Dust Sniper (quiet extractor system)

Step 4 Enclosure construction - material choice & general notes

On average, people in the UK trade their kitchen in for a new model every four to five seconds (I may have made that up) - that is a whole lot of kitchen worktops being thrown out and replaced. Indeed, composite wood counter worktop seems to be one of the most commonest things to pop up in skips here there and everywhere. That was of course, until I thought of using it to make part of the enclosure - being MDF'esque, dense, stiff and heavy, it should be a useful material for sound proofing. After looking and incredulously not finding any kitchen worktop for some time ("Credit crunch curtailed peoples propensity towards kitchenocide, discuss."), freecycle came up trumps and delivered an ample bounty of fire door material.

When I went to collect the two freecycle fire doors, they were actually getting rid of four of them (nice big heavy strong composite things), some kitchen worktop, and some useful bits of hardboard too - score! I ended up using some of these bits to make the DS and having plenty to spare besides. 

When it comes to making sound enclosures, those 'audiophiles' and DIY speaker builders are somewhat ahead of the game - by that I mean they are quite happy to try experimenting with unusual materials and techniques and also perfectly willing to share their experience and knowledge. We can learn a fair bit from their build techniques and material preferences.

Here are some things that speaker enclosure makers experiment with that you might be able to scavenge or otherwise get your hands on:

• Plywood (without voids is best), mdf, hardboard, etc. All these laminated sheet materials are rigid and easy to construct into airtight enclosures - look out for them turning up in skips.

• Plasterboard - Used extensively in construction, can be laminated with acrylic latex-silicone caulk to provide very effective damping.   

• Sand. This is well known as a good dampener of sound, I used some of this in the DS and also to damp my bandsaw. Best of all it is free if you know where to look (a beach might be a start, though in the UK it is technically not legal to just take stuff off beaches).  

• Oil based plasticine. This is the stuff that never really dries. I have no personal experience with this, but apparently it can be rolled into flat sheets and adhered to panels to damp sound.

• Scrap steel, can be used to stiffen up panels, and to change their resonant frequency. angle iron makes excellent bracing because it can easily be screwed (and glued with damping glue).

General construction points:

1. Use lots of glue to make joints air tight. The reason for this is twofold: one, so that we can control the flow of air leaving the vacuums and make sure it is filtered and clean, and two, so that no sound escapes. Even little cracks can make a big difference to the sound reduction index on an enclosure - think about a car window - opening it just a little makes a big difference to the noise you can hear outside.    
2. Ensure straight well fitting edges - all gaps must be filled. 
3. MDF and chipboard resonate at averagely 150-400 Hz, with the strongest resonances usually at 250-300 Hz. All materials when they vibrate produce sound waves, so If we don't brace it properly we may have small movements in sides of the DS, but because of the area involved even this could be quite loud. 
4. We need to treat both structural borne sound (so called 'impact sound') and airborne sound. The first involves mechanically isolating any sources of vibration with the main structure of the enclosure. The second, ensuring that we have good rigidity and mass.
5. As I already mentioned, when we add bracing to panels, we want to divide up the various panels into sections of unequal area. If not there is a chance that you will have several panels with a common resonance frequency that will combine (and sound loud).