My wife works for Tektronix, the
oscilloscope company. She also happens to work in the same department
as one of the members of the Portland Triode Society, who does support
for Rohde & Schwartz vector analyzers (Tektronix partners with them,
and provides support in the US)
So I got the chance to have my speakers measured by a professional engineer
who has a penchant for tube amps and $80,000 worth of measuring gear on his
desk. Dave McDonald was a lot of fun to talk to, and I learned a lot just
by being there as he set up the equipment. Since the cabinets aren't finished,
we measured the drivers by themselves, and then in combination with the
crossover. Dave was very impressed with both the drivers and the crossover.
The impedance graphs measure impedance versus frequency. Impedance is sort of like
the more complex version of resistance, it measures how much resistance an object
gives to electric current at a particular frequency. It shows were the resonant
frequency of the driver is (the peak) and at which frequencies it's inductive or
capacitive.
There happened to be a meeting of the Triode society
that night, so Cecilia and I went to the meeting after we measured the speakers.
It was a lot of fun talking to a bunch of rabid audio guys, plus it was at a pretty
good chinese restaurant. I'm thinking my next project might be a
tube
amp.
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What I love about this picture is the $80,000 measurement device, the
really expensive braided measurement cable, all hooked up to some Rat Shack
aligator clips and my $16 tweeter. Got to love progress, eh?
This is the graph for the woofers. We measured 2 woofers (one is blue, the
other purple) The top graph shows were the driver is inductive/capacitive, and
the bottom graph shows impedance versus frequency. Notice how both drivers
measure out pretty much the same.
These are the tweeters, which measure a little differently, but the resonant
frequencies are pretty close, and the overall differences aren't too bad.
Here's the whole system. Dave liked that there was only one major peak
in the impedance, and how smooth the graph basically is. Pretty cool! Oh,
we only measured one complete circuit, not two like we did with the woofers
and tweeters.
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