# Sound System Engineering – Common Parameter for Reference

The most useful parameter for comparison of a sound system would be the Max dB value. This calculates the variables that include the amount of power recommended (speaker program power) and the speaker or cabinet sensitivity to provide a common parameter that can be used for comparison from system to system.

The Max dB calculation defines the dB value or ratio of rated amplifier power applied to the reference of one watt at one meter. This power is added to the speaker sensitivity or dB SPL level at reference value.

The speaker sensitivity is the amount of SPL measured in dB produced when applying one watt of power or 2.83 volts at eight ohms and measured at one meter from the speaker.

The power calculation above provides the increase of dB for that given wattage. The result provides for the Max dB SPL at rated power at one meter.

Power Ratio Calculation
Max dB SPL = 10 * Log10(Amplifier Wattage/Reference of 1W)+Speaker Sensitivity at 1W

• Amplifier Power             600W    600W    500W    1000W
• Speaker Sensitivity        98 dB   95 dB     98 dB   98 dB
• Max dB SPL                  126dB   123dB    125dB    128dB

Note: A change in Speaker Sensitivity has an effect of 1 to 1.
Note: The doubling of wattage is required to provide an increase of only 3 dB.

Now that this value has been defined, using the inverse square law, the dB level may be determined for a given distance. With the doubling of distance, a loss of – 6dB shall be realized for point source system where only a -3 dB loss shall be realized for a line array system.

• Distance in Meters         1          2          4          8          16         32
• Distance in Feet            3.2      6.4    12.8   25.6     51.2     102.4
• dB Loss w/ref 98dB       98       92        86      80        74         68