Ribbon Field Strength

[tinitus]

Originally Posted by Borat

in other words i don't see a planar as having an advantage over a ribbon simply because it has higher impedance.

I would never claim that
It was only ONE of several points

Also dont forget that having just a couple more signal strings makes it possible to make them a bit wider, and maintain the same impedance
Which will result in improved power handling

I have made several long ribbons, a long time ago
And I do remember the flapping back and forth
Completely out of control at anything higher than "normal" low SPL
Sure, you can deal with that by using steep aktive filters, or higher xo point

I would like it to go down to 300hz

[thadman]

Originally Posted by Borat

it seems to me that you can always double efficiency by making the ribbon material twice as thin.

i mean you can always picture a ribbon as two ribbons in an iso-barik alignent and then just remove one of them so you get same output from 1/2 power input.

the point of isobaric is to work smaller box but if you're running a dipole its just dead weight.

in other words i think reducing ribbon thickness can go a long way in increasing efficiency without the need for a strong field.

lets do some quick math. a prosound woofer that is 95db efficient will have about 1/3 of its coil inside a field about 0.8T so the average field on the coil is about 0.3T

it will also have about 1/3 of its moving mass being the voice coil so you can say that the average field on the mass is 0.1T
f
so 0.1T gets it up to 95db despite having a moving mass of about 250 grams. the only thing it has going for it is large surface area. but if i keep surface area on the same order of magnitude ( say 4" wide ribbon, 2 meters long ) and field strength only a little lower ( 0.06 vs 0.10 ) but reduce moving mass from 250 gram to ... 10 gram. efficiency should go above 100db/watt.

A loudspeaker is a system, the diaphragm is simply a constituent of the system. In a traditional ribbon alignment where a magnetic circuit is utilized, the mass of air behind the ribbon is coupled to the diaphragm. The mass of air is often much larger than the mass of the ribbon. We thus must include the total mass of the system (ie mass of ribbon + mass of air) if we wish to reach resolution on its efficiency.

By reducing the mass of the ribbon, you are simply approaching the mass of the air. The differences in mass quickly become negligible and an increase in sensitivity may not necessarily be observed.

[a.wayne]

Originally Posted by tinitus

I would never claim that
It was only ONE of several points

Also dont forget that having just a couple more signal strings makes it possible to make them a bit wider, and maintain the same impedance
Which will result in improved power handling

I have made several long ribbons, a long time ago
And I do remember the flapping back and forth
Completely out of control at anything higher than "normal" low SPL
Sure, you can deal with that by using steep aktive filters, or higher xo point

I would like it to go down to 300hz

Try more tension .....

[a.wayne]

Originally Posted by LineSource

Many DIY ribbon tweeters are built with the goal of getting higher effiiency than the common 91-94db/watt 25mm dome, and this requires a gap field of about 0.6-0.8T. This is easy to achieve with NdFeB magnets. For a tweeter, I would design the gap flux to reach 96-98 db/watt effiency to provide some magical musical dynamics. A high efficiency ribbon tweeter avoids the need to play with horns and compression drivers.

A longer, larger area midrange ribbon with efficiency <90 db/watt requires very high currents into very low a resistance, so there is value in keeping the gap field >0.1T.

For large ribbons, it is so difficult to generate high currents that the steel and magnet cost to stay above 90 db/watt is worth the effort.

==============

Bl - The product of magnet field strength and the length in meters of ribbon suspended in the magmatic field

Re - DC resistance of the ribbon, measured in ohms.
Mms - Mass of the diaphragm, including acoustic load, in kilograms.
Sd - Projected area of the driver diaphragm, in square meters.
η0 - The reference efficiency of the driver, in percent


η0 =(5.445×10-4 m²·s/kg * (Bl²*Sd²/Mms²*Re ))*100%
dB(1 watt) = 112.02 + 10*log(η0)

SPL at 1 meter for an input of 2.83 volts is then:
dB(2.83 V) = dB(1 watt) + 10*log(8/Re)
= 112.02 + 10*log(η0) + 10*log(8/Re)

Hello Line source ,

Interesting , as i have never seen a big ribbon having 90 Db/2.83 V/M sensitivity , could you explain more .

[tinitus]

Originally Posted by a.wayne

Try more tension .....

Sure, but not possible with corrugated ribbon

Another significant problem with tention, be it ribbon or planar, is the resulting "drumskin-effect"
And the tendency to "rattle"
Which makes the corrugation crutial

[Borat]

Originally Posted by thadman

A loudspeaker is a system, the diaphragm is simply a constituent of the system. In a traditional ribbon alignment where a magnetic circuit is utilized, the mass of air behind the ribbon is coupled to the diaphragm. The mass of air is often much larger than the mass of the ribbon. We thus must include the total mass of the system (ie mass of ribbon + mass of air) if we wish to reach resolution on its efficiency.

By reducing the mass of the ribbon, you are simply approaching the mass of the air. The differences in mass quickly become negligible and an increase in sensitivity may not necessarily be observed.

well i understand that. but i think by the time ribbon mass is on the same order of magnitude as air mass efficiency should already be quite good.

[thadman]

Originally Posted by Borat

well i understand that. but i think by the time ribbon mass is on the same order of magnitude as air mass efficiency should already be quite good.

Instead of mass, you may consider compliance. Would you not admit that a weaker spring is easier to deflect (less required force) than a stronger spring?

[Borat]

Originally Posted by thadman

Instead of mass, you may consider compliance. Would you not admit that a weaker spring is easier to deflect (less required force) than a stronger spring?

but compliance only becomes a factor at lowest frequencies. it would effect a cutoff frequency more than efficiency.

[tinitus]

Originally Posted by Borat

but compliance only becomes a factor at lowest frequencies.

Ehh, no I think not

it would effect a cutoff frequency more than efficiency.

And why not? you gave the answer yourself