The Low Down

The higher the PSI, the louder your horn will be; 200 PSI being the max.  PSI Stands for Pound Per Square Inch).

The bigger the air tank, the longer your horn will sound; often times, also  longer it will take to fill the air tank again to re-sound.

The lower the AMP draw, the better the compressor; max should be 30

Pay attention to the gauge of your air line.  It DOES effect the volume and quality as well.

You want typically at least a 3 Gallon talk to run multiple horns.

A manual air valve, vs electric, will help you adjust the sound