Changing a speaker's impedence?

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lamarth

Limp Gawd
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Sep 22, 2004
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I've got a general electronics question - I've got a replacement car speaker for my car that's got a impedence rating of 4 ohms. My original speaker though was 8 ohms, otherwise the replacement is a perfect fit. However I've been told that the 4 ohm speaker will eventually burn out the car stereo's output amp as it was originally designed to handle 8 ohm speakers.

My question: is it possible to add - say a LC circuit for example - between the amp and speaker (for each channel) so that to the amp I'm running a 8 ohm speaker without seriously degrading sound quality?

Thanks!
David
 
I have never really heard of this being done before but if you get, say a 4 ohm resister able to handle the wattage you would be putting through it, you could wire it in series with the speaker and that should work. But your better off getting a 8 ohm speaker
 
um, I'm pretty sure it won't work like you think it will. I have forgotten the reason- but I'm posting this so that you will research it more before going with this solution.

Sorry if this isn't of much help....
 
Sesheron said:
I have never really heard of this being done before but if you get, say a 4 ohm resister able to handle the wattage you would be putting through it, you could wire it in series with the speaker and that should work. But your better off getting a 8 ohm speaker
Click to expand...

Well I have found this one place that's got the correct 8 ohm replacment speakers- at $40 each :eek: If it comes down to it I'll do it (I'll have to buy 2 of them, too :( ) but I'd like to look into this possibility, first.

And yes I had thought that maybe a resistor in series would work but then I got to thinking that impedence is usually a AC resistance. A resistor would work for DC but I'm not sure of AC, which is why I had used a LC circuit for an example.
 
Resistor will work fine. The resistance at DC is based on the inherent DC resistance of the wire in the speaker. From there, AC impedance adds to the total resistance, 4 ohms is merely a minimum number (although it's really a nominal 4 ohms so it can be, and usually is, less). Adding a resistor will give you another 4 ohms, but you will only get 1/4 the power out of the speaker. Depending on the sensitivity of the speaker, this might be OK or it might not. All things being the same, a 4 ohm speaker is usually more sensitive (standard 2.83v test) than an 8 ohm one, but draws more current. I would try adding 1 ohm at time in series until the apparent loudness matches the other speakers - just a couple of ohms will make a big difference in sensitivity and load on the amp.
 
I agree with Fenris. Resistors in series are added as a whole. If you were to add one in series you could potentially match the required resistance.

However, in adding more resistance you are limiting your current and thus your power output (everything is related remember). You may not get the required wattage to power the driver in the speaker correctly. I can't confirm that at all because I have never done speaker work but I have done a lot of electronics work.
 
There are subtle differences between resistance and impedance, primarily in that impedance is ac oriented and will change value depending on frequency... The impedance rating of speakers is an average value over the audio frequency range and will actually be higher or lower at any given time. This is very different from the fixed resistance of a resistor which will be the same across the bandwidth.

That said, you can probably use a properly rated 4ohm resistor in series to protect your amp, though the better solution is to use the correct speaker as that will also ensure both channels sound the same.

Another solution would be to use a matching transformer, but I can't see how that would jusity itself in terms of cost.

Oddly, I believe most car audio systems are 4ohm, not 8.
 
agent420 said:
There are subtle differences between resistance and impedance, primarily in that impedance is ac oriented and will change value depending on frequency... The impedance rating of speakers is an average value over the audio frequency range and will actually be higher or lower at any given time. This is very different from the fixed resistance of a resistor which will be the same across the bandwidth.

That said, you can probably use a properly rated 4ohm resistor in series to protect your amp, though the better solution is to use the correct speaker as that will also ensure both channels sound the same.

Another solution would be to use a matching transformer, but I can't see how that would jusity itself in terms of cost.

Oddly, I believe most car audio systems are 4ohm, not 8.
Click to expand...

yeah, don't use a resistor. Go to a car audio forum like http://www.icixsound.com/vb/index.php and ask.

Actually, car audio speakers vary in impedance- 4 and 8 ohm being very common, but there are 6 ohm out there, etc.
 
Correct, from what I understand most modern car stereos use 4 ohm speakers, which I guess is why it's almost impossible to find a 8 ohm speaker nowadays. What I have is a older stereo (about 40 years old) and they used 8 ohm speakers at that time. I think the total wattage per channel on this stereo is 8 watts. At least I think it's per channel... :/

TOOL1075 - thanks for the link, I'll pose the question over there, too.
 
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