Train Horn Glossary
Every term, signal, and standard you'll encounter in the train horn space — sourced from FRA, GCOR, manufacturers, and rule books.
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Nathan AirChimeAirChime
AirChime — brand owned by Nathan Manufacturing, supplies 90%+ of America's locomotive horns. K, P, M, C, KSJ series across single to 5-chime configurations.
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dBDecibel
Decibel definition for train horns — logarithmic SPL scale, +6 dB doubling, dB vs dBA, OSHA limits, why 150 dB at the source isn't 1.5× louder than 100 dB.
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TermDuty Cycle
Duty cycle for train horn compressors — ratio of ON time to total time, why 33% at 100 PSI is typical, what 100% duty XD-844K dual-compressor means, thermal limits.
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TermK3LA
K3LA — Nathan AirChime 3-chime locomotive horn, smaller cousin of the K5LA. Common on Metra cab cars and EMUs, lighter manifold, simpler chord with 3 bells.
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K5LAK5LA
K5LA — Nathan AirChime 5-chime locomotive horn, B major 6th chord (D♯/F♯/G♯/B/D♯). Most common North American freight horn since the 1980s. Specs and history.
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Pounds per square inchPSI
PSI (pounds per square inch) for train horns — air pressure unit, operating ranges for K5LA (90–140 PSI), tank-fed kits (110–150 PSI), why PSI determines dB output.
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TermQuiet Zone
Quiet Zone — community-established exception to FRA train horn rule under 49 CFR Part 222. Routine horn-sounding silenced via supplementary safety measures.
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TermSolenoid Valve
Solenoid valve in train horn systems — electrically actuated air valve, 12V coil, 1/2 inch NPT, normally closed. Releases tank air to the horn on trigger.
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Sound Pressure Level meterSPL Meter
SPL meter — sound pressure level meter used to measure train horn dB output. Type 1 vs Type 2 IEC 61672, A vs C weighting, why dB ratings need calibrated meters.
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TermTrain Horn Pattern (Long-Long-Short-Long)
Train horn pattern — long-long-short-long is the FRA grade-crossing signal. Full table of GCOR/NORAC horn signals, history from the 1887 Standard Code.