| Re: 7 Pi impedance range [message #61835 is a reply to message #61829] |
Thu, 11 February 2010 21:38   |
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Wayne Parham
Messages: 18778
Registered: January 2001
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Illuminati (33rd Degree) |
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It really is a nice impedance curve for tube amps, without any real peaks. It's scaled to show what little fluctuation is there, but you'll notice minimum impedance is 5Ω and max is about 13.5Ω. That's really good. Most loudspeakers have peaks of at least twice this high, and only the most well behaved speakers are even that.
It's not uncommon to see loudspeakers that average 8Ω to have maximum impedance of over 50Ω, and I've seen some go as high as 200Ω. So 13.5Ω is just nothing, an easy drive for a tube amp. That's really important, because amps like those have relatively high output impedance - a couple ohms, typically - and this forms a voltage divider with the load.
When the load impedance fluctuates a lot, the voltage division proportions change between source and load, and this causes response fluxuations. A ten-fold change is pretty significant, and can be seen in the response. But a two-fold change is nothing. It's rare to find a speaker that's as flat as that, but it's an important attribute to consider when using low-power SET amps.
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