oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 717
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Post by oldnorton on May 16, 2018 19:42:09 GMT
Well done Pete, it is nice to see theory turn into some results.
For the quick swap experiments perhaps hold the inserts in place with countersunk screws. A little leak between insert and bore probably does not matter.
If you are getting overblowing then what about taking the slot down in size - try some in the 0.004" to 0.008" sizes. That would keep the velocity up and the acoustic volume. Reducing the pressure with an inline valve/restrictor is kind of avoiding the problem rather than curing it.
I found that the alignment of the insert with the bottom of the slot was important - perhaps it ensures the fluid stream flows directly toward to top of the slot. I also used dead square cut tops to the slots, with sharp edges. I note you have a chisel top edge and wonder how this changes the result.
My last thoughts are wondering if a copper tube behaves any differently to a harder one in brass? and I did find that most everything would sound OK on air, but it was steam that would find out the 'shriekers'.
I am very envious of your spectrum analyzer - I will have to look and see if there Apps that will run directly on an iPhone.
Norm
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Post by doubletop on May 16, 2018 20:10:50 GMT
Norm
Thanks for the feedback
I'll admit laziness when it came to the fixing screw. It was another couple of operations vs grab the loctite bottle.
What I really wanted to confirm was that the whistle worked to the spreadsheet parameters. Which it did far better than anything I'd done previously. The pipework really is a factor, the small whistle suffered from too large pipework and the large whistle wasn't getting enough air when directly connected to the compressor using the blow gun as a whistle valve. Adjusting the slit size is an option but part of the installation is the pipework so testing should really be done with a representative setup.
I did bevel the lip as a matter of course I think the instructions from Richard Weisenberger suggested that. Probably not needed when using thin wall brass but if you use thicker material a bevel would be preferred. I'd guess it would work, to some degree, without the bevel.
The spectrum analyser is "Spectroid" I've checked and it is available for Iphone/Pad as well as the Android devices I'm using. It's free, at least it is for Android and there are others available
Pete
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Post by doubletop on Sept 7, 2018 5:57:35 GMT
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oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 717
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Post by oldnorton on Oct 12, 2019 12:37:16 GMT
Roger's recent thoughts on whistles in his thread caused me to look at this thread again, and I had completely forgotten Jim's contribution on his chime whistle and Pete's calculations and frequency measurements. Thank you Jim and Pete! You have helped me because I have recently being looking at the theory behind chime whistle tube lengths and frequency and came up with some thoughts on a set of three tube lengths for my Britannia. I went back to square one to determine these because the dimensions for a chime whistle given by Doug Hewson in his (excellent) drawings for his Britannia design did not agree with my calculations. It seems to be agreed on the web that American Chime Whistles, and our new build Tornado whistle, have tube pitches that correspond to the musical notes Ab, F and C. Now I have assumed that Britannias had whistles of the same pitches as I can find no statements either confirming or denying this. There is plenty of theory on the web from air pipe organ design about the lengths and diameter of organ pipes and the frequencies being produced. We know that steam will produce different frequencies because its different mass means that the speed of sound in steam is different from that of air. But the different notes from steam 'should' simply be a shift up in frequency in proportion such that the notes Ab, F and C sound in the same relationship to our ear (like an orchestra retuning to concert pitch or a specific instrument). Apparently, one cannot simply rescale pipe lengths, nor change diameters, and expect the chord to be the same. According to organ pipe theory the internal length (") required is equal to (3386/frequency)-(pipe i.d.). This constant of pipe i.d. subtracted means that we cannot simply rescale a set of pipes in length by a fixed proportion and expect the new tones be be in the same harmonic relationship. Using this formula I calculated three (internal) tube lengths to give me the chord of Ab, F and C. I chose a frequency shift that gave me tube lengths comparable with Jim's so that we could compare numbers. I was pleased that my calculations agreed with Jim's actual whistle with just a percent error, i.e. a tube length difference of 0.050". I don't know who designed your whistle lengths Jim but I am mighty relieved that my calculations from organ pipe theory agree, and they give the same chime chord relationship. Note that I have made calculations for a 5/8" OD pipe whereas I think that Jim's is 1/2", yet the lengths agree. I was grateful to see Pete's harmonic analysis of Jim's actual whistle confirming that the frequencies under steam were close to steam theory, however the frequency differences from Ab, F and C are +6% and -8% and that should be perhaps audible. I must look at your spreadsheet Pete and see how you have determined pipe lengths. At least we seem to agree, whereas there are other dimensions for chime whistles published that differ. Norm.
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Post by Jim on Oct 12, 2019 19:08:31 GMT
Thanks Norm for doing so much research into what is often a neglected topic, as Julian noted much effort goes into building a scale model locomotive and it should have a proper whistle to compliment it.
Jim
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Post by doubletop on Oct 12, 2019 21:02:03 GMT
I have to say that none of the work I did was original. I only consolidated the information I had found.
If you look at the Frequencies tab on the spreadsheet you see the dimensions for the various frequency scales. Scroll over to the right and you'll see 'x's, these are the frequencies of various Americann chime whistles that somebody on the Yahoo stream whistle forum had tabulated. Take your pick.
Pete
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oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 717
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Post by oldnorton on Oct 13, 2019 9:19:49 GMT
Thanks Norm for doing so much research into what is often a neglected topic, as Julian noted much effort goes into building a scale model locomotive and it should have a proper whistle to compliment it.
Jim
Hi Jim Now I am guessing, but I don't think your whistle design is on the Perrier drawings, because you have mounted a bigger whistle between the frames? Could you kindly confirm this for me please or put me right. If correct, where has the design come from? and could you let me know the tube OD and wall thickness? Many thanks Norm
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Post by Jim on Oct 13, 2019 11:51:44 GMT
Thanks Norm for doing so much research into what is often a neglected topic, as Julian noted much effort goes into building a scale model locomotive and it should have a proper whistle to compliment it. Jim
Hi Jim Now I am guessing, but I don't think your whistle design is on the Perrier drawings, because you have mounted a bigger whistle between the frames? Could you kindly confirm this for me please or put me right. If correct, where has the design come from? and could you let me know the tube OD and wall thickness? Many thanks Norm,You've guessed correctly Norm. The Britannia's whistle is based on a design I was sent by a member of this forum and whose name has slipped my memory for the moment, it happens a lot these days. Due to the length of the whistle I located it between the frames at the front of the loco so I could access the whistle relatively easily by dropping the front bogie. This is the drawing of the 3 chime whistle I was sent: This photo shows the whistle in position with the leading bogie removed to give access should it be needed. RegardsJim
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Post by doubletop on Oct 13, 2019 14:55:33 GMT
I was grateful to see Pete's harmonic analysis of Jim's actual whistle confirming that the frequencies under steam were close to steam theory, however the frequency differences from Ab, F and C are +6% and -8% and that should be perhaps audible. I must look at your spreadsheet Pete and see how you have determined pipe lengths. At least we seem to agree, whereas there are other dimensions for chime whistles published that differ. Norm. I've revisited the spreadsheets to see where the variance between the Norm/Roger vs the Richard Wiesenberger figures come from 3386 broadley correlates with 3390 (1130x3) but that figure is for air operation not steam. The figure Richard uses for steam is 1453x3. What is not clear from Norms formula is why the tube diameter is subtracted whereas for steam use the tube length really should be increased to maintain frequency. The one piece languid is the way to go as it provides the means of confirming best slit width for the operational pressure and if secured with loctite the languid can be reused for various tube lenghts to get the frequency right. I guess the proof will be in making Roger's and Norms whistles and using a mobile phone spectrum analyzer to confirm the frequencies on air and steam. Pete
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uuu
Elder Statesman
your message here...
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Post by uuu on Oct 13, 2019 17:44:58 GMT
I suppose if you could accurately make a tube to exactly the right length for a given note then pipe organs wouldn't need a method of tuning every note. That they do have every one adjustable shows that trying to pre-make an exact note is probably futile.
Wilf
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Post by Jim on Oct 13, 2019 20:08:28 GMT
That's a good point Wilf.
I had toyed with the idea of making the pipes so they could be tuned but in the end opted for keeping it simple as the sound produced was acceptable to my 'non pitch perfect' ears.
I might add that the whistle needs at least 30 psi to make a sound of sorts, at 50 psi it really speaks with authority.
Jim
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oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 717
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Post by oldnorton on Oct 14, 2019 12:44:06 GMT
Many thanks Jim and Pete for your replies. It has got me thinking a lot more and I have spent a few hours going through Jim's drawing and the Weisenberg spreadsheet (as referred to by Pete) to try and understand what is going on. I will try and keep the response as brief as possible but still informative for you both, and if others find it boring then tough! Jim, Your drawing is by Alan Gent of the UK who exhibited a very nice 7 1/4" LNER B1 here at the 2018 MME Show, and I know he has made a nice 5" Duchess in the past. I would tend to respect anything he draws. I like the whistle design. Although it uses thin brass tubing and consequent 0.015" languid (slots), many people get these to work and the thin tube will produce additional harmonics that will add colour. I think your whistle sounds just fine, in fact really nice, so if I mention differences from theory in the following text it is not criticism at all. You are to be congratulated for being the only engineer (that I know of) who has published the design of a chime whistle he made and a video of the sound it makes! So thank you, it has helped Pete and me have a discussion based on actual observations. Pete, The dimensions in the Jim/Gent drawing show the longest tube being 6 11/16", that is 6.6875" and not 6.875" as you gave in one of your tables. In practice this makes only a trivial difference to the examination of sounds but I only mention it because I have used my figure in the tables below. I agree of course with your deductions of 0.0625" and 0.4375" from tube lengths. I have tried to find reasons for the Air Organ Formula (length = (3386 / frequency) - (pipe id)) differing from the Weisenberg (air) Formula being (length = (1130 * 3 * 1.025) / frequency)). We can ignore the speed of sound * 3 differences of 3386 vs (1130 * 3) = 3390. The factor 3 somehow relates the speed of sound to wavelength, since (in Hz and inches) wavelength = 13543 / frequency and 13543 / 3386 = 4 (near enough). The organ people say that a stopped pipe contains a 1/4 wavelength. The Weisenberg factor of 1.025 is true for Bell whistles and also for pipe whistles of around 140 deg mouth opening. For 180 deg openings the factor becomes 1.000 so perhaps that is why the Air Organ Formula ignores it? I also wonder if the subtraction of pipe id is because 'cut up' (mouth height) usually equals pipe id, and perhaps they measure their pipe length from the top of the cut up? I am guessing in the absence of written definitions. I will now put to rest the Air Organ Formula and use the Weisenberg one, but for steam, from now on since that is what we want to test for. The table below reworks the figures for Jim's three tubes. The second column shows the Hz numbers I get from Weisenberg's sheet, which differ from your's, slightly, so that is the first complication. The third column repeats your frequency measurements showing the moderate deviations from theory. I then though it interesting to compare these numbers with the desired musical chord of Ab, F and C. Weisenberg's musical notes data agrees with data that I took from the Air Organ report. I have shifted the frequency for all three 'true' notes up (in the same proportion) so that Ab agrees. Our ears will still hear that as a chord. The third column computes the tube lengths (using Weisenberg for steam) If we compare the tables we can see that Jim's tubes only differ from theory (to obtain a true Ab, F and C chord) by +/- 0.1" on the longer and shorter tubes. Does this matter and is it truly audible? I somehow doubt it. But we still have the issue that the test frequencies do not agree with what Jim made. Well the Gent drawing lengths are not perfect and these account for a bit of the deviation (+/- 0.1") and of course Jim might have had some of his cooling nectar and this could have contributed another +/- 0.1" here or there. If the test results are correct (small spectrum analyser errors possible?), and we take Ab as the reference tube (test matches theory) then Jim's F tube deviates from ideal by 126Hz and the C tube by 58Hz. The former equates to the difference between two adjacent white keys on a piano, and the latter to the difference between adjacent black and white keys. Is that audible? normally yes. Does it matter when there are all types of other harmonics from the whistle? probably not. Norm
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