Nathan P2

P2 is shorthand for any two-chime P-series horn. There are many possible variants;
known types are illustrated below (click thumbnails for larger images).

Before the 1990's, most known two-chime P horns in the US used the same manifold as the P5 with three positions blanked. The horns pictured have the bells attached to the two positions underneath the manifold, but in theory they could be attached to any of the five available positions.

A more compact P2 appeared in the 1990's that utilized a very thin manifold with a horn bell attached to either side. The horn was well suited to commuter railroads that wanted to mount the horn under the cab or behind the pilot of locomotives and cab cars to direct the horn's sound forward and minimize the noise in surrounding residential areas. The horns illustrated use bells 1 and 2.

P2's are relatively uncommon on US freight railroads, but Lehigh Valley is known to have used P2's with bells 1 and 2 on many of their Alco C628's. The horns are more common on commuter lines. In Chicago, Metra's ex-IC "Highliner" electric multiple unit cars had P2's reportedly fitted with bells 2 and 3. Metrolink in southern California used P2's of unknown configuration to replace Ohio Brass air whistles, which in turn had replaced K5LA horns delivered new with their equipment, all in an effort to minimize noise complaints from residents living near the tracks. San Francisco Peninsula commuter operator Caltrain similarly replaced K5LA's with P2's using bells 1 and 2 over noise concerns in 2001.

A P2 with bells 1 and 2 will play C# and E, a minor 3rd interval.
A P2 with bells 2 and 3 will play E and A, a perfect 4th interval.

Use of newer casting, slightly off-pitch bells have resulted in other combinations.

P2 sound samples:

Caltrain, bells 1 and 2:
Sample 1...173kB...11 seconds
Sample 2...235kB...15 seconds
Sample 3...231kB...15 seconds
Sample 4...345kB...22 seconds
Sample 5...408kB...26 seconds
Sample 6...135kB...9 seconds
Sample 7...113kB...7 seconds

Metrolink, possibly bells 2 and 4, or 2 and 4a (Courtesy Patrick Lopez):
Sample 1...139kB...9 seconds
Sample 2...59kB...4 seconds
Sample 3...109kB...7 seconds

When bad things happen to good horns:

Like any horn, a P2 can get fouled by dirt or oil in the air line. Horns mounted below the frame are especially vulnerable to outside debris, silencing one bell or causing it to squeal (harmonically overblow to a higher pitch). Some Caltrain installations have unusually long pipe runs between the horn valve and the horn, resulting in horns that don't sound crisply.

Horns with one bell squealing:
Sample 1...329kB...15 seconds
Sample 2...57kB...4 seconds
Sample 3...129kB...8 seconds
Sample 4...116kB...7 seconds

Horns with one bell silent:
Sample 1...194kB...12 seconds
Sample 2...96kB...6 seconds

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