impedence

[emf28]

How can I tell what the impedence is on my speakers?

[dekuda]

You need a meter that would measure resistance and place one lead on the positive and one on the negative terminal of your speaker.It would help to include the model so we could help answer!

[emf28]

RTi A3

[TNRabbit]

What's the big question; WHY do you need to know?

[Solumnus]

The RTiA3's are 8 ohm speakers. I'm pretty sure all Polk speakers are 8 ohms, with the exception of the LSi line, which is 4 ohms. hope it helps.

[CoolJazz]

Actually a typical Volt-Ohm-Meter (or VOM) that measures DC resistance isn't the right thing to determine impedance at all. You need to make AC measurements to look at impedance.

DC, is of course 0hz, which we spend little time listening to...depending on your favorite musical style. :p As frequency varies, so will the impedance measurement. An 8 ohm rated speaker system may very well have some frequencies where 30 or 40 ohm values are measured.

And just to make it more confusing, the actual power needed is dependant on not just the impedance, but the simultaneous phase angle of the load and the rate of change of that. That's why one 8 ohm rated speaker can be run by a lower powered amp, while another equally 8 ohm rated speaker may be notoriously power hungry and bring an average powered amplifier to it's knees.

CoolJazz

[zarrdoss]

They all vary, most of the older Polk's and most of the sda line are 6 best way to be sure is research it or check with an multi-meter.

[TECHNOKID]

They all vary, most of the older Polk's and most of the sda line are 6 best way to be sure is research it or check with an multi-meter.Exactly, multimeter is the tool to use while an ohmeter is also adequate. It is a fact that the coil impedance will vary with different frequencies however, the rating of a speaker is measured when idled, that is the impedance reading that is of importance when trying to match with an amp.

You could also use a search engine for the actual specs or even user manual. IE: http://www.google.ca/search?hl=en&q=RTi+A3%2Bspecs&btnG=Search&meta=, http://www.google.ca/search?hl=en&q=RTi+A3%2Buser%2Bmanual&meta=. Of course, if you know the brand you can usually inquire for the specs/manual on line. Even 30 -35 years old speakers can often be successfully researched on line even if the company doesn't even exist anymore.

Cheers!
TK

[gmb2428]

Tech support said my RTi line can dip to 3.5 ohms!

[slowpolky]

like rti6? 8's ? or csi5 ?

would these lil speakers dip lower than 8

[CoolJazz]

Exactly, multimeter is the tool to use while an ohmeter is also adequate. It is a fact that the coil impedance will vary with different frequencies however, the rating of a speaker is measured when idled, that is the impedance reading that is of importance when trying to match with an amp. TK

Good night!! :confused: English is the only language I know and since it's obviously failed to communicate the difference between AC and DC, I'll get back to you in a couple of years after I learn French. :D Maybe that language will better explain it!!

But if there is a confused noob reading this thread in the future that does understand English...an ohm meter or an ohm reading on a multi-meter (same thing folks!) is a DC reading! Tells you nothing at all about an AC impedance value. :p

CoolJazz

[apphd]

EMF, Welcome to CP. To eliminate any confusion or doubt here is a link, you were only a couple clicks away.
http://www.polkaudio.com/homeaudio/rtia/specs.php#bookshelf

As others have told you 8 ohms, and the impedance is given at a nominal value because it will vary with freq.

[nguyendot]

Good night!! :confused: English is the only language I know and since it's obviously failed to communicate the difference between AC and DC, I'll get back to you in a couple of years after I learn French. :D Maybe that language will better explain it!!

But if there is a confused noob reading this thread in the future that does understand English...an ohm meter or an ohm reading on a multi-meter (same thing folks!) is a DC reading! Tells you nothing at all about an AC impedance value. :p

CoolJazz

Incorrect.

With the coils static - the AC and DC resistance will be exactly the same.

A standard multimeter will do fine for the static impedance value.

Measuring the dynamic impedance will be a bit more difficult.

[CoolJazz]

:eek:Incorrect.

With the coils static - the AC and DC resistance will be exactly the same.

A standard multimeter will do fine for the static impedance value.

Measuring the dynamic impedance will be a bit more difficult.

OK. If that should be true...then why would a DC resistance measurement always be lower than anywhere on an impedance sweep? How would you choose to relate the typical 3-4 ohm DCR to an 8 ohm speaker? That makes no sense on any level.

What AC frequency are you going to use to compare it to DCR?

Come on...this is the first few minutes of the first day of Electronics 101! :confused:

And WTH is a static impedance value anyway? You either are measuring it with a signal across it or not. A coil laying in the corner with no signal across it really has a value in all cases of a million zillion ohms. Prove otherwise!! :eek:

Again...DC resistance is listed in an ohm value, that's where the relationship with impedance ends!!

CoolJazz

[Face]

Want to know a speaker's true impedance?
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-803

[hearingimpared]

Welcome to Club Polk emf28.

[TECHNOKID]

Good night!! :confused: English is the only language I know and since it's obviously failed to communicate the difference between AC and DC, I'll get back to you in a couple of years after I learn French. :D Maybe that language will better explain it!!

But if there is a confused noob reading this thread in the future that does understand English...an ohm meter or an ohm reading on a multi-meter (same thing folks!) is a DC reading! Tells you nothing at all about an AC impedance value. :p

CoolJazzSorry but I don't see what you are talking with AC DC? I only acknoledge previous post mentionning the impedence change with various frequencies. I do not understand the French comment(s) on AC DC as AC DC are English correct abreviations. AC = Alternative Current while DC = Direct Current. French = Courant Alternatif etc... so I do not understand your point. Also, while my French may play tricks on me, allow me to correct you as an ohmeter = measure resistance/impedance solely/only and a multimeter = reads/measures either volts, ohms/impedance, current, in some more elaborate/expensive ones it could even possibly read lower frequencies, measure/test diodes and even possibly transistors. Multi stands for multi purpose meter. All in one if you prefer.

Cheers!
TK

[TECHNOKID]

Want to know a speaker's true impedance?
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-803Hummm, very interesting innexpensive tool! Thanks for the info!

Cheers!
TK

[nguyendot]

After some reading i retract my statements :)

[TECHNOKID]

Measuring the dynamic impedance will be a bit more difficult.
You would measure with such a tool as Face suggested, it isn't neither an ohmeter nor a multimeter. Measure speaker parameters "Woofer Tester"http://www.woofertester.com/sales/wtpro.pdf http://www.woofertester.com/sales/st.pdf

Ohmeters/multimeter and woofertester/speakertester are totally different tools and have totally different applications.

[jvc]

this is like Home Improvement for Speakers
all these neat tools

[TECHNOKID]

this is like Home Improvement for Speakers
all these neat toolsThe one that Face provided is ratter innexpensive if of course you already own the laptop. Nice toy/tool however, if too expensive many of us wouldn't be able to justify the expense. This is more technical, engeneering like which most hobbier really don't need. Knowing the nominal impedence and properly match with the appropriate amp is the basic for proper and efficient set-up. If one has the knowledge, money and willingness to experiment with such tool is great otherwise it is useless to most.

Cheers!
TK

[CoolJazz]

A couple of models of a true impedance meter...

http://www.mcmelectronics.com/product/72-6947

http://www.toaelectronics.com/zm-104.asp

Both just simply measure at 1khz. No other frequencies...though at 1k you will typically get pretty close to knowing the rated value. As you go higher in frequency, the actual impedance value does rise slowly in the typical driver.

A functional, if not extremely accurate way to measure a speakers impedance can be done this way...

- Connect about a 50 ohm pot in series with the driver voice coil and then to the amp.

- Connect a frequency generator or CD player with suitable test CD in it to the amp input, keeping the level pretty low to begin with.

- Start walking up the frequency scale in steps. For each step, measure the voltage (has to be AC!!) across the voice coil terminals and then across the pot.

- Adjust the pot until both voltages match.

- Now shut down the amp and measure the resistance across the pot. This is the driver impedance for that specific frequency.

- Repeat the measurement for each frequency you want to know the actual impedance for.


Teknokid...don't scratch your head too much on the reference to French. I was trying to kid and that doesn't always come through the web very well. The point though is to not leave the information laying around that would lead people to believe they can pick up a multi-meter and read the impedance of a speaker.

I still don't understand the reference to dynamic or static measurement though. That sounds like stuggling to explain something that can't be explained. I immediately visualized someone walking down the road, whistling along, with ice skates thrown over their shoulder, headed towards the farm pond...in the middle of the summer! :eek: :eek: This can't lead anyplace good!!!


Again, the typical meters ohm measurement is a simple DC measurement and is not the same thing as measuring impedance which is an AC measurement for which you must pick a frequency.

CoolJazz

[megasat16]

Impedance in a nutshell is the combination of both the Resistance (R) and Reactance (X) in the AC circuits.

For the speakers made of single speaker driver or multiple drivers will have a Crossover Networks (aka filters) which contains resistors, capacitors, inductors; etc. will have varying Reactances (capacitive, resistive or inductive) depends on the frequency of the AC signal in used.

Generally, the impedance of a loudspeaker is given by the manufacturer. It's usually is the average value from the impedance curve generated over a spectrum of frequency (20Hz-20KHz). The phase angle is never given out as numbers since it means little sense to the general consumer. But a handful of manufacturer provided the RTA (real time analyzer) analysis of the impedance curve and the phase angle of their speakers in the graphical form.

Since most manufacturer provided only a mean or average value of impedance curve, the actual impedance of the speaker could be lower for some frequencies and will be higher for the others.

If you want to truly understands the impedance and phase angle of current vs. frequency, you'll need an Oscilloscope (either Digital or Analog), An Amplifier, a Signal Generator, and RTA (Real Time Analyzer). And true impedance needs to be measured for the minimum of 20Hz-20KHz frequency spectrum.

But CoolJazz provided a functional method for measuring the impedance without the necessity of the expensive test equipments.

And I concur with CoolJazz that you can't use multimeter to measure true impedance of the loudspeaker. The multimeter measurement of a voice coil of the speaker driver is resistance only and it's only applies to DC measurement.