Important areas of ribbon motor design

[goskers]

What does everyone feel is the most important areas of motor design for a full range ribbon?

FEMM seems to be the best piece of freeware for magnetic motor design. Someone correct me if I am wrong but this will only allow you to design for the field strengths. Speaking with a friend who does a fair amount of motor design for DC and permanent motors, he does not feel that designing motor for AC using just field strength and saturation does not give you a great end result. Personally, I don't know what other tools are at the fingertips to use.

Once I find out the field strength in the gap I will start modeling different ribbon elements in pro-e. Once this is completed I can begin testing these elements using mechanica. This should allow me to find out what type of pattern implemented to a ribbon element allows it to be the most rigid. From my understanding, a ribbon element should be pistonic in nature just like a cone.

So, if we have a motor with which we know the field strength and we have a ribbon element with which we know it's break-ups then what else can an everyday person be concerned about? Are things such as EMF and back-EMF something that needs to be considered? I am thinking that this will not be too much of an issue since the ribbon should be well in the direct field among all travel and the element is so thin to begin with.

Any ideas as to the next step in design before I jump into build?

Thanks and sorry for all the rookie questions.

[LineSource]

A single ribbon will not be able to cover the full 20-20,000Hz audio range. An expensive multiple ribbon design could do this, but using only "true" ribbons is probably not the best sonic or cost solution.

Most designs start with selecting a system size and radiation pattern: dipole, monopole, waveguide, point source, linesource, line array, horn loaded, ...etc. What speakers have you listened to and liked? What speaker reviews describe similar sonics to what you like? What room will they go in?

Divide up the audio range based upon sonic goals, crossover slopes, and number+type+capability of drivers.

Design the ribbon motors with FEMM, and then experiment with physical ribbon construction using tools like Pro-E, or a finite element package to find the best few designs to build prototypes for measurement. It is possible to run AC analysis in FEMM, but it cannot show the physical affects like break-up or dampening on a thin ribbon.

It might be worthwhile to start experimenting with thin aluminum, glues, plastic films, ribbon pleating or embossing, heat treating, etc... before you jump into Pro-e.

Electrically the ribbon is almost purely resistive, but if you use a step-up transformer, then its inductance will create EMF and phase shifts. Most crossovers add phase shifts.

[Paul W]

The motor will also influence acoustics in the area immediately surrounding the ribbon. Consider gap depth resonance, any asymmetry in the motor in front of or behind the ribbon (like crossbars, grills, etc), transitioning from the ribbon in the gap to free air, etc. etc.

[goskers]

Linesource,

Thanks for the comments. I totally agree with them. I should clarify a little bit of my comments to say that I am not looking to do a compete full range ribbon but pseudo full range. This will be similar the ribbon that valveitude is making with an anticiapated xo point of 200Hz or so. Everything below this will be handled by woofers.

I would like to build a line source as I like the presentation style. I feel that a line source is more 'real life' size than a point source. I have heard a couple different line arrays which approximate line sources. A couple of days ago I just took delivery of a pair of MMG's which I wanted to audition in my own environment with my own tooling. So far, so good. Great deal for a mere 500 bucks.

The guy that is helping me with the motor development uses Ampere for design. This can do everything to optimize the magnetic field itself but can not do any sort of modeling for AC circuits. So, after this modeling is completed would I gain anything from using FEMM?

Thanks.

[LineSource]

Hi goskers,

Your thread sounds like you are considering building a wide BW tall dipole linesouce. Modern NdFeB magnets are strong enough to saturate steel pole pieces, so higher fields can be achieved FOR WIDE BW RIBBONS with a magnet-to-magnet field gap. The the two most common constructions I've seen are attached. A 5.8 um thick pure AL foil is the thinnest that has held up for me. For good high frequency extension, a 0.7" wide ribbon might be a good design start.

[tryonziess]

Where do you source the ribbon material for the speakers? I have not had much luck on the internet finding material suitable for this application.

Doing a little experimenting with neodymium magnets at home I have found that the field is quite strong between two magnets even at distances of well over 1 inch. They will effectively interact with each other at over 12 inches. It might be possible to use much smaller magnets in the motor structure, hence less steel, with these incredible monsters. There pull strength is quite awesome. Let me know how your simulations turn out. Tad

[moray james]

small caps can be cut open with a razor knife any you just unroll the foil, You might want o set up a jig to hold the cutter and the cap.