Do real steam engines get quieter the faster they go?

[cudaken]

 OK, I know at first this sounds like a stupid question. But there is a reason I ask.

 On my steam engines the faster they go they lose the bass in the chuffing sound. My first thought being a Audiophile is there small amplifier do not have sufficient power for a deep bass sound at the higher speed. But, after watching a lot of steam videos they seem to lose some of the bass sounds when at main line track speed.  

 Thanks For Looking.

 Ken

[selector]

Sort of, yes, Ken.  The reason is that as the engine speeds up, and in the interests of economy, the engineer 'hooks up' the reverser so that the valve sliding back and forth spends more time covering the inlet and outlet holes.  This has the effect of letting less steam into the cylinder, and not a lot of steam as they do at startup.  At the same time, the lesser volume of steam is allowed to expand more and be more efficient instead of only expanding partway before the valve uncovers the exhaust port in its rapid travel back and forth.  Since the steam has done more work, it is under less pressure when it is allowed to vent out of the cylinder, ahead of the piston that is now coming back at it.  With less energy, it is quieter when it exits the blast pipes and goes up the petitcoat pipe and up the stack.  In other words, there is less of an 'explosion' of steam up the stack.  Also, it is much more rapid, which makes it more of a roar instead of discernible chuffs...depending on speed of course.

What I described above is what is referred to as 'cut-off'.  The cut-off is a higher value, often 80%, when you want a lot of steam admitted during the part where you first get underway.  Later, the cut-off is less, nearer 20-40%, when at speeds near 50 mph and above.  It also depends on the diameter of the drivers and the speed they are meant to sustain.  Drag engines will be cycling more rapidly at speeds near 30 mph, whereas the high-drivered Pacifics and Northerns would be at the same cut-off at 60-79 mph.

Crandell

[bogp40]

Crandell thanks, very informative. I should stop being such a diesel guy and learn more of  "Those real machines"  Have to hand it to those shops- lot of work to maintain those "Beasts"

[tomikawaTT]

Another factor that enters into steam noise level is the design of the, "Front end," - the venturi, exhaust openings and their exact relationship.  Old (and relatively slow) locomotives were, "Crackers."  The individual exhaust chuffs were almost explosive.  More modern designs are much softer, but they are also more efficient at creating draft through the boiler tubes (which, in the final analysis, is the reason for routing the exhaust up the stack.)

Chuck (Modeling Central Japan in September, 1964 - with low back-pressure exhaust steam)

[mlehman]

Ken,

Now that you've heard the prototype side of the story...

Depending on your decoder, you may be able to adjust the chuff volume, rate, and equalizer settings. I know my Tsunamis do this, although I've not really explored what these settings can do.  If you have JMRI/DecoderPro, this will be easily accessible there.

You can probably make 'em really bark, if you want.

[Texas Zepher]

mlehman

Depending on your decoder, you may be able to adjust the chuff volume, rate, and equalizer settings. I know my Tsunamis do this, although I've not really explored what these settings can do.  If you have JMRI/DecoderPro, this will be easily accessible there.

I will have to explore those options too.  That is one thing that I really miss with the DCC sound systems - easy control of the exhaust cut off sound.   My PFM sound systems have this feature.  I used to spend much time playing with getting the sound just right as the loco pulls away after a station top.  

[C&O Fan]

LOL Ken i'd say it depends on how close you are standing

see

http://cs.trains.com/mrr/f/88/t/211591.aspx

and make your own opinion

sorry i didn't have time to get a disciple count but it was loud enough to make me shake

[cudaken]

 Thanks for the explanation Crandell. So it is prototypical for the engine to lose some of the bass.

 Mike, I do use decoder pro and I can adjust the sound levels and chuff rates of the Loksound 3.5 decoder. In fact, it is the Loksound decoder that Terry From Texas gave me from his Allegheny. It is now in my PCM Big Boy and it sounds great.

 It is not just the Loksound decoder that I have noticed that does it. All of my steamers loses bass as they speed up.

 Thanks again for the reply's

 Ken.

[mlehman]

cudaken

SNIP

 It is not just the Loksound decoder that I have noticed that does it. All of my steamers loses bass as they speed up.

 Thanks again for the reply's

 Ken.

I suspect that you're running up against the limits of audio amp in the decoder. Getting bass out of the tiny speakers used in HO scale is always going to be a problem. They do pretty well at slow speeds and low volume, but the limits become more apparent with faster speed and higher volume.

Maybe you need a sub-woofer?

[mobilman44]

That's a tough question............

I guess the only sure way is a decibel reading in the cab and/or on the outside of the loco in start up mode and at speed.   I could see support for both sides of that discussion.

In my mis spent youth VERY close to the C&NW tracks in Chicago and the IC tracks in Southern Illinois (Anna), I tend to say they are louder at speed.   But, when they went by so close, it was almost like an explosion in my ears.  

Anxious to read the other posts..............

[CTValleyRR]

selector

Sort of, yes, Ken.  The reason is that as the engine speeds up, and in the interests of economy, the engineer 'hooks up' the reverser so that the valve sliding back and forth spends more time covering the inlet and outlet holes.  This has the effect of letting less steam into the cylinder, and not a lot of steam as they do at startup.  At the same time, the lesser volume of steam is allowed to expand more and be more efficient instead of only expanding partway before the valve uncovers the exhaust port in its rapid travel back and forth.  Since the steam has done more work, it is under less pressure when it is allowed to vent out of the cylinder, ahead of the piston that is now coming back at it.  With less energy, it is quieter when it exits the blast pipes and goes up the petitcoat pipe and up the stack.  In other words, there is less of an 'explosion' of steam up the stack.  Also, it is much more rapid, which makes it more of a roar instead of discernible chuffs...depending on speed of course.

What I described above is what is referred to as 'cut-off'.  The cut-off is a higher value, often 80%, when you want a lot of steam admitted during the part where you first get underway.  Later, the cut-off is less, nearer 20-40%, when at speeds near 50 mph and above.  It also depends on the diameter of the drivers and the speed they are meant to sustain.  Drag engines will be cycling more rapidly at speeds near 30 mph, whereas the high-drivered Pacifics and Northerns would be at the same cut-off at 60-79 mph.

Crandell

Crandall has the technical aspects nailed, but the short answer was in your HS Physics class:  Newton's 2nd Law of Motion:  An object in motion tends to remain in motion unless acted upon by an outside force; an object at rest tends to remain at rest unless acted upon by an outside force.

So, yes, the engine is working harder (and hence, creates more noise) as it builds speed from a dead stop, and less hard as it slowly gains speed from a condition of already being in motion.  The same reason that the EPA estimate for gas mileage on the Highway is almost always greater than in the city.

And, before anyone nitpicks me for oversimplifying it, remember what NASA learned on the way to the moon:  Relativistic descriptions and calculus based analysis of gravity-warped 3D space were more accurate, but Newtonian physics and algebraic equations were close enough for interplanetary travel.

[selector]

There is more to the phenomenon of a quiter-running steamer when it is at speed.  Much of it is generated by the human brain.  When we are stationary and observing a locomotive lifting a heavy drag of coal hoppers from a dead stop, all the things I described are true.  Each slow exhaust will bark up the stack when it is released finally, and that only happens when the slow-moving linked valve sliding back and forth above the large cylinder clears a port and opens it.

As the train gains speed, and if you wish to continue to monitor the noise levels from the same relative position...for accuracy of measurment,...you must begin to move and to match the speed of the loco as it accelerates.  At some point, your hearing will be affected by the movement of air around both your head/ears and the vehicle.  Similarly, the train will begin to generate louder noises from its own motion that it did not generate when it was first getting underway....and moving at a crawl.  Between those two, and the hooked-up reverser allowing less steam into the cylinders near, say, 50 mph, you get an entirely different auditory experience.  You still get a roar, but it is wind noise, car noises, engine noises, metal-wheels-over-joint noises, flange squeal noises, coupler straining noises, rod clank noises, and so many others that mask the sound issuing from the stack.  Even the on-rushing air running over the stack orifice will have a dampening effect on the sound issuing from the stack in the same way it affects the issuance of the smoke and of the steam that creates the chuffs in the first place.

Mostly, we hear our own ears being buffeted by the wind moving over them.  And when you look at the many youtbue videos by Skip Weythman, for example, where he paces UP's 844, you don't hear much from the locomotive except its steamboat whistle at crossings, some valve gear clanking, the steam turbo-generator whine, and the occasional suspension chirp when the engine runs across a slight dip or rise in the rails.  But mostly you hear the roar of the air across his videocam's microphone.

Perception.

Crandell

[cudaken]

 If a box car falls over in the woods and there is no one there to hear it, does it still make a noise?

 I guess I really started the post wrong at the beginning. I was wondering more about there being less bass sound more than anything. 

  After thinking about it a little I think I have my answer as far as the Loksound 3.5 decoder. My tender has two 2. 2 inch speakers and cabinets that are fairly long. Has a good deep sound to the slower speed chuffs. This not my tender, mine uses the 21 pin Loksound 3.5 decoder, just to show what the speakers look like.

 

 

 Whistle has a deep tone to it as well. I an sure a 5 watt amp would help, but that is not going to happen.

 At higher speed when the chuff loses it bass sound, the whistle still has the deep sound as before. So, I conclude that the chuffing sounds is prototypical in losing the deeper tone and not due to the amp being out of power.

  Thanks for all the answers and sorry the video is such poor quality.

 Ken

 

[CTValleyRR]

selector

There is more to the phenomenon of a quiter-running steamer when it is at speed.  Much of it is generated by the human brain.  When we are stationary and observing a locomotive lifting a heavy drag of coal hoppers from a dead stop, all the things I described are true.  Each slow exhaust will bark up the stack when it is released finally, and that only happens when the slow-moving linked valve sliding back and forth above the large cylinder clears a port and opens it.

As the train gains speed, and if you wish to continue to monitor the noise levels from the same relative position...for accuracy of measurment,...you must begin to move and to match the speed of the loco as it accelerates.  At some point, your hearing will be affected by the movement of air around both your head/ears and the vehicle.  Similarly, the train will begin to generate louder noises from its own motion that it did not generate when it was first getting underway....and moving at a crawl.  Between those two, and the hooked-up reverser allowing less steam into the cylinders near, say, 50 mph, you get an entirely different auditory experience.  You still get a roar, but it is wind noise, car noises, engine noises, metal-wheels-over-joint noises, flange squeal noises, coupler straining noises, rod clank noises, and so many others that mask the sound issuing from the stack.  Even the on-rushing air running over the stack orifice will have a dampening effect on the sound issuing from the stack in the same way it affects the issuance of the smoke and of the steam that creates the chuffs in the first place.

Mostly, we hear our own ears being buffeted by the wind moving over them.  And when you look at the many youtbue videos by Skip Weythman, for example, where he paces UP's 844, you don't hear much from the locomotive except its steamboat whistle at crossings, some valve gear clanking, the steam turbo-generator whine, and the occasional suspension chirp when the engine runs across a slight dip or rise in the rails.  But mostly you hear the roar of the air across his videocam's microphone.

Perception.

Crandell

Newton vs. Einstein.

[ATLANTIC CENTRAL]

And in any case, two 1" speakers in an HO tender don't have a shot at reproducing the experiance.

Sheldon

[mlehman]

Ken,

Since two speakers are involved, are they wired properly in phase? Because out of phase speakers will tend to cause low frequency sounds to cancel each other out.

[sandusky]

No guarantee that out of phase speakers affect only lower frequencies.

[BRAKIE]

Remember to that once a engineer got up to track speed he could shut the throttle and "drift" letting the momentum move the train and as the train started to slow he would open the throttle.