Steve, Christian
I built a spine on my small canvas. It's not easy to place the exciter in an absolute horizontal, and "no pressure" height. If the exciter position not at this "floating" stage. The voice coil is still slant or got pressure from the panel constantly.
And the reason I don't use spine method is, it increase the trouble to change exciter. If I use glue instead of screw to fix the spine, means there is no way to change exciter.
So I prefer keeping use the light weight exciter on canvas without spine.
About the washer. The Aiyima 50mm original disk is actually a metal washer.
If metal is too rigid for other light weight exciters, can use other material to build your ideal washer. Such as a similar meterial as the original voice coil ring. The exciter just see this washer as a thicker ring.
I built a spine on my small canvas. It's not easy to place the exciter in an absolute horizontal, and "no pressure" height. If the exciter position not at this "floating" stage. The voice coil is still slant or got pressure from the panel constantly.
And the reason I don't use spine method is, it increase the trouble to change exciter. If I use glue instead of screw to fix the spine, means there is no way to change exciter.
So I prefer keeping use the light weight exciter on canvas without spine.
About the washer. The Aiyima 50mm original disk is actually a metal washer.
If metal is too rigid for other light weight exciters, can use other material to build your ideal washer. Such as a similar meterial as the original voice coil ring. The exciter just see this washer as a thicker ring.
Last night I glued the 6x4 ply panel back onto my canvas panel for comparisons with the new panel I will be making.
I'm busy today so this will give the panel time to dry properly before testing it , to see if it is ok ?
I might have to coat the front with some pva to fill in the cracks in the cascamite ?
Steve.
I'm busy today so this will give the panel time to dry properly before testing it , to see if it is ok ?
I might have to coat the front with some pva to fill in the cracks in the cascamite ?
Steve.
1w at 1m with two speakers would be a very unusual reference to use regardless, and would mean 101 dB sensitivity per speaker, which is still much more than they claim elsewhere.
Hello Leob
You are going fast with this unusual technique for DML. 8dB above acrylic is a good result.
The FR has common points with other FR shared here. The bass extension is good. There is a loss of level from 2k to 8k we have with different materials. It will be interesting to have the opinion of other DML builders about the peak at 700Hz. Is there a possibility of an effect of the boundaries like a rear wall that might increased some characteristics?
To have a side some plywood is a good idea : the plywood can give a smooth response with a good high frequency extension. So even if it is not your target it is a good support for comparison. As you did for efficiency or to check if the exciter mounting technique is good.
The key point in my opinion is to understand if it is possible to increase the level above 10k.
For the PS, what I remember from previous posts is to find 30kg/m³ density. Here (France) in DIY store is it quite easy to find XPS of that density in 20mm thickness but I was not satisfy with the result. I haven't found easily EPS of this density. I have 20mm thick EPS 15kg/m³ which seems not work well.
I think the spectral contamination test (see #4656) is interesting to evaluate the quality of a material. Really easy to do.
Christian
hkguy6,
Yes a spine is a mechanical challenge to have no additional strength on the exciter and not suitable for quick tests of different solutions but nevertheless recommanded. You should find in the previous posts the hanging method Spedge uses : see #4659
I have to admit that my last panel (canvas) is still without... but it helps for the plywood panel which have an heavy membrane. By the way, I made a mistake designing this spine which is based on a 10x10cm plywood piece around the exciter; it reinforces the exciter "noise". A spine should not stop or reflect the rear wave.
If you have time, have a look to the paper linked in #4691. It is about the idea to reinforce the voice coil what a washer does.
Christian
Leob, Spedge,
I have to confirm my skills to listen to english video is not high enough and to apologize... I should have also think to use the subtitles.. 104dB 1W 1m is in the video. 2 panels is the configuration of the PL12. See the PL12 data sheet where a 100dB sensitivity is mentioned. As I think there is a limitation in the material, the other possibility is to work with exciters with a higher BL factor.
Thanks for the input Christian. Will include spectral contamination test when I do a proper comparison.
Yes, room is small and untreated, and it is a cheap uncalibrated mic. Most issues in the room are around 300-400hz though and the peak around 700 I have only seen in this panel. This is a 295x205mm plate, and with 295x273mm the peak was around 300-400hz instead, but with larger peaks and dips in low mids in general. I'm guessing that the peak at 700Hz is the resonance of the short side, which before was placed very close to the peak of the long side making the response less smooth.
About the FR, I agree that the only major issue is really above 10k. I don't want overly bright sound and, and if I EQ out the peaks in the low mids the overall response is just about right...apart from above 10k which would require much more heavy handed EQ to fix.
It also seems like when attempting to improve efficiency by having as thin skins and sparse and thin honeycomb, what happens is that I get stronger mids, but not much stronger treble. Sounds like the plate resonates more, but mostly in the mid to low frequencies, resulting in stronger mid peaks.
So if I go with printed probably I need to be mixing with other materials in different plates to get an overall nicer response. Or do like in the PL11 and use ribbon tweeters, but I rather not.
Surely if you have 2 panels in a speaker and measure 1w at 1m you measure with 1w total input, not 1w per panel?
And even if they would input 2w and claim it is 1w in the rating, it would still be much more sensitive than DML500.
It is all very confusing.
Actually, one thing that strikes me is that the trade-off between efficiency and treble response I suspect from my printing experiment could explain the differences in sensitivity between the PL12 and DLM500. With the DML500 they are not using a ribbon tweeter, perhaps sacrificing sensitivity for better response so they can use only DML.
Thanks Christian.
Yes I used Spedge's hanging methold. I also added a zip tight for fine adjust the hanging force.
I also found spine problem as you. My spine used bolt with nuts to fine tune the height of the exciter. But more parts involved in the whole system will increase the chance to have vibration noise. Glue spine is the way but just for permanent system.
After few days of testing my exciter attach method. I prefer add a nut between the washer and panel. Seems a smaller contact point which has a better vibration transmission. Sounds a bit more clean and fast.
Hello Leob,
A cheap mic is not by itself a problem. The question is more the knowledge of the complete measurement chain performance. I use 2 kind of mics : one Umik1 (it performance is known) and cheap omni electrets with a Zoom H1n hand recorder. I know this second chain has a limit in high frequency compare to the Umik. It is in my plan to investigate the reason but not done. In case of mic input in some devices like phones, it might be not easy to disconnect the different filters. For test you can build a resistive divider to input a signal and check for attenuation. See for exemple Audio loopback dongle .
Your panels show in a certain way the same incredible quality of the DML that we have with a 41x33cm canvas panel which is the possibility to go quite low without enclosure.
This reminds me my canvas have also an unexplained peak at about 300Hz... not as high as yours but nevertheless present. Your hypothesis about the role of the dimensions is interesting. I tried to investigate in this way by baffling my canvas panel (some important surface all around) but I have found nothing...
About the FR correction by EQ I agree even if I haven't tested it yet. If you have the possibility, check also the spectrogram in parallel of the FR to see when in time, a peak appears. When it is close to time zero, probably no problem for EQ. Later, additional investigation probably needed.
With plain membrane, I am in the opinion (meaning I have no proof and no experience of honycomb) for now that the HF behavior is a characteristic of the material by itself. I plan to try to investigate around the frequency absorbtion. Spedge wrote several time that the frequencies are not spread the same across the panel according to the material.
One big quality of DML is the possibility (even if difficult to reach) to be a wide band loudspeaker so I don't like the idea of a tweeter which might not go well with the DML because of important dispersion differences.
Christian
For now, I don't know a (direc ?t) link between efficiency and treble response. The efficiency is driven by the bending stiffness, the density, the capacity of the xciter to transform the current in force. Some papers show a high frequency filter between the voice coil mass and the panel mechanical impedance but I was not able to have evidence of that... I have in fact evidences going the opposite : cardboard with a low mechanichal impedance and a good HF extension, small thickness acrylic with a high impedance but a lack of treble. Hmm?
Christian
Testing with a smaller contact point is also in my plan. I have a step before which to choose the membrane material... some tests on going.
I'm not sure about anything yet, and just speculating based on the impressions I got so far.
But seemingly any material has an ability to carry HF vibrations that strongly correlate with its stiffness, but the HF response seems to depend less on resonance of the plate than the mids and lows. So the DML doesn't really work the same way across the spectrum.
For example, the sound of the polycarbonate has a lot of treble because it is hard and dense, but that also dampens resonance which would amplify the mids more, hence it seems harsh. Infact it is more a lack of mids due to lack of resonance boosting those frequencies.
Now, if you get something that with very stiff skin and a hollow body with good compressive strength to allow resonance to amplify the signal, you can get both efficiency and good HF response. Since my carbon is mixed with too much plastic I do not get good enough HF response, but can still increase the total SPL by making the body resonate more. But nothing I can do will improve the HF response.
So when you have the opportunity to do things like modify how dense the core is and how thin the skin is, it could be possible that you are able to push the SPL higher, but you end up boosting the really strong modes in low mids only.
Yes definitely need more test. On my case smaller contact point will decrease efficiency.
Hello everyone,
I'm brand new here, just made an account to participate after so much reading the thread and watching videos. I am not an engineer of any kind but I like making stuff, including a few inventions. Since I was young I thought often of making my own speakers then, like many people I saw the Tech Ingredients videos and that sparked my interest in DML. I ordered some exciters (they should have arrived by now). Already I'm second guessing which exciters I chose...there seems to be very little information comparing the various options. The Dayton official info is pretty thin and general on the consumer website. I saw mention of some other brands here but haven't actually seen them for sale.
I'll soon be making my first build. From all my reading and listening and watching videos...I definitely want to start with multiple exciters per panel. Independ of the graphs and numbers the examples just seem to sound much better to my ears...of course it's hard to tell without hearing in person.
Like many of you I've had many ideas already and different evolutions of understanding. I originally intended to make the XPS 1" thick panels from Tech Ingredients and work from there. Then I looked at a bunch of other options...then saw Tectonic doing dry unidirectional layup carbon fiber honeycomb....
Of course I've scoured ebay and others for surplus honeycomb panels to experiment but no luck yet finding the right dimensions at a good price.
That's a long into....here are some questions:
1) I have run across casual flreferences to people experimenting with simple carbon fiber plate or fiberglass plate but haven't seen any posted results. Tech Ingredients said he experimented with all that stuff but didn't give any details. It seems the devil is in the details. Tectonic settled on honeycomb for a reason, and I can see why, but also they are putting a lot of power through the panels. At much lower power it seems just the skin might work? Of course they are doing detailed analysis and placing small dampers to level out modes that might just be uncontrollable for a DIYer who doesn't have lasers to optically analyze the panels in action.... Based on my current (limited) understanding it seems a thin carbon fiber plate with a low resin ratio should work well with the edges somewhat constrained to ease standing waves. In my other (non audio) endeavors I have come to really appreciate the power of CF to return energy in dynamic uses. That intrigues me...though I suspect others have already found the pitfalls outweigh the benefits or else these would be out there already. Still.... I'm tempted to buy a pair of these:
https://www.rockwestcomposites.com/47959
#2 I forgot what #2 was...
I'm brand new here, just made an account to participate after so much reading the thread and watching videos. I am not an engineer of any kind but I like making stuff, including a few inventions. Since I was young I thought often of making my own speakers then, like many people I saw the Tech Ingredients videos and that sparked my interest in DML. I ordered some exciters (they should have arrived by now). Already I'm second guessing which exciters I chose...there seems to be very little information comparing the various options. The Dayton official info is pretty thin and general on the consumer website. I saw mention of some other brands here but haven't actually seen them for sale.
I'll soon be making my first build. From all my reading and listening and watching videos...I definitely want to start with multiple exciters per panel. Independ of the graphs and numbers the examples just seem to sound much better to my ears...of course it's hard to tell without hearing in person.
Like many of you I've had many ideas already and different evolutions of understanding. I originally intended to make the XPS 1" thick panels from Tech Ingredients and work from there. Then I looked at a bunch of other options...then saw Tectonic doing dry unidirectional layup carbon fiber honeycomb....
Of course I've scoured ebay and others for surplus honeycomb panels to experiment but no luck yet finding the right dimensions at a good price.
That's a long into....here are some questions:
1) I have run across casual flreferences to people experimenting with simple carbon fiber plate or fiberglass plate but haven't seen any posted results. Tech Ingredients said he experimented with all that stuff but didn't give any details. It seems the devil is in the details. Tectonic settled on honeycomb for a reason, and I can see why, but also they are putting a lot of power through the panels. At much lower power it seems just the skin might work? Of course they are doing detailed analysis and placing small dampers to level out modes that might just be uncontrollable for a DIYer who doesn't have lasers to optically analyze the panels in action.... Based on my current (limited) understanding it seems a thin carbon fiber plate with a low resin ratio should work well with the edges somewhat constrained to ease standing waves. In my other (non audio) endeavors I have come to really appreciate the power of CF to return energy in dynamic uses. That intrigues me...though I suspect others have already found the pitfalls outweigh the benefits or else these would be out there already. Still.... I'm tempted to buy a pair of these:
https://www.rockwestcomposites.com/47959
#2 I forgot what #2 was...
Had the same thought NaRenaud, but was told that those that tried didn't like the result. Of course carbon plates can be somewhat different, but from the experiments I have done so far, simply a thin plate is not ideal. You want something with high stiffness but low density. Making the plate really thin doesn't make the density lower, so still will not allow resonance to build up as intended. So it might not sound much better than the much cheaper acrylic.
My impression is that the advantage with carbon is that you can make skin layer that is fractions of a mm thick, but that still has sufficient stiffness and strength to carry the waves. You don't need the stiffness of a 1.5 mm thick carbon plate, it is just a lot of unnecessary work for the exciter. But you do need the body that a core will provide, and cannot simply put an exciter on a paper thin skin.
DML is very fascinating in that is is so simple in many ways, especially when it comes to minimal implementation effort needed to get started. But understanding how the plate actually works when excited seems very hard. In the beginning I mostly saw it as waves on the water when you throw a stone, which then translates to soundwaves. However I start to realize that it is only part of the picture. The modes created is a very important factor that doesn't fit in to that analogy. Guess it is obvious from the name. It is not DWL (Distributed Wave Loudspeaker), but DML, since it depends on those modes to make anything more than the slight buzz than the exciter does on its own.
Think of a musical instrument. It has a body that vibrates when excited, but if you make an acoustic guitar of just a thin board, it will also vibrate, but never sound as loud or as good as a proper guitar since it lacks all the resonant modes filling up the sound. It is counterintuitive, but you do want to encourage resonance. So I would guess it is to allow resonance the materials considered successful are all containing a lot of air (foam, sandwich composites, balsa wood) and typically are at least some 3mm thick.
My impression is that the advantage with carbon is that you can make skin layer that is fractions of a mm thick, but that still has sufficient stiffness and strength to carry the waves. You don't need the stiffness of a 1.5 mm thick carbon plate, it is just a lot of unnecessary work for the exciter. But you do need the body that a core will provide, and cannot simply put an exciter on a paper thin skin.
DML is very fascinating in that is is so simple in many ways, especially when it comes to minimal implementation effort needed to get started. But understanding how the plate actually works when excited seems very hard. In the beginning I mostly saw it as waves on the water when you throw a stone, which then translates to soundwaves. However I start to realize that it is only part of the picture. The modes created is a very important factor that doesn't fit in to that analogy. Guess it is obvious from the name. It is not DWL (Distributed Wave Loudspeaker), but DML, since it depends on those modes to make anything more than the slight buzz than the exciter does on its own.
Think of a musical instrument. It has a body that vibrates when excited, but if you make an acoustic guitar of just a thin board, it will also vibrate, but never sound as loud or as good as a proper guitar since it lacks all the resonant modes filling up the sound. It is counterintuitive, but you do want to encourage resonance. So I would guess it is to allow resonance the materials considered successful are all containing a lot of air (foam, sandwich composites, balsa wood) and typically are at least some 3mm thick.
Also want to add that for home use it might not matter that much if it resonates less than an ideal material. Sensitivity becomes very important for large PA systems, but for a small home system it is not usually a problem to compensate.
But don't think the carbon plates are worth it anyway, then you most likely get much better result for less money with the tried and tested plywood or canvas solutions.
But don't think the carbon plates are worth it anyway, then you most likely get much better result for less money with the tried and tested plywood or canvas solutions.
I get what you are saying but I'm skeptical. I haven't seen any accounts or stats of anyone actually doing it with a good sized panel. No one I've found has actually said what kind of carbon panels they tried, how thick, what size, how much resin, what kind of surface, etc. There is a reason Tectonic is using what they are using, beyond just the honeycomb shape... sure, they seem to use paper for the BMLs but even there I'm not convinced it's wood pulp paper...
There are different physics going on at different frequencies. A harder surface definitely gives a stronger HF response than a soft one, but not necessarily a clear one. Lower frequencies are more piston-like so the size and stiffness of the CF should help. CF plate is VERY different from acrylic in most ways. It's also (like wood and foam) not a homogenous material but has a defined structure. I was ready to go with XPS panels like Tech Ingredients until I read and watched and listened to a lot more. He said plywood was unsuitable but obviously plywood has it's place...likely he used totally the wrong size and thickness. His ears likely don't work past 8k Hertz since he didn't seem to notice the foam rolls off so much there.
I guess what I'm saying is there is still a lot to experiment with rather than write off.
I should also clarify my goals....I am not looking for a "warm" speaker. I want precision on the voice range with enough clear treble to not need a separate tweeter and I'll run a powered subwoofer at 180 crossover (because that's as high as mine goes). I'm more interested in avoiding distortion and hot frequencies than I am in output levels. I'll be using them with my 84 inch TV in a rather smallish and oddly shaped space that is hard to treat. There is a fireplace on one side and an open wall to a larger room on the opposite side with a kitchen behind it...clarity and management of bad room dynamics is part of the draw, hence wanting to avoid a separate tweeter.
There are different physics going on at different frequencies. A harder surface definitely gives a stronger HF response than a soft one, but not necessarily a clear one. Lower frequencies are more piston-like so the size and stiffness of the CF should help. CF plate is VERY different from acrylic in most ways. It's also (like wood and foam) not a homogenous material but has a defined structure. I was ready to go with XPS panels like Tech Ingredients until I read and watched and listened to a lot more. He said plywood was unsuitable but obviously plywood has it's place...likely he used totally the wrong size and thickness. His ears likely don't work past 8k Hertz since he didn't seem to notice the foam rolls off so much there.
I guess what I'm saying is there is still a lot to experiment with rather than write off.
I should also clarify my goals....I am not looking for a "warm" speaker. I want precision on the voice range with enough clear treble to not need a separate tweeter and I'll run a powered subwoofer at 180 crossover (because that's as high as mine goes). I'm more interested in avoiding distortion and hot frequencies than I am in output levels. I'll be using them with my 84 inch TV in a rather smallish and oddly shaped space that is hard to treat. There is a fireplace on one side and an open wall to a larger room on the opposite side with a kitchen behind it...clarity and management of bad room dynamics is part of the draw, hence wanting to avoid a separate tweeter.