DML PA systems

L

Leob

Member
Joined 2022
While there is a very long thread in full range regarding DML speakers, I think they are also very interesting for PA applications, and deserve their own thread since it is quite a different application then when making a pair of speakers for home use.
So here might be a good place to discuss things like what materials offer the best sensitivity, how to get maximum power density per plate, what power amplifiers are good to use with DML speakers and how do you construct a good frame and protect the exciters and plates from rain, etc.

Personally I started looking at DML speakers simply out of curiosity since they just seemed very novel in the the way they actually work as well as how they perform. Initially I hoped to get a pair of half decent home speakers at best, but quickly realised both how much I like the sound, but also how interesting the properties are for PA applications.

So why is DML interesting for PA sound?
1. SPL does not reduce as much over distance. This means a more even spread of the sound over the audience. The decay rate is more like a line array even if you have a single plate set up as a point source.
Basically if you stand on a dancefloor with plates directed to the middle from each corner, it feels like the stacks are half the distance away compare to where they actually are. It is hard to describe, and it is a weird feeling when you walk around between them.
2. The diffuse waves generated by DML really helps with acoustic issues. Not only by reducing the amount of reflections we perceive in a closed space, but also the interference between multiple speakers. It is also weird and seems to defy logic sometimes, but in combination with the previous point it means the whole dancefloor sounds like a sweet spot with both loud and clear sound.
3. Dispersion is really wide, covering a lot of area with a few speakers.
4. Good sensitivity, even when looking at the usual on axis response, and amazing total efficiency when taking the dispersion into account.
5. Low distortion even at high SPL.
6. Despite the diffuse nature of the waves emitted, spatial imaging is excellent. Even when standing very close to one speaker stack you can hear stereo effects from speakers on the other side of the dancefloor in a way that I have not experienced before.

I make a small festival each summer, and as it happens this year the guy who I usually rent from couldn't do it, so I decided to quickly try to put together a DML system since I had done enough experiments to be confident it would be viable.
I will add post in this thread describing the system I built in more detail and add some videos of it in action, but for now a quick description.

4 plates per stack, each plate made of :
1 graphite enhanced EPS plate, 500x330x25mm:
https://www.dekokopf.com/neopor-styroporplatten-3er-set-50x33x2-5cm.html
4 DAEX30HESF-4 exciters:
https://www.soundimports.eu/en/dayton-audio-daex30hesf-4.html
Frame built with wood and 3d printed corners.

I have 4 stacks, so a total of 16 plates. Each stack is driven by one of these:
https://www.china-sanway.com/D2S-2CH-900W-DSP-Built-in-Amplifier-Module-Class-D-pd353583.html

Subs was rented 4xL'Acoustics SB218.

I tried to make construction as quick and simple as possible, and think I succeeded with that, but still of course it become stressful to finish in time. I didn't have much time to tune it with the subs, and never got time to test it properly at war levels before the party, so I was nervous to say the least. The guy I rented the subs from brought tops as backup if it would seem like a flop.
We turned it on and without even tweaking the XO it just was way beyond expectation, sounding really loud and clear, and no problem to keep up with the subs, rather the other way around. Sound guy admitted he was very sceptical initially, and probably thought I was crazy not using his Kara tops instead, but admitted he was very impressed when he heard it 🙂

During the party I just got constant comments about the sound. Everyone positive, and lots of people that would never do that usually. The actual sound geeks present was over the top ecstatic 🙂 Common comments where "everywhere seems like a sweet spot", "I always have to wear earplugs, but not with this sound", "best sound I have ever heard" and "it is like listening to quality headphones but from a PA system". After a couple of days of hearing the same comments it almost went from total relief that I was not crazy and it was not a flop to it becoming a bit too much and annoying 🙂

Since it was such a resounding success I'm really surprised there hasn't been more interest in DML technology for PA applications.
One tricky aspect with DML is the patent situation. Since I do this as a private person and not for profit (my festival is also non commercial) it is not an issue, but getting started with DML commercially might not be so easy. The only commercial manufacturer of DML PA speakers are Tectonic. They seem to produce a very high quality product, but at a price level only big established rental firms can afford. However, those tend to be quite conservative and go with the products that are typically requested, and have no interest in having to sell in customers on something completely new. And Tectonic also seem to have very limited marketing and no presence outside US, and importing their product to the EU would end up very costly.
In the end, with nothing else on the market, no one hears DML systems and no one demands them from the rental firms.

So it seems to be up to DIY'ers has to build some systems and get the word around! 🙂
Anyone else doing DML for PA applications, or is interested in doing that?
 
I am looking forward to seeing the pictures and videos! What SPL is it capable of, how large was the area and how many people? If these were able to keep up with the subs, the output must have been quite high. I find this concept very interesting. I yet have to finish my first DML pair , panels are built but put aside while I was waiting for wood to be delivered and they are still there🙂 The only potential issue I see is the durability of exciters and panels during road abuse - but only the time will tell.

Compared to "classical" PA boxes, will the driver cost and also box volume and weight be less for similar output? I would expect so. I still need to build a small PA for garden parties (have subs already) and this might be an iteresting alternative to boxes to take less storage space and easier handling.
 
I haven't actually measured the SPL. I only have a uncalibrated measuring mic for FR analysis. I did order a SPL meter but it got lost in transport, so have to try again :\
So the best reference I have is really that the SB218 had trouble keeping up. Amps still had power, but the subs was pushed to the limit.

But also one has to keep in mind that with less amplitude decay over distance, the SPL needed at source becomes less. You don't want say 140dB next to the speaker to get 110dB at the furthest part of the audience. Since it spreads so well both in direction and distance, the overall loudness for the audience would be much louder than the on-axis spec would suggest.
Perhaps 16 plates was overkill to match those subs. The amps I use should give 1000w RMS per stack into 8 ohm, and the exciters are rated in total 640w RMS per stack. Pushing them to the max for over 12 hrs didn't even make the exciters lukewarm, and there was no hint of neither plates or exciters distorting.
I will do some more experiments with a single plate that is rated at 160w RMS total driven by 900w into 4 ohm, but might not get many opportunities to do testing at max levels for while.

I saw claims from Tectonic that one of their DML500 can replace 8-16 line array speakers. They should have double the power handling of my plates, but probably sensitivity is quite close. I will have to see how hard I can really push mine, but it is very possible that 1-2 plates per sub could be enough.
At any rate they are very cost efficient. A quality line array speaker will cost a few €K for sure. My DML plates cost not much more then €200 per speaker. Of course I don't really have a professional quality touring grade product for that price, but the sound per buck is incredible.
 
That sounds promising, a small system like I imagine could do with two or four panels. This definitely goes to my ever expanding list of projects🙂
 
So here is some more details about the system and event I used them on.

First a little about the plates. They are graphite enhance EPS (GPS). I found the GPS to sound slightly tighter that the EPS of same density, but I think there is more variation between different EPS materials then between EPS and GPS. Link to the specific plates I use is in original post.
The corners are 3d printed and holds together the two frames that the GPS plates are clamped between, using some adhesive foam strips:
https://www.amazon.se/gp/product/B091HPDSH4/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

suspension_placement.png

The corners fit the wood bars for the frames very tightly, and plate pretty much holds together as it is, but they of course have screws to secure the frames.

The exciters are fixed with epoxy to the GPS plate in a configuration similar to what Tectonic use.
Here is a sketch for the template I used to fix the exciters, which I put in the middle of the plate:
exciter placement.png


I attempted to make a support spine, and I tried a couple of variations, but got issues with distortion. The exciters should stay glued on without issue, but doing stress testing during a very hot day on my veranda and and instead of using a HPF, boosting bass a lot, the exciters also started distorting. Conditions was very extreme and I doubt I'll be able to replicate the issue unless I organize a party in a sauna without using any subs 🙂
But as a desperate quick fix I added some strings to hold up the exciters just very slightly, making the distortion disappear. I probably do some more experiments printing a holder to hold up the exciters, but also want some kind of back bracing anyway to protect exciters during transport. Although now the do stack very well, so is quite easy to transport safely.

I did various experiments with coating the plates with PVA glue, shellac and hide glue, and found that at least on the EPS plate I'm using, hide glue with a very thin layer of shellac gave best sound and sensitivity. You have to be very careful with the thickness though. I used a roller with 3 parts water to one part hide glue granules to apply one thin layer, and when that dried I rolled on a single layer of very thin shellac solution.

I decided it was simpler to build a roof over the speakers than try to make them protected against rain.
I made construction as simple as possible and could do it all myself without a proper workshop in a couple of weeks. While it doesn't look very finished and professional it worked really well, and I will try to tidy it up and optimize it as well as get my own subs so I have a complete system I can tune carefully.
The Sanway plate amps I use give 500w per channel in 8 ohm and 900w in 4 ohm. With 4 exciters in series-parallel on each plate, each plate is 4 ohm, and I'm running 2 plates per channel for 8 ohm. If I would run half that, one plate per channel instead of two, that would quadruple the power per exciter, which I think would be beneficial even if it is well over the spec of the exciters. Initially I was thinking to use active subs, hence wanted plate amps, but think I will go with passive subs and will get an amp rack to drive them instead so I have plenty of power to run all 16 plates along with amps powerful enough to drive some really power dense subs.

The event is a small private psy/goa festival over a couple of days in the forest in Sweden that we held for 10 years in a row now. Usually it is around 200 people and dancefloor is a little bit over 20x20m.

Here is a video showing a speaker stack during sound check:
https://drive.google.com/file/d/1kdh1yNhkZY9F1waNljSoVIBvRwwy2Uj0/view?usp=sharing

Here is a video of the dancefloor during the night:
https://drive.google.com/file/d/17_3u1bt28VpCXvznFyX0TkftK3jj4rHK/view?usp=sharing

Here is a video shot some 30-40m away from the dancefloor:
https://drive.google.com/file/d/1fxUo9T3XxfEODbqAU8kiqNXHstAyVmD4/view?usp=sharing
 
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TNT said:
Cool!!

How low did you run the plates?

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I set the XO to 90Hz, but they start rolling off at 100Hz by themselves. Getting them to play lower than that would mean bigger plates and looser suspension, and the advantages of DML doesn't apply to sub frequencies really since they are any way omnidirectional, so it is a bit pointless to even try I would say. But even relatively small plates like mine can go deep enough for the typical sub at least.

One thing I noticed is that it seems like the diffuse sound helps making the crossover less problematic when it comes to phase, so I find they actually don't seem very fuzzy about having some overlap with the subs.
 
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I see you mounted the exciters into the center of the panel - or that is just how it looks in the video and you used the standard 3/5 mounting point as a center of the cluster? Or maybe the 3/5 rule does not apply to multiple exciters in this configuration, since none of them is actually in the center and is closer to 3/5 mounting point?
 
I cant help to be inspired to build myself a pair of floor to ceiling lines sources - sectioned into say 10 pcs stacked 2,4m high (24x15cm) with one exciter on each - sat tight in corners. 🙂

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I have just ordered 10 pieces (8 for PA panels, two for smaller for home). Do not tell me I need to order another 10🙂 I read that the Tectonic panels use carbon honeycomb panels. I am trying to find some local source, until now I found only 200 x 300 mm on AliExpress for around 50 Eur each. Would a thin (1 - 3 mm) carbon board work as well?
 
pelanj said:
I see you mounted the exciters into the center of the panel - or that is just how it looks in the video and you used the standard 3/5 mounting point as a center of the cluster? Or maybe the 3/5 rule does not apply to multiple exciters in this configuration, since none of them is actually in the center and is closer to 3/5 mounting point?
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DML is as the name suggests about distributing the modes, which will give you a smoother response. Exciter placement seems to have less effect on the response than I assumed, but avoiding dead center seems to be good. But with multiple exciters, indeed none of them will be dead center. Looking at Tectonic they also use a similar configuration that looks placed in the center.
 
pelanj said:
I have just ordered 10 pieces (8 for PA panels, two for smaller for home). Do not tell me I need to order another 10🙂 I read that the Tectonic panels use carbon honeycomb panels. I am trying to find some local source, until now I found only 200 x 300 mm on AliExpress for around 50 Eur each. Would a thin (1 - 3 mm) carbon board work as well?
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Most ready made nomex core honeycomb doesn't seem ideal for DML. My guess is that you want around 0.1-0.2mm thick carbon skins. I did get equipment and materials to try to vacuum bag my own plates, and will dig in to that again when I have time. But it will be much more work and much more expensive, and since I was so happy with the performance of the GPS I decided to settle for that for now.

In the DML thread in full range, someone recently linked to an italian supplier that does 0.3mm thick skins for a reasonable price...looking forward to see how that works out, but I fear it will result in lower sensitivity than the GPS plates at a higher cost.
 
As for pure carbon boards, they are way to stiff for good efficiency. There are users who tried it in the full range thread, and they didn't get better results than with much cheaper materials.
 
TNT said:
Leob - have you done any measurements on your panels?

FR / Dist / directivity?

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Indeed, I have posted some FR graphs in the full range thread, but need to do some more measurements really since I haven't been able to do them outdoors or in a decent space yet. I noticed quite large discrepancies depending on which space I tested them in, making the graphs a bit useless.
But will try to do some more proper measurements and post the FR, distortion and spectrograms from REW.

To summarize what I have seen is that you should expect some 10dB swings in the response , especially in the lower mids, and around 6dB HF rolloff overall. I also compared the dist graphs in REW to my regular speakers (Tannoy Reveal 802), and saw much lower harmonic distortion.

The swings and HF rolloff can be adjusted with EQ as needed...the plates seems to respond really well to EQing somehow. By adjusting suspension and plate dimensions, and that way distributing the modes, it should be possible to get down to around 5dB swings instead, reducing the need for EQ.
 
Thanks for the answers! So the distortion was higher in Tannoy?

Anyways, would you say that a line source endeavour could be successful?

I will use DSP EQ so not so scared about FR not being ruler flat.

Would you buy those Neopor Styroporplatten again?

If I would go for smaller plates, do you think that 10mm would be better or is 25 the one to get?

Or will these be to small all together perhaps - go for larger?

dml_line.jpg


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TNT said:
Thanks for the answers! So the distortion was higher in Tannoy?

Anyways, would you say that a line source endeavour could be successful?

I will use DSP EQ so not so scared about FR not being ruler flat.

Would you buy those Neopor Styroporplatten again?

If I would go for smaller plates, do you think that 10mm would be better or is 25 the one to get?

Or will these be to small all together perhaps - go for larger?



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Sorry, yes, the distortion in DML panels was much lower than the Tannoy. I'll get back with actual graphs eventually.
I don't see any reason it would not work well in a line source configuration, but I guess it will not really be a line source any more.
While it is good to avoid square ratios, I have the impression that having a very long rectangle is not very optimal from a power density or response perspective. The shortest side dictates the lowest mode, and you don't want the longest side to have the exact same mode of course, but you also don't need to move it very far to smoothen out the response. So looking at your drawing you might get even better response and more power by using say 5 plates instead of 4, or making the whole thing a bit less tall. And I think you want them at least 300mm wide, depending on where you hope to set the HPF.

I'm very happy with the neopor plates. I will do some carbon/nomex experiments eventually like I mentioned, but I'm not sure that it will be that much of an improvement since the EPS seems very hard to beat being both very sensitive and good sounding.
I did get the 10mm to test as well, but they feel a bit flimsy for outdoor use, and didn't notice the 10 mm sounding better or being more sensitive during my tests. If you want smaller plates I think 10mm plates can give you a little bit lower extension, but have not really experimented with that.
 
Thanks! I was actually aiming for 10 with the 25cm height. But yes, maybe I should go a bit wider also. Total height I would like to be 2,4m. If they would do 150 I would be very pleased. 200 is probably OK also.

241.jpg


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How about this for a 2m line. How many exciters do you think I need per plate for a say 30 sqm room and playing to 200 Hz?

30x40.jpg


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