Gearslutz.com - View Single Post

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.

8th June 2009	#1
Nordenstam Lives for gear Joined: Aug 2005 Location: Norway Posts: 1,741 Thread Starter	Styrofoam 2D diffusor 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.