Why does a driver need to have DC resistance - Page 4 - diyAudio
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Old 25th July 2004, 11:44 AM   #31
Mudge is offline Mudge  United Kingdom
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You're all aware that as Re tends to zero, Z tends to infinity, right?
Without Re, you can have no potential difference, and if you have no PD you can't make it time variant. That's the theoretical basis for the Bybee filter - though whether it actually works or not is a matter of conjecture.
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Old 25th July 2004, 12:57 PM   #32
Svante is offline Svante  Sweden
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OK guys, to straighten things out (maybe) this is what happens if we take an ordinary bass-reflex system and make the voice coil resistance decrease from 6.1 ohms to 0.1 ohms. Everything else is kept constant (that is, things that are not affected by Re. Qts for example drops to about 0.006, but that is a direct consequence of the reduced Re).

Red is 0.1 ohm, blue is 6.1 ohm. Thick lines are the system responses, lower thin lines are the electrical impedances, other thin lines are responses from the ports and drivers.
Note that there are peaks in the response that corresponds to resonances between reactive components (For example, the leftmost at 300 Hz is between the voice coil inductance and the "capacitance" that originates in the moving mass) Also note that the phase angle of the electricla impedance tends to be either plus or minus 90 degrees (this is the lowest thin red line at 200 Hz in the phase display)

So, what will happen is that the electrical impedance will be dominated by reactive components, at some frequencies there will be resonances, efficiency will be high ie little active power will be needed for a certain acoustic power, but a lot of reactive power will be needed. This will be difficult for the amplifier to handle.
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Old 25th July 2004, 03:19 PM   #33
moamps is offline moamps  Croatia
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Default Re: Let me explain my question clearly

Quote:
Originally posted by goldyrathore
I was wondering if we could lower the DC resistance of the coil (for practical reasons we could gold-plate it) to a very low value.
Hi,
gold has higher resistance than silver and copper.

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Old 25th July 2004, 06:21 PM   #34
Svante is offline Svante  Sweden
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Default Re: Re: Let me explain my question clearly

Quote:
Originally posted by moamps

Hi,
gold has higher resistance than silver and copper.

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Milan
I think aluminium is the metal that has the best (lowest) density*resistivity factor. In rare cases it is used in loudspeakers.
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Old 25th July 2004, 06:31 PM   #35
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Default Re: Re: Let me explain my question clearly

Quote:
Originally posted by Paradise_Ice


I understand what you are saying.

I have had this type of discussion before and it was geared towards thermal heat energy that is a by product of high power and DC resistance, coating the voice coil in gold sounds like a nice idea, forget about the cost and the weight but its not.
The best Voice coil i have ever seen in my life was a Silver voice coil, i believe its the best material for a voice but it is very expensive, and tarnishes very easily, so special care is needed.
Carbon-Graphite could be used in the future?
The problem is drive unit tecnology is very old and has not changed in the last 100 years for all intense purposes.
Its good,but has its limitation,and this is one of them.
You could post this thread in the Amplifiers section and get some interesting post?
Corrosion is not a problem - you forget that voice coil wire must be insulated electrically, and that solves also the problem of the metal reacting with the air.
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Old 25th July 2004, 06:42 PM   #36
moamps is offline moamps  Croatia
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Default Re: Re: Re: Let me explain my question clearly

Quote:
Originally posted by Svante
I think aluminium is the metal that has the best (lowest) density*resistivity factor. In rare cases it is used in loudspeakers. [/B]
Hi,
most JBL tweeters have aluminium coils because the most limiting factor for tweeter coils is their weight. In LF drivers, on the other hand, copper appears to be a better choice and it is used quite frequently (higher current capacity and problem-free connections).

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Milan
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