Sincerely, I apologise. It was not my wish to antagonize you.
Rather, as one who is new, and has spent the last week pouring over old threads, I just wished to provide a perhaps slightly distanced perspective. The pattern is quite obvious if one wishes to look. Not trying to spoil anyone's fun, each will respond as they see fit. But if the Forum is to be a resource, and most enjoy that status when they can achieve it, then a certain degree of lateral movement within threads must be constrained. I suppose this thread got off to a sideways start, but as others have mentioned this has become a very thought provoking excursion and there's much to be learned within for someone (like myself) that's new to TL design.
The mob welcomes you - you fit right in here. 🙂
Keriwena speaks for the people, I'll do as he says: No my trolling for me in this thread. I've made my points in any case.
The questions are too hard to answer, some show their frustration by lashing out. I understand.
Why do you even need to know this? I'm mean what's the big deal about it? If you're even a little bit good at visualization, it's very easy to see the answer to this question even for a grade school kid...
Perhaps it would be better to just let the easy things go, re-read the thread and go from there etc.. There are real experts at diy for sure, everyone knows that!! But unfortunately there are also others who maybe understand a good part of the picture but not all, and like to claim they are just as knowledgeable etc... Some ego's are strong IOW 🙂
What's the point of this thread or it's purpose ??
I mean there are constructive ways of seeking answers to questions for the betterment of all, and destructive ways to go about it , sadly?................
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Resonance of bottle can be an many frequencies as with any Helmholtz style resonator. The bottle is easiest to stimulate its lowest frequency. Higher frequencies require a little more skill or luck for the person blowing over the bottle.
With the flute the air enters the flute hole and pressurizes that end of the flute. This makes the air rush out of the hole against the breath of the player. Because the flute player is pushing back the air stops coming out and goes back into the hole. This occurs as a resonance. Laminar air flow goes in and then out and then in.
Helmholtz wrote a whole book or 3 on these subjects and is available through many libraries. That is the place to learn about this I think.
Actually the pipes below the vibraphone are for loudness first and fatter resonance second. The pipes are not perfectly tuned but the bars are. The bars produce very pure tone of frequencies. The pipes are not perfect so the pipes drag the resonance off a little bit and change from a pure sine wave to a sweeping (slightly) tone with many side bands. This makes the tone rich in harmonic content. A common instrument like a vibe without pipe is called marimba I think.
It is easy to find the theory of church organ pipe showing how the air first enters over the reed and then exits. Same as these other instruments.
Here is a picture version:
http://www.acoustics.org/press/132nd/5pmu9.html
Originally Posted by tinitus View Post
Air mass ressonance of bottle is excited by a force
And force needs to be applied correctly to work, thats the trick
Only, I dont think its possible to make more than one tone, from the same bottle
It ressonates at its tuning, and only that, like a flute
Wrong!!
Get a bottle, blow into it just enough to start making a sound, the tone will be low.. Now blow harder, the tone will be higher.. Blow very hard with a burst of pressure and you will get a very high pitched squealing tone, and feel the bottle actually vibrate in your hand.. You can take an average empty beer bottle for instance, and produce a few tones from that one bottle by varying the amount of air velocity that you blow into it.. Easy to try at home 🙂
Air mass ressonance of bottle is excited by a force
And force needs to be applied correctly to work, thats the trick
Only, I dont think its possible to make more than one tone, from the same bottle
It ressonates at its tuning, and only that, like a flute
Wrong!!
Get a bottle, blow into it just enough to start making a sound, the tone will be low.. Now blow harder, the tone will be higher.. Blow very hard with a burst of pressure and you will get a very high pitched squealing tone, and feel the bottle actually vibrate in your hand.. You can take an average empty beer bottle for instance, and produce a few tones from that one bottle by varying the amount of air velocity that you blow into it.. Easy to try at home 🙂
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Many of your points I do not agree with, but the one premise with which I do agree, to put it into my words, is that there is an initial wavefront that impinges on the walls of a T/L or a standard box. We know that a driver in the front (and irregularly in the back) emits a roughly spherical wave. The question really is what follows after the initial contact with the walls?
Back to a closed box, drivers are not point sources and much of the original source must pass through basket openings from a source that is anything but flat as well. The angular nature of the diaphragm and the total masking of the central section by the motor structure creates an initial wave of unusual shape, I would think. Diffraction around the motor structure further complicates things. How a wavefront interacts at this level that I cannot describe mathematically, but there are certain things that are easily measured empirically.
To continue the closed box edition, with no stuffing, internal resonances are usually very pronounced. Those that impinge significantly on the rear of the diaphragm cause measurable SPL anomalies and at times are sufficient to be reflected (excuse the pun) in the impedance measurement. These are related to the box dimensions. Most often I see them in the front-to-back dimension, reflections from the back panel.
However, accelerometer measurements of each side wall from the exterior pick up resonances that are not panel resonances, but are those of the interior not sufficiently damped by the wall and/or stuffing and are easily related to the internal dimensions. All three dimensions. How could this occur if the resonance requires a direct axial excitation?
The key seems to me to be the wavelength relative to the dimensions and what happens when a wave contacts a boundary. The way diffraction is usually modeled is to create virtual point sources at each point of contact. Theoretically you'd need an infinite number of points to perfectly model it, but we get reasonable results with limited numbers. Each of these point sources re-radiate, so-to-speak, as a new spherical wavefront. Angle of incidence must have an impact due to conservation of energy, so I certainly can't say exactly how the reflected energy is distributed from each virtual point source, but if resonances in a closed box arise for those two axes with walls that do not have a driven source (such as side-side and top-bottom), then the angular incidence of wave contact must be re-directed in such a way that the movement of some of that energy is truly axial otherwise a resonance inside of a closed box could never arise.
That then begs the question, how do the resonances of those two axes above affect a driver at all? To do so, those resonances must at some point have a wavefront that either contacts the diaphragm or that interacts with the continuing output from the rear of the diaphragm such that they impede the movement of the diaphragm as it is generating the continuing wave. What the actual mechanism is here, I don't know. But we do know that these two axial modes can indeed be reflected in the external frequency response measurements at times.
A T/L should have the same initial conditions. That is, the initial wavefront is going to impinge on all walls at some angle. There will not be much of an axial angle even if the driver is placed on the front, rather than a side wall, due to occlusion of the diaphragm. That is, unless at low frequencies the wave does not fully "coalesce" (for want of some better descriptive) for some short distance that would allow it to do so in a more truly spherical nature. That I do not know if it is an issue at all. As this wavefront moves down the T/L, those of long wavelength with little change in phase after contacting and reflecting off of the side walls will appear as a nearly perfectly flat wavefront at the terminus (stretching the concept a bit) for low frequencies simply due to the small opening relative to the dimensions of the wavelength.
Dave
A line open at both ends (or closed at both ends) will be a 1/2 wave resonantor.
The driver offset changes the relative magnitudes of the resonance chain.
dave
Competition results
Lets see how our competitors stack up:
Villa posted the last of his silly assertions on page 24, while John's stretched the thread to a healthy 51 pages with his silly questions.
It's seems neck and neck at first glance, with John slightly ahead.
But wait! John only seriously entered the fray at post 270, giving him a total troll-span of only 233 posts including his resignation.
Final score:
Villa: Post 1 to Post 234 => Total troll-span: 234
John: Post 270 to Post 502 => Total troll-span: 233
Looks like "Silly Questions" came close but "Silly Assertions" remains unbeaten.
Unless anybody wants to debate the scoring system, of course....
Aha - John resigns from the trolling competition! But do we have a winner?
Lets see how our competitors stack up:
Villa posted the last of his silly assertions on page 24, while John's stretched the thread to a healthy 51 pages with his silly questions.
It's seems neck and neck at first glance, with John slightly ahead.
But wait! John only seriously entered the fray at post 270, giving him a total troll-span of only 233 posts including his resignation.
Final score:
Villa: Post 1 to Post 234 => Total troll-span: 234
John: Post 270 to Post 502 => Total troll-span: 233
Looks like "Silly Questions" came close but "Silly Assertions" remains unbeaten.
Unless anybody wants to debate the scoring system, of course....
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Reread what you wrote:
Now reread my answer. A sealed box certainly resonates. So does a PR box- you managed to misquote yourself twice in one sentence, quite a feat!
If you read what's been written very carefully, you'll understand HOW and WHY it does, and the difference between a fundamental spring-mass resonance and a standing wave.
And yet your postings to date speak volumes to the contrary since the link I referenced has all the info necessary to answer your Qs, so 'troll' it is........
GM
dlr,
Thought provoking. It raises questions for me about how I will adjust my construction of the next set of speakers.
Concern for the back wave: Can they be reduced?
Will it be beneficial to construct (holey) baffles or other angled partitions to obstruct or decrease the chances for back waves to get to and out of the diaphragm?
Are the back waves a pressure event? If so, does it follow that obstruction is of little relative value?...I believe this is frequency related.
I now will focus on the "line of sight" to the back of the diaphragm. I'll let the magnet and supporting structure do some of the dirty work for me.
More work/thought to be done...
Thought provoking. It raises questions for me about how I will adjust my construction of the next set of speakers.
Concern for the back wave: Can they be reduced?
Will it be beneficial to construct (holey) baffles or other angled partitions to obstruct or decrease the chances for back waves to get to and out of the diaphragm?
Are the back waves a pressure event? If so, does it follow that obstruction is of little relative value?...I believe this is frequency related.
I now will focus on the "line of sight" to the back of the diaphragm. I'll let the magnet and supporting structure do some of the dirty work for me.
More work/thought to be done...
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Why bother? As long as ignorant/ill informed/obtuse folks can come behind you and change it, it's an exercise in futility, so as always the 'few ruin it for the many'.
GM
We have losers: free thought and open discussion. It's the common "thread" throughout this thread.
There was no competition going on (yes, I know you are making a joke, I get it) other than the point at which I would be called a troll - a bet I had with myself. 😉
It's disappointing to see so many who refuse to think. The recent post by dlr is the only serious reply.
Oh well, nothing I didn't already know.
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What's up? Was the caster of the first stone wrong? Do you still need to keep this "discussion" alive?
I've said all I need to say, if you don't quite understand my intentions or motives, contact me in private.
I've said all I need to say, if you don't quite understand my intentions or motives, contact me in private.
I see they've taken him to task on this, and other, claims he's made there. His 'welcome mat' and credibility is just about worn out already.
GM
I think a lot of people just declined to play your game of devil's advocate.
I could have spent hours responding trying to provide better and more detailed explanations. I have spent a lot of time thinking about TL's over the past 20 years. But why bother you already knew the answer, I made the correct decision to drop out early.
dlr's explanation was very good and more could be added to help visualize it applied to a TL. But why bother you already know the answer.
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