How do the monitor10's have 8ohm rating

[ben62670]

I looked at the monitor diagram and it has 2 mw6500's in parallel, and an 8 ohm tweeter. The speks say 8ohms for the whole speaker. How can that be? I am building some frankenpolks with 4 mw6500's, would that be 4 ohms or 2?
Thanks Ben

[markmarc]

Ben:
I'm no electrical engineer, but I can tell you that the 10B's I owned in the 1980's were very efficient, easy to drive boxes. The great sound was the best part, of course.

[F1nut]

How can that be?

It has to with the earth's rotation and magnetic field, not to mention alien communications and navigation signals.

[mhardy6647]

I can only vouch for the original Monitor 10, which was identified as a nominal 6 ohm speaker in Polk's specifications.

[jakelm]

The later models changed the crossover. That change and the fact that the new tweeter and the new mids have a higher impedence rating , change the whole speaker.

Jake

[ben62670]

Yes I think you hit on something F1Nut. Yes Yes I think you have. Does anyone no how to get actual spec specs?

[Deadof_knight]

Impedance..resistance to flow The crossover with the coils and caps and the natural resistance of the drivers. At certain frequencies the speaker will be much greater than the 6 ohm rating. The 8ohm rating is kinda a class so to speak all the polks I have seen and purchased have been nominally rated for 6 ohms.

[mhardy6647]

Impedance is the AC analog of the DC quantity called resistance. Like resisantance, it follows Ohm's law: E = IR (voltage = current times resistance or impedance). Unlike resistance, impedance is a complex (in the mathematical sense) quantity comprised of resistance and capacitive and inductive reactance. For the purposes of this discussion, the most important concept is that impedance is frequency dependent. The "rated impedance" of a speaker system is a nominal quantity, usually measured at a frequency somewhat above that of the peak impedance of a system (which occurs at its (low) resonant frequency). There's usually a flat 'valley' of impedance somewhat above the resonance impedance peak. At higher frequencies, above that valley, impedance tends to increase.

Measuring speaker impedance is straightforward but not trivial :-) Yes, you CAN do it yourself, especially for a single speaker driver in free space.
Here's a good tutorial. http://sound.westhost.com/tsp.htm


EDIT: Here is a typical impedance curve of a single driver with no crossover or network for impedance compensation:


The 'nominal' impedance of this driver would be that observed out in the region of about 200 Hz.

[ben62670]

Thanks much mhardy very informative