I can't really answer....the surface is flat but doesn't really seem harder.
I think they are made in a similar way to the building isolation plates, expanding styrene granules into a mould, so I would think the surface is pretty much the same. It is possible that the building material is coated in chemicals to conform to building regulations that add an extra surface. Anyway, gonna sand one this evening and see if I notice a difference.
But I'm mostly concerned with the lacking HF response before I go further with any experiments. I wrote the manufacturer, and they should get back with some FR graphs comparing some of their exciters to confirm if the 50mm does in fact lack HF response.
Leob,
I don't remember from previous post if you have already mentioned the type of tape you use. I guess that than most of us, you use and reuse the exciters from one panel to the next one. For now I don't have really good replacement to the original 3M VHB. There are posts before about that (listed in the history file I post some time to time). Currently I use a thin quite strong double face tape but not strong enough to keep the exciter on the panel. A light panel can stay on the exciter the time of a test. Currently this one goes to about 10kHz. No problem in the low frequencies. I have an other one with the appearance of a mesh? with it the HF limitation is more severe. No problem in the low frequencies.
So in my experience, possible limitation in HF. No limitation in the low frequencies.
If the hypothesis that the band limitation is in the exciter to panel interface that mean you should hear it? Then too early for comparison?
Christian
Getgoin
In my knowledge there is unfortunately not such doc "where we are about DML". The best I can propose to you is the "history file" I try to keep update according to what I think to be relevant... So of course there is a filter in that. You will find a page about the DMLs with best details.
If you want to post details of yours, I will add them with pleasure.
No streaks. I do think he moulds the plates directly into the correct size, and doesn't cut with wire. Not sure if I would classify the scratch sound as hard and brittle really, and sounds the same if I scratch on an exposed area where some of the surface is gone.
I tried with glue and hairspray initially, but got some 3M 9088 that I have been using lately. It should be one of the thinner tapes they have, but holds my 200g exciter without problem.
If anything I had issues before with even more dull response, so unless the glue and hairspray was really lousy the tape is not the issue.
Shouldn't I hear decent treble just holding the exciter against the panel...or is FR always sloping like that unless you have the ideal bond?
Steve,
My dmls are 20" x 30" x 1"xps with Dayton DAEX320MB-4 exciters. They are pretty much modeled after the tech ingredient You Tube DMLs. I've added a sub woofer. I've only used xps. I've not ventured into XOs. The speakers are playing straight from the amp. In terms of size, 2' x 3' would be as big as I would want to go. Exciter support, edge attachment and frames, other materials than xps-- these (and others) are all areas that seem to capture a lot of attention in the thread. If you were to build something that sounds better than what I've got, what would it look like?
My dmls are 20" x 30" x 1"xps with Dayton DAEX320MB-4 exciters. They are pretty much modeled after the tech ingredient You Tube DMLs. I've added a sub woofer. I've only used xps. I've not ventured into XOs. The speakers are playing straight from the amp. In terms of size, 2' x 3' would be as big as I would want to go. Exciter support, edge attachment and frames, other materials than xps-- these (and others) are all areas that seem to capture a lot of attention in the thread. If you were to build something that sounds better than what I've got, what would it look like?
I cannot speak for Steve, but I would bullet the key design issues as follows:
- Panel Material
- Panel Dimensions, including ratios
- Panel Thickness
- Panel Treatments, including sanding, rounding, coatings
- Panel Clamping, Suspension, Supports
- Panel Edge Treatments, including Foam, Wood
- Panel Frames if any
- Exciter used
- Exciter attachment method
- Exciter Placement
Leob,
I had a look to your exciters (this link : https://www.alibaba.com/product-detail/50-100W-Powerful-8ohm-Flat-Panel_1600078111958.html ?)
It is not a standard quality specification to me : no information about the force factor (BL), the voice coil mass, its inductance, no impedance curve, no FR.. do you have some documentation?
A curious point is the nominal impedance : 8Ohm @1kHz and DCR = 3.6Ohm what I interpret as a 3.6Ohm resistance and some inductance in addition so that the impedance is 8Ohm at 1kHz which sounds like that as a strong high pass filter.
Could you confirm the DC resistance?
An impedance measurement would clarify the role (or not) of the inductance. Possible with REW and a sound card.
Christian
DC resistance is 7.8 ohm. Could very well be that they forgot to change it when they copied the information from the 4 ohm sheet. It is of course a chance to buy from a less well known brand, and even if they did have graphs I don't know if I could trust them.
Been really impressed with the amount of power they can handle and seems pretty much indestructible, but seem like I have to use another exciter or perhaps have some more mid focused plates combined with treble plates with smaller exciters.
Well... So it just says the specification is unclear. At least it is checked. Sorry no more idea for now.
Christian
Just to share a test to see where are the nodes and the type of modes. More detail in Application of Impulse Excitation for DML Design and Analysis #48.
In the family of the basic tests, this one shows that some modes can have mechanical vibrations with no sound
It shows also that the humps in the hundreds hertz are linked to modes or combination of modes.
Need further investigations but promising
Christian
In the family of the basic tests, this one shows that some modes can have mechanical vibrations with no sound
It shows also that the humps in the hundreds hertz are linked to modes or combination of modes.
Need further investigations but promising
Christian
Are you saying you've never actually experimented with XPS >5mm? I don't even have access to XPS that thin. The infamous videos that steered so many people to DML used XPS 5 times as think and you categorically dismiss it? I must be misunderstanding. I'm sorry.
@spedge Tried sanding the EPS, and perhaps it sounds a bit better...but if there is a difference it is quite small. Will AB with an untreated later, but perhaps these plates have a different surface that the typical building isolation plates.
Been looking for new exciters that offer high power but better HF response. Seller of my current exciters only had impedance graphs and could not prove FR graphs. I found that billionsound that supplies dayton also has a 50w 8ohm exciter that looks identical:
https://www.alibaba.com/product-det...l?spm=a2700.shop_plgr.41413.38.2ecc263bs2yHKy
They don't provide any FR graph for that model either, but they do for a very similar model but 32mm and 30w instead of 50mm 50w:
https://www.alibaba.com/product-det...l?spm=a2700.shop_plgr.41413.38.2ecc263bs2yHKy
That also shows a quite reduced HF response.
Main reason I went with an alibaba supplier was really that there was no exciters available with the same power rating elsewhere, but perhaps I should just go for the Dayton range available at soundimports.eu.
Any idea if it would be better to have for example 2x DAEX30HESF-4 per panel or 4x DAEX25FHE-4? Price per watt becomes slightly less for the DAEX25FHE-4, but don't know if many smaller exciters will perform better or worse than fewer but larger.
Been looking for new exciters that offer high power but better HF response. Seller of my current exciters only had impedance graphs and could not prove FR graphs. I found that billionsound that supplies dayton also has a 50w 8ohm exciter that looks identical:
https://www.alibaba.com/product-det...l?spm=a2700.shop_plgr.41413.38.2ecc263bs2yHKy
They don't provide any FR graph for that model either, but they do for a very similar model but 32mm and 30w instead of 50mm 50w:
https://www.alibaba.com/product-det...l?spm=a2700.shop_plgr.41413.38.2ecc263bs2yHKy
That also shows a quite reduced HF response.
Main reason I went with an alibaba supplier was really that there was no exciters available with the same power rating elsewhere, but perhaps I should just go for the Dayton range available at soundimports.eu.
Any idea if it would be better to have for example 2x DAEX30HESF-4 per panel or 4x DAEX25FHE-4? Price per watt becomes slightly less for the DAEX25FHE-4, but don't know if many smaller exciters will perform better or worse than fewer but larger.
Leob,
Would yours be more this one which is 8Ohm? RMD003215K02-BS
The hypothesis of a too high inductance seems serious.
The impedance graph of this exciter says 50Ohm @20kHz so something like 0.4mH for the 4Ohm, 95Ohm @20kHz for the 8Ohm so 0.8mH. In both cases this produces a Low Pass filter at 1.6kHz.
I wrote it before : my criteria to choose the DAEX25FHE-4 was low moving mass, high BL, low inductance. It was not clear for me but the idea was not to comprise the HF. Its inductance is given for 0.1mH which is not so low if we think in low pass words giving a cutoff at about 6.4kHz or something like 15Ohm @20kHz (4Ohm DC)
NaRenaud,
So it was the 3mm x 400mm x 500 mm panels that you got? The link showed 5 options but only this one was 3 mm, so I guess that's the one.
Eric
what I was trying to say was ,that if the EPS does not have the hard melted eps skin, then there is no point in sanding the panel .
the two exciters in your post are the same exciter, and the same as the one you have.
you also keep mentioning your 50mm exciter ? How does this 50mm relate to your exciter ?
The 30HESF ,according to their measurements seems to have a better frequency response ,than the 25THE ?
This is tested on 1/2 inch XPS.
Steve.