Reading the tutorial that Christian posted a while back, I find some support for chdsl statements about edge excitation of cylindrical objects:
"In most flat plates, bending and membrane (longitudinal) waves are uncoupled. Take a flat plate and bend it statically, and those waves become coupled. Take the flat plate and wrap it around a circle to form a cylinder, and the coupled bending membrane waves become continuous around the circle. This is a circular cylindrical shell—a structure that has received almost as much attention over the years as flat plates have.
...
When bending waves travel around a structure with curvature, they are coupled strongly to in-plane longitudinal waves, which travel at much higher speeds than the bending waves do (recall our discussions of wave speeds earlier). The coupling occurs because curvature causes the transverse displacement to be resisted not only by flexural stiffness, but also by the membrane, or ‘hoop’ stiffness. Bending waves sped up by membrane stiffness resonate at higher frequencies than they would in an equivalent flat plate.
Skimming a few papers, I find:
"Cylindrical shells exhibit a dense frequency spectrum, especially in the lowest frequency range. In addition, due to the circumferential symmetry, frequencies occur in pairs. So, in the vicinity of the lowest natural frequencies, several equal or nearly equal frequencies may occur, leading to multiple internal resonances."
"For cylindrical shells under harmonic external forcing, Chen and Babcock [9] observed that the modal solution must include not only the directly driven mode, but also the circumferentially symmetric companion mode. This additional mode has the same linear vibration frequency and the same wavenumbers as the directly driven mode; hence, the term companion mode to describe it [10]. The presence of the companion mode in the response of the shell may lead to the appearance of traveling waves
...
"Therefore, the radiation efficiency of an acoustically thick shell could reach unity at a frequency much lower than the critical frequency. Also, because the acoustic behaviour of each vibration mode would be affected by the boundary conditions at both ends of the shell, the radiation efficiency of the shell has been shown to depend strongly on the boundary conditions.
It does pique the interest...
"In most flat plates, bending and membrane (longitudinal) waves are uncoupled. Take a flat plate and bend it statically, and those waves become coupled. Take the flat plate and wrap it around a circle to form a cylinder, and the coupled bending membrane waves become continuous around the circle. This is a circular cylindrical shell—a structure that has received almost as much attention over the years as flat plates have.
...
When bending waves travel around a structure with curvature, they are coupled strongly to in-plane longitudinal waves, which travel at much higher speeds than the bending waves do (recall our discussions of wave speeds earlier). The coupling occurs because curvature causes the transverse displacement to be resisted not only by flexural stiffness, but also by the membrane, or ‘hoop’ stiffness. Bending waves sped up by membrane stiffness resonate at higher frequencies than they would in an equivalent flat plate.
Skimming a few papers, I find:
"Cylindrical shells exhibit a dense frequency spectrum, especially in the lowest frequency range. In addition, due to the circumferential symmetry, frequencies occur in pairs. So, in the vicinity of the lowest natural frequencies, several equal or nearly equal frequencies may occur, leading to multiple internal resonances."
"For cylindrical shells under harmonic external forcing, Chen and Babcock [9] observed that the modal solution must include not only the directly driven mode, but also the circumferentially symmetric companion mode. This additional mode has the same linear vibration frequency and the same wavenumbers as the directly driven mode; hence, the term companion mode to describe it [10]. The presence of the companion mode in the response of the shell may lead to the appearance of traveling waves
...
"Therefore, the radiation efficiency of an acoustically thick shell could reach unity at a frequency much lower than the critical frequency. Also, because the acoustic behaviour of each vibration mode would be affected by the boundary conditions at both ends of the shell, the radiation efficiency of the shell has been shown to depend strongly on the boundary conditions.
It does pique the interest...
Also,
Asymptotic analysis is used to study sound radiation from cylindrical shells driven by on‐surface forces. The far‐field sound is analyzed in terms of radiations from helical waves in the shell excited by the forces, which are shear and compressional waves in frequency domains well below the coincidence frequency of the shell plating where thin shell theory is applicable. These shell‐borne waves are shown to be crucial contributors to the far‐field radiation; they dominate the frequency dependence of the radiated field, because they carry with them features of the elastic waves such as resonances, their radiation covers a wide spatial domain, unaffected by the shadowing effects of the shell, and they may overwhelm in amplitude the direct radiation from the forces in some directions, the latter following a direct fluid‐borne propagation path from the driving forces to the far field. It is found that tangential forces on the shell cause more acoustic radiation than normal forces, because the former excite radiating shell waves more easily than the latter.
Radiation from cylindrical shells driven by on‐surface forces
The Journal of the Acoustical Society of America 95, 2014 (1994); https://doi.org/10.1121/1.408664Asymptotic analysis is used to study sound radiation from cylindrical shells driven by on‐surface forces. The far‐field sound is analyzed in terms of radiations from helical waves in the shell excited by the forces, which are shear and compressional waves in frequency domains well below the coincidence frequency of the shell plating where thin shell theory is applicable. These shell‐borne waves are shown to be crucial contributors to the far‐field radiation; they dominate the frequency dependence of the radiated field, because they carry with them features of the elastic waves such as resonances, their radiation covers a wide spatial domain, unaffected by the shadowing effects of the shell, and they may overwhelm in amplitude the direct radiation from the forces in some directions, the latter following a direct fluid‐borne propagation path from the driving forces to the far field. It is found that tangential forces on the shell cause more acoustic radiation than normal forces, because the former excite radiating shell waves more easily than the latter.
Share a link to what you said before, or repeat it. Otherwise you might as well be dmbles. In other words, annoying and not helpful.
Eric
Veleric,
Well, Merry Christmas to you, too! Are you actually trolling Spedge, probably the premier DML expert on this forum? He has over and over again provided excellent but humble advice and mentorship and has continually shown his overwhelming evidence, and the one time he just says in effect, "I have posts all over this forum, and an easy search will have you find the ones you need". What a nerve you have! I have watched you over the years repeatedly snipe at him, and bite at his ankles. It appears to be a case of sour grapes and lacking in self-dignity. Enough of the trolling and sniping, you and anyone else! If YOU don't have anything positive to say, please remove yourself from this forum. I too had a momentary lapse in judgement when I myself trolled chdsl. I am better than that, and I apologize. This is a community. Let's treat it that way. The world is too full of strife for us to add to it.
On another note, I think we are too much in the weeds with this esoteric splitting of hairs on sound waves. Let's please get back to the design and experiencing of DMLs so the majority of us can again enjoy this forum.
Well, Merry Christmas to you, too! Are you actually trolling Spedge, probably the premier DML expert on this forum? He has over and over again provided excellent but humble advice and mentorship and has continually shown his overwhelming evidence, and the one time he just says in effect, "I have posts all over this forum, and an easy search will have you find the ones you need". What a nerve you have! I have watched you over the years repeatedly snipe at him, and bite at his ankles. It appears to be a case of sour grapes and lacking in self-dignity. Enough of the trolling and sniping, you and anyone else! If YOU don't have anything positive to say, please remove yourself from this forum. I too had a momentary lapse in judgement when I myself trolled chdsl. I am better than that, and I apologize. This is a community. Let's treat it that way. The world is too full of strife for us to add to it.
On another note, I think we are too much in the weeds with this esoteric splitting of hairs on sound waves. Let's please get back to the design and experiencing of DMLs so the majority of us can again enjoy this forum.
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chdsl,
I'd like to apologize for my earlier remarks regarding you. That was beneath me, and I am sorry.
On another note, I am very interested in the edge-driven bent sheet method of DML. I would like to see any pictures and anything to report on how your experiments with them have turned out.
I'd like to apologize for my earlier remarks regarding you. That was beneath me, and I am sorry.
On another note, I am very interested in the edge-driven bent sheet method of DML. I would like to see any pictures and anything to report on how your experiments with them have turned out.
Just because I wont give out my personal design some people think I am unhelpful when in fact I have helped many through out my 8 years of my DML journey. Most recent person I helped was a person named AllenB , not sure if it is the same AllenB on this forum or a totally different person using the same handle name at P.E. Techtalk.
Well as far as I have seen, Eric has been unfailingly polite and helpful, and in terms of practical, repeatable value-add, he has contributed more substance to the forum and our collective ‘state of the art’ than anyone. This last post was quite brusque I have to agree, but for pity’s sake, if we can forgive the consistent outlandish claims stated repeatedly without evidence, or pride-filled boasts, or day to day sarcasm and nastiness, we can overlook a single outburst.
I know your intentions are good, and there has been a decline in the cordiality of late. Probably the stress of the festive season. There may also be a splintering or tension of approaches, from wholly hands-on to more scientific , theoretical or instrumental. Both approaches are useful I think, and you never know where new inspiration will come from.
I think that a best rule for any forum of this kind could be based upon Postel’s Law (originally from the context of IT communications programming):
Be conservative in what you send, be liberal in what you accept.
Hi Pixel,
I use a solid frame with a soft mounting along the long edges that has worked well on a number of builds. I have included a couple of shots of my latest builds below. The foam is very soft but wide and has very good adhesive qualities so it acts as damping and suspension.
Another approach is a ‘clamped end’ which I used on my Tall Blondes where one short edge is attacked to an upright via thin ( 2mm) foam tape, five tapes strips at 30mm wide and 90mm long. This is not a ‘normal’ DML but sounds great and still plays in my dining room.
I suggest you stick with the frame approach for now as it has been tried and tested by more builders so you will get more input should you run into problems
Burnt
Attachments
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In the design of this forum the developers included a useful function that allows each person to edit their feed. It allows you to edit out those contributors that annoy you and retain a feed that is informative, friendly and positive.
I have only discovered the ‘ignore’ button recently and have used it only twice. The result is a return, for me, to a thread with a very high signal to noise ratio where I continue to learn and share what I have discovered, in detail, for the benefit of all.
The function allows you to reverse the block at any time and has no effect on the people you decide to edit out.
It might save a lot of confrontation and frustration.
Burnt
I have only discovered the ‘ignore’ button recently and have used it only twice. The result is a return, for me, to a thread with a very high signal to noise ratio where I continue to learn and share what I have discovered, in detail, for the benefit of all.
The function allows you to reverse the block at any time and has no effect on the people you decide to edit out.
It might save a lot of confrontation and frustration.
Burnt
Veleric and pway,
I was a bit heavy-handed in my denunciation of Veleric's post, and for that I apologize. I could have toned it down more. Pway, you are right about the tension of the season. What with illness in my family and our president and his administration trying their best to destroy my country that I love and spent 20 years defending, my temper was a bit short. When I saw my guru attacked, I over-reacted. Forgive me for that, please. I am normally a much more jovial and easy-going person than this.
I was a bit heavy-handed in my denunciation of Veleric's post, and for that I apologize. I could have toned it down more. Pway, you are right about the tension of the season. What with illness in my family and our president and his administration trying their best to destroy my country that I love and spent 20 years defending, my temper was a bit short. When I saw my guru attacked, I over-reacted. Forgive me for that, please. I am normally a much more jovial and easy-going person than this.
No need to apologise, it’s obvious your heart’s in the right place. Interesting you mention politics (and let’s not go there!), but I think that anyone who’s paying attention has noticed how the world is becoming more divided , with less trust in people and institutions, and crazy people everywhere. That can make one a bit crazy oneself, but a forum like this can be a little refuge from all that. Even if it is a bolt-hole where only crazy people would visit in the first place. 😬
Again, a video of the floor with no photo or description or sketch of the setup is no good. You really should try aiming the camera at the DML. The microphones are omnidirectional within a 45deg tilt so I don’t buy the “the mic is on top so I want to aim the mic at the speaker for best sound quality” (I’m paraphrasing) excuse. It’s a 2 way, so two panels, or two exciters on one panel, what is XO and at what frequency etc. Without details, this post is not contributing to the DIY knowledge base on this thread.
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I do feel that a certain degree of frustration has crept in to the postings of late, maybe because the discussions seem to be all over the place, with little focus and some entrenchment of views... Sometimes it's like looking into a tumble dryer .
I for one have become reluctant to become involved
Not sure what the answer is ...or if anyone agrees for that matter, but some degree of calm would be good
Eucy
I for one have become reluctant to become involved
Not sure what the answer is ...or if anyone agrees for that matter, but some degree of calm would be good
Eucy
Again why are you so offended by my videos? If you dont like them I can take them all down again?
Best sound is when mic is facing speakers I thought that was common knowledge? Fact is mic is on the top of my cellphone, where is your mic on your phone on the side?
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The curved panels remind me of the Linaeum driver used on tweeters from a RadioShack Omni speaker.
There is a thread here with a curved tweeter by AnthonyPT:
https://www.diyaudio.com/community/threads/a-diy-ribbon-speaker-of-a-different-kind.69450/
There is a thread here with a curved tweeter by AnthonyPT:
https://www.diyaudio.com/community/threads/a-diy-ribbon-speaker-of-a-different-kind.69450/