School: SANTA FE HIGH
Area of Science: physics
Interim: Sound Reflection and Absorption
Directionality of sound. High frequencies tend to be very directional and radiate from their source like a beam of light from a flash light or a laser. Low frequencies of sound, on the other hand, tend to spread out from their source like a pebble dropped in a pool of water. These factors must be considered when recording sound. Directionality of the source sound to be recorded will affect microphone selection and placement.
Reflected sound is such a common occurrence we, as casual listeners, fail to notice how much of the sound we hear is reflected off of some surface after it is initially emitted from its source. Our brains have a very sophisticated method of deciphering the reflected sound from the direct sound, but because even the best contemporary recording equipment makes these reflected sounds very obvious upon play-back, much must be done to control or at least minimizes reflected sound when recording for motion pictures. Some surfaces reflect sound better than others. Of these surfaces, they diverge into types by how they reflect different frequencies of sound. For example: a thin pane of glass may reflect high frequencies very well but will allow low frequencies to pass. Sheet rock, a common wall material in houses, will absorb many of the high frequencies but will reflect mid, and low middle frequencies, and depending on how the material is attached to the support structure of the building, it may or may not reflect low frequencies. A basic rule of thumb is that plush soft materials absorb high frequencies and large massive amounts of porous material absorbs low and mid frequencies. (more mass is required to the lower the frequency of sound) Hard surfaces reflect sound but again mass plays a factor. Thin hard surfaces will only reflect higher frequencies the thicker, and more dense, the hard surface the lower the frequency of sound it will reflect.
Sponsoring Teacher: Anita Gerlach