164, 188

Room Length B:  7.848

Hz : 21.6, 43.2, 64.8, 86.4, 108, 129.6, 151.2, 172.8, 194.4, 216, 237.6, 259.2


On-line page that calculates it for you :
 http://www.marktaw.com/recording/Acoustics/RoomModeStandingWaveCalcu.html