What is SPL regarding Loudspeakers?

... and what does it really mean?

SPL is an abbreviation for Sound Pressure Level.

It is the sound level (volume/pressure) reproduced by a speaker, usually measured one (1) meter in front of the speaker. Max SPL is how loud the speaker can play before it breaks or starts to sound really bad.

Most sound systems & PA used for Live Music or DJ's usually have a MAX SPL (Sound Pressure Level per speaker) that is between 100-130dB. But, just to make things more complicated, there are manufacturers that state SPL that deviates from the standard, by writing SPL as "Quarter-space" or even "Eight-space". Which gives a higher dB (theoretically).

A good picture and more information can be found here.
(The Sound Reinforcement Handbook: books.google.com)

The only tip and advice that is worth anything, is to listen and decide for yourself. If you think that it sounds good and that the volume is enough for your purpose, then OK.

Acoustic Glossary

This is how much the decibel number corresponds to:

 30 ㏈ - Office ventilation.
 60 ㏈ - Normal conversation.
 70 ㏈ - Vacuum cleaner.
 80 ㏈ - Motorway traffic.
 90 ㏈ - Chainsaw.
110 ㏈ - Rock concert.
120 ㏈ - Pain threshold.
130 ㏈ - Jet plane 25 meters away.
150 ㏈ - Rifle shot.
170 ㏈ - Cannon shot.
180 ㏈ - The eardrum breaks.
190 ㏈ - Atomic Bomb.
Source: Environmental Administration, Stockholm, Sweden.

Read more: Info about hearing range

Important! The number of watts in an amplifier, whether built into a speaker or stand-alone, doesn't have anything to do with the sound quality delivered. It is the quality of the speaker diaphragm and amplifier as well as how the speaker cabinet is constructed, and the material used in production, that is decisive for how it sounds. As an example, here at our rental service, we have active (amped) speakers with a stated wattage of 600W, and they do not only sound better, but also play more than twice as high volume as some of our other speakers, with a specified power of 1,000 watts. Something to consider before renting or buying. "Your ear is your best friend". © www.uns.nu