What is Loudspeaker Sensitivity?
Loudspeaker Sensitivity allows us to compare how efficient different loudspeakers are. It a measure of Sound Pressure Level (SPL) at a specified distance for a specified input signal. Put another way, it shows how much noise a loudspeaker will make with a certain input signal.
What units is it measured in?
Often you will see loudspeaker sensitivity quoted in decibels at one watt at one meter. This can be displayed as-
Are all watts equal?
When comparing the sensitivity measurements from different manufacturers you need to be careful. It is worth checking the small print in tech specs. This should tell you how they have calibrated their watt. This includes telling you at what impedance they have measured the power. If they don’t do this be wary about trusting their data.
2.83 volts is one watt at 8 ohms.
One common nominal impedance for loudspeakers is 8 ohms. If we apply Ohms Law to the 8 ohms we discover that one watt of power has 2.83 volts. This is a handy place to start and a good place of reference when working with loudspeaker sensitivity.
What about when the speaker has a different nominal impedance?
If the loudspeaker has a different nominal impedance then the volts needed to achieve a watt also changes. Some manufacturers calibrate their one watt to the different impedances. Other manufacturers stick with 2.83 volts regardless of impedance. This is why we need to be careful about reading specifications.
If we have a 4 ohm cabinet then 2.83 volts is actually 2 watts. As we have doubled the power the loudspeaker sensitivity will appear 3dB louder.
Is this fair?
Imagine that you have two loudspeakers. Both loudspeakers have a sensitivity of 100dB referenced to 2.83v at 8 ohms at 1 meter. Your black loudspeaker is an 8 ohm box and your white loudspeaker is a 4 ohm box. You put them both on a separate channel of the same amplifier and play some music. You hear that your white speaker is twice as loud. Should both these speakers have the same sensitivity in the spec?
We would argue that referencing to 2.83v is more honest than specifying a nominal 1w/1m. It makes it clearer what your input signal is.
Please use the table below as a quick reference to help you compare sensitivity measurements calibrated to different values.
|2.83v / 1 m (16 ohms)||92dB||97dB||102dB|
|2.83v / 1 m (8 ohms)||95dB||100dB||105dB|
|2.83v / 1 m (4 ohms)||98dB||103dB||108dB|
|2.83v / 1 m (2 ohms)||101dB||106dB||111dB|