SPL is an abbreviation for Sound Pressure Level.
It is the sound level (volume) 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 (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 SPL.
A good picture and
more information can be found here.
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 dB - Office ventilation.
60 dB - Normal conversation.
70 dB - Vacuum cleaner.
80 dB - Motorway traffic.
90 dB - Chainsaw.
110 dB - Rock concert.
120 dB - Pain threshold.
130 dB - Jet plane 25 meters away.
150 dB - Rifle shot.
170 dB - Cannon shot.
180 dB - The eardrum breaks.
190 dB - Atomic Bomb.
Source: Environmental Administration, Stockholm, Sweden.
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. And remember "your ear is your best friend".