Transformer-less Ribbon Driver?

[RogerGustavsson]

Compare the resistivity and mass for these materials. For a given resistance you want the lowest mass, at least if you want to use for higher frequencies. Beryllium wins, just ahead of aluminium and magnesium. Copper and silver has double mass or more for the same resistance. Titanium is about 25 times heavier than aluminium. Beryllium is toxic. Magnesium easily go up into flames. Aluminium seems to be the winner in every day use.

[DBMandrake]

Originally Posted by Groove-T

thinner foil = higher Resistance= lesser Current flowing= lower Efficiency= need more power

thinner foil = lower thermal capacity

more power & lower power handling = ribbon fails

Not quite. Halving the thickness of the foil doubles the resistance which all else being equal would halve the efficiency, (-3dB) since it would take twice the voltage to get the same current, but all else is not equal - halving the thickness of the foil also halves the moving mass, which all else being equal would increase output by 6dB. (twice the acceleration and excursion for the same current)

So the net change for halving the foil thickness is a 3dB increase in sensitivity and a 3dB reduction in power handling, (half the thermal mass) leading to the same maximum SPL capability.

Once the foil gets REALLY thin things change though - the air mass load on the foil becomes a large part of the total moving mass, so you just lose sensitivity due to increased resistance and don't gain much increased excursion to compensate. There is a point of diminishing returns as it gets thinner.

On the other hand when the foil is really thin the air mass load is such that the air itself helps to damp any mechanical resonances in the foil - so a thicker foil won't be as well damped as a thin one.

An optimal design balances these factors. Not too thin to throw away maximum SPL capability, but not too thick to throw away damping.

Aluminium has good power handling, good damping properties, low structural resonances and pretty stable when corrugated or similar

Yep, although quite a bit of the damping comes from the air itself when the foil is really thin...

[DBMandrake]

Originally Posted by mondogenerator

Ive recently got a pair of Fountek NeoCD3.5H (its a horn-loaded version), and they may/may not be a true 'ribbon'. The driver uses a polymer diaphragm with foil laminate, i think. Maybe its vacuum deposited.... I don't know.

If it has a polymer diaphragm it's not a true ribbon, it's a type of plannar driver. Similar, but not the same. A key defining attribute of a true ribbon is that the entire diaphragm mass is directly driven by the magnetic force, as it's all homogenous conductive material.

[Andrew Eckhardt]

I haven't done much calculation, but it seems to me one of the biggest problems, alongside the fact that you're only dealing with a single pass through the magnetic gap, is that the gap is absolutely huge compared to a typical voice coil motor, severely driving down flux density. Since force = IxB, and you need to maximize them both for efficiency, I'd offhandedly say that means every bit of the mass should be conductor. Electrical grade aluminum has half again better mass to conductivity performance of copper, and is therefore the absolute winner of available materials. In other words, forget metallized film. Do everything possible to create maximum gap flux (including minimizing gap width), since no matter what you do electrical Q is going to be too high / back EMF nil. If overall power efficiency is a concern, water cooled electromagnets are out. Several pounds of NdFeBr magnet are probably required. Then you need an amplifer with the usual volt/current delivery reversed, a few volts, and several tens of amps output capacity.

[mondogenerator]

ok.

I had always been confused by the varying types...

I thought planar was a sort of push-pull magnetic system, with a ESL type diaphragm, and wires running in patterns on it. my bad.

right. perhaps a perforated 'straight' ribbon (if it is one) of thicker foil? if you could get the perforation up to a high enough percentage, then you could reduce weight accordingly. As long as the holes are fine enough...

I dont dislike the idea of Aluminium, btw, im just trying to be creative. If it sounds like Kaka ill probably still love it!

Mind you it'd be good if it was half decent

[a.wayne]

Originally Posted by mondogenerator

ok. I assumed copper voiced worse tbh, like the alloy bells are made of. But i am just riffing really.

The idea of many small gauge ally or copper wires, superglue and mylar seem a basic way to test a simple home made job.

A flat braid of small wires may be worth a try, it just occured to me.

planer magnetic , not for ribbon speaker ....

[Andrew Eckhardt]

Since flux density will not be uniform and increases toward the edges, maybe a profile could be rolled in the conductor to decrease thickness toward the edges... To balance drive force across the ribbon. This might help mess up resonance tendencies, along with usual attemps at that.

[a.wayne]

Decrease, wouldn't it be better to have it increase towards the edges ... ?

[Andrew Eckhardt]

Total efficiency-wise yes it would. It might be something to think about one way or another. Some slight improvement may be made there with mechanical and thermal considerations together.

I also wonder if a quasi magnetoplanar approach might be better. With two ribbons and a magnet in the middle (complete with phase plug and outer flares). Possibly this might help increase average gap flux while maintaining area for acceptable lower cutoff point. It would still require the same moose of an outer magnet structure. I'd need software to model it to be sure. But if someone were a ribbon driver purist they would't accept it anyway.. Just some silly ideas..

One problem with that is the polarity of the gap flux would be the same on both sides, so electric series connection requires a very low impedance jumper, somehow.

[mondogenerator]

you lost me now. Lol. The weirdest idea i can think of is a kindof orthodynamic ribbon, stacked in groups of alternating phase. Multiple ribbon elements, pinching AMT type motion. Perhaps hornloaded or dipole. I have no idea what youd call it though.