Impedance rise

Bwcad1 · Post by **Bwcad1** » Thu Jul 17, 2008 9:11 am

I get a lot of questions from guys asking about impedance rise and if i can explain it. Sure but i figured instead of writing a long ass faq id just open up a discussion and get everyone's opinions ideas and input. please feel free to ask any questions related to that topic. The main idea is after we answer most questions i'm hoping to get this added to the faq so please stay on topic.

Ryan from Ohio · Post by **Ryan from Ohio** » Thu Jul 17, 2008 10:46 am

We talking about impedance rise and affects on amplifiers or how the impedance actually changes?

I guess I will start with the basics.

Ohms on a DC circuit is resistance. Its constant.

Ohms on a AC circuit (audio) is Impedance. its variable. The reason its variable is the fact the conductor (coil) is inside a magnetic field. When the coil moves inside the magnetic field the resistance will change also.

A simple way to see this is to take your DMM and plug it on a speaker not in use/unwired. Gently press on the cone and note what happens.

Obviously when the impedance goes up the power output from your amplifier will go down and vice versa.

Bwcad1 · Post by **Bwcad1** » Thu Jul 17, 2008 10:57 am

Most of the questions surrounding it i have gotten have been about the affects of it both on the amp and the sub which ill get to tonight after work.

cargodz · Post by **cargodz** » Sat Jul 19, 2008 5:59 am

Bwcad1 wrote:Most of the questions surrounding it i have gotten have been about the affects of it both on the amp and the sub

^ With this being the case wouldn't it be a good idea to show people the formula for calculating and how to get it...

AC Voltage divided by AC Current (amps) =s impedance

How do we get these numbers...
First you'll need a Multi-meter and a Clamp meter.
Place your multi-meter on AC voltage and put leads in each speaker wire pos and neg...
Next clamp the Clamp around the Positive speaker wire set to AC amps...
Turn up the volume and watch each meter simultaneously, remember the two numbers...
You then divide Voltage by Amps which will give you Impedance Rise

Side Note: If your meters have a Peak Hold button it will save you the difficulty of watching the meters like a hawk.

Bwcad1 · Post by **Bwcad1** » Sat Jul 19, 2008 8:53 pm

remember to use test tones not music you will not get a constant measurment unless you do. ill post soon sooo damn busy!

cargodz · Post by **cargodz** » Sun Jul 20, 2008 4:51 am

Bwcad1 wrote:remember to use test tones not music you will not get a constant measurment unless you do. ill post soon sooo damn busy!

Thanks Bill... I knew I was leaving something out LOL ... Yes tones are pivotal for an accurate reading... And you will probably have to take some time playing different tones from one to the next to find the optimum for your system.

Tim · Post by **Tim** » Mon Jul 21, 2008 2:23 pm

I like many others have asked Bill about this. The thing I am confused about is, if you wire for say a 2 ohm load, with impedance rise factoring in, it may go up to 3 ohms or higher right?? So how do you know that you are getting a true 2 ohm load??

What about if you wire lower than that, providing your amp is stable, to maybe 1 ohm??

From what I have gathered thus far into the topic, the only way to really tell what it is, is to have meters and physically measure it.

One question about it I have is what load do you wire to, to actually recieve the desired load?

Tim

Ryan from Ohio · Post by **Ryan from Ohio** » Mon Jul 21, 2008 3:39 pm

You wont get "true" ohms unless you run DC signal to it... lol.

The ohms will rise and dip.

Bwcad1 · Post by **Bwcad1** » Mon Jul 21, 2008 4:10 pm

To be 100percent safe with most equipment always wire to reccomended lowest impedance. you may see myself or some other wiring down to lower load because we know our impedance rise. we typically do this when burping because the impedance will rise and stay steady at that frequency so when you say im wired at .5 dcr rising to 1.5 your amp is actually seeing the 1.5 ohm load and producing power by it.

here is an example from my experiance after working with my MM4000.1s for 2 years i found that at 3ohm mono reactive load was the loudest. my box rise would typically be 3x that of the nominal load so even though the amp is 2 ohm mono stable i could wire to one ohm at 54hz because i knew the rise would bring it up to 3 ohm reactive. keep in mind that most of this does not pertain to music and dropping below recommended impedance on music rarely works out to your advantage.

cargodz · Post by **cargodz** » Mon Jul 21, 2008 4:11 pm

Yep... as Ryan stated earlier:

Ryan from Ohio wrote:Ohms on a DC circuit is resistance. Its constant.

Ohms on a AC circuit (audio) is Impedance. its variable. The reason its variable is the fact the conductor (coil) is inside a magnetic field. When the coil moves inside the magnetic field the resistance will change also.