Yes , And the 80 x 40 panels could have 3 mm Poplar glued to the canvas , while the 60 x 40 panels could have 10 mm EPS glued to them.
If we work out one day how to produce Subs from a DML then that can go in the center panel.
What contrast and balance that gives without EQ ? I dont have the experience to predict it yet , I am 10 - 15 years behind the wisdom of some people on this page.
Being Chinese made "canvas" it could be closer to plastic than any traditional art canvas so the construction aspects would need alot of experimentation
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I am not sure you will enjoy doing that on a mill , the plys will grab and rip out , it will bulge up with heat and grab the cutters even if you have ceramic inserts , maybe try an orbital sander with #240 and take off half of a ply thickness in a radius around the outside perimeter ?
The panadol consumption might cost more than the job.
Deude... Put the ply sheet on the bathroom scales and convert those lbs to real mass units 🤭
For one blinding, millingth moment I thought you were serious...😵💫😱💥
Shame about the human lifespan
Regarding discussions about USB mics. There are two calibrations:
One calibration is for flat frequency response where the mic has a (downloadable?) calibration file that goes with it.
The other calibration is for absolute SPL.
Even a USB mic does not have an absolutely flat frequency response and therefore needs a calibration file.
But the SPL level, I assume at 1khz, into the UBS port, can be an absolute reference level that bypasses the internal gain stages of a computer sound interface.
Thirdly, one can use cell-phones to get a rough estimation of absolute SPL level and use this reference to set up the test mic SPL calibration on REW.
You would set up your test system with your speaker-under-test and your measurement microphone properly distanced, and then run REW's test signal through that system. Your cell-phone can then be used (at the microphone position) to check absolute SPL, and then reference that back to REW. It's not squeaky-clean, but it does get ball-park figures.
One calibration is for flat frequency response where the mic has a (downloadable?) calibration file that goes with it.
The other calibration is for absolute SPL.
Even a USB mic does not have an absolutely flat frequency response and therefore needs a calibration file.
But the SPL level, I assume at 1khz, into the UBS port, can be an absolute reference level that bypasses the internal gain stages of a computer sound interface.
Thirdly, one can use cell-phones to get a rough estimation of absolute SPL level and use this reference to set up the test mic SPL calibration on REW.
You would set up your test system with your speaker-under-test and your measurement microphone properly distanced, and then run REW's test signal through that system. Your cell-phone can then be used (at the microphone position) to check absolute SPL, and then reference that back to REW. It's not squeaky-clean, but it does get ball-park figures.
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Pink noise vs white noise.
If one sets up a white noise periodic signal under REW (RTA synchronised with the Generator) then one can get live results very close to swept-sine measurements without actually doing the swept sine.
I use this RTA method for finding exciter positions, and then with swept-sine to confirm.
White noise contains all frequencies with equal distribution, whereas pink noise has more power at lower frequencies and less at higher frequencies, making it sound bassier.
If one sets up a white noise periodic signal under REW (RTA synchronised with the Generator) then one can get live results very close to swept-sine measurements without actually doing the swept sine.
I use this RTA method for finding exciter positions, and then with swept-sine to confirm.
White noise contains all frequencies with equal distribution, whereas pink noise has more power at lower frequencies and less at higher frequencies, making it sound bassier.
It might be also an effect of your very large room dimensions. The effect of the distance between the panel and the surrounding walls is not well documented (or not clear in my mind!). If you move the panel closer to the side and rear wall, you might get "more classical FR"? Making outdoor measurements won't probably show big difference with those one.
This is an interesting characteristic of DML in room reported several times. It is also the reason an average measurement over the listening space is not as important.
Yes. Close to a line array behavior but without the drawbacks
For poplar plywood, I would have expected a little wider HF extension. Have you already checked your test set up against known speaker (tweeter)?
Same conclusion here but still no EQ... after months of use, that's ok.
Keep us inform
Christian
Yes for sure. That diagram I posted is to scale. The panel is oriented vertically (long edge flat) roughly in the middle of the floor but offset a few feet along the length of the room. The measurement mic was about 11 feet away from the panel.
Agreed! That is the reason in fact why I am building these for this space. It is a workshop so there is no single sweet spot to set up and tune for. I thought about line arrays, and they are pretty magical when done correctly, but I do not want to go there for this. Too expensive.
It is actually birch since I could not find poplar ply locally.
I was testing another set of speakers with the same mic/system a few days ago and the response of those (on-axis) was right at one would expect based on the manufacturer's response data. I don't think that rolloff at either end is the mic.
Will do.
OK all, finishing these birch wood panels... I want to apply something just to protect it from the elements though the panels will be used inside. Reading through the threads it looks like shellac has been successfully used as the lone sealant; this makes sense since it is commonly used by luthiers for acoustic string instruments. I am also thinking of spraying since I have a big compressor and a decent Devilbiss HVLP spray gun.
Spraying will work fine... Shellac shrinks on drying so either weigh them down or do both sides .(or both)..1/4" ply will be 5 ply I guess so will resist curling more than thinner 3 ply
Light coats will also help reduce shrinkage
Eucy
@Eucyblues99 thanks for chiming in. I saw your previous posts about shellac, including the shrinkage, so I get a chance to say thanks for that. I will probably stand it upright and coat both sides at the same time, and go with light coats. I'll watch for warping.
That's what struck me but how to hold the exciter in position is still a bit of a problem. It would be nice to be able to just move it around. That could be achieved by arranging it to be pressed onto the panel with some degree of force but that will flex the panel. I have a feeling that at lower powers that may not matter. That based on exciter parts have limited travel just like loudspeakers have.
LOL I don't like Dayton's idea. Move it around by hand and listen to the tone.
Thanks for the posts Leob.
You must have experimented alot with these coatings so thats very valuable to me , i didnt begin any coating yet so i can make sure i have refined the process as much as possible in my mind before i put a tool near my EPS.
I have options of 200 gram or 400 gram double bloom Hide Glue , which did you find best ?
The instructions i found appear to indicate a consistency of "running flow" off the brush , then add your 3 - 4 parts water and bring back to 60 c for application.
Did you also apply the coatings on the edges of the sheets or faces only ?
Did you apply the coatings where foam will be adhered for structural mounts or did you leave the attachment surface taped off to allow a good bond ?
The Shellac method is clear enough with a standard mix diluted 1:5 with alcohol , Is ethanol required or will methylated spirits do the same job ?
Eucy also mentions using weights to counter the bending from surface tension so i will prepare something to counter that.
Does the hide glue smell still linger after the shellac coating goes on ? My wife owns a cat so i will have to watch it doesnt try to chew a hole in the panel
I did haste quite a bit, and would like to make more experiments, and of course the material used will require a bit different treatment. Main point is really to use a high dilution since it will dampen a lot more than at least I expected.Thanks for the posts Leob.
You must have experimented alot with these coatings so thats very valuable to me , i didnt begin any coating yet so i can make sure i have refined the process as much as possible in my mind before i put a tool near my EPS.
I have options of 200 gram or 400 gram double bloom Hide Glue , which did you find best ?
The instructions i found appear to indicate a consistency of "running flow" off the brush , then add your 3 - 4 parts water and bring back to 60 c for application.
Did you also apply the coatings on the edges of the sheets or faces only ?
Did you apply the coatings where foam will be adhered for structural mounts or did you leave the attachment surface taped off to allow a good bond ?
The Shellac method is clear enough with a standard mix diluted 1:5 with alcohol , Is ethanol required or will methylated spirits do the same job ?
Eucy also mentions using weights to counter the bending from surface tension so i will prepare something to counter that.
Does the hide glue smell still linger after the shellac coating goes on ? My wife owns a cat so i will have to watch it doesnt try to chew a hole in the panel
The glue I use doesn't specify bloom factor, I get it from a building restoration shop in Sweden.
It is suggested to use 1 part granules and one part water for normal carpentry use. So using 3 parts water would be like using PVA diluted 1:1 with water, but that will be on the thick side. For best results, let the granules soak for an hour, then heat it up while sirring and use when it has reached 60 degrees. At 65-70 it starts to degrade.
I use cheap rubbing alcohol mix, I think mix of iso and methyl, and seems to work fine. I think that if you are doing a french polish, to get prefect shine you want something very pure to avoid any water content that will not dry as cleanly, but I don't think it will affect the sonic properties.
I haven't experimented with coating the edges, and like I mention do both sides very quickly to avoid bending and haven't had any issues with the 20mm GPS plates doing it like that. I don't glue the edges but clamp them, and cover the whole surface.
The hide glue does smell, and it will linger for some time also after coating. My dog is very curious since they smell like his treats, but so far he hasn't chewed up any plates