I can think of no reason it would not work if you used reasonably heavy gauge wire, say at least 16 gauge. Try it and check to see if the amp is running cool, if the heat sinks become hot then you have a problem.
10 responses Add your response
Be aware, though, that wiring them in series, while making life easier for the amplifier, will degrade the sound quality, especially if the two sets of speakers are not identical.
If the two sets of speakers have different impedance vs. frequency curves, the frequency response of each pair of speakers will be altered by the impedance vs. frequency curve of the other speaker.
And even if the two sets are identical, damping factor (affecting the bass) goes down the tubes because the source impedance driving each speaker becomes the amplifier output impedance plus the impedance of the other speaker, rather than just the (very low) amplifier output impedance.
None of that may matter too much, though, if the speakers don't have much bass response anyway, and if sound quality is non-critical in this application.
Let us know the make and model of the speakers (and any technical parameters that you can readily provide, e.g., rated impedance, efficiency, power handling, etc.) and we could make better informed recommendations.
I did find these specs on the G-9000DB (don't know what the "DB" means, but I would suspect that it doesn't mean anything significant as far as power output and load impedance are concerned). They indicate 160W into either 4 or 8 ohms. But of course many "8 ohm" speakers are really less than that at many frequencies, which would mean that two of them in parallel would drop below 4 ohms, as Rodman pointed out. I would feel comfortable if the combined impedance dropped SLIGHTLY below 4 ohms at some frequencies, given that the receiver is rated for 4 ohm operation. But I would not feel comfortable, for example, if the speakers were nominally rated at 6 ohms, meaning that their parallel combination would be nominally 3 ohms, and would drop down lower than that at some frequencies.
The oudoor speakers I am using are Presidian and they are rated at nominal 8 ohms. I'm really concerned that I don't harm this old classic amp. 2 speakers in the screened room area and 2 in the pool area. At an impass as to how to wire them. In series might be good but sound quality may suffer. I really appreciate your time and trouble here guys, thanks a bunch.
Markus -- I couldn't find an impedance vs. frequency curve on those speakers. I did find this descriptive information, which might be of interest:
The fact that the low frequency driver has no crossover elements in series with it lessens my confidence that its impedance does not drop below significantly below 8 ohms over a significant part of the spectrum. So I would not hook them up in parallel to the G-9000.
If all four speakers are the same Presidian model you could try wiring them in series, and see how you like the sound. The main sonic consequence of the series connection, given that the speakers are identical, would be to bass damping, but they probably don't have much bass response anyway. Also, the maximum power available to each speaker would be reduced substantially, perhaps to 25% of the amplifier's capability (the nominal 160 watts reduced to 40 watts), because each speaker would see only half of the voltage being put out by the amplifier at any given instant.
Alternatively you could add a second amp as Bob has suggested, or else purchase an amp known to be able to drive low impedance loads. The older Adcom models (GFA-535, GFA-545, GFA-555, GFA-565 etc.) would do fine, and are not expensive. Also, probably any amp that can be strapped for use as a monoblock would do well, because a bridged mono amp sees a load equal to one-half of the speaker's impedance, and therefore presumably is designed to drive low impedances. Bridgeable amplifiers usually specify that nominally 8 ohm speakers should be used in bridged mode, as opposed to nominally 4 ohm speakers, btw.
Hope that helps,
How loudly do you intend to play these extension speakers? If you won't be using the receiver at it's higher output capabilities; it's not going to have any "thermal runaway" issues. If you just intend to provide music at moderate volume levels, you'll never have to worry with them hooked in parallel(though hosting poolside disco reviews may require some rethinking). Then again; are there any children, with access to the volume knob, to be considered in the equation?