# tweeters with resistors

dalfe5
Member - Posts: 19
Joined: June 20, 2006
Posted: October 06, 2006 at 3:40 PM / IP Logged
Could someone please explain why a resistor is used on some tweeters. I know about a capacitor but not why a resistor. From my understanding of a resistor it is to limit the power coming into it to a lower power coming out. I bought a pair of tweeters with a rating of 100w RMS but to use them with power over 60w you would need a resistor that is 16ohm/25watt. If it is used to lower the power to the tweeter then it's RMS shouldn be 100w. Alson the power rating was for the pair so anything over 60w per pair (30w per speaker).
dalfe5
Member - Posts: 19
Joined: June 20, 2006
Posted: October 06, 2006 at 4:37 PM / IP Logged
that doesnt help me understand. will you still have the same amount of WATTS coming out of the resistorand going to the tweeter? not trying to be an @\$\$ but just wanted to try to understand. So if it lowers the AC voltage the tweeter will still see the same amount of power?
hemanjoyman
Copper - Posts: 77
Joined: August 18, 2006
Location: United States
Posted: October 06, 2006 at 4:48 PM / IP Logged
Actually, I believe resistors limit the amount of current, not voltage. If there is a resistor in series with the tweeter, the tweeter will see less power as the resistor will dissipate some of the power.
geepherder
Platinum - Posts: 3,668
Joined: October 27, 2003
Posted: October 06, 2006 at 7:01 PM / IP Logged
Easy, killer. No one was trying to step on your toes. Wattage, resistance, voltage, etc. are interrelated. Yes, the resistor eats up some of the power and voltage, which limits the current to the tweeter. Basice ohm's law tells us that if resistance (impedence) goes up, current goes down. In a series circuit, if you have more than one load (a tweeter as well as a resistor), the voltage will be split between them.
Let's use this example: your daytime running lights probably use your high beams. Why are they dimmer than turning on your high beams with the headlight switch? They   run at a lower voltage because they are connected in series instead of parallel (using relays, etc.). They don't both use 12 volts, but rather 6 volts each, since they are connected end to end.
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stevdart
Platinum - Posts: 5,816
Joined: January 24, 2004
Location: Pennsylvania, United States
Posted: October 06, 2006 at 8:43 PM / IP Logged

Good info on the daytime headlights, geepherder.  Now I know...

(I love that feeling of knowing something that all those other drivers don't know.)

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geepherder
Platinum - Posts: 3,668
Joined: October 27, 2003
Posted: October 06, 2006 at 11:41 PM / IP Logged
Nouse, my post was not directed towards you, but the original poster who jumped your case. I guess you posted while I was still typing.
Yeah Steve, I've never been a fan of drl's so I did some research on how to disable mine. I had to remove a relay, pop the cover loose, and isolate the contacts with tape.
My ex once told me I have a perfect face for radio.
DYohn
Moderator - Posts: 10,741
Joined: April 22, 2003
Location: Arizona, United States
Posted: October 07, 2006 at 10:40 AM / IP Logged

The purpose of resistors in a speaker circuit is to match its sensitivity to other speakers being used.  It generally has nothing to do with protecting the speaker from over-power, although I suppose it could be used for that purpose.  If a tweeter operates at 91db sensitivity and you want to use it with a woofer that operates at 88db sensitivity, for example, you need to reduce the tweeter's output by -3db.  This is done by using resistors (or an L-pad, which is a variable resister bank.)  Resistors work by changing the voltage and current distribution in a given circuit, which changes the power utilization by the speaker.

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dalfe5
Member - Posts: 19
Joined: June 20, 2006
Posted: October 09, 2006 at 9:42 AM / IP Logged
the tweeter i am talkin about is rated at 100 watts rms.
on the instructions it says for use with systems over 60 watts rms use a 16ohm/25watt resistor. thanks for all of your help.
"killer"
DYohn
Moderator - Posts: 10,741
Joined: April 22, 2003
Location: Arizona, United States
Posted: October 09, 2006 at 11:05 AM / IP Logged

dalfe5 wrote:
 the tweeter i am talkin about is rated at 100 watts rms. on the instructions it says for use with systems over 60 watts rms use a 16ohm/25watt resistor. thanks for all of your help. "killer"

What's the tweeter?  What kind of crossover are you using?

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dalfe5
Member - Posts: 19
Joined: June 20, 2006
Posted: October 09, 2006 at 12:04 PM / IP Logged
it was a power acoustic NB-2. it had crossover built-in. but also needed a resistor. i returned it because nobody in town carried the resistor that was needed. did not even find the exact one stated online. close but not same. i tried tech support for power acoustic but he said it was for frequency to block the lower frequencys but i thought that is what a capacitor(buit-in crossover) was for. i thought power acoutsic was a dec ent brand but after finding them online for around ten bucks guess not.
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