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For a line array with eight midwoofers, each being an 8 ohm impedance driver, the usual wiring choices yield either a 16 ohm or a 4 ohm nominal impedance. The 16 ohm wiring is good for use with tube amps, especially SET's and OTL's. The 4 ohm alternative might be a better choice for use with a solid state amp. If you know in advance you will be using the array with both tube and solid state amps, is there any reason why you wouldn't wire it for 8 ohms nominal impedance using a quasi 3-3-3 arrangement, with an 8 ohm resistor substituting for the 9th driver?
Fred, I asked this question of several respected EE types. I've been told by everyone that you cannot substitute a resister for a speaker. A resister is static, and a speaker is dynamic, and you won't like the results. Marlboro
My budget array has a toggle switch to select midwoofer array impedance, low impedance or high impedance. I believe I bought a 15A 4PDT switch, one for the mids, another for the tweeters, per cabinet. If you use a passive crossover, not active, then you need to make a second set of crossovers.
Fred, With the assumption that you have a two-way crossover of some sort, you would need two different crossovers--one for 4 ohms and one for 16 ohms. Let us assume that the woofer line is either 4 or 16 ohms. Then the impedance sensitivity would be different for these two impedances so the tweeter (or tweeter line) would necessitate separate crossovers or else their sensitivities wouldn't align across the frequency band. Now if you just added a resistor into for a WWW/WRW/WWW configuration, two things are of concern. First, the series resistor would impact the box tuning for the center set of drivers. Second, the SPL output of this center set would be less than the outer two sets. Typically, you would prefer a constant output level from all drivers in the line or a taper of high SPL to lower at the ends of the line. Jim
Thanks all for the responses. Sounds like a 6.9 ohm 3-2-3 power tapered midwoofer arrangement might be a better option. It will be easy to convert to this wiring arrangement and then convert back to 16 ohms if the 6.9 doesn't work out. Like the 8 ohm version this would require a different crossover and less tweeter padding, but it's still a reasonable match for tube SET amps and capable of extracting more power from solid state amps. The solid state amp power issue is relevant because all my ss amps are low power: a 50 watt NAD, a 25 watt class A Monarchy, and a 6 watt (into 8 ohms) Trends TA-10.1. Getting a more powerful amp would also be an option, but I prefer the sound of these amps, especially the Monarchy and the T amp, more than the sound of the affordable higher power amps I've heard.