Decibels are the units of measurement used to describe voltage and power levels. The abbreviation for a decibel is dB (Sauvala). Some decibel comparisons are: 10 dB is about 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 expressions of ratios.
Some formulas for decibels are power = 10 log (P 1/P 2) (P 1 = power 1 and P 2 = power 2) and voltage = 20 log (v 2/v 1) (V 2 = voltage 2, V 1 = voltage 2) (). Decibels are measured by 6's. For example, 6 dB is twice the original value (0 dB) and -6 dB is of the original value (0 dB) (Sauvala). O dB is the minimum a human can hear and 140 dB is the threshold of pain for a human (Freedom). Decibel means the measurement is a ratio measured on a logarithmic scale and whenever you add 6 dB the voltage doubles (BBC Online). The average human ear cannot notice decibel changes of less than one decibel ().
Every time the distance from a sound source doubles, there is a drop of 6 dB and the formula for this is DC = 20 log (distance 1/distance 2) (DC = decibels of change). You round decibels to the ones place (Mc Squared System Design Group). There is only one decibel system, but there are two ways to express values-power decibels and voltage decibels. Power decibels are used to express sound pressure levels and power amp and speaker specifications. They are used for equipment that translates signals back to sound and to someone's ears for hearing.
Voltage decibels are used to express gain, loss, levels, noise, and line equipment specifications. These are used in most equipment that pick up sounds, converts them to electrical signals and sends them from one point to another. Both of these can be converted to each other. If you have power dB all you have to do is double it to get voltage dB and if you have voltage dB than you take half of that for power dB (). Sound has thre measurable parts: frequency, amplitude, and duration.
Frequency is the rate of vibration that determines how high or low the pitch is. "Amplitude is the magnitude of the vibration, which determines how loud the sound is." (Freedom) Duration is how long the sound lasts, measured in seconds. Sound absorption is the effectiveness of a material at preventing the transmission of sound. The formula for sound absorption is A = .
921 Vd / c (V = volume of room, d = the measured rate of decay in decibels per second, and c = the speed of sound). Another way of measuring the effectiveness of soundproofing is by measuring the Sound Transmission Loss (SLT) which is the effectiveness of a wall at preventing sound from getting from one side to the other. The formula for this is STL = L 1- L 2+10 log (s / a ) (Freedom) (STL = sound transmission loss, L 1 = source room sound level, L 2 = source room sound level, 10 log (S/A) = correction for absorption) STC values are based on the number of dB of transmitted sound reduced by a wall. An example of STC values is that 50 dB is four times louder than 30 dB and 50 STC is four times quieter than 30 STC (Nash, Sound Control). Some products that will help increase the STC include: absorbent mat, barrier material, neoprene vibration strips, resilient channel, and sound control insulation. "Resilient Channel is a thin metal channel designed to substantially improve the sound insulation of drywall, sheetrock, and plasterboard walls and ceilings." (Nash, Soundproofing) Use of resilient channel usually results in an STC gain of 3 to 5 points." (Nash, Soundproofing).
Just basic wall with studs and drywall with no caulking has an STC value of 30. When you add caulking the value goes up to 35 and if you add double drywall on one side it becomes 37 (Nash, Sound Control). Bibliography BBC Online. "What is a decibel (dB) " (4 December 1999): n. pag. On-line.
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