Do all train horns/air horns need a compressor/tank system?
Train Horn Compressor
The only horns that do not need a compressor/tank system are direct drive models. Direct drive models come with a pump that shoots the air directly into the horn, vs pressurizing it in tank. Direct drives will be louder than a stock horn, but not as loud as those that use a separate compressor/tank system.
Marine Outlaw, PBmissions.com
What determines the loudness and type of sound of an air horn/train horn?
Of course, the larger the train horn, typically the louder and deeper the sound. This is because the larger, broader trumpets allow more air flow at one time and will be a lower pitch than a more narrow trumpet that is restricting air flow somewhat and resulting in a higher pitch. Also, the larger horns typically accommodate larger compressors and air systems, which also improves loudness.
Where, on the vehicle, should I mount my train horn/air horn?
Depending on your vehicle, some air horns will fit under the hood or behind the grill. This is ideal in terms protecting the horn itself. However, most people must install under the vehicle on a body rail, due to space restrictions. If under the body or behind an open grill, you will want to angle the horns in a position that is slightly downward. This protects the inside of the trumpets from debris, dirt and liquid collecting. Also, from something (such as a rock) getting stuck inside the trumpet. Downward facing trumpets also allow anything (such as water) to drip back out of the horn automatically. This also prevents unnecessary wear and tear on the horns.
See also our ”Compressor Mounting & Advice Post”