Fertin Full Range Speaker

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#21
Back on Critical Damping.

By principle, critical damping acts only on the resonance(s) frequency(s) of the speaker or the box. These resonances are way in the low frequencies region of the speaker response.
We can measure how the critical damping changes the bass SPL response and only the bass.

But this SPL change does not reflect the extend of the openness that our ears perceive. A critically damped speaker sounds very different at all frequencies.

Music is not sine waves we measure critical damping with, it is impulses, just impulses after impulses, most of the time non symmetrical impulses.
Overshot or undershot on bass impulses are already of great detrimental importance, but successive resonances and harmonics of them keep the whole music muddy, dull and tiring.

Playing with a serie resistor on an average Qts (0.4) Full Range speaker to reach critical damping is an amazing experience.

Reaching critical damping on a very low Qts full range speaker, I mean a Qts in the order of 0.2 or 0.1, i.e. a very fast speaker indeed, is the experience to come.

May be we should change sequence in which we combine speakers to amps.

We may select first the speaker and the box we want it in.
Then we shall play with a conventional voltage source amp and a variable serie resistor to find out the optimum output impedance of the amp we want ultimately use, this time without the serie resistor and its power loss.
 
#22
Some thoughts about an other fullrange driver with exotic suspension:
In former Babb (now DC Gold) fullrange drivers the voice coil slides directly on the pole piece via teflon coating.
If one combined this with a conventional spider, there would be no need for a surround, and it would work without manual centering like in the Fertin.
 
#23
Hello el'Ol.

Your ideas of spiderless speaker are of great interest to me.
Intresting you mention the teflon coating on the center pole.
The stick in center is an other way. Why do you want to combine both ?

I spoke to Ferrotec a company that is providing ferro fluids.
During testing they find out that if you maintain ferro fluid in the inner gap only, it does center the voice coil, while if you have it in the outer gap only it offcenters the voice coil.

They sent me several small samples of different ferro fluids (different magnetic composition and different viscosity). I tested them on midrange and full range speakers. It does work with improved magnetic field, but according to choosen viscosity it really damps the bass response.

The trick is to close the inner gap from the outer gap. It requests an 5 mm extension of the voice coil below the windings and you need to close the coil cylinder on the side with glue and varnish.
 
#24
Cherel said:
Hello el'Ol.

Your ideas of spiderless speaker are of great interest to me.
Intresting you mention the teflon coating on the center pole.
The stick in center is an other way. Why do you want to combine both ?
Click to expand...


Hello Cherel!

Obviously you read my post before I modded it, so I´ll clear that up for the others: The Babb type voice coil leads to only one degree of freedom for the movevent, but then one still needs a retracting force.
The Jordan (at least the little one) has a stick through the pole piece that ends on a foam pad instead of a spider. A foam has good damping, but not so good linearity. So I thought if there is a way to enhance the damping of a conventional spider this would be the better solution.

Regards,
Oliver
 
#25
Hello El'Ol.

Thank you for the clarifications. I did not catch that the foam was providing the retracting force.

The outer diameter of the diaphragm of model 7 (kept constant by a carbon ring glued to the diaphragm) is moving in a polished steel ring fixed to the speaker basket. In order to have little leaks for bass reproduction, the gap between the diaphragm and this ring is of a tenth of a milimeter. The trick is to keep a free motion without friction i.e. maintaining a very precise 3D positionning of the diaphragm.

Is this diaphragm precise positionning possible by the voice coil alone (spider and central rod) ?
Only the experience would give the answer.

The Fertin suspension with carbon rods looks odd but is very effective. It is light, precise and very flexible.
The kneeled two diameter carbon rod version is even better because it accounts for large diaphragm displacements on small diameter speaker.

This types of carbon rod suspension applies a slight retracting force. The main retracting force comes from the flexible carbon spider, very precise as well, in order to keep the magnetic field gap the smallest possible.
 
#30
Felixx,
I am no so sure to understand what you mean by "mark of sound". Could you explain ?

One thing stays whatsoever : the sound quality of Model 7 would always be very distinctive (clearer) of any other full range with surround.
The surround has an adverse direct effect up to may be 200hz, so for about 4 octaves.

The corrections business is more or less inherent to any full range driver. But the way to do these corrections is very sensitive.
 
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