How to Calculate dB Loss

Professional sound engineers use dB loss calculations to help determine the quietness of a room.
••• jeb efird/iStock/Getty Images

Decibels (dB) determine the relationship in signal strength between two sources. When the power of the first signal outweighs that of the second, a loss occurs; this can be desirable, as with the use of carpets to quiet a library, or it can be detrimental, as when a bad cable weakens electrical signals from an antenna on their way to your TV. Use the formula for finding the decibels as a ratio of the power of the signals to calculate the exact value of the loss. A scientific calculator with a log function helps to solve the equation.

    Measure the full-strength signal with an appropriate meter; to measure radio signals, for example, a radio signal power meter indicates the strength of radio waves at a particular location in units of milliwatts, microwatts or similar units. Write down the results, labeling them “full strength.”

    Measure the attenuated signal with the same meter; this is the signal for which you expect a reduction in power. For example, an antenna picks up a radio signal; right at the antenna, the meter measures 20 miliwatts, but the long cable connected to the cable reduces the power to 5 miliwatts. In this instance, you measure the attenuated signal at the output end of the long cable. Write down the results, labeling them “attenuated.”

    Divide the first signal's power by the second signal's power to find the ratio of the two signals. For instance, if signal A has a power of 20 mW and signal B has a power of 5 mW: 20/5 = 4.

    Take the log of the the ratio of the signals by pressing the log button on the scientific calculator. For instance: log 4 = 0.602.

    Multiply this answer by 10 to find the decibels. For the example: 0.602 x 10 = 6 decibels (dB).

    Determine if the decibel reading reflects a loss or gain of power by looking at signal A and signal B. Record a loss if signal A had a greater value than signal B, and a gain if signal B had the greater number. For the example, since the first signal (signal A) measured more than signal B, the result indicated a loss of 6 decibels (dB).

    Things You'll Need

    • Electronic signal measuring meter
    • Scientific calculator with log function

Related Articles

How to Calculate Signal to Noise Ratio
How to Calculate KVA from KW
Duty Cycle Formula: How to Calculate the Duty Cycle...
How to Measure Noise Pollution
How to Calculate Percentage Decrease on a Calculator
How to Convert HP to BTU/hr
How to Design an RC Snubber
How to Convert mW to mA
How to Use a Variac
How to Convert Hertz to Milliseconds
How to Measure Electric Motor Torque
How to Calculate LED Power
What Is a 52 dB(A)?
How to Read Oscilloscopes
How to Calculate Limit of Detection (LOD)
How to Convert Candle Power to Lumens
How to Linearize a Power Function
How to Troubleshoot a Servo Drive
How to Build an EMF Detector

Dont Go!

We Have More Great Sciencing Articles!