Ribbon material (a silly question!)

[Marik]

[quote author="crazydoc"][quote author="xvlk"]
... and the ribbon itself {current path perpendicular to magnetic field}
voltage=B*l*velocity = B*l*diff(x,t)
where B is induction in the gap {you can measure it
by Hall probe from old videorecorder}
l is efffective length of the ribbon
diff(x,t) is ribbon velocity

This is one part of equations of the electrodynamic conversion.
[/quote]

So the faster the ribbon moves, the greater its output, (voltage or current, assuming a constant impedance and a constant displacement of the ribbon.) So intuitively (to me) this means that for electromagnetic portion of this system, output is proportional to frequency.

[/quote]

Crazydoc,

Your intuition is right!
The "v" (velocity of ribbon) identifies as (P1-P2)/zA, where P1-P2 is pressure difference, z-acoustic impedance of the ribbon, and A is ribbon area. If z is a mass reactance, then v=(P1*d/c*M*A)*cos0, where M=mass of the ribbon, and c=velocity of sound.

So something must be damping this frequency dependent increased output, which I assume is a decreased displacement (excursion) of the ribbon as frequency increases, because of either the mass of the ribbon or the mass of air it has to displace.

Because the ribbon workes as a mass controlled system, there is a natural fall with frequency increase.

 

[Guest]

[quote author="crazydoc"]
F=B*l*I
where I is currrent trough the ribbon.
.....
What is F? Frequency?[/quote]
Crazydoc, F is force on the ribbon caused by electric part.
It is second equation (antireciprocal) of electrodynamic conversion
and for the ribbon with open load (ohmic load toooo high,
== amplify ribbon directly by FET without transformer)
you can not take it in mean.
xvlk

 

[Marik]

[quote author="xvlk"]
What are you on the bridge measurements ?
Some values of your mic for me?

xvlk[/quote]

No, not ? yet. And the reason why? OK, now I want to reveal one thing, but since there is such a lively discussion here I?ll do it in the thread, where it belongs to.

 

[crazydoc]

[quote author="PRR"]The ribbon mike is an elegant combination of an electromagnetic system that has a rising response with frequency, and a acoustic-mechanical system that has a falling response with frequency, to give a transducer with flat response over a wide bandwidth. [/quote]
[quote author="xvlk"]
Crazydoc not use frequency- rise transducer. His microphone will
not have frequency - constant transfer. I had explained him it. [/quote]
So I could take the displacement-sensing optically transduced output of a ribbon, which falls at 3dB/octave (I think), and put it through a +3dB/octave filter, and get a flat frequency response?

However, the filter would probably add unacceptable levels of noise with increasing frequency, and is certainly not as elegant as the offsetting frequecy responses of the electromagnetic versus mass-controlled systems.

 

[PRR]

> displacement-sensing optically transduced output of a ribbon, which falls at 3dB/octave (I think),

Displacement of a classical ribbon mike falls 6dB/octave over most of the audio band.

Output voltage of an electro-dynamic (magnet and conductor) transducer, for constant displacement, rises 6dB/octave. (It senses velocity, not displacement... to maintain constant displacement at higher frequencies you have to move faster.)

xvlk has a point about output current. But in fact we "always" load ribbon mikes with a high or semi-matched impedance, not the low/zero impedance needed to sense current. There may be special applications where it is done the other way. Baxendal describes a way to use any hi-fi speaker as a microphone, by loading it in "zero ohms" and boosting the output 6dB/octave. You get the reverse response of the speaker: same frequency curve, same directivity. But for practical and historical reasons, that's not the usual way to load microphones.

Stick with your stretched diaphrams, tuned to the high end of the audio band, back side sealed. These will be nearly constant displacement below resonance. If you can't seal the back-side (hard on your clever experimental rig), keep the back-side opening small and don't judge too much by the far-field response. The near-field will be nearly flat. I gather at this point you are struggling with signal-noise, and not yet ready to worry about far-field flatness. The opto-sensor will be flat over most of the audio band (far-far above the audio band in most cases) so get a usable opto-system and then deal with the diaphragm.

For maximum sensitivity, use a large diaphragm tuned as low as possible. Your experimental setup looks fine. That diaphragm is already "too big for hi-fi", but not too big to invalidate experiments. You may only be tuning to 3KHz or 6KHz, but that gives enough bandwidth to test S/N on voice and guitar. When you have "good" S/N, then you can try smaller stiffer diaphragms versus loss of S/N.

 

[CJ]

Sounds like we are gonna need some integral symbols and stuff.
And phasor matrices! Sheesh!
Oh, and maybe toss in a diferential or two just to spice things up a little!
Eigenvalues for desert?
Keith, what do I hit for an integration symbol. alt-F117 or some weird thingy?

 

[PRR]

> what do I hit for an integration symbol

While this is the "same" software as "the old place", there is one big (to me) difference. Whats-his-name had "HTML On". Here HTML is Off.

The obvious reason is that there are some Bad Things you can do with user-entered HTML. Scripts that steal passwords.

OTOH, HTML Entities are the only safe way to put funny-symbols in messages; "safe" in the sense that EVERYBODY sees the same symbol. Alt-xxx is a Windows-trick, and generally will not show the same character on Macintosh. Or even on all Windows machines! HTML Entities are standardized and most web browsers support most of them, and correctly.

For example, I'm very used to typing Ω (ampersand Omega semicolon) to get the Ohms sign. I find it very distressing not to have it. I have not made a stink because of the security issue. HTML Entities are quite safe, but I don't know if this board can allow those while blocking ALL unsafe HTML tricks.

 

[crazydoc]

Thanks for your usual thoughtful and helpful reply, PRR. Yes, I'm just looking ahead to the point where the S/N ratio of a small, tightly stretched membrane just ain't gonna cut it, trying to find a mechanism with a larger membrane excursion.

Still lots of problems to overcome before I get to that point, though.

 

[Consul]

Actually, it would be possible to allow special HTML characters and still block tags, but how easy that would be to implement depends on how phpBB was coded. The whole thing is up to Ethan, though, so I'll leave it to his better judgement. :thumb:

Personally, I'm just glad we have a place to hang together.

 

[Marik]

[quote author="Marik"][quote author="PRR"]>

The ribbon mike is an elegant combination of an electromagnetic system that has a rising response with frequency, and a acoustic-mechanical system that has a falling response with frequency, to give a transducer with flat response over a wide bandwidth.

Take out the electromechanical side, and none of it makes sense.
[/quote]

PRR,

It is hard to argue with person like you, but at least I will give a try. :grin:
[/quote]

Output voltage of an electro-dynamic (magnet and conductor) transducer, for constant displacement, rises 6dB/octave. (It senses velocity, not displacement... to maintain constant displacement at higher frequencies you have to move faster.)

PRR,

Of course you are right! Sorry, I misuderstood you, at first. I see what you meant.

 

[Guest]

[quote author="cjenrick"]Sounds like we are gonna need some integral symbols and stuff.
And phasor matrices! Sheesh!
Oh, and maybe toss in a diferential or two just to spice things up a little!
Eigenvalues for desert?
Keith, what do I hit for an integration symbol. alt-F117 or some weird thingy?[/quote]
Nice.
[quote author="cjenrick"]
Eigenvalues for desert?
[/quote]
It is desert of my examiners.
I like Carlin s method in electronic circuits.
Some circuit analysis unclear in matrices (exist they ?) can
by clearly done by circuit topology + nullators + norators, and
negative capacitances and so on.

In acoustic it is used seldom,
in the past by (F.V.) Hunt, but what will be in the future ?
xvlk

 

[CJ]

testing:

x+3y=z

x+3y=z

I don't know, this is a long way to go just to dispay symbols.
What about some of our favorite math symbols as emoticons, filed under the regular emoticons?
This would eliminate the html issue?

 

[Guest]

[quote author="cjenrick"]testing:

x+3y=z

x+3y=z

I don't know, this is a long way to go just to dispay symbols.
What about some of our favorite math symbols as emoticons, filed under the regular emoticons?
This would eliminate the html issue?[/quote]
YES !

and some stupid notice:
Why we have maths only for some kind of circuits:

CIR=(R1+C1)//(C2+L2+R2)

it is connection ring (analogon to convolution ring) - it is good to learn calculator to understand
paralel (//) operation.

xvlk
... and to paralel substract:
R3=R1-R2 (where R1>R2)
R3=R1(//-)R2 (where R1<R2)

math is old and complicated,
if we use operations not directly coupled with circuits.
...general circuits are nice...

 

[SilverhammerNZ]

A formula for this?

A tambourine sounds better recorded using a good ribbon microphone. All the jangly bits are there.

Larryk

 

[SilverhammerNZ]

Why is that? why does a condensor, even a good one, reproduce keys/tambourines like clicks whereas the ribbon has it all there?

A tansient thing I guess, but one would have thought a very thin gold sputtered membrane would handle such things, turns out it's the chunky bit of aluminium that does it better.

Larryk

 

[Guest]

[quote author="SilverhammerNZ"]Why is that? why does a condensor, even a good one, reproduce keys/tambourines like clicks whereas the ribbon has it all there?

A tansient thing I guess, but one would have thought a very thin gold sputtered membrane would handle such things, turns out it's the chunky bit of aluminium that does it better.

Larryk[/quote]

Transient response of microphone causes it.
Have two microphones with nearly the same
frequency modulus response.
One of them sounds better,
but what differs them?

Their phase characteristics

(after M.L.Gayford)

And phase characteristics plus modulus amplitude characteristics =
impulse response. And ribbon microphones have different
impulse response then condensers.
And ribbons have second pleasant property,
They are principially linear.
Condensers are principially nonlinear and only for small displacement
we can they linearize.
Thus ribbons can handle higher pressure without distortion
but only if that pressures not damage ribbon

xvlk

 

[maneco]

[quote author="salty"]Hi I've had bad results and spent a lot of time with signwriting leaf too. A bloke I work for has an old Tannoy ribbon mic that he re-ribboned using silver foil from a cigarette packet, and it works really well, I used it recently on some backing vox.

Would there be any interest in a group buy of some foil? I'd be willing to put in $20 or so.[/quote]

Is the cigarette foil a joke?

thanks!

 

[kvintus]

Can an aluminium metallized mylar film be used as ribbon material?

/Anders

 

[Scodiddly]

I just pulled a blown (literally) film capacitor from a guitar amp - nice little roll of foil and dialectric. Seems promising, how would I actually measure the thickness?

 

[ToobieSnack]

hey people,

Is the cigarette foil a joke?

no .... the cigarette foil does work... how well? I can't tell you..the mic i built had low output but seemed to sound really nice.
I wasn't happy with the output so i didn't get any frequency data for comparison. I do like working with the cig foil...it's pretty easy ...really... try it...

i think cheaper cigarette have thinner foil..

cigarette foil is about 4-6 microns....

you can see a pic or a ribbon I made from this foil at my post on the drawing board ...ts ...ribbon mic...

http://www.groupdiy.com/index.php?topic=6973

of course as marik and others have pointed out... the ribbon is only one variable along with the flux in your gap and trafo ratio's ,magnetic return circuit and the focus of the magnetic strength.

I'm still learning but as I undersatnd ...the mass of the ribbon needs to be as low as possible but...as the ribbon gets thinner resistance goes up..

one thing I would like to know is:

how to compensate for the thicker ribbon when building a mic....more flux? trafo ratio?

any way best way to find out ...i guess... is to try it...

ALSO: I have another post at the drawing board "ribbon material /readily availabe substitutions" ...something like that...that goes into detail how I did it with cigarette foil.

http://www.groupdiy.com/index.php?topic=6941

I think you may find it interesting

anyway hope this helps
later
ts