One Systems has published several articles on "loudspeaker throw". This topic and its associated question "How far will that loudspeaker throw" continues to be one of our most frequently asked technical questions. These articles can be found in the Tech Papers section.
A simple solution is to provide "throw" calculators to help everyone deal with this issue. These calculators require some simple input and will yield a results based on the desired calculator output. There are two calculators. Both calculators require you to enter a specific loudspeaker's 1 watt at 1 meter data sheet rating and will then calculate specific results.
The first calculator, Calculator 1, asks for a specific distance and power level and will provide an SPL based on those inputs. ("If the bleachers are 50 meters away and I have an 800 watt amplifier and use a 212CIM what is the resultant sound pressure level?") The second calculator, Calculator 2, asks you to input a power level and desired sound pressure level (SPL) and will yield the distance that that specific power level will produce the desired sound pressure level. ("How far away can I still get 95dB SPL if I have a 212CIM and an 800 watt amplifier?")
NOTE: The sound pressure levels are assumed to be on axis. You will need to subtract 6dB from these values to determine the nominal sound pressure level at the rated included angle limits of the specific loudspeaker.
Enter the 1 watt at 1 meter rating. This is found on the data sheet for a specific loudspeaker:
1 watt at 1 meter (in dB)
Next enter the distance that you are interested in. This value should be entered in meters.
To convert from feet to meters simply multiply the distance in feet by 0.3048. If you wish the calculator to convert simply enter the distance if feet here
and then use this result to enter into the distance variable.
You may either enter the distance directly below in meters or use the converted result and enter below but either way, you must enter data below.
Distance (in meters)
Now enter the electrical power level.
NOTE: be careful with this number. Many people use the continuous power handling rating of the loudspeaker. Although this is will yield a calculated value it can be very misleading. The loudspeaker system should still have some "mechanical" headroom. The loudspeaker should be able to produce the required sound pressure levels without being driven to its limit. A good value to start with is 50% of the rated continuous power handling found on the product data sheet. It is certainly possible to increase this value to the continuous rating, or even exceed it and experiment with the program power handling or peak power handling rating but care should be exercised. Program and peak power handling ratings are duty cycle dependent so, based on the musical content of the material, these values can vary greatly.
Electrical power input (watts)
Now that you have the result all you need to do is evaluate that value against the needed or specified SPL. If the result is lower than specified you will need to either increase the power (be careful) or use a loudspeaker with a higher 1 watt at 1 meter rating. WARNING: There are many "horns in horns" loudspeaker designs that offer very high 1 watt at 1 meter ratings. Many of these products are excellent designs but make a performance tradeoff. They offer very high on axis sound pressure levels, long throw, but have very limited bandwidth (limited low frequency response). If the specified requirement is for vocal range performance only, then these all horn designs are a very good option. If, however, full range, or musical requirements are specified then you will need to compare the 1 watt at 1 meter rating versus the low frequency limit of the products you are comparing. Alternately, you may use multiple extended bandwidth enclosures of the same type in an array.
Enter the 1 watt at 1 meter rating. This is found on the data sheet for a specific loudspeaker
Enter 1 watt at 1 meter (in dB)
Enter desired electrical power input.
As noted in the comments from the first calculator, care should be taken with this number. Continuous, Program, and Peak power handling data are all duty cycle dependent. They will vary based on a manufactures testing methods and on the electrical input conditions. A safe method is to use 50% of the rated continuous power handling. This insures excellent "loudspeaker mechanical headroom!"
Enter desired SPL.
This is the value, in dB that you wish to achieve.
NOTE: To increase the desired distance (throw) you either need more electrical power or a loudspeaker system with higher 1 watt at 1 meter sensitivity. Again, it is important to note that a higher 1 watt at 1 meter sensitivity may mean using an all horn loaded enclosure, which will provide increased sensitivity at the expense of bandwidth. Alternately, you may use multiple enclosures of the same type in an array configuration.