Whistles

[Speedy Builder5Participant @speedybuilder5]

If I make a whistle to LBSCs design for Speedy, and test it on compressed air, would I get the same/similar results when used with steam. I will be using a bit of brass tube from a crumpled trumpet picked up at a car-boot sale for 50p. Why? I read that ordinary brass tube does not resonate the same as "Music quality brass" !!

[Speedy Builder5Participant @speedybuilder5]

Compressed air versus Steam

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

You can test a whistle on air to see whether it works at all and if so what note is produced . Note will be a bit different to that produced by steam but not much .

The problem is that you can't test the secondary problems of steam whistles on air . Ordinary boiler steam arriving at whistle contains both intrinsic water vapour and variable quantities of water droplets from condensation . All this wet water causes no end of problems . Most commonly the water gets spat out , trapped or recirculated near the mouth of whistle and produces a lot of hissing and bobbling sounds which won't show up on air test .

Clearing this water is an important part of whistle design – as far as possible arrange whistle so that any water just falls away . One way is by having voice slot on bottom and slight downward slope on voice tube .

Michael Williams .

[Speedy Builder5Participant @speedybuilder5]

Thanks for the info Michael – I think that just about wraps it up.

[Sub MandrelParticipant @submandrel]

I think the note will be noticeably different as the speed of sound is very different in each medium.

<googles>

The speed of sound in steam lies between "1453 feet/second and the 1520 feet/second" . the speed of sound in air is about 1100 feet/second. I'd guess the difference in pitch of the notes will be roughly in the ratio 11:15 air to steam.

Neil

[mgjParticipant @mgj]

I rather agree.

I have a couple of traction engine whistles in service. They are adjustable, in that the bell screws down for tuning.

You can set them on air, but they always require a bit of additional tweaking to get them working really well on steam. So if you are going to set a whistle on air, you need to be sure you have set it right in the middle of the range, because it can end up sounding pretty feeble on steam.

There was a good article on sizes and dimensions. The original was published as an SMEE article, but it then appeared in ME quite recently under the heading of "Wheezeless Whistles". It will contain all that one needs to build a good whistle.

Edited By mgj on 18/08/2012 22:15:47

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

The ratio of speeds of sound is closer than stated but even taking the median value which gives a frequency ratio of 14.8/11 the notes produced would only be different by about a musical fifth . Heard separately in the open air I doubt whether many people on this site could even tell the difference between the two whistles .

The difference in sound quality rather than note is due to steam being more 'energetic' and exciting the whistle to produce more overtones than air would . Worst case a steam whistle can produce an unstable range of overtones only and that gives the 'screech' sound some full size whistles have .

Just one final mention – the area of opening of the voice slot has to be smaller than the area of opening of the whistle valve for proper operation and clean notes . I mentioned some of the reasons before in connection with steam turbines .

Michael Williams .

[DMBParticipant @dmb]

"Music quality brass" Whats that? Would it be the thin-walled "treblet tube" referred to by LBSC?

John.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi DMB ,

'Treblet' tube is ordinary brass tube that has had three finishing passes through the drawing process . This results in tube which is thin walled , true and hard . It may have had some limited application in musical instruments – such as in trombone slides – but in reality few components of brass instruments are simple tubes – many bits are curved and some are tapered or flared as well .

'Treblet' though descriptive of the manufacturing process may just have been a trade name – it is shown with a capital 'T' in some places .

I doubt whether 'Treblet' tube was actually better for any practical purpose than modern thin wall drawn tube would be .

The quality of brass used makes a difference to the tone quality of percussive instruments such as chimes and tubular bells .

What difference it makes to the tone quality of wind instruments is not so obvious . It could be subjective .

On a related topic :

Some brass band enthusiasts claim that silver instruments have a richer sound than brass ones – and this does seem to be true . It is quite possible however that the silver ones being much more costly are just made better .

Regards ,

Michael Williams .

[Sub MandrelParticipant @submandrel]

> Some brass band enthusiasts claim that silver instruments have a richer sound than brass ones

Probably the same effect which makes car stereos sound better with a £60 gold-plated fuse

Neil

[David Paterson 4Participant @davidpaterson4]

Its OK for a brass band, but you won't see all that many silver plated instruments in other forms. One of our really good local companies has a service stripping the shiny lacquer from instuments to get the 'tone purer'. Takes on a nice patina after a while, but that could be just in context with dark bars as venues.

Military likes sivler so you can polish it – noting to do with the sound.

dave (trombone)

[SteamshyParticipant @steamshy]

To get a steam whistle working properly, if you can drain

the condensation out of the steam line prior to it reaching the whistle

you should get the same sound every time.

Andy

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