Mechanisms of distortion in ribbon loudspeakers

[thadman]

What are the sources of distortion in ribbon loudspeakers, whether they be significant or insignificant. Are these questions / statements accurate? If they are incorrect or incomplete, I would much appreciate some feedback.

Longitudinal waves are the source of translation (displacement) within the system.

Are transverse waves the source of distortion in the ribbon element itself? If so, are there any other mechanisms within the ribbon element that cause distortion?

As far as I understand, the inductance of a ribbon is very low, thus EMF will not be a significant source of distortion, removing the need for shorting rings that are very popular in dynamic cone drivers.

The uniformity of the magnetic field is likely to be a primary source of distortion. Non-linear motor force should be the same mechanism that causes distortion in subwoofer drivers.

The linearity of the spring force is likely to be a primary source of distortion (air-spring, mechanical reactive force). Is there a way to calculate the linearity of the mechanical reactive force?

The distance between the edge of the ribbon and the magnet allows air to pass. I believe the circumstances may be analogous to hydraulics (damping). I'm not sure what distortion mechanisms would arise because of this.

Thanks,
Thadman

[tinitus]

I would think that a big and relatively weak magnet gap could be one issue
And if impedance trafo is involved, that could be another one

[thadman]

Originally posted by tinitus
I would think that a big and relatively weak magnet gap could be one issue
And if impedance trafo is involved, that could be another one

If we assume the field is of uniform strength, couldn't the distortion due to that mechanism be considered insignificant.

[Andersonix]

Zaph Audio on ribbon tweeters
(In case you hadn't already seen this.)

I don't know what I'm talking about, but I had mostly believed the 'shimmer' was from the break-up of the foil.

[Mx]

As i see it, two main problems are magnetic field and material for ribbon.
Magnetic field is not even remotely linear in almost all ribbons in production now, and that's a big problem. Usually magn. field tends to be much stronger at ends of ribbon which is crazy. Controlling this is very hard and needs a lot of steel and weaker magnetic field as result, and is also more expensive which makes ordinary ribbons better choice even when they have bigger distortion.
Second is off course material itself and how much tension is applied to it. Using very thin aluminum foil only makes sense in smaller ribbons, and makes them very vulnerable in transport , in wind etc.. Adding mylar makes them heavy...
All in all, it takes much more money for ribbon that will be closer to ideal, and because off that majority off ribbons that we can buy are in sweet spot in terms of compromises between great sound and not to expensive.

[tinitus]

Originally posted by Mx


Magnetic field is not even remotely linear in almost all ribbons in production now, and that's a big problem.

Usually magn. field tends to be much stronger at ends of ribbon which is crazy.

Fits well with what I found many years ago when I made big ribbon line source

With no magnets at the ends of the ribbon there was a clear audible improvement

On small ribbons its not possible, obviously

But small bits of foam, just where the ribbon is attached to chassis does good too
The same goes for planars as well

[a.wayne]

Originally posted by tinitus



Fits well with what I found many years ago when I made big ribbon line source

With no magnets at the ends of the ribbon there was a clear audible improvement

On small ribbons its not possible, obviously

But small bits of foam, just where the ribbon is attached to chassis does good too
The same goes for planars as well

Interesting ,
As i have found this myself ( leaving mags out at end ) ..............

MX interesting that you mention using lot of steel to control this , but why results in weaker field ..

regards,

[Mx]

Put simply, magnets tend to be smallest part of the system which is designed to have equal magnetic force in all regions. That is crazy as we look in constructions of common ribbon drivers. You're wasting magnetic force and "shorting it" in regions were that force should normally be higher. Doing that makes magnetic field weaker than usual and construction much more complicated and costly.
Smaller ribbons have this problem very pronounced, and i think because of that they tend to have higher distortion than dome drivers. They have very strong magnetic field, which then gets very hard to control. In comparison, better ribbon construction would be 4 times bigger with much more magnets and steel and would have same magnetic field strength but with homogeneous magnetic field. Cost would be much higher for just a little improvement. Off course, if somebody is looking for the best ribbon, that is the only way to go.

As much as i love ribbons, problem is that normal dome drivers are getting better every day and cost less. Ribbon technology has its limits (which, if ribbon is good, are very high) but dome drivers are catching up fast.

Best regards

[a.wayne]

MX,

It would take a lot of domes , say at least 6 per side to have lower distortion than say a 4 ft ribbon and of course with the usual lobing problems associates with such , cost would still be higher than single ribbon driver .


When you say smaller ribbons , what size?
Technically speaker don't all magnetic circuits ( speaker related ) suffer from shorting ?


I do hear a larger degree of distortion when listening to planers (including electrostatic) vs point source , subjectively the planer is closer to the realism of sound , just not as truthfull to the recording ..

[Mx]

Ok, i wasn't clear. When i say small ribbons, i mean high frequency ribbon speakers for use from 3kHz or higher, with aluminum foil as sound source with low impedance and with transformer. Also known as true ribbons.
By "big" ribbons, i assume quasi ribbons, made of mylar ribbon with aluminium stripes, having real impedance, without matching transformer, much longer/larger than true ribbons, and almost fullrange (400Hz or higher).

For small true ribbons you do need midrange/ midrange bass driver and off course, same for dome tweeters. So same logic for line array can be applied for true ribbons. Btw, big quasi ribbons also suffer from line source problems regarding high directional sound.

All magnetic circuits do suffer from shorting, but in attempt to make magnetic field equal you do need to, lower the peak magnetic induction to lowest one, having that lowest magnetic force now being in the gap. You can't make lowest magnetic force in the gap, somehow stronger, only to weaken stronger areas to least strong ones. By deliberately shorting magnetic circuit in some places, you can make pretty uniform field, that will cost you sensitivity of the ribbon.

As you can see, i love big quasi ribbons , because they can sing whole midrange (and treble) region with such purity, speed and resolution. They do suffer from directional sound and from adding nonexistent depth to songs. True ribbons are having hard time to fiend friend in midrange speaker who will have similar characteristics. Probably big fullrange speakers like b200 with open baffle, are closest to being ideal.

As i see it, for distortion, ribbon speakers are really pushing the limits to reach dome cousins, and dome tweeters are running behind ribbons in terms of speed (reflecting in resolution).