studiot

Just the lower frequencies. Compare the two spectrograms. Ouside the bell there is significant response in the lower frequencies (hundreds of Hz) Inside the bell the response is skewed towards the higher frequencies (thousands of Hz) Perhaps you could engage Acme's graphics department? A sketch or three is worth .............

My ears are too old to catch the high frequencies involved. A helmholtz resonator requires a nearly enclosed chamber of air coupled to the source by a narrow constriction. The plug of air in the constriction bounces up and down on the air in thachamber and, if the dimensions are correct, extracts energy from the outside air, transferring it and trapping it within the chamber where is is dissipated as heat. That is how a car exhaust 'silencer' works. The energy is transferred from the air to the walls of the chamber. My bell is the opposite (has no cosntriction) , it transfers energy from the walls of the chamber to the air, flaring out like a horn. The flaring does not assist the transfer of energy directly (the walls of a horn do not intentionally vibrate) it assists the spread of that energy. I keep repeating that I have looked for nodes and antinodes in the sound, but not yet found any.

Here are some results. I offer them initially without comment other than they are obviously different.

Your graphics department definitely produces prettier work than mine. Do they work for free? Your ears are not reliable equipment for detailed investigation of the phenomenon. Even function, who is much younger than I am, and deserves all the credit for noticing this, does not have good enough ears. But remember, it is the sound in the air we hear, not the vibrations in the bell. Here is the key phrase, extracted from your reference, which exactly mirrors my suprise finding. The diagrams from your link are similar to those from my post#14 and the comment noted above is exactly what I said about my diagram c in post#14. I did not fully pursue the implications of that at that time but it is the underlying mechanics of the effect.

No the actual pressure levels obviously depend upon how hard I thump the bell, but the values quoted in post 4 are indicative. I did try to find nodes and antinodes but could really find any discernable variation either inside or ouside. This was noted in later posts. I am feeling like Agatha Christie here. All the clues are in the previous posts in fact.

Hello, Lizzie, welcome to the thread. Firstly you are correctly referring to a phase-difference phenomenon, which S was not. I don't want to dwell on the departed, but I got my ear chewed out for making the correction to phase difference. I actually said originally, "the ear is not sensitive to phase", which I stand by and offered an simple experiment to demonstrate. You can actually take a single sound (which is what we are dealing with in the thread), run it through a phase shifter to induce whatever phase shift you like and then into a loud speaker and your ear will not be able to detect any difference in the sound. Just so long as you are not comparing it with the same signal received via another source. But we are not discussing binaural spatial location here. In any case for very low frequency sounds we posess no sense of aural location. That has already been discussed earlier as well. Really though this was a digression from the thread which is why the sound is measurably of lower volume inside a vibrating vessel than outside.

Thank you for further explanation, Lizzie. The bottom row second square in (yellow) from left my dropper reads R = 250 G = 230 B = 050 For the left hand block R = 140 G = 150 B = 155 For the right hand block. Is that what you mean? I am still trying to absorb the implications of this.

There is indeed a quantity called "effective mass" in solid state and vibrational physics that can take a negative value. That is its respose to acceleration is in the opposite direction to positive mass. However this still leads to positive energy as the energy involved depends upon the square of the effective mass.

One of the things I suggest you need to clarify is what exactly you mean by "compress" Do you mean reduce the volume, with or without additional stress, or do you mean apply a compressive stress, with or without change of volume?

Actually no, I refer to the last two paragraphs of post52.

I feel that this particular digression has gone far enough. So I will say no more until someone posts some predictions as to what my new measurements will show or I have finished them and post them here.

Defining phase in terms of oscilloscope knobs is nonsense. If you have trouble with mathematics, I will happily explain. Your difficulty appears to be failure to distinguish between phase and phase difference. You have been describing phase difference. This is a common error, and applies to many quantities as well as phase, such as potential and pressure. You cannot describe a wave without first setting up a coordinate system. Such a system is inherent in the equation I quoted (which was the simplest I could think of). As soon as you have set up a coordinate system you have a reference or datum. That is its purpose. That is why you do not need a second wave. If you do compare two waves the comparison is meaningless unless you reference them both to the same coordinate system. When this is done the result is the phase difference. In each case the two quantities are measured in the same units which I think exacerbates the confusion. What do you think the units of phase are?

This looks to me like the classic fallacy "Appeal to Authority" Are you claiming to be that authority? Are you stating that the definition, which you will find in many mid level textbooks of physics and applied maths, is incorrect? Unlike some here I don't want "to be right", I want "the right answer". If a better theory is offered that mathematically analyses the observations and offers further measurable predictions, different from mine, then I will happily embrace it. So far alternative derivable mathematics has been sadly lacking.

Consider the wave defined by [math]\zeta[/math] = [math]A\sin (\omega t - \varphi )[/math] The phase is defined to be the value of [math]\varphi [/math]

I have no idea what you mean by either of those statements.

What you say is true, but not relevent since the experiment I described did not present that condition. Yes, of course you can, the signal is then different. What does that have to do with the case in point? So I look forward to your prediction about the results I am now measuring.

Thank you , Lizzie. I did try bicarb/vinegar but it had no effect (except for the fizz).

Thank you for your comments. 1) Phase. Try the following experiment. Take a loudspeaker and listen to it. Now reverse the connections. Can you hear any difference, the phase between the two connections is as far apart as possible? You can also do this with a pair of loadspeakers, with the same result. 2) I agree, the ear is a complicated sound receiver with many signal processing and conditions features. 3) I have yet to see any of the multitude of those claiming the measurable difference to offer anything other than hand waving statements in support of their claim. Nor have I seen anyone else prepared to make experiments or measurements. I have offered both measurements and solid mathematics that results in the same values as measured. When I read the OP I had not come across this effect so I experimentally confirmed it for myself. Since it is interesting I have not yet finished and yesterday received a real time audio spectrum analyser with a much finer pickup than my own meter. Preliminary results have confirmed the overpressure levels, but produced one suprise so far. I have not had a chance to complete the measurments yet so will hold off reporting more detail until I have proper data. This is taking some time as I must refresh my technique on this kit as I last used it a couple of years ago when doing some consultancy audio work on the noise of rotary aero engines. Unfortunately I have not yet gained any access to accelerometers or vibration monitors to detect the actual frequency my "bell" is vibrating at - I can only test the sound in the air. A really good challenge for alternative theories is "Can they predict what this suprise is in the new measurements"

I didn't dare try acetone as it dissolves or softens too many plastics or, almost as bad, the plasticiser in some harder plastic. I think the wellies are pvc of some sort.

Well I, for one, don't understand the coloured blocks or what you are saying about them Lizzie. What should I be seeing on these blocks?

Agreed. But there is much more to this since even after a law is passed it and its effects are not certain until substantial case law has been established. There is always room for another side to argue a case and sometimes they prevail. What for instance if you click on a link, that has been maliciously altered, believing it to be one thing, only to find you have downloaded soemthing entirely different? In the UK I know of no cases where someone has inadvertantly clicked on a single link and downloaded one thing and gone no further. Al the reported cases are about individuals who have systematically downloaded large numbers of files and then proceeded to sell them for profit. But there are still caveats. It has also been held that if you are in an East London pub one dark night and some stranger offers you a £2000 Rolex watch for £20 you should be suspicious.

imatfaal is the guy to elaborate on what I will now say but the UK is an occasional member of the EU as well. However the Uk law stems from vastly different roots than the Napoleonic code. In particular we have different civil and criminal codes. To be against the criminal code an act must not only be performed it must be perfomed with the intention to commit a criminal act, or soemtimes in criminal negligance. I do not think that inadvertantly clicking on something without realising a criminal content could be construed as criminal intent. I look forward to inmatfaal's comments.

Well, difficult to suggest specific titles without knowing what level, as ajb says. However on a more general note, although you are not studying a formal course at school (and presumably not going for an exam) school textbooks offer a balanced presentation of the subject at a common level so are better than targeted or single subject books. Popsci books in particular are designed to push a particular message. You often require combined input from several differnt parts of the subject to understand a point. For example to properly understand the working of your electric fire you need input from the mechanics and heat (thermodymics) branches of physics as well. Since you are not following a formal course, you do not need the latest textbook, so you can pick up older editions or older books for very little from second hand sources. these will be perfectly adequate for your needs. In a school environment you would also learn associated subjects (mathematics and perhaps chemistry) in parallel with physics, most physics books will assume this so will be deficient in this area. If you looked at what tech colleges call "engineering science" you might find more useful material. Engineering science is basically less mathematical physics with a smattering of chemistry and is more down to earth so easier to digest on one's own. Good luck in your personal studies.

A bit like castor oil into the ears of small children? Thanks for the thought. I did try elbow grease in the form of various brushes on the end of a modellers drill. Not really a huge success. Finally got it all out by soaking in cellulose paint thinner (composition not stated, but the Lidl cheap one worked better than the glassit proprietary one "contains toluene") and scraping with a toolmakers small cleaning kit of scrapers and brushes. I am just left with a stain in the bottom, which is acceptable. Please note that if anyone is thinking of using these techniques, I do this in the open air on a concrete slab fore safety reasons. Thanks all for your thoughts.

White sheets of paper, white bedsheets, white sheets of plastic, the situation is the same and you can compare. White bodies reflect all wavelenghts of visible light. Coloured bodies remove some of the wavelengths so the colour you see is what is left and reflected. The difference between a mirror, which also reflects all wavelenghts and a white body is that mirror reflection is called specular reflection. The surface of a mirror is smooth at the microscopic dimension sizes of light wavelengths, the surface of a white body is rough. This means that the light from a mirror reflects in an organised fashion, whereas the light form a white body bounces off in random directions. https://www.google.co.uk/images?hl=en-GB&q=specular+reflection&gbv=2&sa=X&oi=image_result_group&ei=I0lGU5OBK8rdPauFgLAM&ved=0CC4QsAQ