And just why do I need a new sub box? Well,I’ve had the old one in my car for over a year now,and as I go away camping quite a lot,I struggle to get all my gear into the boot,so I decided it was time for something a bit more compact to free up some boot space.
So what did I decide to go for,and why? Well the 12in sub I had before although capable of shifting a decent amount of air,wasn’t particularly tight or punchy,or at least not for my taste anyway.It’s fact of life that the bigger the cone,the deeper the bass they will give,but as the cone and motor assembly get heavier,the less well controlled the bass will be,if you’ve ever heard an 18in sub in a car,you’ll know just what I mean.
So I decided to go for a pair of 8in subs instead,this will give me almost the same surface area as the 12in had before,but as the individual cones are a lot lighter,they will sound a lot more “musical”.
I’d heard a lot about Vibes new Space 8 subs that have a very lightweight and thin aluminium cone,so they should be very fast and react to dynamics a lot better.They are designed to work in a 0.55cu.ft. sealed box,which is actually quite large for an 8in sub,as some 12s are capable of working in a box that small now,so I need to end up with a little over 1 cu.ft.,or actually about 1.2 cu.ft to also allow for the volume the cones take up inside the box.
The first job is to make a template where the box is going to live,cardboard is best,but if you don’t have any big enough then use newspaper as I did,but it will work just as well if there isn’t a picture of Alan Titchmarsh on it,and do try to get it as accurate as possible at this stage.
Transfer this to 6mm MDF,I used spray glue to stick it down,then carefully jigsaw around it but a few mm oversize.Offer the new template up to the car and file or sand it down until it’s a perfect fit,BUT NOT TOO TIGHT as you need to allow an extra 3-4mm clearance all round for the the thickness of the carpet or whatever you eventually cover it with.This template will also come in useful on the other side of the boot when I make one of the amp racks that will go there.
Draw round the template a couple of times on 18mm MDF,and then jigsaw it about 1-2mm outside of the line you’ve just drawn,clamp the template to the bottom of this with G clamps,and using a profiling router you can now rout it down the exact shape and size of the template.This isn’t really essential and an accurately jigsawed finish would be ok,but if you have a router it will save work later as it gives the straightest cut and smoothest finish at a DIY level.
AS WITH ALL POWER TOOLS,PLEASE BE VERY CAREFUL IF YOU HAVEN’T USED A ROUTER BEFORE.IF YOU TRY TO TAKE TOO MUCH OFF IN ONE GO IT CAN DIG IN AND JUMP,NORMALLY TOWARDS YOUR FINGERS,SO NO MORE THAN A FEW MM AT A TIME.
It’s normally reckoned that a sub box needs to be at least half as deep as the diameter of the sub,so in this case mine needs to be at least 4 inches deep.I got the guy in the sawmill at the timber merchants to cut my 8 X 4 ft sheet of MDF up for me to save me some work,including some lengths 4 inches wide.
I’ve found the timber merchants are normally more accurate than the DIY stores are when it comes to cutting wood like this,so even if you have to pay up to £1/cut as some places do charge,it’s worth it as mine was 100% spot on.He will also thank you if you come prepared with a diagram of exactly how you want your sheet of wood to be cut up and/or a cutting list,don’t just have it in your head as this is where misunderstandings and mistakes normally come from.
To cut the correct angle on the ends of the sides that have to butt up together,I make a template against the corresponding side of the front or back of the box,and then use this to set my chop saw correctly.Don’t forget that every one saw cut that you make will give you two pieces of wood with the angle you need.
I jigsawed and routed out the oval shaped cutout that will let the subs sit slightly below the front surface of the box,and made a baffle to go behind this that they will be fixed to.
Always do a dry fit with just screws before you get the glue out,to make sure everything fits to together as you intended,and don’t forget to drill pilot holes in the end you will be screwing into to prevent the wood from splitting,I normally use a 3mm drill with #8 screws @ 2 inches long.
Notice the off centre bracing to make the box stiffer,and the compartment at the bottom is because the total box volume of 1.8 cu.ft. was too big,this now brings it down to the required 1.1 cu.ft,it also has another unique use that I’ll cover later.
The box can now be taken apart and glued,I normally start with the front and the longest side firts.You’ll have to be quick with the glue,and don’t start doing the screws up until they are all in,and don’t overtighten them as well.
Give the glue at least a few hours to set if you need to take any screws out to rout or sand the edges to a pleasing shape,and when you’re happy (it doesn’t have to be perfect),you can cover it with carpet or the harder wearing trunkliner material that I used,I was lucky to get an almost perfect match with the OEM boot trim material.
If you’re using aerosol spray glue (or any other type of glue),spray some onto the back of the trunkliner to seal it,then some onto the box,and finally another coat onto the back of the trunkliner.I normally only do one panel at a time to help avoid having the material stick to itself.The excess can be lost on the corners by cutting as close to the surface as possible with some sharp scissors,and finally if there is a hidden face to the box,the loose ends should be stapled here.
I kept the piece of wood that was cut out of the speaker recess hole,and used it to stretch the material down onto the baffle until the glue could hold it properly.
The second to last job is a slightly mad idea that I had that may or may not have any significance at all,and involves filling the cavity at the bottom of the box with dry sand.The main reason for this is to dampen down any resonances that the box may have,and with the added bonus that is now so heavy that unless any thieving scumbag is a champion weightlifter,he won’t be legging it up the road with it under his arm.
This only leaves the subs to be screwed into the box and wired up,and it’s very important at this stage if they are new to leave the gains and bass boost turned down,as all new bass speakers will need at least 15 – 20 hours of gentle use before they loosen up enough to give their full potential.Turning them up while they are still new and tight to try and get bass out of them that they can’t yet give could damage them.
More stuff about it as below:-
http://uk-mkivs.net/forums/thread/977718.aspx
Chris.