High fidelity Audio & My Ribbion Speaker Project

[FrankCashio]

I've been reading theses threads for a few weeks now and I've started my own ribbon speaker project. A few things were immediately evident.

Firstly, is that the knowledge that is needed to build a speakers isn't very transparent. That is it's nearly impossible to find any source about audio design and theory.(at least for me ) and secondly, that it's hard to find a source for the materials and equipment you need in order to build such devices.

It just seemed a shame to me, financial markets are pretty efficiently. knowledge is shared relatively easily through all participants, why not so with engineering. It just seems like we are hindering ourselves. but, i digress...

I built a simple prototype ribbon out of stuff i had laying around the house and 2 4"x1/2"x1/8" N42 Neodymium magnets.


The ribbon area is 4"x1/2" and is standard kitchen aluminum foil so I'm assuming it's 99% pure aluminum with a thickness of 12.5 microns.

Using the totally unvalidated formulas(eq. 1) I found on this page that gave me a theoretical performance of 84 db/watt @ 1 meter and I had no idea how to calculate the sensitivity. The number I got didn't make a bit of sense.

I don't understand why you would divide by log(10) when that just simplifies to 1 so why not instead wright (eq. 2) Also what happens when m goes to 0? does Efficiency go to infinity? If so then light would be the ideal sound source.

(eq. 1)
# SIMPLE RIBBON EFFICIENCY EQUATIONS
#
# A=ribbon area meter^2
# B=magnetic field in Telsa
# %= percent of ribbon which conducts current(100=100%)
# m= mass of ribbon in grams
# Efficiency = A^2 * B^2 * % / m
# spl 112.2 + 10*(LOG(wfficiency)/LOG(10))
# senS effeciency + LOG(8/resistance)/LOG(10)


(eq. 2)
# SIMPLE RIBBON EFFICIENCY EQUATIONS
#
# A=ribbon area meter^2
# B=magnetic field in Telsa
# %= percent of ribbon which conducts current(100=100%)
# m= mass of ribbon in grams
# Eff = A^2 * B^2 * % / m
# spl 112.2 + 10*LOG(Eff)
# senS Eff + LOG(8/resistance)


When I first hooked it up the foil was uncorrugated and rattled a lot. I first fixed this by tensioned the foil then using different size foil, latter I realized that corrugation increased horizontal rigidity and cut down on the rattling.

I have no way of checking the impedance on the speakers. DC resistance is well below an ohm. I don't have a transformer to present a descent load to the receiver so I just directly drive it with the audio turned down. The receiver also has a safety relay that trips when too much current is passed through. thankfully.


Latter in the stages in the prototype development I installed a high pass filter, and this improved performance a lot.

I have a load of pictures that I'll post later.

I plan on a few projects, first I want to complete a pair of full range ribbons, I plan on building my own subs and woofers for them from either a carbon fiber or Kevlar composite. Anyway I'll post something more in depth later.

[a.wayne]

Hello ,
Kitchen foil has very poor memory and while it can sing it is not a good choice . then again a 4x .5 inch diaphragm is pretty small so you might get away with this .

84dB /W / M seems to be the sensitivity of the unit , not sure why you would state this then ask what is the sensitivity .. I would also place a 2 ohm resistor in series for testing , your amplifier will find it more palatable..

Regards ,

[FrankCashio]

I was referring to the last two lines of the group of equations

1) spl 112.2 + 10*(LOG(wfficiency)/LOG(10))
2) senS effeciency + LOG(8/resistance)/LOG(10)


It seems like it yields two different variables SPL and SenS which i'm assuming is sensitivity.

also I remember a post by Linesource that read

A 42" x 0.7" ribbon using 5.8 micron aluminum in a 0.5 T magnetic field would have SPL ~ 97 db/watt @ 1m sensitivity ~ 98 db/2.83 V

and he was using the same formulas so thus the confusion about sensitivty. Unless I'm missing something?

What do you mean by poor memory? I wanted to put a resistor in series but I don't have one that below 100 ohms.

[FrankCashio]

This is the FEMM model for my ribbon motor. I'm using ferrite bars to shield the magnets and it gave me around .65 tesla flux in the gap I was hopping to get around 1. I ended up not having enough ferrite to cover it the way i wanted to so the gap flux is probably a good deal lower.

[FrankCashio]

I used two knobs off an old computer monitor to corrugate the ribbon. Sorry I took these pictures with my phone and they are kinda blurry.

[FrankCashio]

The magnets I used.

[FrankCashio]

And the speaker prototype..

[FrankCashio]

I didn't want to waste any bell wire on making a resistor so I chose instead to use aluminum foil cut into very small strips. It has a resistance of around 3 ohms. Now my receiver doesn't kick off any more. I was testing the limits I could push it and The current vaporized a small piece of the resistor it was pretty freaking awesome. So It's a kinda fuse/ resistor but it also brought about a timely realization. when I create my main ribbons I need to keep in mind the maximum power I can deliver to them safely so this will limit me to the size I can make them as too small of ribbon will flash over too easy.

So I need a few thing when designing the next ones.

1) How much current does it take to vaporize a ribbon
2) What will be the maximum current that will be expected from a standard receiver.


I've decided on building my ribbons from a modular frame. I'm designing it now in Autodesk and I'll post more on it latter.

[FrankCashio]

There ya go added baffles. I know it's amazing.


cheers!

[tinitus]

Originally posted by FrankCashio


1) How much current does it take to vaporize a ribbon
2) What will be the maximum current that will be expected from a standard receiver.

I have seen a Krell fry a ribbon
But it was the bearing film that crumbled
I the foil leads were ok still

But if you use very thin foil it may happen
A known problem to some of the best ribbons

There are a few ribbons for pro studio use
Though they are also with good sensitivity, and need less power

btw, your proto ribbon looks about the size Im working on