Train Whistle Construction

[slo pok]

Concerning Train Whistles, I'd like to ask all you "smokers" out there (hopefully this time without creating a controversy),
about the construction of a real train whistle but in miniature (G scale), not a electronic imitation one and whether this idea is worth pursuing.

With some gracious help from Barry's Big Trains (what a class act!) "Ole Blue" is on to the road to recovery, turned out to be minor problems (a lot to do with original design & construction), and I was considering a Whistle.

First problem is a source of compressed air..... Well we do have side rods connecting the wheels, those could be replaced with metal ones, (I believe Barry sells these) and then we have the fake (please pardon me if I don't use the correct terminology) piston and rod assemblies these are connected to. With a little bit (?) of machining, these could be made to be real, as could the air tanks above them for storage.

There, now we have a source of compressed air. But the real question is if a whistle is constructed in miniature, will it produce a sound (and I suspect this to be correct) that will be so high pitched that he only thing it will do is drive my dogs crazy?

Just the same, I'd like to know how a whistle is constructed......

Any ideas out there Guy's?       

[mhampton]

Since frequency is directly related to the length of the whistle, I think your idea that it might just drive dogs crazy is pretty accurate.  Then there's your air compressor.  You won't have much compressed air storage capacity, so if you do get any human-audible sound, it's probably only going to be a "chirp" and not the prolonged blast you hear from the real thing.

[mabloodhound]

The pitch of the whistle is actually related to the volume of the sound chamber, not just the length.   In theory, you should be able to create one that would give and acceptable sound.   However, the compressed air storage is a valid concern and would need a large storage tank to hold enough air to make a decent length whistle sound.

[NarrowMinded]

G scale whistles can be found on many live steam engines, and can produce lower tones.

If you wanted a whistle on your locomotive that is "Real" you will need a solenoid or some other valve to trigger it and a way to control it. a decoder could handle the control but even a micro solenoid valve is going to be to big to hide.

Get yourself a sound decoder and some really good speakers and you will be mile ahead.

Or just get a live steam locomotive.

NM-Jeff

[slo pok]

Thanks for the great answers guys, they were appreciated!

Not all ideas are great one, and usually something you thought of has been done or attempted to be done before...
A smart man learns from his mistakes, a real smart man learns from someone else's mistakes.


Famous last words of some wanna be inventors, " Hay ya' watch this!"

[NarrowMinded]

I thought of this when I went to the autoparts store today, there I saw a 12vdc Airhorn, you could not put this in a locomotive but the parts could fit in three box cars

The horn would go in one, an airhose would lead to the second contaning the pump and remote reciever, the third could contain an Motorcycle 12vdc battery.

I know it's silly but it would sure shock the heck out of people.

NM-Jeff

[Doneldon]

sp-

I would expect that the drag resulting from turning the decorative cylinders into functioning compressors (you need to do both sides to avoid jerky, and destructive, vibration) would choke your motor down to stop so I don't think it would be worth the effort. But why not either make custom pressure vessels which you can fill from a regular compressor or use something like the CO2 cartridges for air guns? Or use empty propane  bottles? You'd want to flush them out several times before using them but they should easily fit inside large scale rolling stock.
                                                   -- D

[Jim Banner]

Maybe compressed sulphur hexaflouride would do the job.  Five times denser than air at 20^o C, it would lower the note of a small whistle by over two times (over one octave.)  Alternately, turn the boiler into a whistle and turn the tender into a propane cylinder.  Use the whistle exhaust for jet engine effects.

Hmmm.  I think I will stick to digital recordings of real whistles.

Jim  

[Jim Banner]

It is almost impossible to get a prototypical locomotive steamwhistle sound out of a miniaturized whistle because, while the cell sizes can be proportionally reduced, the physics of the medium (steam or air) cannot.

If you cannot change the physics of the medium, then change the medium.  The higher the density of a gas, the lower the speed of sound in that medium.  The lower the speed of sound, the lower the tone of the whistle.  This is quite obvious when you blow a steam whistle with compressed air.  The air being denser than steam can drop the frequency more than 10%.  With Sulphur Hexaflouride, the frequency would be less than half of that in air.  With propane or even better butane, the pitch would also be lowered but not as dramatically.  If you wanted a higher pitch from the same whistle, you could blow it with Helium.  You may have inhaled helium from a balloon and then tried talking.  Your voice is pitched higher for the same reason applied in reverse.

As important as the length of the resonator (the pipe of the whistle) is the shape of the resonator.  Helmholtz resonators are enlarged at one end to reduce their pitch relative to a straight tube of the same length.  Perhaps a different resonator combined with a denser gas would be the answer.

But I am still going to stick to digital recordings of full size whistles.

Jim

p.s.  7.5" gauge representing 3' gauge is 2-1/2" scale (2.5" = 1 foot.)