Issues in calibration. Primary reference standards. A reference standard for a unit of measurement is an artifact that embodies the quantity of interest in a way that ties its value to the reference base. At the highest level, a primary reference standard is assigned a value by direct comparison with the reference base.
Refraction of Sound Waves. The speed of a wave depends on the elastic and inertia properties of the medium through which it travels. When a wave encounters different medium where the wave speed is different, the wave will change directions.
In other words, how loud things seem is a subjective thing and not something we can easily measure. However, what makes one sound seem louder than another is the amount of energy that the source of the sound is pumping towards the listener in the form of pressure variations in the air. That's the intensity of the sound and it's an objective thingâsomething we can easily measure and agree on. Meters that measure sound levels work by calculating the pressure of the sound waves traveling through the air from a source of noise. That's why you'll sometimes see them referred to as sound pressure level (SPL) meters.