Sebastion
Just tried to check the mass of the panel - Google couldn't find the Rely-A-Ply but it's a hardwood ply so I presume it would weigh about 1.2kg (2.6 maple leaf lbs).
So assuming the panel and frame assembly is laid flat on a table and the exciters attached - what is the downward extension when it is picked up. If the frame is supported with the panel suspended and then the exciters attached, will the BL values of 2 small exciters be enough to 'suck' up the panel mass on the upstroke, (that's also assuming the exciters are fixed to a spine - probably no chance otherwise).
How do the commercial 'hidden speaker' manufacturers handle this issue - big exciter motors ??
And..in a ceiling mount, there's probably a need to centre mount the exciters to better balance the load ?
Eucyblues
Just tried to check the mass of the panel - Google couldn't find the Rely-A-Ply but it's a hardwood ply so I presume it would weigh about 1.2kg (2.6 maple leaf lbs).
So assuming the panel and frame assembly is laid flat on a table and the exciters attached - what is the downward extension when it is picked up. If the frame is supported with the panel suspended and then the exciters attached, will the BL values of 2 small exciters be enough to 'suck' up the panel mass on the upstroke, (that's also assuming the exciters are fixed to a spine - probably no chance otherwise).
How do the commercial 'hidden speaker' manufacturers handle this issue - big exciter motors ??
And..in a ceiling mount, there's probably a need to centre mount the exciters to better balance the load ?
Eucyblues
Has anyone heard of people trying to make their own exciters?
Current exciters are an offshoot of conventional loudspeakers, and are optimised for that purpose.
I imagine that to optimise for panels designs and experiments, you might want:
I think it may be worth trying the same process with foam.
Current exciters are an offshoot of conventional loudspeakers, and are optimised for that purpose.
I imagine that to optimise for panels designs and experiments, you might want:
- Excitation area closer to a point, rather than a circle.
- Somewhat decouple size of excitation area from its power
- Design for easy detachment - eg through-hole mounting
- Design for symmetry across the panel so the exciter is not pulling down on one side. Again, through-hole or frame mounted with a stress-relieving linkage.
- Maybe simplify the design - eg by using the inherent spring the panel, rather than designing the exciter spring for a given frequency response.
Congratulations on your success Sebastian.
I think it may be worth trying the same process with foam.
Hi pway,
I have made several exciter by 3D printing the coil forms and acoustic suspension forms and their frequency response was not all that great. The best I could do is about 8KHz for the top end before distortion raise its ugly head. I would suggest one take the time to build a laser velocity to measure the exciter motion it will really open your mind to see the problems of moving mass. I have moved away from the DML technology since it taints the music with it's "Distributive Modes " of the panel and wiping out any fast transit response due to its mass the pesky Newton's laws of motion always gets in the way ..But if you are happy with the sound that's really all thats matter in the end.
Cheers,
Steve
I have made several exciter by 3D printing the coil forms and acoustic suspension forms and their frequency response was not all that great. The best I could do is about 8KHz for the top end before distortion raise its ugly head. I would suggest one take the time to build a laser velocity to measure the exciter motion it will really open your mind to see the problems of moving mass. I have moved away from the DML technology since it taints the music with it's "Distributive Modes " of the panel and wiping out any fast transit response due to its mass the pesky Newton's laws of motion always gets in the way ..But if you are happy with the sound that's really all thats matter in the end.
Cheers,
Steve
Sebastian,
Another great post, thank you.
The only decision to made that I would perhaps second-guess is starting with the assumption of 2/5, 3/5. That "rule" seems to have very limited use which doesn't extend to your design. I would think it would be more effective to do your bracing as you describe except without a preset exciter position and then test the panel with exciters at different positions between the bracing.
Also, I would not look at your hole in the low frequency as a bug, but rather a feature. A sub at the low end is going to be your best best anyway and having a panel resistant to those frequencies would seem to help resist distortions in the frequencies that matter.
I agree you should expect more HF power with thinner wood.
Another great post, thank you.
The only decision to made that I would perhaps second-guess is starting with the assumption of 2/5, 3/5. That "rule" seems to have very limited use which doesn't extend to your design. I would think it would be more effective to do your bracing as you describe except without a preset exciter position and then test the panel with exciters at different positions between the bracing.
Also, I would not look at your hole in the low frequency as a bug, but rather a feature. A sub at the low end is going to be your best best anyway and having a panel resistant to those frequencies would seem to help resist distortions in the frequencies that matter.
I agree you should expect more HF power with thinner wood.
With similar thoughts to yours, I bought a pair of Aiyima 50mm exciters off AliExpress because they looked well built and had an interface plate that screwed in with what would presumably be a standard metric thread. My intent was to discard the aluminum interface plate designed for glue and instead run a bolt though the panel with small washers and some epoxy and screw the exciter on to that. They are a standard thread and I ordered the bolts (in nylon, assuming less mass was good) but abandoned the experiment when playing with the Aiyima exciters side by side with my Daytons showed poor results. As Aiyima states these are very sensitive to gravity and being horizontal (likely because they are so heavy) and their frequency response is very limited.
Sebastian
I just had a look to the specification of the exciters you chose... The surprising point for me (but I have experimented only one model...) is that the 30HESF has a 0.31mH inductance, the 32EP a 0.21mH inductance and the 25SHF has a 0.41mH inductance.
So we could expected with the 25SHF a lesser HF performance than with the current one. With those exciters, I'd try a capacitor in parallel of the 30HESF. Not sure of all of that but you will find post #5065 a quick test I did adding a 0.33mH inductance in series with my exciter.
Like that I don't understand your choice of the 25SHF
For now, I have only used the DAEX25FHE-4 I chose for its low voice coil mass (no proof it is a must) and its low inductance 0.1mH (here some indication it is a good choice for HF)
Christian
It took me time to install the last version of REW on my Linux computer!
So if somebody wants to do it, the trick is to enter "export INSTALL4J_JAVA_HOME_OVERRIDE=/usr/lib/jvm/default" at the terminal line before launching the script. This says to script where to find Java environment. Sorry no link to our topic but if it can help somebody...
So the box you show is the one I suggest to keep.
The smoothing I suggest to remove is the one on the graph.
2 possibilities :
Graph > remove smoothing or Ctrl+0
or under All SPL
controls > no smoothing
Thank you for those clear explanations Sebastian.
Thank you also for the idea to post a paper.
Even if I have made the parallel between the DML and instrument soundboard, read papers about that, it took a long time to me and need experiments to start to understand what means the modal nature of DML, and that among the modes, some don't produce sound. What you add here is the possibility of instrument soundboard technique to give a linear device. This was not obvious to me.
It arrives at the moment, after a set of experiment, I am convince of the role of the suspension and the need to find some damping or way like bracing to equalize by construction the modes.
If I cross with your post 5305, the main cross is made of red oak (which stiff and quite heavy) and the other one from poplar... In France I wonder if it is even possible to find nowadays such woods!
May I ask you 2 additional information :
- the section of the bracing?
- some more details about the suspension? In which way is it different from the other one?
Christian
How would you solve this dml problem as best as you could?
Lighter panel, more exciters, higher motor strenght?
Light composite panel 20x30 cm can weigh 20…30 grams, how much motor strenght would be optimal?
Attachments
Sorry about mixing a post about exciters with another to Sebastian. Meant to reply only to Sebastian but a draft post about exciters was added to it automatically.
I think that a paper is a great idea - reports of more-or-less resolved designs, approaches, proofs-of-concept, rules of thumb, heuristics or theory would all be candidates for 'papers'. A wiki would also be a good place to organise content more permanent than is typical of the forum.
I was thinking last year to start a 'DML primer' section on the wiki. Good thing I didn't because the wiki seems to be gone now.
I think that a paper is a great idea - reports of more-or-less resolved designs, approaches, proofs-of-concept, rules of thumb, heuristics or theory would all be candidates for 'papers'. A wiki would also be a good place to organise content more permanent than is typical of the forum.
I was thinking last year to start a 'DML primer' section on the wiki. Good thing I didn't because the wiki seems to be gone now.
I don't understand precisely the problem you are referring too...
The DML is by nature modal. It leads to interesting properties like no need to enclosed the rear wave, about no directivity, no relation dimensions high frequency. The bad side is an uneven frequency response which by its nature is I think (not tested) a good candidate for EQ. The exchanges here show countermeasures before EQ might be possible working on the damping or the panel structure (bracing).
It is perhaps a matter of requirement but at the moment I have no problem to live with the sound of my current panel (without EQ) even if the FR is "ugly" according to the standards, thanks to the other qualities. Despite this strange frequency response, the sound is really pleasing. The point is to be at ease with the new paradigm.
About the question of mass, there is for me no problem. It might be strange to think a small exciter can drive an "so heavy" panel. Just it is. The proof is in the sound, the frequency response. If the exciter was not able to move the panel enough we won't have the SPL at the considered freqency. The results shared here show a panel can reach a bit more than 10kHz. Not all do that and the reason why they don't is not clearly explained. The material has a key role. An other assumption for me is the role of the coil inductance. It seems that the mass at the voice coil is not a so big parameter. This is something I can't explain and I have even a difficulty to accept it but the measurements are here... Even adding locally a mass don't reduce in the same factor the bandwidth. The exciter remains able to accelerate the panel. If the mass is really important, I think other problem appear like to long decay time to stop the membrane at some frequency when the mass is important (not the mass of the panel, the local one added).
Other tests show that thickness of the panel doesn't have a key role on the efficiency or the HF. I think it is a good think to test by our self that. It has a role in the lower frequency.
If the requirement is to have a system going far beyond let say 10k, the panels shared up to now are not the right candidates. And here again I have no difficulty in the trade off loosing part of the last octave and the living sound and spatial scene of a DML.
Thinking in words of mass is even for pistonic loudspeaker not th right approach. The literature describes the low pass fiter happening between the voice coil inductance and the membrane mass. With no flexibility in the cone, no HF, no full range.
Hello Sonnar,
your thoughts sound familiar to mine. However, there were some considerations, ideas and limitations that made me change my path.
1. If I understand it correctly, then a human can't really tell the origin of a sound when it is below 100 Hz. I wanted to have a panel that would reach below that so that I would not have to suffer the directionality of a subwoofer, when DML is so much better at hiding that. I can tell you that DML (well, I have 5 days of experience in that now) can't be compared to regular speakers. I laid my speakers flat on the floor today and I thought that I had the band in 1:3 scale sitting in my room.... just amazing. I'll show later that the sound was not really affected by that.
2. I know that a guitar reaches at least down tow 80 ish Hz,.. so, there must be a way to get a DML down into that reagion, too. my panels are 4ft tall,so pretty close to a guitar.
3. When my brother asked me what DML is, I told him, that where speakers try to reproduce the vibrations of the air via membranes that move in pistonic mostion, DLM can be imagined like the wall in a studio that reproduces the vibrations it "felt" during a recording. Hence, I doubted that it is necessary to engage different materials to reproduce a brass or a wooden instrument. One just would have to build a DML that can reproduce "any" wall felt. Imagine you could drive a cement wall so that it would vibrate exactly like it did when a singers voice hit it.... I have read mixed feeling about any material, but plywood. plywood was always mentioned on top of the list when it came to sound, so I decided to stick with it. I also considere metal sheets until I saw this video and imagined that I would have to dampen that sheet of metal to reproduce just a dull knock.
4. I was afraid that a multi-panel and even more a multi-material-multi-panel dml speaker would result in the challange of differnent sensitivity and therefore different volumes that I would have to deal with on top of everything,... so I decided to keep it "simple"
This is not to tell you to not pursue it, this is only to tell you that I had similar thoughts. Please give your ideas a try and report back what you found. I'd be happy to try to reproduce your findings.
Sebastian
Hello Eucyblues,
I am by far not done with removing material from the bracing, but I had to wait for the microphone. However, I can already tell that as soon as you remove a little too much, the ply sheet starts to bend towards the front side. At least mine.
I am working on a stereo pair. Maybe I was not explicit enough about that. I have to panels, one has the exciters placed on the blue and the other one at the red markings in the picture.
The braces stiffen the board significantly. I was too afraid that the sheet would bend into several directions once I hang it up at the ceiling. The bracing introduces drum like behaviour when tapping onto the ply wood sheet. At first the big sheet didn't really "sound" at all, it was in fact dull, now it has clear tones. My goal is to produce as many as possible tones and to then efficiently dampen the panel so that resonances are avoided.
Always dabbleing, yes. I will climb the ladder very often soon :-D.
I am not 100% sure if I understand you damping upward question correctly. Can you please further elaborate on that?
I laid the panels don onto the floor today, to see how dampening might be an issue. I have 1 inch thick sheet of foam that will cover the backside of the frame. today it was below the frames with the panels. No real difference except for a little more bass.
I'll post a picture tomorrow that that the construction is clearer.
Cheers
Sebastian
Hello again,
yes, the 4fx4f 5.2 mm Rely-a-Ply you can g et at e.g. Lowes for 11$ a sheet.The weight sounds about right. I have some cut offs, but must measure and weight them, to truly know.
I put the panels on the floor and did some tests today.
It was amazing!!! It "felt" like I had a 1:3 scale miniature band in my room standing on top of the panel. the sound quality was identical, although I sat in a distance in a very shallow angle. Both panels have quite a different sound, but I will post about the how and why at some point later.
Here are the differences.
The microphone was not moved, but unfortunately the volume knob was different compared to yesterday.
The panels laid in their spots from the day before but quite a but closer to the microphone. I just turned them and dropped them towards the mic. The "average" distance was now 1m instead of 2m. The mic was 70-ish cm off the ground.
Purple was yesterday's graph, panels upright, no subwoofer, 2m from the mic
Orange was today, flat on the floor, no subwoofer, 1m in average from the mic.
300Hz to max has not really changed.
And now a test with the subwoofer and the microphone 2 meter hanging above and centered between the panels. 3.5m away from the sub.
The subwoofer volume was the same in both recordings, panel was different volume, but same difference to the day before as in the above graph.
Red yesterday's panels standing up + subwoofer with 100Hz cuttoff
Blue today panels on the floor, mircophone hanging above them, sub as above.
I do not really see a noteworthy difference. but what I observed is that the room modes play very much into the measurement below 300Hz.I moved the microphone up a little and I got quite different responses around 100Hz.
The 4ft length of the panels should translate into a DML low end of around 68Hz for 1st mode at half wave (if I understadn that correctly). Most of my measurements see peaks in that range and therefore I will try to get the panels as linear as possible towards 80 Hz,... and then the sub may take over,...
But much more reading in this thread will be necessary....
Sebastian
Ha! "Naive" remember?!
Picture me in a hardware store with sticks in my hand, bending them, looking at the price and just putting some into me cart 🙃
Well, I knew that poplar is a good wood for guitar and I knew that oak is tough in general.
If you want to really dive into tonal properties, then you might able to find proper information in guitar building websites, like this one:
https://warmoth.com/guitar-body-woods
Here you can find a lot of information about body and neck woods and how they affect sound.
I'd pick any soft wood for the smaller braces and a stiffer one for the cross and the main bass strips.
Struce and Pine might be available in France?
Now, I see your question.
Ok, let me try to draw that into the pick,... but that is just "me". No experience or true thoughts behind it: I hope this is correct. I can't have a look at the panels right now, but his should be correct. red is red oak and the two pieces that shape the square on top are only 4mm thick. I'll make proper photos tomorrow if you like.
Lol! I am still debating about coffee grinds, sand, sawdust or glitter :-D
It would be cool if I could run a video with the Hz blended ins and then in the end overlay all modes to see the spots where the panel never trule moves, those might be great holding points.
But that is future stuff, I'll look into the posts you mentioned.
Thank you,
Sebastian
Hello NaRenaud,
I think you are 100% right, and I think I can prove it, I just have to wait for my other set of exciters, then I can make some placement comparisons.
I'll try to make outdoor recordings for that. But this will take a little time.
Meanwhile, I can show you the differences between both panels and the positions I published earlier.
Somebody here might have more experience to comment how a non-braced panel would behave on these different positions, and how the FR might look different.
No subwoofer used in the following recordings but mic only 40 cm away from the panel.
red is the exciters in red position, on the epoxy spots (more "dabbling on that idea coming later").
purple are the exciters in blue position, where the hole in a guitar would usually be.
however, the bracing is a little different, I assume.
Anyhow, the purple panel expresses much more brilliance than the other panel. I assume more bass is due to the fact that the blue exciter position is closer to the center of on part of the 2nd mode.
The red panel has tighter mids.
Sebastian
Attachments
Sorry, I mixed the exciter positions up. the pruple curve is the exciters in the red position.
red curve is the exciters in the blue...
Sebastian
Hey! I would never have thought that rice is too big.
Thank you!
I finished the panel front with a 1 Odie's oil : 20 Odie's solvent mixture. I am a little worried that stuff gets stuck and riuns the nice finish.
But brown sugar might actually work.
And for completion, I finished the backside of the panels with a similar ration of polyurethane and mineral oil.
I thought finishing the panels should prevent the penetration of moisture, which might add to warping of the panels.
Thank you again!
This thread is an excellent possibility to learn about many think! Odie's oil... Never heard about before... I had a look at their site. One picture reminds me the color of the wood floor at cousin's in Canada (Québec) I found so nice.
Polyurethane and mineral oil : is it a diluted polyurethane varnish?
I applied a diluted varnish (no sure it was polyurethane) on my plywood panel. On one side first... bad idea not doing the both side the same time because it then warps but after gluing with the full peripheral foam (17x17mm) no problem. The membrane has been still perfectly flat since.
Christian