I have never managed to get a plate to distort really, apart from if there are issues with mounting. I did manage to burn some exciters from overheating, but then distortion eventually happened as a consequence of mechanical damage to exciter or mounting. So I don't think the plates can distort really, at least it is not enough to use a cluster of the most powerful models.
I have not done any calibrated SPL tests yet, but have a basic SPL meter now to use as reference, as well as a scope, so will test sensitivity and max SPL soon!
I have done rough SPL calibration when doing my most recent tests with REW, and tried to play really loud then to pick up as much distortion as possible, but I'm limited by what measurement mic can handle, so end up measuring around 100dB at 30cm, and then have very minimal distortion.
My best guess based on the level I give them then, is that a single plate with 4 exciters at least can get close to 110dB.
I print small blocks using TPU, which is a flexible thermoplastic. I find that they need to be soft but most foam that is appropriate softness will degrade with time. TPU is much more stable, and when printing I can make it hollow to adjust how soft they are.
I have not done any calibrated SPL tests yet, but have a basic SPL meter now to use as reference, as well as a scope, so will test sensitivity and max SPL soon!
I have done rough SPL calibration when doing my most recent tests with REW, and tried to play really loud then to pick up as much distortion as possible, but I'm limited by what measurement mic can handle, so end up measuring around 100dB at 30cm, and then have very minimal distortion.
My best guess based on the level I give them then, is that a single plate with 4 exciters at least can get close to 110dB.
I print small blocks using TPU, which is a flexible thermoplastic. I find that they need to be soft but most foam that is appropriate softness will degrade with time. TPU is much more stable, and when printing I can make it hollow to adjust how soft they are.
Weather getting better here, gone from freezing and snow to +18c in a few days 
So planning to take a sub and a couple of plates outdoors and do some measurements. I finally have a scope, and since I now can measure AC voltage properly I was planning to measure response with calibrated sensitivity, but turns out that is not that easy with a class-d amp
There is a sine wave at 240kHz from the switching in the amp, and while it is quite many dB down from the max output of the amp, it is constant regardless of amp level, and with an overpowered amp like this the signal is still 1.33Vrms. So turns out I need a RF filter to be able to check the output voltage with decent accuracy.
Not sure I will bother making a filter since absolute sensitivity figures are not that important to me, and at least after a little testing, trying to ignore the FR component from the scope readings, my meter read 105dB at 2.83V into 4 ohm at 1kHz. That would mean sensitivity of 102dB with 1W/1m, so I'm at least confident sensitivity is very good. I can have misjudged the RF component a little bit, but should still be over 100dB. When doing outdoor test I will also test with higher voltage to reduce the error from RF signal.
So planning to take a sub and a couple of plates outdoors and do some measurements. I finally have a scope, and since I now can measure AC voltage properly I was planning to measure response with calibrated sensitivity, but turns out that is not that easy with a class-d amp
There is a sine wave at 240kHz from the switching in the amp, and while it is quite many dB down from the max output of the amp, it is constant regardless of amp level, and with an overpowered amp like this the signal is still 1.33Vrms. So turns out I need a RF filter to be able to check the output voltage with decent accuracy.
Not sure I will bother making a filter since absolute sensitivity figures are not that important to me, and at least after a little testing, trying to ignore the FR component from the scope readings, my meter read 105dB at 2.83V into 4 ohm at 1kHz. That would mean sensitivity of 102dB with 1W/1m, so I'm at least confident sensitivity is very good. I can have misjudged the RF component a little bit, but should still be over 100dB. When doing outdoor test I will also test with higher voltage to reduce the error from RF signal.
Hi Leob, glad it's warming up for you there, we are having a lovely Autumn on the other side of the world.
That's great your plates are so sensitive, so in theory you won't need a lot of watts for your output needs even at party levels.
Glad you can do some playing with your system now you have the subs to try it all together.
I have found your suspension method is great as it lets you tune the plates by moving and adding more clamping blocks in different places, I got rid of a broad 8db peak around 500hz by adding a third clamping point on one long side. I also had a 8db peak at 9000hz that I removed by adding a little felt infront of the exciter.
I sourced some 12mm epdm tape which I am using as blocks to clamp them with now instead of the closed cell foam. It holds better and I think I was getting distortion from the plate and foam rubbing/buzzing at higher SPL levels.
That's great your plates are so sensitive, so in theory you won't need a lot of watts for your output needs even at party levels.
Glad you can do some playing with your system now you have the subs to try it all together.
I have found your suspension method is great as it lets you tune the plates by moving and adding more clamping blocks in different places, I got rid of a broad 8db peak around 500hz by adding a third clamping point on one long side. I also had a 8db peak at 9000hz that I removed by adding a little felt infront of the exciter.
I sourced some 12mm epdm tape which I am using as blocks to clamp them with now instead of the closed cell foam. It holds better and I think I was getting distortion from the plate and foam rubbing/buzzing at higher SPL levels.
I await your report including video with great interestWeather getting better here, gone from freezing and snow to +18c in a few days
So planning to take a sub and a couple of plates outdoors and do some measurements. I finally have a scope, and since I now can measure AC voltage properly I was planning to measure response with calibrated sensitivity, but turns out that is not that easy with a class-d amp
There is a sine wave at 240kHz from the switching in the amp, and while it is quite many dB down from the max output of the amp, it is constant regardless of amp level, and with an overpowered amp like this the signal is still 1.33Vrms. So turns out I need a RF filter to be able to check the output voltage with decent accuracy.
Not sure I will bother making a filter since absolute sensitivity figures are not that important to me, and at least after a little testing, trying to ignore the FR component from the scope readings, my meter read 105dB at 2.83V into 4 ohm at 1kHz. That would mean sensitivity of 102dB with 1W/1m, so I'm at least confident sensitivity is very good. I can have misjudged the RF component a little bit, but should still be over 100dB. When doing outdoor test I will also test with higher voltage to reduce the error from RF signal.
Hey there, I was just wondering if you do the coating for durability reasons or sound reasons?! I didn't find any info about that... many thanks for all the interesting information!
How thick is the poly-carbonate disk? Was there a drop in efficiency when you did this? Thanks.
The disks were 100mm dia, 5mm thick twinwall polycarb, the kind you use for awnings and light-weight patio roofs.
Due to its extremely low density (<34kg/sqm) EPS by itself is massively efficient in the midrange. And depending on on the acreage you use, it's pretty good for bass too. But because of its softness, it's useless for HF no matter how you skin it.
Twinwall is also quite efficient due to its low density (190kg/sqm.) It's homogenous in composition, but not as anisotropic as I would have expected comparing the stiffness across the ribs to that along the ribs. It's fairly hard between the front and back, but not hard enough for decent HF. I suspect either that the vacant space in the grooves between the ribs plays some role as far as cavity resonances go; or the ribs might collapse at HF in the same way the the voice coil formers collapse at HF in drivers (such as the DAEX 30HESF) with long coil formers.
Having said that, when the two materials are combined as described, the overall efficiency drops dramatically. So much so that I cannot use it for PA work, but it might be okay-ish for hi-fi, albeit with a rather beefy amplificator.
I think the disk, when attached to the hole in the EPS, drops the efficiency enough in the mid range that said midrange lines up neatly with the bass and HF extremes.
@Andre Bellwood I must disagree with the assessment that EPS cannot give enough HF. I played my plates to many 100´s of people, including several PA specialist and sound freaks, and have not had a single person complaining about a lack of HF.
I doubt that it is the GPS instead of EPS or the skin I apply. Those can make a marginal difference, but did not notice a major boost in HF compared to raw regular EPS. My guess is simply that my preferred house curve coincides quite well with the response of EPS, see my earlier post with a commonly recommended curve: https://www.diyaudio.com/community/threads/dml-pa-systems.390363/page-13#post-7630946
Are you tuning you PA flat? In that case EPS would need a lot of EQ, and the extra efficiency in the mids would be kind of wasted. But if we are talking full power PA levels, a flat response is not actually a desirable target IMO.
I doubt that it is the GPS instead of EPS or the skin I apply. Those can make a marginal difference, but did not notice a major boost in HF compared to raw regular EPS. My guess is simply that my preferred house curve coincides quite well with the response of EPS, see my earlier post with a commonly recommended curve: https://www.diyaudio.com/community/threads/dml-pa-systems.390363/page-13#post-7630946
Are you tuning you PA flat? In that case EPS would need a lot of EQ, and the extra efficiency in the mids would be kind of wasted. But if we are talking full power PA levels, a flat response is not actually a desirable target IMO.
Leob, aren't you using a higher-density graphite-impregnated XPS, not EPS? XPS has much higher compressive modulus than EPS, and could be the reason you're getting decent tops?
Yes, for HiFi, I run the EQ flat. But in any case, for HiFi, I'm trying to design a flat-response system to run without any DSP or EQ at all.
For live PA I usually (probably always) run the box speakers with a 6dB notch at about 200Hz, and with a rising response up to about 7kHz, assuming that the cabs are flattish in response. Of course this HF is wasted if one has an audience more than about 90deg wide from the stage, and I therefore toe the cabinets inwards to give a wider spread. For pre-recorded tracks I would pre-eq that channel to sound the same as the live inputs (generally a little less on the top end.)
No, it is enhanced EPS. I ordered a selection of the plates they offer here: https://www.dekokopf.com/styroporplatten/ and did some quick testing of how they sounded. I did not notice any major difference in FR compared to same density regular EPS, also 25kg/m3, but did find the sound a bit clearer and tighter with the GPS.
I really think we simply have different targets. For HiFi of course, efficiency is not that important, and for the plates I use in the studio at more normal levels I might boost HF slightly, but of course could instead use use a material with better HF. Having said that, I never thought really flat monitors are nice to work on either...gets fatiguing when spending many hours, and I just do a very small HF boost for regular listening levels and a small reduction for PA use.
I really think we simply have different targets. For HiFi of course, efficiency is not that important, and for the plates I use in the studio at more normal levels I might boost HF slightly, but of course could instead use use a material with better HF. Having said that, I never thought really flat monitors are nice to work on either...gets fatiguing when spending many hours, and I just do a very small HF boost for regular listening levels and a small reduction for PA use.
Unfortunately I don't have measurements for the different EPS materials I tried, so cannot say with certainty now what the actual differences where. But from what I recall from listening, it was a similar difference to when comparing the Daytons and Xcite, where REW showed lower distortion using the Xcite. So I think that GPS mostly help to contribute to the low distortion I'm seeing for my plates.