Here I will now include some tips and tricks I forgot to place on the original docs here on the site. I have felt compelled to do so due to a few mails that I have received from friends around the world. Here we go:
Aluminium conductor foil
I know this has been one of the very hard parts of this project, how the h… do I cut a perfect strip of aluminium foil that, to make things harder, is very fragile and then stick it on the membrane in an easy way?
Well, this is not my own original idea but I used it very successfully while building my model. In Chile there is a special type of paper that is used for chocolates, it is a waxed paper that on one side has a very thin aluminium foil, much thinner than the foils used for food. The only real issues was where to go in Chile to buy a sheet large enough to include the complete design in one piece.
I had to travel to Santiago and then go to a packaging industry, there in the trash (they didn’t sell any of that material, no surprise), I found some 10-15 meters of the stuff, enough and even some extra material I could use for future projects. The guy there could not believe I would use it to build a loudspeaker, he gave me his address so I could send him a picture… never did… but if he has access to Internet he might find this site one day… if he cares 🙂
In Denmark this paper is used to package sandwiches (well, the Danish style sandwiches smørrebrød) and can be bought in the right width at a normal supermarket (lucky them). If you live elsewhere you must see where you can find it – good luck – but it is very much worth the effort.
Once you have it, this is what you do:
You design your membrane by drawing it on the foil, then you use two very sharp blades stuck together, separated by a small coin or equivalent, be careful to align them well. These blades you will use to cut the covering aluminium foil without cutting the underlying paper, so be careful and control the pressure as precisely as possible (don’t do this after a long night or party). This way you will obtain the design by removing, once again, very very carefully, the thin strip created by the cuts between the blades. With some sweat and patience, you will have the complete design of the membrane on supporting wax paper, with the strips much closer and perfect than you could ever do by sticking aluminium strips onto the plastic membrane.
Now you stretch the plastic membrane on a table, attach the edges with tape and spray the adhesive onto the surfaces. Stick the aluminium side on the plastic membrane – be very careful when you flatten and remove any wrinkles on the membrane, the supporting paper is humid with the spray glue liquids, when the paper is wet it can easily tear, a horrible thing that happened to me killing one membrane…
Now it’s a matter of taking off the paper without taking the aluminium off… and that’s where the wax comes in handy, you use a hairdryer in the hot setting and heat the paper until the wax melts and you are able to pull it off from the aluminium! This is delicate too, but quite a bit of fun too.
The membrane material
Now another interesting subject is the membrane material. In the first model I used a rather thick Mylar membrane my brother had for windsurf sails around 50 um. (micrometers) and later I used a sticker material with golden colour of half the width.
In the second model I used what the original design recommended, two slit oven bags. I did not test them out before and the surprise was that the speakers became gigantic hygrometers, I was able to predict bad weather by looking at my speakers, they would go limp and stretch out on sunny and dry days… 🙁 This my recommendation is that you test the membrane material’s response
to humidity before you use it. Take a piece of the material, stretch it out over a frame and go into the bathroom and turn on the hot water and see if it goes limp. If it does change the membrane material.
I have since bought a roll of 12 um. (micrometers) Mylar for the next model, Mylar is a very resistant material and considering the good results I obtained in the first model I think this will help considerably with the next model.
The adhesive glue
Here is an interesting subject that can be easily overcome by using a very good, effective and easy to use glue made by the 3M company, free advertising I am doing for them, it’s a spray glue that comes in a black can, Super 77. This is the solution, follow the instructions given and try to use it sparingly and uniformly, practice on useless surfaces before the real stuff.
Once you have designed the membrane you’ll notice there are sections that connect the different portions of the conductors that are between the magnet poles, these are not contributing to the membrane movement, and therefore do not need to be between the magnetic poles, a way to have them do no harm by adding to the membrane dead weight is to place them outside the stretched portion of the membrane, that is on the MDF plate. This way the real portion that is doing the work is suspended between the magnets and the dead weight is lowered help in the efficiency of the system, at least a bit.
OK, that seems to be all for now, if I remember anything more I will add it. Hope this can come in handy for you all.