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-   -   Why does a driver need to have DC resistance (http://www.diyaudio.com/forums/multi-way/38329-why-does-driver-need-have-dc-resistance.html)

goldyrathore 23rd July 2004 02:03 PM

Why does a driver need to have DC resistance
 
Hi,

Why does a driver need to have a DC resistance when most of the power is consumed by it to dissipate into heat? Would it not be more efficient to lower the DC resistance and only have the frequency dependent impedance to work with?

Thanks in advance,
Goldy

richie00boy 23rd July 2004 03:46 PM

We don't 'need' DCR as such, it is just a by-product of winding a coil of sufficient length to achieve a strong enough motor and avoid massive saturation. As such the impedance is related to the DC resistance, and affected throughout the spectrum by induced back-EMF and inductance.

If you just use thicker wire to get the DCR down you add mass which can be undesireable. You would just end up working with massive currents that would be very susceptible to losses.

markp 23rd July 2004 05:44 PM

Very low impedances means very high currents. It is easier to design an amp that does not need to deliver huge amounts of current as output devices are not designed for that level of current even if the voltage is low. p=iv, so bump up the voltage and lower the current to get the same number of watts. A 4 ohm load is a good medium between current/voltage but lower gets hard to do.

BillFitzmaurice 23rd July 2004 05:45 PM

To be concise it's because no one has invented an inductive coil that doesn't have DCR.

AGGEMAM 23rd July 2004 05:50 PM

Quote:

Originally posted by BillFitzmaurice
To be concise it's because no one has invented an inductive coil that doesn't have DCR.
Actually that's not true. Though it does involving freezing the thing to just about 0 degrees Kelvin, so I don't know how much good it'll do you or how useful it'll be in a home stereo.

jneutron 23rd July 2004 06:29 PM

Quote:

Originally posted by AGGEMAM


Actually that's not true. Though it does involving freezing the thing to just about 0 degrees Kelvin, so I don't know how much good it'll do you or how useful it'll be in a home stereo.

OH, geeze...you're exaggerating....

Even with a gap strength of 2 tesla, a 13 mil diameter niobium titanium wire will still carry 45 amps at about 10 Kelvin...

And the HTS stuff is useable at 77K....

Hey, liquid nitrogen is dirt cheap...how about a cryogenic diy subwoofer???

Cheers, John

Paradise_Ice 23rd July 2004 06:29 PM

Quote:

Originally posted by BillFitzmaurice
To be concise it's because no one has invented an inductive coil that doesn't have DCR.

Quote:

Originally posted by AGGEMAM


Actually that's not true. Though it does involving freezing the thing to just about 0 degrees Kelvin, so I don't know how much good it'll do you or how useful it'll be in a home stereo.

Bill you have a way with words! very direct and he is right.

AGGEMAN is talking about a Superconductor and dont worry one day you wont have to freeze it to zero kelvin! i hope.

I think we have a superconducting Niobium Wire but i dont know much about its properties or its use as voice coil.

i have looked into making a Titanium voice coil but it would cost me more than 200 to make just the voice coil and former with a Grade 5, 1 mm titanium wire! that is just to much for me to attempt yet.

Once molecular engineering come true in the next 10 or 20 years we will have room temperature superconductors, it will happen not because we need zero inductive coils but zero inductive chips!

I hope somebody can develope a moving magnet cone instead of the moving coil system we have now, who know if it would be better but it would be different thats for sure!

Eli Duttman 23rd July 2004 06:48 PM

Time out guys. Current and voltage are vector quantities, having both direction and magnitude. Power is the dot (scalar) product of the 2 vectors. The dot product of 2 vectors is obtained by multiplying the 2 magnitudes and the cosine of the angle between the 2 vectors (phase angle).

In an idealized circuit that has only reactance, the phase angle is 90 degrees. Cosine 90 degrees = 0; therefore, the power dissipated is 0.

In an idealized circuit that has only resistance, the phase angle is 0 degrees. Cosine 0 degrees =1; therefore, the power dissipated = IV = I^2R.

Eli Duttman 23rd July 2004 06:54 PM

Quote:

I hope somebody can develope a moving magnet cone instead of the moving coil system we have now, who know if it would be better but it would be different thats for sure!
Way back when, before the dynamic loudspeaker was invented, earphones and speakers used a fixed coil wound around a permanent magnet along with a sheet metal diaphragm as the moving entity. That's not moving magnet, but its close relative, moving iron.

For speaker service the dynamic system has proven superior.

Mr Teal 23rd July 2004 07:04 PM

The car audio company Phoenix Gold used to manufacture a very unique subwoofer call the Cyclone that used a fixed coil and a rotating magnet structure. It didn't produce much upper subbass (I know it's a contridiction ;) ), but it only required 150W and produce HUGE levels of 10-30Hz for the time.

The Cyclone


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