Sound Decibels are the units of measurement used to describe voltage and power levels. The abbreviation for decibel is dB (Sauvala). Some decibel comparisons are: 10 dB is as loud as someone whispering, 70 dB is a shouted conversation, and 110 dB is as loud as a jet engine ("Sound"). Decibels are the expression of relationships. Some formulas for decibels are power =10log(P1/P2)(P1= power 1 and P2= power 2) and voltage =20log(v2/v1)(V2= voltage 2, V1= voltage 2) ([email protected]). Decibels are measured in 6s. For example, 6 dB is double the original value (0 dB) and -6 dB is half the original value (0 dB) (Sauvala). O dB is the lowest audible to a human being and 140 dB is the pain threshold for a human being (Freedom). Decibel means the measurement is a ratio measured on a logarithmic scale and every time you add 6 dB the voltage doubles (BBC Online). The average human ear cannot notice decibel changes smaller than one decibel ([email protected]). Every time the distance from a sound source doubles, there is a decrease of 6 dB and the formula for this is DC= 20log(distance1/distance2) (DC= decibel change). Round decibels to units (Mc Squared System Design Group). There is only one decibel system, but there are two ways to express the values: power decibels and voltage decibels. Power decibels are used to express sound pressure levels and power amplifier and speaker specifications. They are used for equipment that translates signals into sound and into someone's ears for hearing. Voltage decibels are used to express specifications of gain, loss, levels, noise and line equipment. These are used in most equipment that picks up sounds, converts them into electrical signals and sends them from one point to another. Both can be converted into each other. If you have power in dB all you have to do is double it to get voltage in dB and if you have voltage in dB then you take half that for power in dB ([email protected]).Sound has three measurable parts: frequency, amplitude and duration. Frequency is the rate of vibration that determines how high or low the pitch is. “Amplitude is the amount of vibration, which determines how loud the sound is.” (Freedom) Duration is how long the sound lasts, measured in seconds.