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APi 28th June 2005 03:12 PM

Ribbon made of flexible flat cable
 
When ribbons were discovered there was only aluminum foil and still ribbon speakes use these very fragile materials. You or kids can brake them very easily by finger, hoover etc. No good :whazzat:

Then people have glued aluminum foil on plastic foils like Dahlberg does. No audio transformes and stronger membrane:

http://www.dahlbergaudiodesign.se/

I notices that nowdays you can find a lot of ready laminates on market. F.ex. DuPont manufactures flexible printed circuits. You can find few mil thick flat cables like these:

http://www.strataflex.com/products.php

Of course these are much thicker and made of copper, which has worse conductivity to weght ratio that aluminum does. Mut with copper you can make much more reliable contacts and decrease contact resistances.

And in theory it shouldnīt matter if the material is 4 mils thick instead of 0.1 if you can optimize impedance for your amplifier. That you can naturally do either by using a current transformed or having several metal strips on foil and by connecting them in series.

Good tolerances, rigid material, available(?) in reels. Just cut a piece and put it into your speaker. No need to be extremely gentle.

So why not use these flex cables? :)

My questitions are?

1) Can flexel like these to be corrugated?

2) Have anyone bought these cables and if, what its the best place to ask something like >5' long flexes?

3) Why flexes would NOT be suitable as ribbons?

dhenryp 28th June 2005 04:17 PM

I think the issue with using something many times heavier than thin aluminum would be very low efficiency. The efficiency of a ribbon varies at the square of the weight of the vibrating element. If you use something that is 10 time heavier than aluminum, then the output will drop by a factor of 10**2=100. That is a 20db drop. It is quite possible that these ribbons could be even 30 times heavier than 6-10 mil aluminum; that would be a factor of 1000 or 30db.

With these cables I don't even think you would get the advantage of impedance high enough to directly be driven by an amplifier. I assume that these cables are designed to have low impedance so that they can effectively pass signals and power. You only get high impedance when you put very thin conductors on a membrane. It is the very narrow, very thin but very long conductors that add up to reasonable impedance.

APi 28th June 2005 05:13 PM

Quote:

Originally posted by dhenryp
I think the issue with using something many times heavier than thin aluminum would be very low efficiency. The efficiency of a ribbon varies at the square of the weight of the vibrating element. If you use something that is 10 time heavier than aluminum, then the output will drop by a factor of 10**2=100. That is a 20db drop. It is quite possible that these ribbons could be even 30 times heavier than 6-10 mil aluminum; that would be a factor of 1000 or 30db.

True. Weight increases. But at the same time also cross area of the conductor increase and therefore impedance drop and current increase. It means that by the same input power you can still move membrane the same amount.

Force that moves the membrane depends on current. If the mass doubles then resistance halves, current douples and the force douples also. Double force, double mass

-> no loss of efficiency.

Quote:


With these cables I don't even think you would get the advantage of impedance high enough to directly be driven by an amplifier. I assume that these cables are designed to have low impedance so that they can effectively pass signals and power. You only get high impedance when you put very thin conductors on a membrane. It is the very narrow, very thin but very long conductors that add up to reasonable impedance.

1" wide flex cable can consists of 100 pcs of metal strips. You can connect them in both series and parallel to get exactly desirable impedance. No matter if the metal foil is, letīs say, 10 times thicker that in a true ribbon. Total impedance can be adjusted to be just fine for any amplifier.

I am now talking about ribbons 1m and longer :)

dhenryp 28th June 2005 08:47 PM

>True. Weight increases. But at the same time also cross area of >the conductor increase and therefore impedance drop and >current increase.

I'm not sure I follw you here. Unless the cable is made of a single conductor covering the entire surface of the cable, it will have less driven surface area than an equivalent sized foil ribbon.


>It means that by the same input power you can still move >membrane the same amount.

Again I'm not sure I follow but the basic issue is that the efficiency with which a ribbon converts electrical power to acoustic power decrease at the square of the rate with which you increase weight. Increasing current does not help efficiency. It only makes it harder to design a transformer or amplifier to drive the ribbon.

>Force that moves the membrane depends on current. If the >mass doubles then resistance halves, current douples and the >force douples also. Double force, double mass
>
>-> no loss of efficiency.

It seems that you are assuming that your amplifier/transformer is a constant voltage source that can produce any amount of current. It can't.

>1" wide flex cable can consists of 100 pcs of metal strips. You >can connect them in both series and parallel to get exactly >desirable impedance. No matter if the metal foil is, letīs say, 10 >times thicker that in a true ribbon. Total impedance can be >adjusted to be just fine for any amplifier.

>I am now talking about ribbons 1m and longer :)

I'm not sure that hooking a hundred conductors in series (do these cables come with a hundred conductors?) will give you an impedance of 2-8 ohms so it can be driven by normal amplifiers. It might, or might not.

One thing that will happen with multi-conductor flat cables is that your efficiency will take another hit. There will have to be spaces between each conductor for insulation. This means your driven surface area will decrease by as much as 50% if the space = conductor width. This is quite possible if you have a hundred ultra-thin wires. Efficiency also decreases (at a **2 rate) as you decrease the driven surface area. A 50% reduction loses another 6db.

I might be wrong, but I think corrugating the cable would be the least of the problems. You could try it - find an old printer and most will have a flat flexible ribbon cable connected to the print head. Tear that out, get some magnets and let 'er rip!

Regards,

Denis

I_Forgot 28th June 2005 09:13 PM

I think you guys are forgetting about the effect of the greatly increased mass compared to a thin plastic film with aluminum coating. When the mass goes up, your high frequency output goes down.

Since ribbons are small they aren't much good for low frequencies. If you take a driver that is unsutiable for low frequency reproduction and add some mass you also make it unsuitable for high frequency reproduction. What's left?

It might be OK for a telephone...

TD

bear 4th July 2005 02:30 PM

The problem as noted is in the equation for ribbons, which as noted before tells us that if you up the mass, the output level drops, a whole lot.

Which, in short is why aluminum is the material of choice for ribbons, not copper and not metals that are stronger. The combination of conductivity and lightness is the key.

Many speakers have been made with the "foil on substrate" method already... Strathearn (going back), Carver, BG, etc... plus the Panasonic "Leaf Ribbons".

The obvious benefit of paralleled conductors is the increased impedance of the ribbon, making matching an easier task, and hopefully eliminating the xfmr entirely.

And, a greater number of turns in the gap does help the matter somewhat, but you do run into the power vs. temperature issue as a limiting factor.

No matter how you cut it the trick is lightweight and highly conductive "ribbon". If you use 4 mil stuff, you'll get sound, but not much of it... might be interesting for ribbon subs? :rolleyes:

******* physics... grrrr. :D

_-_-bear :Pawprint:

APi 21st July 2005 11:50 PM

Quote:

Originally posted by dhenryp

It seems that you are assuming that your amplifier/transformer is a constant voltage source that can produce any amount of current. It can't.

Right.

I propably thought too many things at the same time when posted my thread. What you said is true: SPL versus driving voltage can be the same with a heavier membrane too but definitely not the power. My mistake.. :whazzat:

But still... There are propably flat cables thin enough to be used as a speaker even if the sensitivity is not good with them.

Audiophilenoob 21st July 2005 11:59 PM

APi

if you're looking for very thin fantastic ribbon material either in 4.3 micron or 5.8 micron gauges email me and I'll send you some for just the cost of shipping


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