Another DIY ribbon progress thread

[Audiophilenoob]

I decided to post some progress pics of my current DIY LCY ribbon copy

the magnets are 1/2"x 1/2" cubes and there are 6 per side of the frame...... and are N50

steel is precut 1"x.5" in sections to make the box and it's 1018 grade

I haven't connected the sides together yet... but that's the really easy part

the gap is .75x1.5" long like the LCY... however it's pushing .95T with the N50 magnets

Couple of quick thoughts I'm having


it was REALLY hard for me to even approach flushing up the magnets inside the gap...

what I was thinking was to lay a thin layer of epoxy over all the sides of the stacked magnets... and on the side facing the gap I was going to lay a very thin (probably 1/32" thick) layer of bondo... and sand that down till all those divits are level...also the magnets themselves aren't always level anyway

this would allow me (I did some prelimenary tests) to come to less than 1/32" between the 4.3 micron ribbon material and the magnets... also the gap would be a uniform .75" wide


Also I was going to weld these pieces together (they are just sitting there for camera shots).... however I wasn't sure I should weld with the magnets already in place (they're too strong to have made the frame first).... should I just go ahead drill and tap them ?

that's certainly very easy and I could do that in under 20 min to both

[Audiophilenoob]

another pic....

[LineSource]

You do not want to expose the magnets to any heat. They will quickly lose their magnetism, and will likely crack at higher temps. Most NdFeB magnets also have a nickel plating which easily chips off.

Some ribbons place a strip of polyimide tape along the magnet pole to create a continuous smooth surface next to the foil. The tape also softens any rubbing between the ribbon and pole pieces. I have not seen bondo.

To hold the magnets in place on the pole pieces I bent stainless steel sheet into a "flat Z" shape that went 0.3" over the edge of the magnets and screwed onto the pole piece. No glue could hold large NdFeB magnets as the plating would tear off.

For longer ribbons a 2 axis stainless steel vise allows accurate magnet placement. Each pole is built separate and then very long screw rods and may 2x4 wood spacers are used to guide the two pieces until the screws can be aligned and tightened.

[Audiophilenoob]

Originally posted by LineSource
You do not want to expose the magnets to any heat. They will quickly lose their magnetism, and will likely crack at higher temps. Most NdFeB magnets also have a nickel plating which easily chips off.

Some ribbons place a strip of polyimide tape along the magnet pole to create a continuous smooth surface next to the foil. The tape also softens any rubbing between the ribbon and pole pieces. I have not seen bondo.

To hold the magnets in place on the pole pieces I bent stainless steel sheet into a "flat Z" shape that went 0.3" over the edge of the magnets and screwed onto the pole piece. No glue could hold large NdFeB magnets as the plating would tear off.

For longer ribbons a 2 axis stainless steel vise allows accurate magnet placement. Each pole is built separate and then very long screw rods and may 2x4 wood spacers are used to guide the two pieces until the screws can be aligned and tightened.

on one magnet I accidentally chipped a very small corner of the nickel off... in the pics those "crusty" spots are actually glue .... it was hard to not get it on my fingers (on my face when the two magnets would smash the glue and splatter it)

tape isn't a bad idea and something that seems like it would work

I'm really glad I didn't weld them... it didn't seem like a good idea once I thought about it... electricity and heat

I'll post some pics tomorrow then the frames and magnets are all together and such

This glue is enough for my applications... however for a longer ribbons or a taller/wider magnet I could see where glue would NOT work properly... a type of "chamber" like you suggested would definitely be in order...

as far as pricing goes... it was only $32 for the 24 magnets needed to make 2 LCY copies

[Irwin AR]

Ahh.. i'm sure i'm gonna have a good time following this thread.
Keep it up guys.

[tade]

how do i measure my field gap strength? i dove intor ribbons with little to no research. Mine are made of good strong magnets, but which have no return path. Mounted in wood... oh well, perhaps my university has a measuring device for it.

[LineSource]

You can build a Gaussmeter from a Hall Effect device. A calabrated Hall Effect device is about $60, but uncalabrated are $2-$5.

http://my.execpc.com/~rhoadley/magmeter.htm


There are other more basic physics methods using:

a loop of wire, a current, and measurement of force.

a loop of wire, a current pulse, and measurement of the reverse voltage pulse generated by the field.

[tade]

cool thanks!

[Audiophilenoob]

Ribbons are pretty much done...

A few problems I've run into...

The 4.3 micron is far too thin to anneal... it creates micro holes that I can only find with a magnifying glass and against the window
... right now un annealed foil is in both ribbons

I'm curious if it's even necessary to anneal it ... the 4.3 is fairly sturdy... If annealing is only to make it stronger... I'm not sure if it's necessary here

the pics below are with the unstained oak flanges (they're now stained dark to match the enclosures)...

underneath the flange is speaker gasketing foam to create a near air tight seal around the opening...

also there is black alum woven screen material over it to protect the material

I can bump up the ribbon thickness to the 5.8 I have...it is a good deal more robust and takes annealing very well... but this would decrease efficency by at least 1.5 db/w

also the pics are deceiving... the ribbon is actually quite flat but the flash made all the very small (VERY) irregularities look very large... looks like I balled it up and reopened it

the gap to the poles is a uniform 1/32".... in the worst area (middle on one side)... it goes to slightly less than 1/16"

there are pads of 30 micron aluminum that connect the ribbon to speaker wire on the underside

[Audiophilenoob]

with flange, I hand rounded the wood to the ribbon ... it's pretty much as curved as a 1/2" wide quarter round, probably more rounded than that on the longer side... but looks way better