Updated Jan 17. 2007

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First Ribbon Speaker Prototype December 2006

 

One of my colleagues, and I have been working on this project for a while. We're only building Tuesday night after work, so the project is deemed to take a while, but with plenty of time for thought :)

The prototype is following the drawings found on the construction page, but the height is limited  to only 50 cm. Here is a number of pictures from the latest building sessions, and of the "finished" prototype.

To sum up the major difficulties in this project, and where we'll need to improve before bringing this further are:

  1. Construction of the membrane, cutting and mounting the voice coil.
  2. Stretching the membrane before mounting it on the frame
  3. Mounting the frame with the powerful magnets without damaging the membrane

 

Outer frame, perforated iron plate and spacer made of 4 mm plywood laid on top of each other.
A few screws inserted to hold the 3 pieces together, and provide a flat "surface" for the membrane.

The 3 rows of neo-dymium magnets mounted at the edges of the frame was mounted with rubber foam strips (used to insulate windows etc.) to work as dampers. Hopefully this will dampen resonances in the membrane and also reduce distortion caused by ripples in the membrane caused by a not optimal stretching procedure.
Here another picture of the mounted frame.

The membrane made of 6 um Mylar, with 11 um aluminum. The Mylar foil is really thin and not that easy to work with. The membrane was build using the process described by Dahlberg. Cutting the aluminum was not easy at all .... it took us some trials to an acceptable result. One wrong cut and everything is ruined.

We used spray glue from 3M

The membrane was stretched by fixing one side and having a weight in the form of two heavy pieces of long wood dragging it down over the other side of the jig.

Maybe not the most sophisticated way to do things, but it worked quite ok. Only problem is of course the top an bottom which will wrinkle some.

First try on putting everything together.

Not such a success :(

Misaligning the pieces during assembly will having the magnets on the front side and the back side attract each other instead of repelling. Remember that north should be mounted over north etc.

When this occurs, there is no way of holding the frames apart.

Result is a ruined membrane and a lot of hours of work wasted!!!

Here we go again. second try.

Things put together, but the magnets started mowing a bit. We used some liquid nails to fasten the magnets from the outside! ..... seems to work.

Next time we'll glue all the magnets into place before putting the thing together.

Screws mounted from the back side to hold every thing tightly together.

Now only the terminals for the membrane is missing :)

Final result
And seen from the back side.

And playing music :)

The sound:

Well as we only have one piece only playing from mid frequencies and up, it's a bit hard to judge.

But this in mind, it did sound quite good. Very clear and crisp. I would say electrostatic in sound.

Ok, next step is to make some measurements.

Frequency response front side

 

Directivity measurement

 

Polar plot