Styrofoam 2D diffusor

Nordenstam · 8th June 2009

Hi board!

Just finished the prototype. The get-some-hindsight-in-advance run, to be more honest! It worked. Learned a lot.

It's blue styrofoam, 32kg/m^3 IIRC. It should be reflective enough above 500Hz, hopefully

, while also providing a bit of mid low frequency absorption. The sheets come in 5cm thickness, standard 2x4 feet construction size. Made a cheap hot cutter jig to make 4 feet 5x5cm squares. Actually, on this one, 4.7cm cuts was used to make the 13x12 grid a bit more square. It's 61x60 cm now.

Here's the $2 hot cutter:

(click for bigger pictures)
A 2x4, some smaller wood strips for guides, a couple of nails and a guitar string. The power is provided from a charger with 6 volt output. The little amount of resistance in the .010 guitar string is fine enough to make it draw between 1 and 2 amperes. More than this melted the wire. An extra bit of wire is attached to one end. An alligator clip from the power supply attaches to this loose end, further or farther away from the cutting wire, giving freely adjustable temperature control in the cut. The extra piece of resistance glows red when the cutter is in use!

Variable temperature control details:

The wire burns the wood when it touches. And it keeps digging into the tip on the finger when I strap it up, giving the small blood stains around the binding post. Am also wearing glassed when dealing with the guitar string. Safety first!

Have gone through two wires to cut four sheets(50 4 feet "2x2"'s). Using the brass cleaner for solder tips to clean the wire between cuts. Be sure to turn on the power as you start and cut it once done. The styrofoam sinks a lot of heat while cutting, if you run enough power to do fast cuts, the wire will melt as soon as it's in free air.

The fire ******ant stuff in the styrofoam smells like death. Doing it downwind outdoors is near mandatory, unless you have ventilation extreme enough to handle toxic fumes.

Did each of the well cuts by hand. Found, after some cuts, that it cuts better in a certain direction. Namely, from the flat/unburnt/outside part. Going across, from hotcut to hotcut side, gave a coarser cut. Used a sharp thin kitchen knife to do each cut. Got the hang of it after a hundred cuts.

As for styrofoam itself, the price almost made me balk when I first ordered a package! Though it lasts well. There'll be 6 to 12 diffusors for each package, depending on depth. All in all - it's very verycheap. The $5 glue can adds a substantial part to the prize of this thing!

It's a 13x12 prime root 157 diffusor with 312mm max depth(about 1f foot), giving a sequence with 156 wells in 2mm successive steps. Measuring and cutting individual pieces doesn't take that much more time than just cutting. It's a time consuming thing anyway, so I figured another half an hour spent is well worth it. Getting the pieces in the right order took more time than the cutting! Placed everything in order without gluing it first. Had to double check everything just to make sure. Found two mistakes too, so it was worth it. Can't go through all that trouble and end up with errors in the precious math! :D

Scratch setup:

And here's the glued up thing:

Notice the sloppy tolerance. The guitar string slipped on the nails while cutting, giving uneven squares. There's a lot of small gaps in the diffusor now! Will try to find some silicone type thingy (whatever works on this type of plastic), to seal the seams and also make it more mechanically rigid. Will be more rigorous in the measurements in the next time. May end up having to modify the cutting jig to make it all a bit tighter. Making notches in the nails could help keeping the string in place.

Will build some shallower diffusors too, to have closer to the sweet spot. The 1 foot depth used here is for the far away diffusors. Figured it couldn't hurt to have some depth to it. It's borderline as to what makes sense, given the reflectiveness of the foam.

Was planning to spray paint them, but don't know now.. Everyone's who's been seeing it have commented on the color. In a positive way! There's an almost fluorescent quality to it, accentuating the cyberspacy feel of the design. Don't know if it fits my room though. Will have to give it a try. Going to start adding diffusion behind the listening position anyway, so I wont be staring into that thing all day! :D The 24 meters of cityscape in the 2x2 feet square looks a lot more in reality than the picture conveys. In all the good ways. It looks very cool.

e-cue · 9th June 2009

Quote:

Originally Posted by Lupo

Was planning to spray paint them, but don't know now.. Everyone's who's been seeing it have commented on the color. In a positive way! There's an almost fluorescent quality to it, accentuating the cyberspacy feel of the design.

Reminds me of superman's home.

Nordenstam · 12th June 2009

Glue! Glue everywhere. Disposable latex gloves have turned out to be handy.

Normal white glue(water based non toxic bog standard paper glue) works on styrofoam too. But it doesn't stick strong and it takes about a day to settle to a solid state. The special glues for styrofoam are more than worth their price. It's a stronger bond and it only takes about 10 minus to settle. Think it's based on silicone, but I haven't checked.

Normal household silicone, for wetroom sealing etc, turned out to be the perfect companion for styrofoam! It also acts like a (slightly flexible) glue, so it makes the fixture more rigid. Using a normal pump(like this) and a tube of clear silicone, it was quite easy to fill in the gaps in the styrofoam. Where I could get a reach - that is! The very lowest wells was hard to fix in the finnished piece.

Am onto glueing number two now. Still haven't learned to do perfect cuts of the sheets. There's still cracks. Will upgrade the hot wire fixture for the next round of cutting(pictures to come!). This time, I do both glueing and silicone sealing at the same time, a little by little. It's a lot easier to get a proper reach with the silicone that way. Takes more time, but the result is far better than trying to chaulk up the cracks after gluing the whole shebang.

As for the colour - nah.. It's cool on its own, but my meager mastering room is all warm and earthy colours. It crashes horribly with the room! Have ordered some spray boxes with non toxic water based colour, safe for indoor use. It'll hopefully work on the styrofoam without melting it.. Going for a gloss black color to start with.

To be continued..

Gohanto · 12th June 2009

Quote:

Originally Posted by e-cue

Reminds me of superman's home.

If there was a recording studio that accurately modeled their diffusion panels with the look of the Fotress of Solitude, and covered the rest of the studio in Superman memorabilia, it would be the greatest thing ever created.

Nordenstam · 16th June 2009

Hot wire cutter version 2!

Now with a thru going bolt with threaded end, some spacers and shims. The most important upgrade is that it's a lot easier to make truly flat cuts with this, as the guitar string can't move around in any way. Almost as important: no fiddling around tying up the guitar string! Insert into right height slot and tighten the wing nut. That's it! Much better.

With the spacers inserted, cuts can be varied in 1mm steps between 4.5 and 5mm. Also went up to 014 guitar string, got tired of the .010 breaking. Made some test cuts with it today and it is a lot more stable than the nail binding post cutter. Though, for those on the cheap, making a notch in the nail is probably good enough to avoid having the string slipping around..

Still waiting for spray paint.. TBC..

Guitar Zero · 27th June 2009

Cool project. I bet it would be really cool looking if you spray painted each size piece in a different color before gluing in on the board. Four colored skyline diffusor would look awesome.

Guitar Zero · 27th June 2009

By the way, this is a 3D diffusor.

Nordenstam · 28th June 2009

Hi!

Quote:

Originally Posted by Guitar Zero

I bet it would be really cool looking if you spray painted each size piece in a different color before gluing in on the board. Four colored skyline diffusor would look awesome.

Nice idea! Most of the paint would be wasted though, as it would be glued onto some other piece. If you can be bothered to do it, I'd love to see the result!

Quote:

Originally Posted by Guitar Zero

By the way, this is a 3D diffusor.

The litterature refers to diffusors with wells going in one direction only (normal QRD's etc) as 1D as they only spread sound in one axis. These are reffered to as 2D as they spread along two axes.

Am onto number four now. The cuts are getting better and the use of silicone is decreasing..

Nordenstam · 2nd July 2009

Babyfusors!

Compared to the 1 foot deep ones, these 6 inch PRD's looks almost flat.. :D Still very cool looking objects, though not quite as crazy looking as the other ones.

Four done so far.. Wonder if I'll start to hear any difference soon?

Anyone got a guess as to how many is needed to make any difference in a room with approx 100 square meters(~1000 square feet) of surface? The four done so far are ~2x2 feet (65x60cm). None of them are going to be near the first reflection points if that helps in the guesswork.

fabricaudio · 2nd July 2009

we used 18 for about 60 square meter ceiling, 3 rows of 6 pieces each. We have also some at the sides

http://www.gearslutz.com/board/4266420-post213.html

Nikolas

Nordenstam · 3rd July 2009

That's a beautiful tracking room! Kudos!

I may add that 30% of the room surface is currently covered in absorption and this is a listening (mastering) room only. The idea with the diffusors is to kill what's left of annoyance from the remaining flat surfaces, in addition to the obvious benefit of providing a richer reverb tail.

Nordenstam · 24th July 2009

Hi!

Quote:

Originally Posted by Mirage

Look like really Pro stuff to me...

Thanks! Have done a few more since last update, larger units based on prime 199 and 211. Bigger looks even better. Though the color is still bugging me. Have wrapped these in the thinnest fabric I could find. The visual effect is very cool, with the crazy innards being partially visible through the fabric, depending on how much light I throw in its direction. Though the fabric does kill some of the high end response.. Not sure what to do about that, may end up putting some posters or similar on some of the porous absorbers to get back some very high frequency reflections in the room. Or perhaps make some very thin diffusers that will reflect high end only, while letting deeper frequencies through.

Am still getting better at making these. The cuts aren't perfect yet and may perhaps never be. Though, it can largely be compensated for by making opposing pairs of fitting pieces. The error in the cuts generally runs across the full length of each 2x2" beam. So I cut opposing pairs, making sure these fit snugly together. Have also started to cut them in the right order. Much better! Started out by making all the cuts first and sorting them afterward. Turned out to be a waste of time compared to simply cutting them to the right length as dictated by the pattern, arranging the pattern as I cut. Much faster!

Quote:

Originally Posted by Mirage

Does it work in reality, against sound waves, i mean?

Haven't blind tested or measured properly. Never grew fond of the previous measurement solution I had so it just slipped into obscurity, a better solution will be up and running in a few weeks.

Did a quasi blind test with closed eyes, two 2x2 feet panels and a friend that covered and uncovered the units with a highly reflective blanket(impossible to blow through). The distinction was clear for both of us, but it's hard to say when it's not truly blind. Have also tried to make a wall of two larger and two smaller units, playing acoustic instruments in front of these. To my non-blind mind, it sure sounded sweet!

I don't see any particular reason they shouldn't work. The lengths are not perfect for various reasons, they're +-2mm or so, but still a lot better than the extremely coarse quantization of the BBC style units. The gaps are sealed with silicone, so there wont be too much viscous loss either. If the BBC style diffusers work, this surely should too!

Michael Loomis · 26th July 2009

Great thread. Thanks for doing this.
Do you have any idea how the use of styrofoam affects performance compared to wood? I certainly understand that weight becomes an issue very quickly when using wood (especially with the large diffusors)! But sonically speaking, can you get equal results with the lighter styrofoam material?

Thanks.

Michael

Nordenstam · 27th July 2009

Hi!

Glad someone gets something out of this thread!

Quote:

Originally Posted by Michael Loomis

Do you have any idea how the use of styrofoam affects performance compared to wood? I certainly understand that weight becomes an issue very quickly when using wood (especially with the large diffusors)! But sonically speaking, can you get equal results with the lighter styrofoam material?

Depends on frequency. The blue styrofoam is 32kg/m^3 and the lightest wood is about 2-300kg/m^3.. Quite a difference! The foam reflect down to about 500Hz where it starts absorbing, having a crossover zone with both reflection and absorption extending 1 to 1.5 octaves below that. Absorption works down to about 150Hz on this. So it should work fine for mid and high end, while wood/concrete etc can provide diffusion to lower frequencies, while avoiding the absorption - which may or may not be a good thing.

Nordenstam · 29th July 2009

Have looked into balsa too and came to the same conclusion as you. There are some types of cedar that have low density. Check it out if you want to shave weight off a wood construction.

The long cuts are made using the hot wire cutter fixture described above and the short cuts(each piece) is done by hand using a sharp kitchen knife.

Make sure the foam you use is dense enough. I wouldn't use anything lighter than what I have, 32kg/m^3. Denser is better..

Nordenstam · 3rd August 2009

Small update to show how it actually looks in the room. I dig the shapes in their own right, but I'm still trying to hide them.. The fabric will of course compromise the high end performance a bit. Have finally got around to purchasing a proper measurement mic/pre/etc, but haven't got around to set up the software yet. It's easy to remove the fabric covering for measurements. Will do covered/uncovered measurement series to check what really happens with the cloth. As for now, it works, aesthetically!

The lower part of the rear wall got some shallow 4" diffusers, since they end up being close to the couch.

Drop into the slot:

With cloth covering:

(click for bigger)

Hard to make a photo of how it really looks. The cloth is semitransparent and the end result is a subtle transparency, depending on lightning. Quite neat!

Nordenstam · 13th September 2009

An update on painting these things.

Styrofoam friendly acrylic spray paint works well, albeit quite expensive in the arts and crafts shop. Taking a piece of foam to the store to test the melting effect first is probably a good idea. Normal (suitable for brush) acrylic paint works well too.

Going for a lighter colour than the blue one in the styrofoam is hard work. It needs lots of layers to hide the blue tint! This "white" one have one layer of spray paint and two layers brush:

As can be seen, it's still blueish. Looks literally cool. Won't try to go for more of those white ones.. If I ever decide to do so anyway, I'll make sure to prime it first!

Darker colours, on the other hand, works well. This is a mix of bluish green and dark blue with some of the original light blue still shining through:

The styrofoam diffuser project V1 is now done. Have built 2 prime 127, four prime 157, six prime 199 and two prime 211, for a total of 2498 "wells" on 6.4 square meters. The primary goal was to breath some life and euphony back into the listening room, without harming the microscopic precision that comes with loads of absorption. Mission accomplished! The listening room is more fun than ever before.

EDIT: PS! Doh! Forgot the practical information. Sealing the cracks with silicone is good. If painting afterwards, the silicone structure will be accentuated and reliefed, giving the surface a rough look. Painting before applying silicone works better.

terry j · 14th September 2009

can you remind me, what is the deepest well you did?

It seems that prd's have the wool on qrds, 2d scattering etc. Been playing with the calculator a little lately...the BIG one we posited for the fireplace if you recall...(and ever mindful of my 'swings and roundabouts' theory in engineering) it seems to me the big disadvantage of prds is the depth needed for a given frequency. Compared to qrds these seem to get very deep quickly to get low.

I'm sure you have realised that as well.

I guess that is a lot of the reason attempts are made to make them out of styrofoam etc.

After having done that many, how much fine tuning did you need to do with your cutting jig, or did it get smoother/quicker at the end due to operator improvements?

Basically, what changes did you make to your procedure (if any) after familiarity, what changes would you make for any next round you may have in mind?

Well done, that is an awful lot of surface area!

Have you worked out how to measure any changes in your room? Where would you see those changes? (always hear about the 'reverbarent tail' or whatever, so what measurements would be best to see the changes)

Nordenstam · 29th September 2009

Quote: