K5LA — Train Horn Glossary

The K5LA is a 5-chime locomotive air horn manufactured by Nathan AirChime, used on the majority of North American freight and passenger locomotives. The model designation breaks down as K (kettle-drum double-diaphragm bell design), 5 (five chimes), L (low-profile manifold), and A (American tuning). It plays a B major 6th chord — the iconic “freight train sound” that most U.S. listeners recognize when a train approaches a grade crossing.

What K5LA stands for

The model designation breaks down as (Wikipedia: Nathan Manufacturing; Locomotive Wiki: K5LA):

• K — kettle-drum double-diaphragm bell design used across the K-series
• 5 — five chimes (five tuned bells in one manifold)
• L — low-profile manifold (designed in 1975 for the EMD SDP40F to clear bridge clearances)
• A — American tuning (vs Canadian)

Chord and frequencies

The K5LA plays a B major 6th chord built from five bells:

Bell	Note	Frequency
#1	D♯4	311.13 Hz
#2	F♯4	369.99 Hz
#3A	G♯4	415.30 Hz
#4A	B4	493.88 Hz
#5	D♯5 (octave)	622.25 Hz

The doubled D♯ at the bottom and top reinforces the fundamental for long-distance projection. The major-6 voicing distinguishes the K5LA from harder-edged variants like the K5HL-R2 (C minor 7♭5) or the K5LLA-R1 (G♯7♯9). Hear an approximation on our interactive soundboard.

History and adoption

The K5LA was developed in 1975 at the suggestion of Amtrak’s Deane Ellsworth as a replacement for the Leslie SL-4T in use on the EMD SDP40F. Production began in 1976. By the late 1980s, the K5LA had become North America’s most popular locomotive horn (Locomotive Wiki: K5LA). It is:

• The standard horn on all CSX locomotives
• The voice of Amtrak’s F40PH passenger fleet
• Common across most other Class I and II freight railroads

Nathan AirChime supplies more than 90% of America’s locomotive horns (Nathan AirChime, official), making the K5LA effectively the default sound of “an American train” in the public consciousness.

Specifications

All numeric claims from the Locomotive Parts Supply standalone product listing (Locomotive Parts Supply) and HornBlasters’ aftermarket kit page (HornBlasters K5 Kit):

• Material: Cast aluminum
• Weight: ≈ 38 lb (horn alone)
• Dimensions: 16.5″ L × 29.75″ W × 10″ H
• Air inlet: 1/2″ NPT
• Operating pressure: 90–140 PSI
• Sound output: 144 dB at 10 ft (Locomotive Parts Supply published rating); the K5 platform has been independently measured at 149.4 dB at 3 ft (Wikipedia: Nathan Manufacturing)
• Standalone horn price: $1,649.95
• Complete aftermarket kit price: $4,999.99 (HornBlasters HD-544K) to $5,199.99 (XD-844K)

For a full review of the K5LA as an aftermarket purchase see Nathan AirChime K5LA Train Horn Review (2026).

K5LA variants in the wild

The K5LA is one of several Nathan K-series 5-chime models. Sister variants (Wikipedia: Nathan Manufacturing):

• K5LA (this entry) — B major 6th, the default
• K5H — D♯ minor 6th, darker variant
• K5HL-R2 — C minor 7♭5, dissonant emergency-service variant
• K5LLA-R1 — G♯7♯9 (“Hendrix chord”), tense
• K5CA-LS — A diminished chord in normal mode, dissonant in emergency mode

All five variants share the same physical kettle-drum bell platform, the same operating PSI range, and the same approximate dB output. They differ in bell tuning — which notes each manifold’s bells are cut to play.

Hearing a K5LA

To hear a real K5LA, you need to be near a freight or passenger locomotive at a grade crossing — which is most freight trains in North America. Train Horn Hub’s sound library K5LA entry (forthcoming) will provide a hosted recording. For an interactive synthesized version of the chord, see the train horn soundboard.

For historical context on the broader Nathan K-series, see Nathan Manufacturing on Wikipedia and SoundTraxx: Locomotive Airhorn History.

Related glossary entries

• AirChime — Nathan AirChime, manufacturer of the K5LA and 90%+ of U.S. locomotive horns
• K3LA — 3-chime sibling of the K5LA
• Decibel — SPL unit used to rate K5LA output
• Horn Pattern — long-long-short-long FRA grade-crossing signal sounded on K5LAs across America
• PSI — air pressure unit for the 90–140 PSI K5LA operating range

Sources

• Wikipedia — Nathan Manufacturing (B major 6th chord notes, K5 149.4 dB independent measurement, K-series catalog)
• Locomotive Wiki — Nathan K5LA Airhorn (1975 development, 1976 production, Amtrak F40PH, CSX standard)
• Locomotive Parts Supply — Nathan AirChime K5LA (standalone $1,649.95, dimensions, 90–140 PSI, 144 dB at 10 ft, bell layout)
• HornBlasters — Nathan AirChime K5 Train Horn Kit (complete kit pricing $4,999.99–$5,199.99)
• Nathan AirChime — manufacturer site (90%+ U.S. locomotive horn share)
• SoundTraxx — Locomotive Airhorn History (industry context)

We do not perform hands-on testing — see our methodology.