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Old 26th October 2007, 01:21 PM   #1
arc2v is offline arc2v  United States
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Default Impedance peak (worry or not?)

I don't have the plot with me, but last night I did some detailed measurements on my OB center channel loudspeaker.

After some tweaking and fixing some mis-wiring, I got everythind sounding great.

The speaker is a 3 way design, crossed at 500 Hz (2nd order) and 3kHz (3rd order).

The ideal impedance plot is below.

the measured response of the speaker is very close to that with one exception:

There is a big peak (over 32 Ohms, which was the scale limit I was looking at) at 3-5 kHz. The ideal plot shows a smaller peak in that area.

Two questions:
1) Anything to worry about? Will it restrict dynamics in introduce any type of distortion? So far it sounds great and the amp (Outlaw) seems to handle it fine.

2)If it is a problem, what is causing it and how should I fix it? Zoebel?

Thanks,
AC
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Old 26th October 2007, 11:03 PM   #2
Svante is offline Svante  Sweden
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If you drive it with a normal amplifier with reasonably short cables; don't worry. The only little concern I could have is the dip at 800 Hz, where the impedance is close to 3 ohms. You should have an amplifier that can take 4 ohms nominally in order to handle that.

You don't get distortion from a frequency dependent impedance unless the impedance is too low for the amplifier. You might get an effect on the frequency response, though, but that is typically small and depends on the output impedance of the amplifier and the cable resistance.

Example:
If the amplifier has an output impedance of 0.1 ohms, and the cable has a resistance of 0.1 ohms there will be different attenuation depending on the varying impedance.

At 25 Hz, the impedance is 15 ohms. This leads to an attenuation of 20*log(15/(15+0.1+0.1))=0.12 dB

At 800 Hz the impedance is 3 ohms, so the attenuation is 20*log(3/(3+0.1+0.1))=0.56 dB.

The difference is 0.44 dB. This means that the frequency response will whiggle by 0.44 dB due to the impedance variation. It is audible, but hardly worth bothering about.
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