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Author Topic: amp impedance matching  (Read 2089 times)

quadnet

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amp impedance matching
« on: March 13, 2006, 10:25:50 PM »

i just realized something and was wondering if its ok to run this setup this way. i noticed on my stereo system, the speakers im using has an impedance of 4 ohms. the amp im using wants an impenace of 8 - 16 ohms connected to it. i know that with this setup im not geting maximum power transfer, is there a way i can fix this by putting a resistor in series with the speakers? or should i not worry about this?

thanks
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wonko

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Re: amp impedance matching
« Reply #1 on: March 14, 2006, 06:44:16 AM »

You talking home stereo or car stereo?
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quadnet

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Re: amp impedance matching
« Reply #2 on: March 14, 2006, 07:48:04 AM »

home stereo
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wonko

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Re: amp impedance matching
« Reply #3 on: March 14, 2006, 05:42:45 PM »

Well, there's several things to check before you change anything.  First of all, If your amp is stable @ 4 ohms, then you shouldn't be loosing any power.  In fact, you may get an increase in the power due to the lower impedence (less resistance) that your speakers are drawing.  I know in alot of high end home and car amps halving the ohm rating doubles the amps output power.  Do a little looking on the web to get some more specs on your amp before you start changing speaker configuration.  If you decide you need to get your speakers up to 8 ohms there are a few things you can do.  If you can give a little more info I think we can solve your problem.
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linear

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Re: amp impedance matching
« Reply #4 on: March 27, 2006, 03:19:40 PM »

Impedance matching would be a transformer, not a resistor.

You aren't getting max transfer, but as wonko points out, if you get stable performance (no flames shooting out of your amp) then I'd just go with it.
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wonko

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Re: amp impedance matching
« Reply #5 on: March 27, 2006, 08:01:58 PM »

If your still concerned about getting everything to match up there are a few things you can do.  By wiring 2 4 ohm speakers in series you will get 8 ohms by the time the signal gets back to the amp.  If your not sure how to wire in series, let me see if I can explain... Take the positive OUTPUT from the amp and connect it to the positive INPUT of the 4 ohm speaker.  Then, take the negative OUTPUT from that 4 ohm speaker and connect it to the positive INPUT of a second 4 ohm speaker.  Lastly, take the negative OUTPUT from speaker #2 and connect it to the negative INPUT of the amp.  Now you will have 8 ohms at the amp.  Basically, all you do when wiring anything in series is add up all the resistance (r1+r2+r3...= total resistance) to get what you need.  BUT, if your using any sort of passive filter (capacitor or coil) as a high pass or low pass filter things will change.  In this case a multi-meter will be your best friend.  Please feel free to IM me if you need more help.  There have been books written on this subject, and I don't want to write my own here lol.  Let me leave you with the 2 formulas you'll need to figure whatever you need for your speaker wiring...

Series...R1+R2+R3...(etc.) = total resistance.
Parallel...R1+R2+R3...(etc) divided by the total number of componants = total resistance.

Example: 2 4 ohm speakers wired in series will give you a total resistance of 8 ohms.
             

« Last Edit: March 27, 2006, 08:05:50 PM by wonko »
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quadnet

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Re: amp impedance matching
« Reply #6 on: March 27, 2006, 10:27:10 PM »

thanks for all the info. i guess i shouldent worry about it, the stereo amp seems to be running fine. so if its not broken, im not going to fix it.

side note: when placing resistors in parallel, the total resistance is 1/((1/R1)+(1/R2)+(1/R3)...)
« Last Edit: March 27, 2006, 10:28:55 PM by quadnet »
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wonko

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Re: amp impedance matching
« Reply #7 on: March 28, 2006, 06:43:28 AM »

That is true, but it's different with speakers.The easiest way to get total impeadance when wiring speakers in parallel is to add up all the ohm ratings of the speakers, then divide that # by # of speakers.
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i7dude

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Re: amp impedance matching
« Reply #8 on: March 28, 2006, 10:52:55 AM »

That is true, but it's different with speakers.The easiest way to get total impeadance when wiring speakers in parallel is to add up all the ohm ratings of the speakers, then divide that # by # of speakers.

Ok, I'm sorry to be "that guy" but I have to point out that its not different at all...

Assuming R1 = R2 = R3

1 / ( (1 / R1) + (1 / R2) + (1 / R3) ) = 1 / (3 / R) = R / 3

So yes you are right, if all speakers in parallel have the same impedance it is simply the average of the impedances.  But quadnet was giving a general equaition for summing resistance in parallel...you are both right, but for general cases, quadnet is more correct.

dude.
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wonko

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Re: amp impedance matching
« Reply #9 on: March 30, 2006, 06:24:21 AM »

Dude, your right.  I guess I didn't go into enough detail when I wrote that (maybe the affect of too much beer?).  I was just assuming that all the speakers were the same impeadance and was giving the easiest way to figure that.  I'm gonna let this thread go now  ;).
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