Erik wrote:
"What huge spike [in the impedance curve]??
"That’s very typical for a speaker with a 2 way crossover. What I’m impressed with is how flat the rest of the speaker impedance curve is."
The impedance curve can matter a great deal when it comes to matching amplifiers and speakers. Most amps approximate a constant voltage source (and most speakers are designed for that) but many tube amps (including McIntosh) approximate a constant power source; that is, the wattage they put out doesn’t change much as the speaker’s impedance changes.
Over most of its range that speaker’s impedance looks like about 5 ohms, but then between say 1.5 kHz and 3 kHz the average is more like about 12 ohms.
If the amp approximates a constant voltage source, then assuming 1 watt into 5 ohms, it will only be putting about .42 watts into 12 ohms.
But if the amp approximates a constant power source, when it’s putting 1 watt into 5 ohms it is also putting approximately 1 watt into 12 ohms.
The SPL difference between .42 watts into 12 ohms, and 1 watt into 12 ohms, is about 3.8 decibels. This is enough to spoil the frequency response OR - in this case - enough to fix it!
You see, the measurements show the Olympia III to have a roughly 3 dB dip centered between 1.5 kHz and 3 kHz.
(In the real world, the actual SPL difference between the two amplifier types would probably be less than the math in this post predicts, because in the real world amps don’t quite behave as true voltage sources nor true power sources. BUT the trend described above is valid in my experience, and explains why sometimes tube amps get blamed for bad sound when the real culprit is poor amp/speaker matching.)
Duke
