Locomotive Wiki


In the early 1950s's, Robert E. Swanson (the founder of AirChime Manufacturing Co, already partnered with Burnett Power Saws, and Holden Co of New York ) designed a revolutionary new type of airhorn - the K-series. Intended as a replacement for the popular P-series of airhorns, they featured two diaphragms per bell and operated efficiently on much less air pressure. They produce a superharmonic , of over twelve octaves , also stirring up "ghost harmonics" . Swanson also employed super-catenoid bell flares , balancing and perfecting this horn to an even higher degree than anything else on the railroad.

Today, K-series horns are the most popular horns in North America, with the "K5HL" ( an "evolution" new GEVO horn) ,K3H, K3LA and K5LLA making up the majority.

The United States Government mandated the decibel , or sound volume of the once popular Leslie RS3L and RS5T to be too high, and forever banished them. The new, deeper toned Nathan K5HL and K5LLA were designed as their compliant, modern day replacement. However, they are not quieter, they are actually louder.


The series began with two variants - the five-chime K5H, and the three-chime K3H.

The original five-chime K-horn, the K5H

The K5H had five bells - numbers KS-1 through 5. It played a chord of D-sharp minor sixth (D#, F#, A#, C, D#), a very eerie and attention-grabbing chord.

The K3H, on the other hand, had three bells - numbers KS-1 through 3. It played a D-sharp minor triad (D#, F#, A#). Due to defects in manufacturing, some K3H's had an odd KS-2 bell that played a G, making a pleasant major triad.

The "American-Tuned" K5LA.

With the introduction of Amtrak in the United States, Swanson was approached to design a more pleasant-sounding horn than the eerie D# minor of the K5H. He agreed, and designed the K5LA, which played a very pleasant B-major 6th chord in the first inversion. The K5LA, again, had five bells, but two were modified for the major chord (KS-1, 2, 3A, 4A, and 5). The K5LA was also built on a new "low-profile manifold" mounting, as seen in the photograph. The K3H was also modified into the K3LA, which plays a major chord, with the KS-3 being swapped out for a KS-4A.


In 2004, the Federal Railroad Administration posted a law stating that all locomotive horns must not only have a minimum volume, but also a maximum. Seemingly in response to this new regulation, AirChime began production of two more five-chime horns for new locomotives.

One is the K5HL, which is a standard K5H but with the KS-5 swapped out for a KS-1L. The resulting chord is a rather unsettling C, D#, F#, A# and C. The other is the K5LLA, which is pretty much a standard K5LA but with the KS-5, again, swapped for a KS-1L. The resulting sound is a very dischordant C, D#, F#, G# and B.

There are two variations of the KS-1L bell. Very early bells are made from a 2-piece casting and play a B, as opposed to the more common raised-letter 1-piece bells, which play a C.

An AirChime K5HL on the roof of a BNSF ES44DC.


GO Transit horn-by Promagstyle

There is a variation of the K5LLA, where the KS-1 bell is replaced with a different sounding one. This "Canadian" tuned K5LLA, called a K5CA-LS, produces a sound resembling older Nathan horns. Only EXOVIA Rail Canada, Sounder, and GO Transit uses this variation.

The K5HL is standard equipment on new GE locomotives, and the K5LLA is standard on new EMD's. Oddly, the K5HL is usually mounted backwards, with four of the bells facing the rear of the locomotive. Some K5HL's are assembled with a KS-3B bell instead of the standard KS-3, and are called K5HLBs, and others have a KS-3A bell, and are called hybrid K5HLAs.

Different eras of the K horns[]

K series horns have many different eras and over time the notes were sharper or more flat.

In the beginning of The K series family in the 1950’s there was just the K3H and K5H which at the time had Adjustable backcaps with ”AIRCHIME“ on them. They were sandcast and sounded mellow, very close to a steam whistle which is what Robert Swanson originally intended.

When the introduction of the 3A and 4A bells in 1975 which would lead to the creation of the K5LA and K3LA they would be distinguished by their Big Tag which gave them the name of “Big Tag” Horns. Many of these horns played notes that were close to the intended and also not.

Wide Front Horns are from the 1980’s and are distinguished by the 3O1O9 on the back caps. Wide Front Horns usually play flat notes, but sound very sharp. For example the Wide Front K3LA/HA would play the E, G, C notes.

Narrow Front Horns started production in 1989 and were distinguished by the 30109 on the backcaps. A lot of the Narrow Front horns play chords similar to the Wide Front but as time went on they started to sound harsher. When the Raised Letter Horns started to pop up they still had the Narrow Front Backcaps until 2013 or 2014.

Raised Letter horns started production in 2005 or 2006 where Micro-Precision bought Nathan Airchime. Raised Letter Horns are distinguished by the “AIRCHIME” lettering on the side of the bells, and a lot of the early Raised Letters had Narrow Front 30109 backcaps until 2013 or 2014 as mentioned above. However newer Backcaps were made with a similar design to the older style Backcaps before the Wide Front design. Raised Letter Horns are also designed to play the intended notes of the horns they were meant to play originally. The Raised Letter K5LA/HA aka ”3rd Gen K5LA“ to railfans has a very high pitched sound to it because of the 5 bell, which has more prominence than that of K5LAs prior; this goes for the Raised Letter K5L/H as well. The KS-3A bells on Raised Letter K5LAs also tend to be sharp to some degree, playing closer to an A note instead of a G# note (forming a B7 chord instead of the intended major 6th), hence the name. The Raised Letter K3LA/HA and K3L/H sound Very close to their original intended chords. However both the Raised Letter K3LA/HA and K3L/H sound very similar to Leslie’s S-3K/RS-3K and the Prime-990 a copy of the Leslie S-3K with some notable design differences. This makes the sound of the Raised Letter K3LA/HA and K3L/H and other Raised Letter Horns very different from their predecessor K horns.

Raised Letter horns, especially Raised Letter K5LAs, are often derided by railfans for sounding very unpleasant when compared to the older horns. Some have said there is an FRA regulation mandating Raised Letter horns on the belief that unpleasant-sounding horns get more attention.

Bell Numbers[]

The K-series horns are comprised of the following bells or chimes, ordered in pitch from lowest to highest:

Bell Pitch Introduced
KS-1L C4 2004
KS-1 D#4 1954
KS-2 F#4 1954
KS-3A G#4 1975
KS-3 A#4 1954
KS-4A B4 1975
KS-4 C5 1954
KS-5 D#5 1954

Bell sets[]

All K-series models are listed below, along with their components and the year they were introduced.

Horn Bells Manifold Introduced
K5H 1, 2, 3, 4, 5 High 1954
K3H 1, 2, 3 High 1954
K5LA 1, 2, 3A, 4A, 5 Low 1975
K3LA 1, 2, 4A Low 1975
K5HL 1L, 1, 2, 3, 4 High 2004
K5LLA 1L, 1, 2, 3A, 4A Low 2004

Sound Clips[]

Horn Link
K5H http://www.youtube.com/watch?v=yUDbOBl_gaU
K3H http://www.youtube.com/watch?v=C5iAr8dMyts (Removed)
K5LA http://www.youtube.com/watch?v=UUNnC-9XMnI
K3LA http://www.youtube.com/watch?v=3zf1_brMYEw (Removed)
K5HL http://www.youtube.com/watch?v=UZebw4OdiuU
K5LLA http://www.youtube.com/watch?v=QPadO-yX7l8

Additional Notes[]

When a K5H is built with a low-profile manifold, it's known as a K5L. The same applies for a K5LA on a high-profile manifold - K5HA. Such a setup is very rare, however, since most railroads that use the K5LA have height restrictions that limit usage of high-profile horns.

Some K3H's have odd KS-2 bells that sound a G, making a pleasant major chord. This is due to an unintended error in manufacturing, but does not affect the volume or efficiency of the horn.

K-series bells can be reversed on the manifold, allowing the horn to be used for back-up movements.

Earlier in the series' production, K-horns were available with adjustable "MKS" bells, allowing the operator to change the pitch if desired. This option affected the reliability of the horns somewhat and was soon phased out. In fact, the K5H sound sample above is an example of such a horn, tuned perfectly to the chord of D#min6. It sounds no different from a standard K5H.

When the K-series started out, the horns were cast in sand molds, making a very smooth, almost clarinet-like, sound. Later on, the sand molds were phased out in favour of the more efficient die-cast method. This affected the sound greatly, making the horns louder and more aggressive-sounding. This did not change the pitches of the bells, however, unlike what happened to the P-series.

The K5LLA is also available as a K5LLB, which uses differently-tuned bells to sound like an older M-5.

Amtrak's Acela and HHP-8 electric locomotives are fitted with an odd variant of the K5LA. The horn has five bells spread across two manifolds - a standard K3LA with bells KS-1, 2, and 4A, but also an odd two-chime horn with bells KS-3 and 5. The two sets together cause a very unique, discordant sound (D#, F#, A#, B, D#, a B major 7th). The horn is known by railfans as the 'hybrid K5LA', and can also be found on some of Amtrak's Genesis fleet. as well as the MARC GP39H-2 #72.

Rarer still, a small number of Amtrak locomotives (most notably P42DC #193) are equipped with a variant of the K5L, with a KS-3A bell in place of the regular KS-3 bell. This has been called a 'hybrid K5L' by some.

There were batches of K5LAs out there shipped in the early 2000s with a Odd bell, most call This a 3B Bell. These K5LAs would gain the name K5LAM or K5LAB for their different sound to a normal K5LA.

There are ways to recreate the sound of a Leslie S-3L with a three chime K horn. what is needed is a early Two-piece 1L Bell, 1 bell, and 3B bell. This horn is known as a K3HLL or K3HLB.



K5H horn through the West Bottoms-0

A K5HR24.