Well, the first thing is that you've got the GK preamp voicing mixed in with your response curve. This is fine if all you want to do is compare the ZacLite to the Schroeder.
If you want to take that factor out of the equation, you have to monitor the output voltage of the amplifier and make sure it's the same at all test frequencies.
What I'm really trying to accomplish with this testing is to get an idea of what the frequency response of each cab is, and compare that to what I hear and to what my design calculations say it should have been. I'm not trying to compare my cab(s) to any published specs.
I hear you about the amps voicing. I would like to take this out of the equation if possible. Do you know how to best monitor the output voltage? I have a nice Fluke multimeter that I could use. Is it as simple at taking an AC voltage reading across the speaker terminals and adjusting the amps level until you get the specified voltage? I imagine that I'd have to build some sort of contraption so that I could tap the line into the cab.
Assuming you put the cabinets in the same spot, you would expect to see reflections showing up at the same frequencies for both cabs.
I do see some similar peaks between the cabs which is what makes me think I'm seeing these reflections. I was pretty close to my house when I took the measurements, so I wouldn't be surprised if that's what I'm seeing. I didn't give too much thought about the whole set up at the time.
One thing you could possibly do to mitigate reflections is to put each cab on its back, pointing up into the sky, and suspend the microphone over it.
This is a great idea! I'll try retesting with this method and I'll try to get out into the middle of my small yard too.
Also, I'm not sure I agree with your method of 'averaging' test frequencies to get the SPL, because the frequencies aren't evenly spaced. I think you need to multiply each SPL reading by the frequency 'bin' width before summing, and then divide by the total measurement bandwidth to get an average that's not biased by the power-law spacing of frequencies.
I just made that method up. I figured it would be my best bet at getting a baseline SPL to then extract F3 and F10. I know what you mean when you say "bin". It is the octave spacing on a Real Time Analyzer (RTA). Typically you see 1/3octave, 1/24th octave, etc. I don't think I have bins in my case since I'm not using a RTA. Do I? Isn't an SPL meter different from a RTA in that regard? To figure out what frequency to take my readings at I started at a low base frequency (30HZ, I think?) , then multiplied by 1.25 to the next. So they would be 30, 37.5, 46.875, 58.594, etc. Would that be an even division of an octave since I'm multiplying it out? I then set the tone generator at each frequency, one at a time, and took an SPL reading. I thought an RTA used filters to create a bin, and that even though the bin has a center frequency the wider the bin the more energy it contains. Therefore a 1/3 octave bin would measure higher than a 1/24 octave bin.
