misconceptions about impedence rise

[nineballsafety8 10+ year member]

i just ran across a post from october where someone asked how to measure impedence rise... well some of the replies... were factual but misleading. i just wanted to put out the closest answer i could give. so i thought i would share it with you all.

v/a=r is a valid representation of Ohm's law... HOWEVER. r does Not equal impedance... it equals resistance... resistance is not the same as impedance...

Z = Impedance (ohm)

R = Resistance (ohm)

XL = Inductance Reactance(ohm)

where Z=the square root of (R^2+XL^2)

The total impedance is not simply the algebraic sum of resistance and inductive reactance. Since the inductive reactance is 90 degrees out of phase with the resistance and, therefore, their maximum values occur at different times, vector addition must be used to calculate impedance.

and to calculate inductive reactance you need to know the inductive force of the driver in Henry's and the frequency at which you are trying to measure

then you use the formula XL=2(pi)fL

where XL= Inductive Reactance (ohm)

pi=exact number, which is about 3.1416 (constant)

f=frequency

L= inductance in Henry's

so in answer to the OP's question... unless you have a program that will calculate it for you... u might want to let the big dogs handle it.

Click to read more...

 

[JimJ 5,000+ posts]

You can put the same driver in two different enclosures, enter in the same frequency and get two very different results, I fail to see how that compensates for that //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

You're on the right track theory-wise, but in real-life use for SPL testing there's no substitute for a clamp meter and DMM.

 

[Chevillac 5,000+ posts]

This should be a pretty good discussion.

subscribed.

 

[nineballsafety8 10+ year member]

im not debating the affects of the enclosure on impedence rise... i was just pointing out that a basic application of Ohms, law MAY get you fairly close, but mathematically it is not correct and will only give you a reference point. If you use the correct equations, then yes a clamp and mm are the best answer

 

[IgnoreMe 5,000+ posts]

This should be a pretty good discussion.
subscribed.

i agree. ill be watching this one.

 

[helotaxi 5,000+ posts]

V=IZ just like V=IR

Ohm's law is still Ohm's law and the fact that current and voltage are not in phase has no bearing on that fact. The voltage induces the current according to Ohm's law, the current is phase delayed based on coil inductance and the current through the coil actually causes it to move.

Last I checked you don't account for phase delay when plotting the impedance curve cause it just doesn't matter. It matters for (dictates) the phase response of the driver which matters when trying to blend drivers together in a system, but as far as actual power applied and the impedance properties of the driver, phase is irrelevant.

What you are talking about is how to derive the impedance from the basic values. You can go that route, or you can not care about the components of the resultant impedance and just measure it indirectly with a DMM and clamp.

 

[nineballsafety8 10+ year member]

i think i just said that.... i have to admit u said it more gracefully than i did, but still, same same

the person who originally asked this question didnt have a clamp or meter, and just wanted to do the math... and i was just clarifying that when doing it all on paper frequency is a factor. and u cant just use voltage and current, because that would be a flat line and not show you any rise anyway.

i was trying to convey the concept behind how the impedence actually changes do to the frequency.

 

[nineballsafety8 10+ year member]

also dont misunderstand... i am not an industry expert. i am a previous installer, so have some background in the biz... but most of my knowledge are from my degrees (aas in electronics, and bas in physics)... i am an electronic warfare specialist from the army and just wanted to clear up any parts of the theory involved that the less educated enthusiest may not have had access to.

all debates and threories welcome here.

 

[azimuth 5,000+ posts]

also dont misunderstand... i am not an industry expert. i am a previous installer, so have some background in the biz... but most of my knowledge are from my degrees (aas in electronics, and bas in physics)... i am an electronic warfare specialist from the army and just wanted to clear up any parts of the theory involved that the less educated enthusiest may not have had access to.all debates and threories welcome here.

electronic warfare specialist. that is one badass title to have. so. when are the nuclear powered amplifiers going to be invented?//content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[nineballsafety8 10+ year member]

lmao... its not as cool as it sounds. but i have been known to play with an amp on occation. with some love i got an old school mtx 275x two channel to run 385watts at 4 ohms

 

[lostdaytomorrow 10+ year member]

Stay safe in the sand box brother.

 

[NDMstang65 10+ year member]

Close as you are going to get to real world wattage that is decently affordable is playing a single frequency tone burst, and taking amperage and voltage readings using fluke equipment...

Which will give you a decent idea on your impedance rise from one frequency to the next..

Typically speaking SPL peaks when impedance peaks...oddly enough, you are loudest with the least amount of power //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[nineballsafety8 10+ year member]

...appreciate the concern, will try not to get blown up for ya.

...and in response to the spl vs. imp I THINK, not sure, but I THINK it has a direct relationship to amplifier effiency and damping factor... ie... when the impedance goes up, while the power may drop a little, the power that IS going to the driver has better control of the cone.

 

[NDMstang65 10+ year member]

Ehhh sort of...

When you are closest to tuning (in an extreme vehicle) you are going to have your impedance spike..which equates to around 179.3dB in the 3-4 van with 3162 watts...more power isn't louder at that point, it just breaks stuff //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif.

Regardless of the damping factor of the amp

 

[nineballsafety8 10+ year member]

ehh... not sure, just my feelings. wonder where to get a solid answer on that one... hmmm let me hit up mr studley and see if he has any answers