resistors for impedance mismatch

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daramagi

Member - Posts: 1

Joined: July 12, 2004

Posted: January 04, 2007 at 2:25 PM / IP Logged

I have a Dual Voice coil speaker where each coil is 4ohms. I am trying to present a 4ohm load to the amplifier by using a resistor (Ceramic wire wound)

I know that if I connect each coil in series, I get 8ohms. Thus needing an 8ohm resistor wired in parallel between the speaker and the amplifier to get 4 ohms.

and

I know that if I connect each coil in parallel, I get 2ohms. Thus needing an 2ohm resistor wired in series between the speaker and the amplifier to get 4 ohms.

The first question is, is there a prefered method between these two schemes?

And the second question is, what wattage resistor? 5w,10w,25w.... ?

I am not concerned about the resistors consumption of power at this point (I've allready read other postings).

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DYohn

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Joined: April 22, 2003

Location: Arizona, United States

Posted: January 04, 2007 at 2:33 PM / IP Logged

Using a resister is not a good idea. Just use one VC of the speaker.

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haemphyst

Platinum - Posts: 5,054

Joined: January 19, 2003

Location: Michigan, Bouvet Island

Posted: January 04, 2007 at 2:35 PM / IP Logged

Is it a mono amp or a stereo amp? What is it's maximum safe load?

ANYTIME you add a resistor, (and in BOTH of the examples you stated above, specifically) one half of your amplifier's output power will be dissipated in the resistor. This will result in a reduction of output of 3dB, but so will running the amp at 8 ohms, and wiring the voice coils in series will use all of the amplifier's power in the voice coil. Forget the idea of the resistor, and wire everything correctly, to start with.

A stereo amp, with one channel of the amplifier running each voice coil, will present your desired 4 ohm load. Wiring the voice coils in series, and bridging the amplifier, will also present the desired 4 ohm load. I have never seen ANY mono amplifier not stable to 2 ohms, either.

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

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resistors for impedance mismatch

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