Would it be physically bad for either the speakers to the receiver if I hooked up two bookshelf speakers to the center channel binding posts of my Harman Kardon AVR-120, effectively creating two center channel speakers?

Depending on the impedence (resistance) of your speakers you would (I am assuming) be hooking them up parallel and halving the total. If your speakers are 8 ohm this results in a 4 ohm load to your amp. If your amp is capable of managing a 4 ohm load, these speakers would sound louder than the rest making your system unbalanced for HT. You could also run the risk of burning out the coils in the speakers if they are unprotected and the current gets too high.

Comments anyone??

4-oHm speakers offer LESS resistance, and that is why when they rate a receiver @ 4 ohms the wattage is always higher?

Exactly. The lower the load, the higher the current. My receiver is rated 130W into 6 ohms and 105W into 8 ohms.

First, make sure both speakers share the same impedance rating (that is, make sure they have the same ohm rating)

Now, let's see if I remember my math correctly...

Connecting both speakers to your center channel binding posts places them parallel in the circuit, so you will want to take the stated ohm value and divide it by 2. Take that new figure and make sure the receiver can handle it. If so, you should be okay.

For example, two 8 ohm speakers connected to the center channel binding posts will actually have a 4 ohm load on that channel. Similarly, 6 ohm speakers will have a 3 ohm load and so on.

I'm sure someone will correct me if I am mistaken.

- David

/edit
Shucks. It looks like Sean beat me to it! :-)

The general concensus on the boards when I proposed the same thing was that it wouldn't be a problem (I originally asked about getting a speaker switch to do it--I think JohnK said that it wasn't necessary). Not that I've tried it yet, but I intend to use 2 M2s as my center channel, if I ever get around to doing multichannel.

Jordan, as other replies have indicated, if you hook the two speakers in parallel, that halves the impedance(e.g.two 8 ohm speakers in parallel present a 4 ohm load).Assuming that the amp can handle the impedance without shutting down, no problem.

Also note that impedances are averages; i.e. given different loads a speaker will change resistances.

This leads me to two comments:
1. If you do this, make sure the speakers are twins, not just nominally 8 ohms.
2. If you can, get a resistance chart for the speaker model (like the M80ti one Alan so helpfully linked to in a recent comment). If the chart shows a big dip in resistance somewhere, don't wire them this way. The severity of the dip will be twice what it normally is if you do.

Hope this makes sense- basically, I'd recommend this only on identical speakers and only if the speakers are a solid 8 ohms given any load.

A good point. Alan, care to supply the chart for the rest of the Axiom speakers?

If there's concern over wiring them in parallel, why not wire them in series? The nominal impedance would double (16 ohms)--still safe for any receiver.

I have read that it is better to wire the speakers in series than in parallel, as that will lead you to double the impedance rather than half it. This will actually make the load on your amp much easier than before, but they will need a 3dB boost in level (that's double the power) to overcome the extra resistance.

To wire in series, connect the receiver's positive to speaker 1's positive, speaker 1's negative to speaker 2's positive, and speaker 2's negative to the receiver's negative. This is much safer for the amp than wiring in parallel.

-Cooper

Hi,

Not a good idea to wire speakers in series except for non-critical applications, because when you do, the impedance curves of the two speakers interact with each other causing potential changes in frequency response, none of which are desirable.

It's true that it will be an easy load for your amplifier, but it comes at the expense of good performance. Keep in mind that all impedance ratings of speakers are "nominal"--a kind of average. Few loudspeaker impedance curves are a nice straight line. In most cases, impedance varies with frequency across the audible spectrum, and it's those variations that will interact when you connect speakers in series.

Regards,

Alan,

Thanks for the explanation. So is that to say that the impedances of individual speakers wired in parallel will not interact in such a way?

kcarlile,

Here's the page at audiovideoreviews.com where you can see the NRC measurements of the M80ti, including its impedance vs frequency curve, which is very smooth. Sorry I don't know how to do the link thing:
www.soundstagemagazine.com/measurements/axiom_m80ti/

If you want to check out other loudspeakers, go to audiovideoreviews.com, then select Home Loudspeakers, find the speaker in the list that has "NRC" after it, then click on the measurement logo at the top of the review and scroll down to the impedance measurements.

In contrast to the M80s relatively smooth curve, take a look at the impedance curve of the M2i, which varies all over the place. This illustrates how impedance has nothing to do with sound quality or a smooth and even frequency response. The M2i's frequency response is very smooth and linear, whereas the impedance curve is quite variable.

Regards,

Does this (the variable impedance curve) that it would be inadvisable to wire the M2s in parallel?

Badger98 and kcarlile,

Correct. The impedance curves of speakers wired in parallel will NOT interact in the manner of series-wired speakers. So it would be okay to wire two M2i's in parallel so long as the receiver or amplifier will drive the lower impedance presented by the two speakers in parallel. The individual frequency responses of the two M2i's will be unaffected by paralleling them.

Regards,