What is flat impedance?


and how do I TELL if a speaker has flat impedance?
groundhog
Who makes some of the easiest speakers to drive?

I'm just curious to see what you all are using with tubes.
I'm looking for a list of speakers to audition that will be kind to my amp.
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Thanks Tvad, I just caught your thread 2 seconds after posting this question...............Looks like it will take a while to sift through but I appreciate the link-up.