AirChime K5HL

US Code of Federal regulations specified in 2004 on December 18 that a maximum noise volume of 110dB(A) sould be audible at 100 feet. Subsequent, Airchime developed the K horns with 5 chimes for American trains that were already using the low-pitch 1L bell, with a C major chord on a volume of 261Hz. The first of these models was the Airchime K5HL.

For a long time, the US Code of Federal Regulations implemented a minimum noise requirement for all locomotives from their horns. This was called the "audible warning device" this mandates that: "railroad locomotives should have a 96dB(A) volume at 100 feet in the direction of travel." This regulation can be found on Section 49CFR229.129 in the US Code of Federal Regulations book.

K5HL horns were first installed on BNSF GE and Union Pacific trains. They were usually placed backwards, with the 1L,1, 2, and 4 bells directed to the exhaust stack. There were also noticeable covers to keep unwanted matter from entering the bells, these were called "shower caps."

The #3 bell was reversed, as a designation for this, the train horn was named K5HLR3 with the "H" indicating that it was a manifold with a high-profile . The "L" suggests that it is using a 1L bell as a substitution for the #5 bell. Usually, #5 bells are a standard design for K5H's. There is also a manifold with a low-profile option to produce a K5LL designation. Although completely different on architecture, both horns still had the same sound.

Factory tuning was keyed at C, D#, F#, A#, C. Having a volume of 261, 311, 370, 470, 512Hz respectively. External design included the K-series #1L, 1, 2, 3 and 4 bells. Sometimes factory defects result in bells that are out of pitch, but this was accepted as another variation of the sort.