Theoretical vs. Actual ohm load...

[pervertatoid 10+ year member]

In theory, when I run my three subs (dual 2-ohm voice coils) in parallel with each voice coil being in series (therefore, three 4-ohm loads in parallel), I should have 1.333 ohms as my load. When I bust out the multimeter, however, (and I've tried it with multiple multimeters), I get a reading of 2.3 ohms. Is impedance rise due to wiring normally this high?

Thanks in advance

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[req 5,000+ posts]

read each coil on all the subs independantly.

you are looking at the nominal impedance verses the actual resistance. aka - most subs will be rated at 2 or 4 ohms. when you put them to test, most often they will be something like 3.6ohms for a "4 ohm load" or 1.7ohms for a "2 ohm load". they just round it up.

in all honesty, you wont hear an audible difference because music is dynamic and so is resistance (changes with the frequency) - ie impedance rise.

so unless all the coils are reading funky numbers like 2+ ohms off the nominal resistance, you are fine. or you wired them wrong //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[brynm 10+ year member]

read each coil on all the subs independantly.
you are looking at the nominal impedance verses the actual resistance. aka - most subs will be rated at 2 or 4 ohms. when you put them to test, most often they will be something like 3.6ohms for a "4 ohm load" or 1.7ohms for a "2 ohm load". they just round it up.

in all honesty, you wont hear an audible difference because music is dynamic and so is resistance (changes with the frequency) - ie impedance rise.

so unless all the coils are reading funky numbers like 2+ ohms off the nominal resistance, you are fine. or you wired them wrong //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Actually, resistance is fairly constant (I say fairly because it can change with temperature) Impedance due to inductive reactance is dynamic and changes with frequency.

 

[helotaxi 5,000+ posts]

Running current through the coil heats it up and resistance changes. This is power compression at its most elemental.

OP- how are you measuring the coil resistance right now? Is the amp still connected? Is it powered on? If you answer "yes" to either, you're measuring wrong.

 

[pervertatoid 10+ year member]

I'm measuring it with a multimeter at the box terminals (one set of terminals on the box, all subs internally wired to it) without external wires connected to the box.

 

[helotaxi 5,000+ posts]

Something is wired wrong, you have a bad coil or you have a bad connection inside the box.

 

[pervertatoid 10+ year member]

I'll definitely double-check everything in there to make sure it's all wired tight, and while I have it out, I'll check each voice coil as well. Thanks for the advice. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[ultimate157 5,000+ posts]

in all honesty, you wont hear an audible difference because music is dynamic and so is resistance (changes with the frequency) - ie impedance rise.

Resistance doesn't change depending on the input. Resistance only changes when something physical changes (Different components in the circuit, or a temperature variance)

 

[mokedaddy 5,000+ posts]

Could also be because your meter isnt totally accurate. Did you touch the leads together and try to get the reading as close to zero as possible? This can add to your total resistance.

 

[pervertatoid 10+ year member]

Could also be because your meter isnt totally accurate. Did you touch the leads together and try to get the reading as close to zero as possible? This can add to your total resistance.

I get a zero reading when touching the leads together on ALL of the multimeters I used. All of them read either 2.2 or 2.3 ohms when measuring at the box terminals.

 

[ultimate157 5,000+ posts]

I get a zero reading when touching the leads together on ALL of the multimeters I used. All of them read either 2.2 or 2.3 ohms when measuring at the box terminals.

I think you have 2 of the subs in series and 1 in parallel. That would be a 4 ohm load and a 8 ohm load (equivalent)

Therefore,

1/R=1/4 + 1/8

1/R=2/8 + 1/8

1/R=3/8

R=8/3

=2.6, and if each coil is slightly less than 2 ohms, you get close to 2.3 ohms //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[req 5,000+ posts]

Resistance doesn't change depending on the input. Resistance only changes when something physical changes (Different components in the circuit, or a temperature variance)

sorry, i meant music is dynamic - and therefore the resistance will be to - aka: impedance rise.

as frequency changes, impedance will change - eventually rising as it reaches Fs, and falling agin. causing a graph where Y=ohms and X=frequency, there will be an upward spike with the Fs at the center. eventually the inductance of the voice coil itself acting as an inductor (aka 1st order lowpass filter) will cause a natural ~3db\oct rolloff somewhere after a few hundred hz or so.

therefore - as the INPUT VOLTAGE TO THE SPEAKER changes, the net resistance to the amp will also change due to impedance rise. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

no?

for example;

or am i wrong, because im pretty sure im not.

 

[ultimate157 5,000+ posts]

You are correct, just a misleading word. I read resistance and thought DC, not impedance and AC //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif