Nominal Impedance of subwoofers? [Archive] - Audio & Video Forums


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05-28-2004, 08:39 AM
I may be way be way off, but what would be a typical nominal impedance for your basic run-of-the-mill subwoofer?
For example, most common mass-market speakers have 8 ohm impedances...what would a subwoofer's be? 8 as well? Much less?

N. Abstentia
05-28-2004, 09:06 AM
There is no answer to that question.

Well okay, there is an answer.

Most subwoofers will be either 1, 2, 3, 4, 6, 8, 12, or 16 ohms. You can also have any combination of dual or single voice coil configurations allowing you to wire the impedance that you want.

05-28-2004, 10:22 AM
Do you mean active or passive subwoofer?

05-28-2004, 10:27 AM
Well again, I could be way off, but isn't completely inaccurate for me think of an active sub the same way as a passive sub with an amplifier attached?
Usually I don't see impedances reported in amplifier power specs, whereas you do for other amps.
Same with speakers, they usually state impedances as a nominal figure 8,6,4 are the most common I've seen.

05-28-2004, 10:57 AM
I don't think you should ever worry or even wonder about the impedance of an active subwoofer's impedance. That's the responsibility of the internal amplifier, which should be well matched to the driver.

As for your receiver's amp, all it will see as a load is the high (~20000 Ohms) input impedance of the subwoofer's internal amp's input.

05-28-2004, 12:25 PM
Cool...then how's about this question.
I've bought 100 watt amps much larger and heavier than the 400 watt amp that's on the back of my PW-2200 subwoofer. What gives there?
My understanding is that subs use a different class of amplifier or something?
I was kind of wondering if the load these amps was driving was into 2 or 4 or ohms or something...I have a hard time figuring out why my 70 wpc Rotel is heavier than the amp unit on my 400 watt subwoofer.

05-28-2004, 12:58 PM
You mean your Rotel is heavier than the whole subwoofer, or can you separately weigh the amp unit on your 400 W sub?
Anyway, your sub's amp may have a switching mode power supply which is a whole lot more efficient and lighter than conventional power supplies (just like the ones in PCs and car audio amplifiers). But they may have rf interference problems.

05-28-2004, 01:05 PM
Just some quick math, MDF and particle board weigh so much, etc...I didn't take into account the cabinet of the Rotel.
I realize it's probably not an adequate comparison, I was just a little curious. Thanks for your help.

05-28-2004, 06:01 PM
The impedance can run all over the map, even from the same manufacturer. The 12" Shiva woofer used in my Adire Rava is an 8 ohm driver. Adire's 15" Tempest and 18" Maelstrom models are also 8 ohm drivers. However, their 15" Tumult (which can move about twice as much air per stroke as the Tempest) is a 2 ohm driver.

As far as the weight goes, I think it has to do with the fact that the PW-2200 uses a Class D amplifier, which means that it uses switching power transistors that negate the need for huge power storage circuits and heatsinks. In general Class D amps are lighter in weight and run cooler. The flaws that people attribute to the cheaper Class D amps (like harshness) aren't really applicable with subs, so I see these a lot more widely used in subs than with receivers or amp separates.