Plur

[Borat]

Originally Posted by kenpeter

Since these line of force do not cut thru the ribbon anywhere,
how is it a current applied to the ribbon supposed to move it?

its gonna move because the ribbon is submerged in the field and because the lines are perpendicular to the direction of current and perpendicular to the direction of excursion.

just consider the fact that the force in a ribbon or a voice coil is felt by electrons. and electrons basically are just points. if i drew the ribbon sideways so the lines cut through it - it wouldn't make any difference for the electrons inside.

consider the motion of individual electrons and it all works out ...

[Borat]

Originally Posted by el`Ol

Could be a really cost-effective way of building ribbons. It really could be that I´ll become a ribbon builder now.
http://cgi.ebay.de/200-Neodym-Magnet...4.c0.m14.l1262

build a tiny prototype

[Ed Holland]

Originally Posted by Borat

the ribbon is where the thin red line is :



in a 3D view it would be like this ( diagram by NeoDan from another forum )


so in this diagram you see two arrays of neodymium bar magnets. and the ribbon element would go right between the two arrays.

Ah, OK, so the ribbon is seen edge on, with the current "vector" perpendicular to the plane of the diagram. The extended design is a vertical slatted array of magnets, within which the ribbon is suspended. I understand better now - thanks for the clarification.

I wonder how your efficiency and frequency response will work out, since driving force is proportional to current, and the increased area raises the mass of the ribbon element. Also, the wide ribbon will have a very low DC resistance and overall impedance, so a matching transformer would seem necessary.

Please do not take my comments as destructive - This is an interesting design, and there is a lot to consider in its implementation!

Ed

[Borat]

Originally Posted by Ed Holland

Ah, OK, so the ribbon is seen edge on, with the current "vector" perpendicular to the plane of the diagram. The extended design is a vertical slatted array of magnets, within which the ribbon is suspended.

correct.

[Borat]

Originally Posted by Ed Holland

the wide ribbon will have a very low DC resistance and overall impedance, so a matching transformer would seem necessary.

yes impedance would be very low, but let's not make any assumptions about how it will be driven.

there is plenty of room for innovation in amplifiers as well. a transformer between amp and ribbon would be an off-the-shelf solution.

one option would be to have a transformer internal to the amp with NFB running around the transformer. McIntosh amplifiers for example use transformers even though they are solid state.

transformer is more linear than gain devices inside the amp anyway. it is only a matter of properly integrating it into the overall gain structure as opposed to just mindlessly connecting it between the amp output and the driver.

[Ed Holland]

Originally Posted by Borat

yes impedance would be very low, but let's not make any assumptions about how it will be driven.

there is plenty of room for innovation in amplifiers as well. a transformer between amp and ribbon would be an off-the-shelf solution.

one option would be to have a transformer internal to the amp with NFB running around the transformer. McIntosh amplifiers for example use transformers even though they are solid state.

transformer is more linear than gain devices inside the amp anyway. it is only a matter of properly integrating it into the overall gain structure as opposed to just mindlessly connecting it between the amp output and the driver.

Absolutely. I have an EL34 amp kit that takes feedback from the secondary side of the amp, and see no problem with that approach. A dedicated amp is no bad idea for a unique speaker design. Moreover, the step-down transformer for a ribbon driver perhaps is somewhat less difficult to design than the high impedance transformation ratio needed for valve amps. Certainly there will be a way to drive it safely.

I think the interesting physics comes in where we consider efficiency, frequency response, directivity etc. as a function of ribbon width. It is width, after all, that is the parameter with which this design offers most flexibility.

Ed

[Capaciti]

Hi,

hopefully i do not misunderstand the concept.

But from what i understand, this ribbon might have significant issues with cavitiy resonances in the high frequency range, due to the array of the magnets


Capaciti

[tiki]

Sure,
as well as all magnetostats have them, including AMT.
Regards, Timo

[Borat]

Originally Posted by Capaciti

Hi,

hopefully i do not misunderstand the concept.

But from what i understand, this ribbon might have significant issues with cavitiy resonances in the high frequency range, due to the array of the magnets


Capaciti

yes above a certain frequency the magnet array would not be completely transparent acoustically.

how significant is that effect ? most metal dome tweeters for example employ a phase lens, such as this:



and such a phase lens operates mostly above 10 khz.

so thats about the size the magnet should be to have a significant effect acoustically. however the magnets could be made thinner than this and push undesirable effects to mostly above 20 khz.

what i think though is that the optimum application for this transducer ( of course this remains to be verified ) would be vocal range using a line source about 3" wide.

for narrow ribbon widths and small excursions a conventional ribbon design will be more efficient. it will also not have that acoustical transparency issue at high frequencies. therefore i think it would be a good idea to hand off the highest frequencies ( 5 khz + ) to a conventional true ribbon. because you would probably want a narrower ribbon to cover the top octave anyway.

so my vision is a 3-way along these lines:



with PLUR being a wide-band midrange/vocal driver ( say 300 hz - 8 khz )

[gymwear5]

Gold ribbon Cocepts in the 80's used a somwhat similatar though - vertical oriented magnets left and right in front and behind the ribbon. Their real innovation was to use vapor deposition of gold on a Kevlar membrane to get the impedance high - very thin coating. 4 ohms over 8 feet of ribbon conductor.