Steve,
I am doing some tests around cardboard. I have row cardboard... the first effect of putting on it some water is warping. Do you have a trick?
About Tectonic, I have seen also this green plate which seems linked to the frame by screws... You are right it is like it goes to cover the voice coil area
Christian
I didn't do A/B testing before/after, but I put some thin fabric on my XPS panels and they look great. I will be doing the same for my acrylic panels.
Christian.
xps I a good sound insulator ,and blocks the hf going through the panel, far more so than eps.
even the 5mm has this problem, but the epoxy seems to solve this somewhat .
I like the epoxy improvement, I have not yet tried to thin the area in the exciter coil area yet ,but would expect an improvement also ?
I presume that row cardboard is , fluted ?
Large panels will be harder to stop warping.
But the method I use works quite well on smaller panels.
I use undiluted pva ,with a small brush about 5mm or so.
try not to use too much pva at a time, apply a blob at a time and quickly spread out as much as possible before adding more, it should start to become tacky very quickly and not be absorbed so much into the cardboard.
Finnish off with a hair dryer on a low heat setting(if too hot it will bubble) when dry to the touch turn over and do the same the other side ,this should pull it back into shape ?
I have with larger sizes ,(and small if in a hurry)hung the panel up and applied the pva on both sides at the same time, they should dry together and straighten equally if you are lucky.
If not ,I usually place the warped panel between 2 sheets of ply in a warm place with weights to make sure they are flat.
You could even use the hair dryer to warm the ply panels and card, when cool and dry they should stay fairly straight ?
But it will not be perfectly flat and could change over time and weather conditions ,humidity, pva is water based.
Good luck.
steve.
xps I a good sound insulator ,and blocks the hf going through the panel, far more so than eps.
even the 5mm has this problem, but the epoxy seems to solve this somewhat .
I like the epoxy improvement, I have not yet tried to thin the area in the exciter coil area yet ,but would expect an improvement also ?
I presume that row cardboard is , fluted ?
Large panels will be harder to stop warping.
But the method I use works quite well on smaller panels.
I use undiluted pva ,with a small brush about 5mm or so.
try not to use too much pva at a time, apply a blob at a time and quickly spread out as much as possible before adding more, it should start to become tacky very quickly and not be absorbed so much into the cardboard.
Finnish off with a hair dryer on a low heat setting(if too hot it will bubble) when dry to the touch turn over and do the same the other side ,this should pull it back into shape ?
I have with larger sizes ,(and small if in a hurry)hung the panel up and applied the pva on both sides at the same time, they should dry together and straighten equally if you are lucky.
If not ,I usually place the warped panel between 2 sheets of ply in a warm place with weights to make sure they are flat.
You could even use the hair dryer to warm the ply panels and card, when cool and dry they should stay fairly straight ?
But it will not be perfectly flat and could change over time and weather conditions ,humidity, pva is water based.
Good luck.
steve.
By the way, it is looking for the weights on Tectonic picture, the weights I haven't found, that I have seen this "green part".
Christian
Yes, that's actually the finished product. You can see a little sag on the right panel, but other than that they look and sound good.
Good thing is with the acrylic panels I can be more aggressive with the glue so the fabric will not sag.
Christian.
yes the green ,what looks like some sort of plate material, but you cannot see the right end of the plate in the photo,it is handily obscured by one of the struts !
But if you look in the drawing ( which I am sure will disappear also) it shows the right end, which looks like it has two electrical contacts? Plus and minus ,maybe ?
it's just a quess, but it could be doing two jobs ,one as a type of spider ,and carrying the lead in wires(three jobs) and as a single mount for the 4 exciters to one position on the panel?( Just thought ,four jobs , as added cooling for the coils) ?
4 exciter and one panel mounting poin.
If it isn't ,maybe it should be ?
Anyways, without actually looking at one it is just quess work.
Steve.
yes the green ,what looks like some sort of plate material, but you cannot see the right end of the plate in the photo,it is handily obscured by one of the struts !
But if you look in the drawing ( which I am sure will disappear also) it shows the right end, which looks like it has two electrical contacts? Plus and minus ,maybe ?
it's just a quess, but it could be doing two jobs ,one as a type of spider ,and carrying the lead in wires(three jobs) and as a single mount for the 4 exciters to one position on the panel?( Just thought ,four jobs , as added cooling for the coils) ?
4 exciter and one panel mounting poin.
If it isn't ,maybe it should be ?
Anyways, without actually looking at one it is just quess work.
Steve.
Going in the documents I store about DML, I found this patent US6553124 from M Azima and Panzer about a DML in a closed box rear load. Too complex in its theoretical part for me, it has connection with recent topic of this thread :
Below the extracts linked to that.
Christian
Influence of the rear wall
About the influence of a rear wall: interference said to start for 15cm. Optimistic!
Material used for the tests :
Leading to a Fc = 8kHz, A.F0 = 7Hz.m², D/µ³ = 11
Here in the material graph
- influence of the rear wall (close to what already shared here)
- advantage of a close rear volume (need a "simple EQ", transform the panel in near cardioid pattern, increase of the covered frequency range)
- test of different composite material in A5 orA2 dimensions among them carbon on Rohacell which is in the site pointed by Leob.
Below the extracts linked to that.
- Does somebody already tested such close box? or other rear load (ie aperiodic) ?
- Some test or knoledge about carbone/rohacell?
Christian
Influence of the rear wall
About the influence of a rear wall: interference said to start for 15cm. Optimistic!
Material used for the tests :
Leading to a Fc = 8kHz, A.F0 = 7Hz.m², D/µ³ = 11
Here in the material graph
Last edited:
Good!
Would you share more about the fabric you choose and your technique to glue it? I thought about this approach in a post before trying to open to plywood on fabric. In your experience, is there a risk for the glue to appear on the visible side of the fabric?
Christian
Hmm... Are you sure? Are you refering to the back view on page 2?
I understand it more as mounting holes in a dimensionnal drawing. 4 are on a square.
What about the "yellow" point on this video.
And here
Other finding of the evening... is this has been already considered here about shear modulus?
The shear tents to limit the wave speed frequency. ie from Stephen A. Hambric web site :
STRUCTURAL ACOUSTICS TUTORIAL—PART 1:VIBRATIONS IN STRUCTURES
The values are probably not from the audio area...
From patent WO1992003024A1
In other words, the speed of the shear waves are greater than the sound speed in the air.
Don't ask me why...
It is just another piece of the jigsaw.
What seems facts is that commercial realizations are based on honeycomb where sandwich material with light foam cores failed. No?
Christian
The shear tents to limit the wave speed frequency. ie from Stephen A. Hambric web site :
STRUCTURAL ACOUSTICS TUTORIAL—PART 1:VIBRATIONS IN STRUCTURES
The values are probably not from the audio area...
From patent WO1992003024A1
In other words, the speed of the shear waves are greater than the sound speed in the air.
Don't ask me why...
It is just another piece of the jigsaw.
What seems facts is that commercial realizations are based on honeycomb where sandwich material with light foam cores failed. No?
Christian
Steve,
Haha, I was actually hoping you would find them! But honestly I have no doubt that weights can be used. In fact, I make wind chimes and place masses along their length at precise locations in order to achieve a desired timbre, so it makes perfect sense to do the same for a DML. I did play with weights on DML plates some time ago myself. I did not find any great benefit at the time, but my knowledge and methods were even more limited then, so those results mean little. I suppose weights could be used reduce the low end, in fact, any weight would. But I'd be more inclined to think that the primary purpose for adding weights would be to smooth the frequency response by preferentially supressing "offending" modes rather than to lower the F6. But who knows for sure? Not me.
Eric
That first article must be a good one, as it's written by a Penn State professor. I did my graduate research in the same lab (but not in Acoustics!).
I agree the effect of the core shear modulus may very well be something that's underappreciated. I do recall this patent family well, as it's the first place I ever saw the B/mu3 criteria.
But check the math, I think there's a typo in the equation. If you read the sentence above it, I think it says somthing different from the "re-arranged" equation.
That is, the words say, effectively: G>(uc^2)/d, right? which correctly rearranges to (Gd/uc^2)>1 , right?
But they wrote (uc^2/dG)>1, which is exactly opposite. Or am I mistaken?
Strangely enough, they buggered up the same equation in the US version of the patent, but in a different way!
Eric
Eric .
Reduce the low end ?
I used weights on my panels to fill in the large dips in the response in the 100hz to 300hz , which it does well .
I thought everyone new this ?
You could also use the weights to extend the low end performance of small panels ,not reduce it .
I'm sure I talked about this over on NXT RUBBISH .
But as I said , I did not like the affect the extra weight made to the sound of the panel.
But in small amounts it was ok.
Steve.
Reduce the low end ?
I used weights on my panels to fill in the large dips in the response in the 100hz to 300hz , which it does well .
I thought everyone new this ?
You could also use the weights to extend the low end performance of small panels ,not reduce it .
I'm sure I talked about this over on NXT RUBBISH .
But as I said , I did not like the affect the extra weight made to the sound of the panel.
But in small amounts it was ok.
Steve.
Tested printing out a 300x300x2.4 mm plate in PLA with honeycomb infill, and it is working surprisingly well, especially considering the size. Have to get a setup for doing proper measuring, but was expecting a noticeable reduction in bass with the small size.
It seems to my ears to go down to 150hz without problem. Have to wait for the glue to dry to test more, but way over my expectations so far.
A lot of tweaking that can be done with thickness and density, and using different plastic with carbon, wood or nanodiamond added should at least marginally affect efficiency and sound. I can print dual materials and make honeycomb core a different material than the surface, but realized I have to make sure they are materials that bond to avoid rattling since there is no adhesive between. So I could for example probably use wood pla for honeycomb and carbon pla for surface, but not mix PETG and PLA.
Weight of my initial experiment plate is around 1.3kg/m2 which cost just above €10/m2 with the cheap PLA I used for test. With carbon or diamond filament the cost increases 5-6x, but still not much per panel. At 2.4 mm it still feels very stiff and sturdy and I might be able to get away with less dense infill and thinner surface.
It seems to my ears to go down to 150hz without problem. Have to wait for the glue to dry to test more, but way over my expectations so far.
A lot of tweaking that can be done with thickness and density, and using different plastic with carbon, wood or nanodiamond added should at least marginally affect efficiency and sound. I can print dual materials and make honeycomb core a different material than the surface, but realized I have to make sure they are materials that bond to avoid rattling since there is no adhesive between. So I could for example probably use wood pla for honeycomb and carbon pla for surface, but not mix PETG and PLA.
Weight of my initial experiment plate is around 1.3kg/m2 which cost just above €10/m2 with the cheap PLA I used for test. With carbon or diamond filament the cost increases 5-6x, but still not much per panel. At 2.4 mm it still feels very stiff and sturdy and I might be able to get away with less dense infill and thinner surface.
https://www.audiocircle.com/index.php?topic=70541.2020On page 2030 of this link from 2014 .
I still agree to everything I said,in this post, the trouble is I am still having to repeat this today, the frequency response from my 7ft panels from 300hz to 10k was as flat as a pond and sounded fantastic.
and the response above was no problem, but is fixable if wanted ?
When I have cleared my room of all this junk I will get them out of the loft ,some day !
till then I will keep playing with small panels.
Steve.
I still agree to everything I said,in this post, the trouble is I am still having to repeat this today, the frequency response from my 7ft panels from 300hz to 10k was as flat as a pond and sounded fantastic.
and the response above was no problem, but is fixable if wanted ?
When I have cleared my room of all this junk I will get them out of the loft ,some day !
till then I will keep playing with small panels.
Steve.