A bit of electronic basics

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90_Black_GTZ
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A bit of electronic basics

Post by 90_Black_GTZ »

OK, I'm seeing a lot of ideas flying around here dealing with putting multiple speakers in parallel, what is the impedence, etc...  I want to put out some facts here for those that don't deal with this stuff normally.  

First off, you can't accurately MEASURE the impedence of a speaker.  What you would be measuring is the RESISTANCE.  Not the same!  I saw a post here stating that he put 3 speakers in parallel and they measured out to 1.68 ohms.  It doesn't work that way.  Impedence is the amount of resistance in an ACTIVE circuit, normally one that is involved with some sort of changing current or changing frequency.  A speaker will actually have different impedence at different frequencies.  There is a formula (ohm's law) that allows you to accurately determine the impedence of speakers in parallel.  You take each speaker impedence, divide each number by one (1/x) add those together, and then divide that whole product by one (1/x).  For example, we will take three 4 ohm speakers.  1/4 + 1/4 + 1/4.  That is .25 + .25 + .25.  This of course is .75.  Now, 1/.75, which equals 1.3333333333333 total impedence in ohms.  You can see how four 4 ohm speakers in parallel equal 1 ohm.  

Be aware of this as you connect your speakers together.  You need to be sure your amp can handle the low impedence.  As the impedence gets lower, you are of course getting closer and closer to zero, which of course is a dead short!  Think about putting a screwdriver across your output terminals of your amp and decide if that's what you want to do.  

I hope this helps.


90 Black GTZ (I am the original owner since May 5, 1990)
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A bit of electronic basics

Post by Guest »

Actually, you can measure the 'nominal' impedance with a volt/ohm meter. 'Nominal' impedance would be the impedance(resistance in ohms) of the device at rest. Most companies give a nominal impedance reading for their equipment, but manufacturing techniques will actually differ from one company to the next, no 2 makes of 4 ohm subs are usually equal. A 4 ohm Rockford can read as a 4ohm sub, where as a 4 ohm Pioneer is normally a 3.1-3.2ohm sub.

Other wise, ohm's law normally is right on the money with a high end Fluke meter, if you do the formula for a true 4ohm sub, such as 3 Rockfords, will yield the exact same result in that equation. But if you put the Pioneers to the test, you'll get a different result.

Ohm's law doesn't even take into account the ever fluctuating impedance of a sub in motion. I've seen impedance curves in the past on some equipment, but it's fairly mute, as their's not much you can really do about it unless you were to design an impedance equalizer and resonant-peak filter network for it. But now we're talking about high end home speakers, and less overall amplifier efficiency.

Another thing to consider is the way an amp drives the load. That 1.3ohm load that you came up with driven with a 1 ohm stable mono block wouldn't be a problem for the amp. But that 1.3ohm load driven by a 2ohm stable 2 channel amp could yield in a major failure in the amp. As the amp would operate as though it's driving a stereo .65ohm load if the amp were bridged mono to it.





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90BerettaGTZ
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A bit of electronic basics

Post by 90BerettaGTZ »

"duh"

hehe =)


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A bit of electronic basics

Post by Guest »

Haven't you people ever heard of an impedence meter... You might find an audioshop with one...
Or of course you could do some complicated stuff with a signal generator and oscilloscope and a calculator also..
If you know the impedence of your speakers in the frequency range you are playing, you could match them even better to your amp.
Thats why if you check on rockfords site they show 3 8 ohm subs in parallel  (1.3ohm resistance) on an amp rated 2ohm without a problem.


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A bit of electronic basics

Post by Guest »

Quote (JasonK @ July 31 2002,6:20)Haven't you people ever heard of an impedence meter... You might find an audioshop with one...
Or of course you could do some complicated stuff with a signal generator and oscilloscope and a calculator also..
If you know the impedence of your speakers in the frequency range you are playing, you could match them even better to your amp.
Thats why if you check on rockfords site they show 3 8 ohm subs in parallel  (1.3ohm resistance) on an amp rated 2ohm without a problem.
3 8ohm subs wired parallel is a 2.6666 ohm load


Guest

A bit of electronic basics

Post by Guest »

Yeah I ment 3 4ohm subs sorry, my brain hasn't been working lately..


Guest

A bit of electronic basics

Post by Guest »

What book that guy copy that out of.. and I'm not talking about Jack...  


Guest

A bit of electronic basics

Post by Guest »

Prob jacked one of my electronics books or something....


90_Black_GTZ
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A bit of electronic basics

Post by 90_Black_GTZ »

Quote (BowtieRocket @ July 31 2002,9:55)What book that guy copy that out of.. and I'm not talking about Jack... ÂÂÂ
All off the top of my head, if you were referring to me.  Honestly.  I also have been a ham radio operator for over 25 years, so electronic equations are part of everyday life.  

I just wanted to post this for people that may not have access to equipment available to check the impedence.  It takes a bit of the guesswork out of it for the regular guy, and maybe they won't cook some cheap amp by putting too much of a load on it.  

I hope it was useful to some.


90 Black GTZ (I am the original owner since May 5, 1990)
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A bit of electronic basics

Post by Guest »

*jumping on coattails*

This is a good article

http://www.lalena.com/audio/faq/wiring/


90_Black_GTZ
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A bit of electronic basics

Post by 90_Black_GTZ »

That's a very good article!  That should clear up a lot of things for electronic newbies.  That should be pinned at the top of the forum!

Good work.


90 Black GTZ (I am the original owner since May 5, 1990)
187,000 miles
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A bit of electronic basics

Post by Guest »

I have a better idea


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