What is impedance rise?

[bkolfo4]

Funny, DC resistance is really not the "coil at rest", it is the resistance of the coil with DC current passing through it. The instananeous current of an AC signal applied (this may be why they say "coil at rest") may cause a coil impedance equal to the DCR for a very brief time, because the coil (an inductor) is not energized yet, but that really is not the true definition of DCR.

Music, burps, etc are not DC current, they are AC. The impedance varies with frequency for multiple reasons, the 2 biggest for praactical sub applications being the inductance of the coil varies with frequency (acting like a low pass filter), and the reaction of the cone changes when different frequencies are played (look at a impedance plot of a sub - it spikes at the drivers Fs).

Since cone reaction can change the impedance, it is of course going to change when the driver is installed in a box with changing back pressure. This is what people refer to as impedance rise.

In every system I have built, the smaller the box is, the more the overall impedance rises. But I build systems to play music. For SPL burps, port tuning and frequency you burp at are going to be the big factors in the impedance the amp sees during the burp, along with some effect from the size of the box.

There is more to it than this, but maybe it give you a better idea. . .

Brian

[Eric B]

Your good posting here.

X2 on the Impedence rise, I know it's calculated after you measure the clamped power on your amp (AC Ammeter around the postitve speaker terminal times the peak AC voltage on the positive and negative terminals). I'm sure its in my MECP Advanced installer book but i would rather have someone explain it here.

Your gunna want a True-RMS Clamp Meter to measure your AC Amperage and jus use a DMM to measure your AC Voltage and your gunna want peak hold on that also.. And just multiply those 2 numbers to get your RMS Wattage.. and to find the Impedance rise on that frequency you divide the voltage by the amperage and then youll see what your impedance rise is. It will vary frequency to frequency. But to help cut down Impedance Rise you typically need to make a bigger box, a smaller box will cause the impedance to rise more than a larger box..

[Big Lo]

Funny, DC resistance is really not the "coil at rest", it is the resistance of the coil with DC current passing through it. The instananeous current of an AC signal applied (this may be why they say "coil at rest") may cause a coil impedance equal to the DCR for a very brief time, because the coil (an inductor) is not energized yet, but that really is not the true definition of DCR.

Music, burps, etc are not DC current, they are AC. The impedance varies with frequency for multiple reasons, the 2 biggest for praactical sub applications being the inductance of the coil varies with frequency (acting like a low pass filter), and the reaction of the cone changes when different frequencies are played (look at a impedance plot of a sub - it spikes at the drivers Fs).

Since cone reaction can change the impedance, it is of course going to change when the driver is installed in a box with changing back pressure. This is what people refer to as impedance rise.

In every system I have built, the smaller the box is, the more the overall impedance rises. But I build systems to play music. For SPL burps, port tuning and frequency you burp at are going to be the big factors in the impedance the amp sees during the burp, along with some effect from the size of the box.

There is more to it than this, but maybe it give you a better idea. . .

Brian

Good info Brian I appreciate you taking the time to explain man.

[Big Lo]

Your gunna want a True-RMS Clamp Meter to measure your AC Amperage and jus use a DMM to measure your AC Voltage and your gunna want peak hold on that also.. And just multiply those 2 numbers to get your RMS Wattage.. and to find the Impedance rise on that frequency you divide the voltage by the amperage and then youll see what your impedance rise is. It will vary frequency to frequency. But to help cut down Impedance Rise you typically need to make a bigger box, a smaller box will cause the impedance to rise more than a larger box..

I'm going to try that when I get a clamp meter. Thanks for the info man!

[LBM]

I am getting a ohm rise of 4.8 ohms (minimum) from a 1 ohm wired dvc sub. And 2.4 ohms (minimum) approx for a pair wired at 0.5 ohms.

Can I run the subs wired at .5 to a 2 ohms stable amp ??? Will it run stable ???

[Austin Hart]

For example, I run an AP3000D (2 ohm stable) At 1 ohm. because i have a rise to 4.2. Thats what the amp sees. so it wont go into protect or anything. if i wire it to 4 ohm, i rose to like 17.5.... so i didnt really like that to much.

-Your rise increases with every kind of resistance.box=less rise

Smaller Box has more pressure on the sub, therefore more rise. bigger box=less rise.

-Also, Shortening or lengthening your speaker wire could increase or decrease your rise. Shorten it and there will be less rise. vise versa.

-Increasing the size of your speaker wire, ex. Changing from 12 ga. to 8 ga, will decrease your rise. bigger wire=less resistance.

Impedance rise could be good in the instance your trying to wire an amp down below its minimum impedance stability. testing testing testing...

Good luck. hope this helped

[LBM]

Anyone else ?

[Ji553r]

wow i always thought it was smaller box = less rise...i got it backwards. im gonna have to remember that

edit:i have my DD wired to 1 ohm on my saz 1500d and with the most rise i saw it went to 4.2. my amp still gave me 800 watts though and its rated at 600 w @ 4 ohm so sundown FTW!!!!!!

[Boon]

For example, I run an AP3000D (2 ohm stable) At 1 ohm. because i have a rise to 4.2. Thats what the amp sees. so it wont go into protect or anything. if i wire it to 4 ohm, i rose to like 17.5.... so i didnt really like that to much.

-Your rise increases with every kind of resistance.box=less rise

Smaller Box has more pressure on the sub, therefore more rise. bigger box=less rise.

-Also, Shortening or lengthening your speaker wire could increase or decrease your rise. Shorten it and there will be less rise. vise versa.

-Increasing the size of your speaker wire, ex. Changing from 12 ga. to 8 ga, will decrease your rise. bigger wire=less resistance.

Impedance rise could be good in the instance your trying to wire an amp down below its minimum impedance stability. testing testing testing...

Good luck. hope this helped

Where did I leave my facepalm gif?

As I've said like 300 times on here, impedance rise varies by frequency. At some frequencies it will be very close to 0. Also when the cone is stationary (i.e. every time it reaches the top or bottom of a wave, aka 50 times per second at 50hz) the impedance rise is 0.

Changing your speaker wire does nothing for impedance rise. Resistance is not impedance. One is in the DC domain, the other is in AC.

You cannot rely on impedance rise for anything except burps where it will always be the same so you can measure it and know what it is.

For the purposes of musical systems (and I don't think many people here drive around playing single frequency sine waves) it is best to pretend that impedance rise doesn't exist. Put it down to something that's there in your system but a. there's not a lot you can do about it and b. it's not worth worrying about anyway.

[Ji553r]

i knew it would only be a matter of time till boon chimed in