Sunday, March 27, 2011
2011 - DIY Isolation Cabinet
Actually, the house starts to rattle a lot lower than that.
To give you an idea of what that equates to on the dial, it's about 30% on an Epiphone Valve Jr, position 2 on a Fender Princeton and about 10% on a Delta Blues. What might sound great for recording, doesn't translate to a good relationship with one's neigbours.
To get the maximum tone out of my amps and to keep things friendly, I decided to build an isolation cabinet to place a speaker cabinet and microphone inside. Simple enough idea, go get some plywood or mdf and something to dampen the sound waves. I totally over-engineered the box in terms of my level of skills.
I'm no carpenter, and it's fairly obvious by the end product, that maybe I should have gone down a much simpler path. But I've made my bed so to speak, and must lay in it!
The materials cost around $120 Australian all up.
Had I just built it out of 18mm ply or MDF it would have cost around 30% less, and taken about 80% less time too!
Anyway, the bill of materials is as follows.
5 x lengths of 19x70x1800mm cut into 600mm sections x 12
1 sheet 9x1200x2400mm Plywood cut into 8 equal panels (leaves two spare to make a pedal board from).
45 x12mm screws
One bag of R3 "Sound Screen" Rockwool
My plan was to make a finger joint for the front and back frame, connected by the side frames which were made as lap joints to the front and back. This arrangement in theory would create a perfect 600mm cube.
What I forgot to account for was the thickness of the plywood and my crappy skills getting in the way.
I'd bought a book on woodworking and gone out and bought a cheap set of chisels.
Only one of the chisels was sharp enough to do any cutting, and by the time I got through making one pocket for the finger joint, it was immediately apparent that I was not going to finish the project in a short amount of time. I'd recently bought a plunge router attachment for my Dremel, and wanted to use it, but had never actually played with a router before. So I put together a jig and fooled about until I had a working setup.
The jig worked ok, but wasn't exactly at the right height to work effectively. Also I think the Dremel itself isn't quite up to the task of making the depth of cuts required for an accurate join. I experienced a bit of shuddering in the slot which caused uneven fingers and pockets as well as at one point, the depth guide failed and I plunged too far into one pocket. After all of this I was getting the hang of the tool. Close to completing the routing and having a set of fingers that would work ok, the Dremel stopped dead in it's tracks.
I ended up reverting to a saw and chisel arrangement that was less than ideal. I lacked to tools to do the job accurately, and often I lacked the patience and just rushed the cutting, only to have very uneven joints at the end of the day. Somehow I managed to get the front and rear frames glued square. But at some later point, I forgot to do this when trying to get the cube assembled. I'm a family man and have responsibilities, so I was often called away from the job. Due to my impatience to get on with it when I returned to the task, errors began to creep in. The final product means that it's mostly square, but not quite. Front, back, sides and bottom are all ok, but for whatever reason, the lid is not.
It was all glued up in a day, and while that set, I put the panels on. Everything seemed fine, and after letting the wood glue set for an hour or so, I began to implement the rockwool. This is an itchy business. The insulation is quite thick and difficult to compress via hand. I'd also run out of timber, so that I couldn't add any mechanical force to press the rockwool against the sides of the box.
Out of desperation to complete the job before the daylight faded (I have to work outside) I placed my Epiphone Valve Jr cabinet within the frame, inside the exposed rockwool. It was obvious right away that this had the potential to tear the insulation on insertion and removal. Since the shops were closed, I decided to cut up the tarpaulin that covers my work bench. I'd cut it in roughly 700mm sections that I could place over the rockwool and stapled it around the opening in the cabinet. The tarp is plastic and made the cabinet slide in and out of the box easy and reduced the amount of particles that would be kicked up, reducing the skin irritation caused by handling the stuff.
After sitting about for a week, due to weather and having to work my day job, I decided to change out the tarp for a rough hessian weave. This isn't completely impervious to the dust and itchiness from the Rockwool, but it doesn't make a crinkling sound when moved about, nor is it reflective like the plastic of the tarp.
I tested the cabinet early in the afternoon, with my Epiphone 12" extension speaker driven by the matching 5w head. It did ok, but there was a lot of bass being let out at maximum volume, which was a little dissapointing to say the least. If it didn't cope with five watts, what chance did it have when three times the power was put to the test? As it turned out, I needn't have worried. Insulation in the lid, wasn't a perfect fit, so I augmented it with a picnic blanket! (Simply because I didn't want to mess around with the leftover Rockwool at this point). I'd adjusted this and then plugged in my Fender Princeton Reverb, the results were more in line with what I expected.
The bass trap absorption in the cabinet isn't great, but even when the amp is at full volume, you can have a conversation at a pretty normal level. The house does vibrate a bit, and I'd done the initial test in the kitchen which has a tiled floor. I spoke with one of my neighbours about it and he told me that he could only just hear it whenhe opened his front door. A good sign! The tone from the speaker and microphone is good too, not boxy compressed sound, it just sounds like the mix is up against the grille cloth(which it is). The box isn't air tight, which might actually be a good thing from what I have read.
Were I to do this over, I'd just get a 1200 x 2400 slab of 18mm thick ply cut to size and glue that together, rather than messing about with crazy joinery that I clearly wasn't up to doing well.
Sound samples and more pics to come.