Amtrak horn placement

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Joined: Fri Oct 03, 2014 1:12 pm

Amtrak horn placement

Postby Evansville-Antiques » Fri Jun 08, 2018 2:14 am

ヤセメチヤマキ (2018)
The sound of a horn is not only affected by reversed bells or other conditions of the horn , it can also be affected by objects in front of the horn. Torn (and intact) debris caps can change the character of a horn (don't use debris caps :lol: ) , but the most dramatic change for sure is the sound reflection effect from amtrak locomotives. The K5LA sits almost fully under roof level , in a metal box on the Genesis locomotives. The horn is aimed stright into a metal wall . The reason for this placement is for clearance. when the horn is blown, the energy transfered to the atmosphere leaves the K5LA at about 767 miles per hour. This energy collides with the walls of the roof recess , but this is not the end of the sound , it reflects back and fourth, actually affecting the diaphragms of each bell , as the sonic equation naturally adjusts to a state of equilibrium when an obstruction is present. for those who dont know, when place your hand inside a horn while it blows, the pitch will drop sharply down. this is the opposite of what makes sense to me, I'd expect the pitch to go up, as the horns thoat is getting smaller when you put your hand in there . there is the atmospheric coupling taking place , which is alot more complicated. in the beginning , Robert Swanson used a transparent k horn bell and a "stroboscopic light" , as he was developing his atmospheric coupling.

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Joined: Tue Jan 17, 2017 9:06 pm

Re: Amtrak horn placement

Postby AmtrakMatt » Fri Jun 08, 2018 3:32 pm

Placing your hand in the bell throat causing the frequency to drop makes perfect sense. You’re hand is becoming part of the air column, causing it to lengthen. Longer the bell = lower note, all else being constant.

The original F59PHI horns were some of the most unmusical K5LAs, caused by several factors that include poor factory tuning (most K5s of this era had several bells being quite sharp), placement (particularly being behind an exhaust stack, but also with many objects surrounding it as you mentioned) and what sounded like an extremely harsh volume and/or pressure at full blast. I’ve read some folks mention these have oversized piping but I’ve never confirmed for myself.

When the P40/42s were new people didn’t believe they had the same horn as the F40. This was because of the mounting location and solenoid valve setup. It’s a shame horns are not up front where they belong, with less pressure going to them to keep them within legal limits, but then again I’m surprised the law doesn’t account for impacts of speed when measuring effectiveness at either midship or up front. Everything is done static, which seems silly.

Rare find to get ahold of an Amtrak diesel horn nonetheless!

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