Yeah I'm sure that if I got some EPS that is the same density as my XPS their performance would be almost identical. The only EPS I've got is very low density at ~10kg/m3. I have plenty of NGX 150 and 250 XPS though, here's the datasheet: https://commercial.owenscorning.com/assets/0/144/172/174/4e330789-b09e-4cf0-b2d9-e16ed89ae5c3.pdf. Idk why they don't state density but ChatGPT says 150 is 24kg/m3 and 250 is 40kg/m3.
I wonder if you had considered pre sealing your panel to minimize the absorption of the shellac? This will result in less added weight along with a little less added stiffness but weight is the major concern here I think. The same could also be done when laminating ply panels.
Yes, you have to be very careful with the shellac, it can easily overdampen the panel. I have Hide glue as a first layer, and dilute the shellac much thinner than normally used when applying to furniture for example, about 4x the alcohol, then just paint one very thin layer with that.
when applying damping in the form of acrylic spray paint you were saying the panel was stiffened in both directions. ad you considered masking off the panel into horizontal strips so you would add desired stiffness to the width but leave the stiffness in the length pretty much unchanged?
Steve I understand why fiber glass cannot be used on Styrene foam ok so why not just make fiber glass skins then prime the fiber glass skins so what ever glue you want will stick to it and then bond the skin(s) to the foam core, or is there a problem I am missing?
the crate material was best guessed as a three ply poplar or similar? with what thickness? Approx. 3/16"?
No.... More versatile, water resistant, and maybe a stronger bond to most materials
So is the shellac finish simply foe aesthetics or is it intended as a stiffening skin or is it both? ThanksHi Christian:
I think you are correct wrt the poplar ply - It will be hard to surpass with more complicated and costly materials.
Shellac = French Polishing yes.
I'm far from an expert in this but I have achieved quite good results with a very basic approach. I'm also after a satin finish not a mirror gloss one.
One issue with poplar is that it has a very bland finish - it's very pale and the grain pattern can be uninspiring. I initially only had Gold/Orange shellac and I thought that it would end up too yellow by itself so I tried first applying a very light stain to the ply which worked OK but I think could be avoided by using a mix of Garnet (dark) and Gold shellac instead.
So I bought flake shellac in gold, garnet and platina (blonde). The flakes keep indefinitely if stored in a dry cool place unlike premixed shellac.
3:1 Alcohol / Shellac mix by weight is a good middle mix (just a bit thinner that a "2lb cut' but you can try different ratios. I thinned out the first coat somewhat for penetration.
I didn't do any grain filling - I relied on judicious sanding back between coats which worked OK - I wanted to avoid too much junk in the panel and I don't mind a trace of grain showing. One luthier uses West System epoxy to seal the back and sides of open grained woods but not the soundboard ()
Application- I have tried the traditional cloth method but it's difficult and takes much practice. I found that with practice I could brush it on quite well. When brushing you have to be quick and only brush with a forward or backwards motion, not both, work from one end to the other as evenly as possible across the panel and avoid going back over wet areas. Apply enough to the brush to get a wet finish and as soon as you start to use the brush load up - dip again and go - it's important to get a flow going so you end up with an even wet coat. I used a 30mm wide brush and stored it in a jar of alcohol between coats.
I haven't tried spraying, but it seem to be an ideal candidate as it's very thin and is easily cleaned out afterwards. Maybe I would revert to spraying if my panels were larger - long narrow panels would still be easily paintable however, it's when they start getting wider that makes it a bit more difficult, but you could probably just use a wider brush
It dries very quickly - I help it along with a heat gun on a low setting waved over it if I'm in a hurry.. make sure it's not dusty if you do that.
You can sand back after each coat dries. I use worn 240 grit paper or fine wet and dry paper.
I applied 4 coats sanding between each, and to remove the gloss after the final coat (which after 4 coats is still a bit uneven) I rub down with grade 0000 wire wool which blends the finish and gives a satin look.
I found the shellac finish is surprisingly tough - tougher I think than acrylic lacquer, so I believe it's and excellent way to finish timber in general - I applied it also to some pine feature strips and it turned out great. It's only drawback is sensitivity to moisture on tables etc but that doesn't apply in this case. It's stood the test of time on musical instruments so that's good enough for me.
Oil - I used no oil - I haven't had any issues with the finish on vibrating panels so I can't see the need for oil.
Go for it Christian
Good Luck
Eucy
Steve with respect to your thin card panels it would be very helpful for those (in world wide locations) who may want to replicate your work if you could provide some basic information about the card stock A visit to a art supply shop could provide information as to card stock thickness weight /stiffness/density etc. from paper suppliers so that others can purchase material to replicate your results. For those like me I can go down to the recycle bins in my apartment bldg and pick out what ever samples there which appeal to me but I too might like to make one just like yours so I have a reference. At the beginning of a building journey it is always nice to have a reference. Thanks
@Eric, @homeswinghome, et al,
I've been trying to get my teeth into LISA FEA, thanks for the very helpful guides, Eric. I've been having fun modelling different shapes with different properties.
Two questions:
1. How would I model a panel assembled from different materials, for example a polycarb plate with a hole in it, and an aluminium disc inside that hole on which the driver is mounted.
2. How would I use LISA to find the coincident frequencies of different panels? None of the equations I use give me consistent or believable results. I've been having arguments with ChatGPT regarding this, and we've eventually agreed to disagree....
Steve what about a veneer in a pie pattern made up of wedges where the grain orientation alternates between straight from outside to centre to across the pie shape? in this way a three layer lamimate could be made where centre disk is offset by one slice from the top and bottom layers?
Steve what is overall dimension for this panel along with the thickness please? The Shirley Horn clip does sound good thanks. Would you say that your double 0.5 mm small card panels (I think they were around 6 - 8" dia ?) do they sound like this?
Steve are you bonding the package label sides together so the sized and print surfaces (probably provide some additional stiffness) are in the middle o the ply? then normally two full strength coats of PVA on the exciter side of the panel and two half strength coats of PVA in the front side? Have I got the recipe correct? Does exact panel size make much difference? What would you normally make the size format ratio? I think you mentioned 6x9 inches? I want to build a panel like this first to see what it will sound like. Thanks for answering my questions.
I've been playing with DML's for about fifteen years.
It is my opinion that one exciter per panel yields the best results.
Here is a photo of a prototype pair. I used corrugated plastic for panels. (Not the best material.)
stacked four panels isolated from each other. One exciter per panel. All panels were suspended
with duct tape.
They sounded pretty good and had plenty of volume. Bass was decent to 70hz.
It is my opinion that one exciter per panel yields the best results.
Here is a photo of a prototype pair. I used corrugated plastic for panels. (Not the best material.)
stacked four panels isolated from each other. One exciter per panel. All panels were suspended
with duct tape.
They sounded pretty good and had plenty of volume. Bass was decent to 70hz.
Attachments
wow that is amazingly smooth response so this is full range and goes down to what 40Hz.? what size would the material need to be to go down to only 100 Hz.? What material is proplex and how does it fair so far as efficiency goes and what exciter was used? Thanks. (does it sound as good as it looks?)
Steve these sound wonderful with lots of energy but they are well composed. so is this the white soft ps foam or the higher density expanded foam? what size were these panels? thanks.
I was co founder of Higwood Audio, we developed a planar magnetic travelling wave transducer using 150 gage HS Mylar it used wave traps at the outer edges and acoustic filter/loading across the panel it was driven by a single layer voice coil 1.25" dia and had a small centrally mounted dust cap to extend response. A heavier diaphragm would have been nice. We also terminated such diaphragms with polyester silk screen mesh which has very high loss and is available in a wide variety of weights. Some damping was added to the silk screen.
Hi Moray
I'm very interested in this... Can you please provide more detailed info on the construction
Thanks
Eucy
Edit...I found an article and realised I also had the patent downloaded... Will re-read with interest
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Our patent was applied for just a short time before the original Manger patent and blocked them. Manger contacted us asking if they could licence the technology or failing that suggested the two companies merge. We declined both options, at that time we were just too busy with a start up company. Our speakers were marketed under the Sumo Audio name. Things did not work out with Sumo which was too bad and we merged with Meitner Audio in Montreal. The speakers were then called the Melior 1and 2 along with an in wall speaker and some hybrid models but those were after I left the business Ed still lives in Calgary and runs EMM Labs with his son.
The Highwood panel had the voice coil placed in the centre of the panel for a specific reason, we did not use a spider on our motor rather we use a magnetic fluid in the v gap a a liquid bearing to replace the spider. This necessitated keeping tension on the vc as even as possible during motion. The DuPont Mylar HS is a biaxially oriented film which helped keep the vc stable. Hope this helps and is of interest.
The Highwood panel had the voice coil placed in the centre of the panel for a specific reason, we did not use a spider on our motor rather we use a magnetic fluid in the v gap a a liquid bearing to replace the spider. This necessitated keeping tension on the vc as even as possible during motion. The DuPont Mylar HS is a biaxially oriented film which helped keep the vc stable. Hope this helps and is of interest.