The Sherwood receivers require a 16 ohm load when using it in A+B mode 4 speaker configuration. This presents a problem since 1) 16 ohm speakers are not readily available, and 2) I don't want to buy four more 8 ohm speaker just to wire them in series. I know you have resistors that are used as a dummy load for bench testing and was wondering if there is a safe way to use this kind of straightforward approach. So the actual question would be: Is there a simple way to turn an 8 ohm speaker into a 16 speaker?
So, basically you want to attach four 8 ohm speakers to this amp? A simple way to do this would be to put 2 speakers in series on both the right and left A channels, and not connect anything to the B channels. This will give a load of 16 ohms on each channel, which will be safely above the minimum load impedance of 8 ohms on each channel. The only problem with this configuration is that each speaker will only get 25W because 16 ohm loads on each channel will only pull 50W/channel, split between 2 speakers --> 25W each. Another problem is that you won't be able to switch between using the two pairs of speakers without actually changing the wire connections, whereas if you used both the A and B channels then it'd be easy to switch: just press the A/B button.However, adding resistors in series with the speakers, as you’re thinking of doing, won’t work well, especially since these resistors would have a fairly high value of 8 ohms. Series resistance with a speaker (especially a woofer) will affect the Qes and Qts values of the woofer driver, which in turn will affect the response of the system, probably in a negative way. So no, you can’t turn an 8 ohm speaker into a 16 ohm speaker by using a series resistor.Personally, if I was in your situation, I would just attach all 4 speakers to the 4 output terminals. I know the specs say the minimum impedance is 16 ohms when hooking up both A and B speakers at the same time, but really most amplifiers these days can handle 8 ohm speakers when using both A and B outputs at the same time. This will give an effective load of 4 ohms on each channel (two 8 ohm speakers in parallel = 4 ohm load), which almost all modern transistor amps can handle. In fact, I have used 2 ohm loads on many amplifiers that were rated for 8 ohms loads, and I haven’t had any problems, partly because I make sure not to crank it too loud when I have loads that far below the rated impedance. There is some risk involved, but in your situation it’s the only way to have the convenience of still being able to use the A/B switch to actually switch between speakers, and to be able to have more than 25W going to each speaker.Alternately, if it’s not totally necessary to use all 4 speakers then just use two: one on each channel. This will give 200W total, which would be more than the 100W that you would get from all 4 speakers using the first configuration I suggested. Also, it will be safer than attaching all 4 in parallel, as in the 2nd configuration I suggested.
Date published: 2012-12-15