I agree with geosand, nice write up.
A couple questions:
What exactly were the elastomeric damping pads you used?
Concerning the 100 mm suspension strips, how far apart were they spaced? About 100 mm also, or different? And if I understand correctly, you used suspension strips only on the long sides, and not the short sides, right?
Thanks,
Eric
I've never experienced that caveat. If solidly secure all the energy is put into the panel so that the only thing actually moving or vibrating is the panel material. Its not really the spine putting energy into the frame, its the panel diaphragm/material in contact with the frame that is putting the energy into the frame.
At 100hz and up the excursion is low so they wont be much problems unless playing it at too loud volumes. The lower the frequency response the higher the excursion.
Although that is one way to reduce exciter rattle its not practical unless you have a huge house with lots of sq.feet.
Thanks Burnt,
I frankly wonder if damping isn't underutilized by DMLers. Not just for taming specific problem resonances, but for smoothing the whole curve. I've seen a technical paper or two suggesting that at the right level, damping should not only smooth the SPL curve, but should even increase the SPL, at least within the so called "short circuit" frequency region. It's a route I have not yet seriously gone down but I think is worth a closer look. I'll have to give Sorbothane a try.
Along the same lines, I liked how in your write up you made a distinction between suspension and damping. Often people use the term damping when they are really talking about suspension. Of course it's complicated by the fact that the most common suspension systems we use (foam surrounds) do provide some damping, but frankly I doubt that it's typically enough to alter significantly the performance of our speakers. I suspect that the effects we do see as we change the amount of foam used around the perimeter have more to do with the fact that we are changing the boundary conditions between "free" and "hinged/simple" than they do to differences in actual damping. But all of this is just my intuition, not backed up by any real evidence!
I'm curious if you've tried exciters other than the Thrusters, and if so which ones? And did the Thrusters provide more output below, say 70 Hz than others? I've tried 4 or 5 different models exciters, including the DA Ultras, and so far have not seen great differences between them. The Thrusters have been on my list to try, but I just have not gotten around to buying any yet. I'm curious how you would compare them to any others you may have tried, especially if you've tried the Ultras, or any of others in my collection.
Eric
I was just pondering about this the last couple of days - suspension vs damping. The stuff that Burnt is using is made from Sorbothane - also used in this patent, which discusses damping. But it is way over my head.
WO2002013575A1 - Bending wave loudspeaker
- Google Patents
WO2002013575A1 - Bending wave loudspeaker
- Google Patents
Hi Eric,
I may have read the same paper Eric and its certainly worth experimenting with. I am currently experimenting with the simplest possible floor standing design as I like to remove all the variables and build up from their systematically. I feel I dived into frames without a compete understanding of the various mechanisms involved so I have gone back so I can move forward in a more controlled way. More news on that when I have something to share, but once I am happy with a minimalist design performance I want to do more with damping.
I agree completely on the boundary conditions effecting the response, I have now had direct experience of how a clamped panel has a completely different bandwidth to a free design. I now aim for just enough suspension to hold the panel securely but allow maximum movement at the edges.
Unfortunately on exciters I have had a limited experience, Just the Thrusters and the Tectonic TEAX32C20-8 32mm Self Supported Exciter 8 Ohm ( link Tectonic TEAX32C20-8 32mm Self Supported Exciter 8 Ohm ) which was dire until I removed the outer ring adhesive as advised by DMLBES. It then proved to be a decent exciter but best for smaller panels. It would be very handy to have a comprehensive list of exciters with their performance evaluated. Maybe we should start one and see if anyone else wants to join in?
Thank you for your comments regarding the write up!
Have a great weekend when you get there.
Burnt
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Great find twocents! The image I have attached from the patent is exactly what Veleric is talking about.
Attachments
That's one I have not tried, although I have tried this:
Tectonic TEAX32C30-4/B 32mm Balanced Exciter 4 Ohms
In my experience this one is similar to the Ultra but has a little more output on the high frequency end, and a little less on the low frequency end. I kinda like combining the two in series to get 8 ohms while widening the overall response range.
I sure agree it would be great to have a list of evaluated exciters but I have no idea how to evaluate them in some generic way.
Eric
Here's an interesting article I had not seen before:
Optimal design of rectangular composite flat-panel sound radiators
considering excitation location
https://ir.nctu.edu.tw/bitstream/11536/23583/1/000329881500008.pdf
I skimmed it a few times but I'm not sure exactly what practical implications it has for us. If I'm reading it right, it seems to be implying that the optimal location of an exciter is at some particular radius from the center of the panel. Which further suggests that to find the optimum spot empirically, we don't have to test every location on the panel, we really only have to test every position along a radial line from the center.
There's still an infinite number of points to test, but it's only infinity and not infinity squared!
But I may be interpreting it all wrong.
Any other interpretations?
Eric
Optimal design of rectangular composite flat-panel sound radiators
considering excitation location
https://ir.nctu.edu.tw/bitstream/11536/23583/1/000329881500008.pdf
I skimmed it a few times but I'm not sure exactly what practical implications it has for us. If I'm reading it right, it seems to be implying that the optimal location of an exciter is at some particular radius from the center of the panel. Which further suggests that to find the optimum spot empirically, we don't have to test every location on the panel, we really only have to test every position along a radial line from the center.
There's still an infinite number of points to test, but it's only infinity and not infinity squared!
But I may be interpreting it all wrong.
Any other interpretations?
Eric
That patent may indeed have been where I first got the idea to try substantial damping. But this article is the one I was thinking of:
The effect of different combinations of boundary conditions on
the average radiation efficiency of rectangular plates
https://eprints.soton.ac.uk/369232/1/Eprints.pdf
I'm not sure how I found this one originally. Maybe it was from you, Burnt.
Of course, as said for the paper I just linked to in my previous post, my interpretation may be flat out wrong. But it looks to me like a pretty high level of damping should at least theoretically be favorable.
In the case of this article, they are talking about the intrinsic damping factor of the panel itself, and not local or perimeter damping.
The paper seems to be suggesting that if the correct amount of damping is built into the panel (say on the surface, or internal to the structure), the panel would provide louder, and smoother frequency response.
If true, I think one big challenge would still be to get that damping without adding too much weight to the panel.
Eric
Gosh I am going to have to read both papers again. I do remember the one you cite Eric and in particular being confused by some of the comments in the conclusion. Certainly application of damping smooths the response, and an increase in thickness increases spl’s. After that I need to sit down and work through the logic whereby in one paragraph the author claims in increase in SPL for clamped panels , which contradicts my recent experience, and then goes onto say literature exists that a freely supported panel increases efficiency as well. I might be misreading that so I will try again.
On your thoughts on integrating damping into the panels I like it. A rigid but highly attenuating foam as the meat in a 1mm ply sandwich might be an interesting direction. You can get foamed polypropylene and PET sheets as well as EPS/XPS and there are probably more types available. It maybe a nomex honeycomb with the cells filled might work as well.
One other comment from the paper that rang a bell for me was that with a highly damped panel the sound source is predominantly from the source. That for me was a bit of a warning as DMLs are supposed to be about diffused nodes of emission, or so I thought.
Hmm, reading to do
Burnt
On your thoughts on integrating damping into the panels I like it. A rigid but highly attenuating foam as the meat in a 1mm ply sandwich might be an interesting direction. You can get foamed polypropylene and PET sheets as well as EPS/XPS and there are probably more types available. It maybe a nomex honeycomb with the cells filled might work as well.
One other comment from the paper that rang a bell for me was that with a highly damped panel the sound source is predominantly from the source. That for me was a bit of a warning as DMLs are supposed to be about diffused nodes of emission, or so I thought.
Hmm, reading to do
Burnt
Yes I got that too Eric, start at the centre then explore the radial vectors.
I've been talking about dampening for ever. Even got dissed for using the word dampening to much by those that quit there dml experiments on P.E. forum. LOL
Its like no one believes me or listens until its written in an article. **** people even believe Tech Ingredients when he said no damping on panels because it reduces output. SMDH Which is the reason most of you started out with free floating panels with no damping.
Finally some of you are starting to realize the power of dampening. Any type of material with dampening properties used on the panel will effect its sound even when used as a suspension. Like I said before anything you add to the panels will effect its sound. Its not just one technique but many techniques combined that will get you better sound. Tech Ingredient claims that painting the panels have no effect on the sound which is false. Paint one panel and don't paint the other there will be a slight change in sound. If you paint the front of the panel and not the back there will be a change in sound. Paint itself can dampen the panels. Certain types of paint will dampen the panels more then others. Wood glue water mixture dampens the panels. With DML panels its all about DAMPING!!!!!! I gave yawl some hints and tips about damping you just have to go back a read my posts. lol
Of course the proof is in the pudding. Yawl need to hear my panels. I will see if I can download my panels playing on youtube with my phone but not sure the quality of the mic on the phone if it sucks then I wont do it.
Its like no one believes me or listens until its written in an article. **** people even believe Tech Ingredients when he said no damping on panels because it reduces output. SMDH Which is the reason most of you started out with free floating panels with no damping.
Finally some of you are starting to realize the power of dampening. Any type of material with dampening properties used on the panel will effect its sound even when used as a suspension. Like I said before anything you add to the panels will effect its sound. Its not just one technique but many techniques combined that will get you better sound. Tech Ingredient claims that painting the panels have no effect on the sound which is false. Paint one panel and don't paint the other there will be a slight change in sound. If you paint the front of the panel and not the back there will be a change in sound. Paint itself can dampen the panels. Certain types of paint will dampen the panels more then others. Wood glue water mixture dampens the panels. With DML panels its all about DAMPING!!!!!! I gave yawl some hints and tips about damping you just have to go back a read my posts. lol
Of course the proof is in the pudding. Yawl need to hear my panels. I will see if I can download my panels playing on youtube with my phone but not sure the quality of the mic on the phone if it sucks then I wont do it.
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Eventually I will get around to fabricating my own version of something like that. But truth be told I'm not sure CF is the optimum skin layer. It may sound wrong but CF is actually, um, heavy, at least compared to wood. My belief is that a wood veneer skin on both sides of a very light (but hard) core could be even better than CF/foam/CF. I have come to believe that B/m^3 is critical, and on that basis, my estimates suggest wood veneer is better than CF.
Eric
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