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capslock 30th September 2002 06:09 PM

diy paper pulp for stiff sandwich cones?
I wonder if the stiffness of a polyprop woofer can be improved by adding a little paper, maybe even wrinkled like Scan Speak does.

In primary school, we soaked newspaper sheets for days in wallpaper glue (the powder that you mix with water) and applied the sheets as they were. A variety was shredding egg cartons to make pulp.

Any experience on preferred paper or pulp? Would white wood glue be better than wallpaper glue?

How would one best make a long fibred pulp? Maybe one could add glass fibre to the pulp? Or some other fibres if sources were evident?


navin 30th September 2002 06:23 PM

polyprop is heavy enough without more mass. mass might help if you want to lower a Fs of a speaker but for small midbass drivers it seriously affects their ability to reproduce higher freqs.

it all depends on what driver you are working with and what you intend doing with the driver.

if you wanted to add mass without the need of making the cone any stiffer you can add silly putty to the dust cap (in the old days we would tune passive radiators this way).

all things being equal i prefer doped paper to polyprop. but that is a personal preference.

if you want to make polyprop stifffer the best way is a thin layer of resin or some other light liquid that will dry stiff.

capslock 30th September 2002 06:44 PM

Don't mind the membrane getting heavier (Morel H6.1).

navin 1st October 2002 09:38 AM

it will limit the HF respnose of the driver. if you add mass and stifen the driver it might make snese to use resin. i would suggest a few thin layers of resin but youd have to be able to measure the added weight of teh resin. the way i would do this is weigh the resin before applying then weight teh remaining resin and substract.

the paper if it does not bond well will cause problems

capslock 11th November 2002 09:39 AM

Experimented with banana paper. This is an "environmentally friendly" gift wrap paper that you can get here. It consists of very thin , long fibred paper and has occasional pieces of banana pulp (maybe 30% of area).

I soaked two pieces in cheap wallpaper glue (with some polymer filling) for 12 hous and deposited them on a piece of newpaper, on top of each other and giving the second piece a bit of wrinkling. The stuff took about a day to dry, but it became very hard and stiff and weighs close to nothing (after all, the glue reduces to the original weight of the powder, which is 20-40 g per liter).

There are some heavily polymer filled and somewhat humidity resistent wallpaper glues, and you don't need to use many more g per liter. Might be a way to optimize stiffness and damping.

Next paper to try might be the local #1 Kleenex which is called Tempo. They advertise a new composition that makes the tissue stay together if you inadvertently forget to remove them before the laundry.


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