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Old 23rd November 2002, 09:20 AM   #1
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Question Inline resistor raise speaker impedence?

If I put a resistor inline with a speaker will it affect the dynamic impedence of the speaker? As in a 4 ohm resistor with a 4 ohm speaker make an 8 ohm load?

I'm wondering cause partsexpress has one hell of a deal on buyout Onkyo car speakers (read not great speakers, but damn cheap), but the one I was looking at was 2 ohms, and I don't think my stock head unit would like so much.

http://www.partsexpress.com/pe/pshow...number=269-727

figured if it worked than a 50 cent resistor and $2.27 speaker would be a good deal
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Old 23rd November 2002, 11:56 AM   #2
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The benefit would be that your stereo amp will see an 8 Ohm load and be happy. The tradeoff is the output power through the speaker will be only 1/4, or 6dB less than, what you would have with a regular 8 Ohm speaker, assuming equal efficiency of the speakers. That may be a problem because that 2 Ohm speaker may not be efficient. And, you would probably be less concerned that an inline resistor lowers the damping factor acting on the speaker, muddying the response.
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Old 23rd November 2002, 12:30 PM   #3
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Since these are car speakers and you mention "stock head unit", I assume you mean to put these into your car. In that case you want to raise the impedance to around 4 ohms. For that, you need a 3 ohm resistor.

If:
X = impedance of the speaker
R = resistance of the resistor

The impedance of the total unit will be given by the following formula:
square root of (X squared + R squared) =
square root of (2 squared + 3 squared) = 3.6 ohms. Close enough to 4 ohms.

The speaker has a Qts of near 1. Put that resistor in series, and your Q will go way up. So instead of being near the midpoint around 65 Hz-which is the Fs-the speaker will boom quite a bit near there. It will be about 4 or 6 dB up or higher around 65 Hz. You might not like that, or maybe you will. Maybe you have an equalizer on board that you can take that down. On the other hand, a lot of people simply like to crank the bass up on their car speakers anyway, so your halfway there to start with.

The following chart gives response shapes for systems with final Q numbers. With the resostor, your Qtc will be either 1.5, 2.0, or higher. You can see how it booms over the midpoint.
http://www.diyaudio.com/forums/showt...ight=chart+Qtc

Bass might be emphasized, but it will NOT be lean and tight. Rather boomy. But again, maybe you might like it.

If you can find a place in the car to hook up a second pair that you have wired in series, then you don't have to worry about any of that. The speakers will play just as they are supposed to, and your car's head unit will see a nice 4 ohm load without any resistors necessary.

In short, hook up the resistor and it will play safely. Whether you like the sound or not is open to question. At these prices, you can afford to experiment.
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Old 23rd November 2002, 01:03 PM   #4
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PS: In my last post I wrote: "In short, hook up the resistor and it will play safely."

Please amend that to say: Hook up a single pair with the resistors and they will play safely. Hook up two pairs in series and they will play safely without the resistors."

Thanks.
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Old 24th November 2002, 01:29 AM   #5
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Thanks for the info. I dont really care about the fidelity in car stereo, so if it has a little accented bass in the rear (these would go in the rear deck), then I can either live with it or fade forward a little. But even so a 65 hz boom is much more acceptable than say a 200 or 400 hz boom. And like I said for about $6 total for the pair, its not like I can complain much.

I just like the fact that the speaker itself is alot better quality than what it came with stock (96 Integra 4 door)
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Old 24th November 2002, 02:27 AM   #6
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Well, I cannot argue with your thinking. For 6 bucks-why not?

Since you are putting these into the rear deck, there is one alternative in case you want to go hi fi with these.

Isobaric.

This is where you make a little enclosure there one speaker is hooked up behind another. The idea is that the rear speaker goes back and forth and gives the front speaker a nice even air load on the backstroke. The rear of the rear speaker would fire into the trunk.

I've never built an isobaric configuration, but many people in this forum have vouched that they do work. It's a proven configuration.

If you hook them up in series, you will have a 4 ohm impedance for your head unit to drive.

Here is an illustration. The front speaker would of course be attached to the rear deck.

The speakers can also be hooked up face-to-face, but that might not be sightly in a car.


Anyway, if you care to do it, the isobaric idea will give better fidelity in the hokup while giving you a 4 ohm load. Remember to hook them up in series.

For six bucks a pair, it might be worth it.
Attached Images
File Type: gif isobaric drawing.gif (3.6 KB, 342 views)
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Old 24th November 2002, 03:45 AM   #7
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Quote:
The speakers can also be hooked up face-to-face, but that might not be sightly in a car.
If you hook them up face to face, you will get little response above a couple hundred hertz....
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Old 24th November 2002, 04:12 AM   #8
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Learn a new thing every day. Thanks, AudioFreak.
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Old 25th November 2002, 03:50 AM   #9
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Quote:
Originally posted by AudioFreak


If you hook them up face to face, you will get little response above a couple hundred hertz....
This is because the magent and stuff is facing you and not the center of the cone, which radiates the high frequencies....right??

Also if there facing each other you wire them out of phase with each other, so they complement each other??
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Old 25th November 2002, 03:55 AM   #10
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So if the resistor raises the Q of the speaker at the resonance freq, then could this be an easy way to reinforce a subwoofers response? I mean could you make a sub have more output down low, since your not worring about anything above 80-100 Hz anyways? Seems like an easy way to make a 10" or 8" have more low end extension, by bringing back the freq that are dwindling away.
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Old 25th November 2002, 04:06 AM   #11
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Well, I guess that might work except that most resistors (like the mills ones) are only rated for like 10-20 watts, so that might not work well in this situation....or can you use like power resistors....or does the driver absorb more of the wattage?
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Old 25th November 2002, 05:47 AM   #12
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What is the output of your head unit? How many watts?
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Old 25th November 2002, 05:31 PM   #13
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Well, Im making a Sonotube sub for home, and I have a bunch of 8" driver sitting around and was thinking maybe this would extend the lower freq's so that it could easily play down to ~40 Hz. But of course I would be using at least a 50 watt amp on those, so thats what I was wondering about the resistor. Parts Express sells "Audio Dummy Load" resistors that can handle up to 100 or 200 watts (pn# 019-015)
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Old 25th November 2002, 06:12 PM   #14
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I'm confused. I thught you said these were for the rear deck of your car.

Did you mean you want to put a resistor in series with your subs at home?

Doing so will cut the output of the subs at home.
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Old 26th November 2002, 04:00 AM   #15
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KW,

It appears that Westrock has 2 projects going at once.
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