The Unofficial Mamod and Other Steam Forum

Caprice · Posted: Tue Oct 20, 2009 8:38 pm Post subject:

Bugsy (and others), thanks!

I'm a little bit of the eremite type but we'll see...

xlchainsaw, that's sounds fantastic!!!
(Is there a difference sound wise between ordinary "willow" type whistles and yours, with a smaller diameter air gap plate?)

My whistle sounds best at 15-20 PSI, higher it goes up in "falsetto"

C.

xlchainsaw · Posted: Wed Oct 21, 2009 12:46 am Post subject:

xlchainsaw · Posted: Wed Oct 21, 2009 1:01 am Post subject:

Caprice · Posted: Wed Oct 21, 2009 8:27 pm Post subject:

whistleman · Posted: Sun Oct 25, 2009 8:38 am Post subject:

great!!!!!

Caprice · Posted: Tue Oct 27, 2009 9:23 pm Post subject:

Thanks!, still a long way to go on the (low pitch) whistle road though.

Caprice · Posted: Tue Nov 03, 2009 9:19 pm Post subject:

I did another (longer)video, this time outdoors(on a chilly day) with lots of (mildly super heated)steam.

The safety valve blows on a little more than 15 Psi.

The burner is the "Japanese type" from this thread:
http://modelsteam.myfreeforum.org...aporizing_burner__about23196.html

mogogear · Posted: Tue Nov 03, 2009 9:36 pm Post subject:

Sweet whistles there gentlemen....I am in love with that low B...I have the same preference for long tubular wind chimes... the big deep and throaty types are so pleasing...

A bit like Demi Moore's voice.......

Off to the lathe
_________________
Lagniappe readily offered and accepted,

Mo

This week I are His Most Noble Lord Mo, the Apocalyptic of Old Tonbridge Wafers

mogogear · Posted: Wed Nov 04, 2009 2:27 am Post subject:

A little more on Helmholtz whistle design( you just have to love having this stuff laying about on the internet

"Whistle Components"

The whistles have three main components. The aperture, bell, and resonator.

Aperture
The aperture is responsible for creating a thin curtain of fluid that impacts the edges of the bell mouth. The aperture assembly produces a circular fluid curtain by allowing the fluid to pass through a narrow gap. The gap dimension is 0.0065 inch. It is critical for good operation of the whistle that the aperture gap be even or symmetrical all around the aperture. The two parts that are used to construct a Bangham whistle aperture assembly for Gauge 1 sized whistles are produced on commercial CNC Swiss lathes to maintain tolerance on the width of the gap when the parts are assembled into an aperture assembly.

Bell

The bell was previously referred to as the resonator tube (SITG #66). Larry has decided that it really functions as the bell on a prototype whistle and should be called such. This portion is the neck section of the Helmholtz Resonator. Either way, the part of the bell that the jet of steam from the aperture strikes is the mouth. After the jet strikes the mouth, the bell can either go straight or have an angle put into it.

The actual realized physical length of the bell is interdependent upon the frequency desired, and the volume of the resonator. This has to be calculated using the Helmholtz formula.

The maximum total length of the bell is ten times the inside diameter (ID) of the bell. This works out to 1.6 inches (40.64 mm) when using the currently standard 0.1875 (3/16) outside diameter, 0.014 wall, .159 inside diameter Brass tubing. This length is inclusive of any bends, and parts inserted into the resonator cavity. The minimum length is usually dependent upon mechanical mounting concerns for attaching the aperture assembly to the bell.

Resonator

The magic thing that makes it work. Actually, it's proper name including the bell is "Helmholtz Resonator". Stick that in Google and have fun.

The resonator can take many shapes, normally sticking with tubular and rectangular sections since they are easier to fabricate. The resonator also has been made in "C" shapes for inclusion in dome style whistles.
Tuning or Sizing the Bell and Resonator

The Helmholtz resonator formula determines the sizing of the bell and resonator. The formula requires the inside diameter of the neck, the neck length, and the resonator volume. I found that creating a Microsoft Excel sheet and utilizing the solver function was the easiest way to get the dimensioning of the various parts. Also, it is easier to let the computer figure out a square root.
Helmholtz Formula by Larry Bangham in SITG #67 rephrased

freq = K * SQRT( (Aperture Area / Resonator Volume ) * ( Bell length + (( .96 * Aperture Area) / 2)) ) )

Where K = Speed of sound in air / 2pi = 2156 for air
_________________
Lagniappe readily offered and accepted,

Mo

This week I are His Most Noble Lord Mo, the Apocalyptic of Old Tonbridge Wafers

Caprice · Posted: Wed Nov 04, 2009 10:07 am Post subject:

Thanks mogogear

, I like that low pitch also, at the end of the video you can hear it "choke" in falsetto though, when I open the valve to much.
I will make a lever as xlchainsaw did on his(which sounds much better than mine IMO.) to remedy this.
-----------
I read that Helmholtz text also, after I was finished (Don't remember where though). Thanks for posting it here! On the next whistle I build think I will try and follow some of that instead of doing it the Laurel and Hardy way.

Gap dimensions of 0.0065" could be hard to achieve without a lathe though...