Wayne Parham Messages: 18787 Registered: January 2001
Illuminati (33rd Degree)
We can definitely see the response change corresponding to C1 value changes. So that's good, to be expected. But for whatever reason, the system takes a nose dive at 8kHz or so. It will be interesting to see if all tweeters show this trend (indicating a likely measurement anomaly) or not (indicating a tweeter problem). Thanks for keeping us posted.
I just remembered that my daughter had a little Samson USB Mic, so I thought I'd give that a go just for grins.
It's too late to do any serious measurements or super accurate mic placement (and I forgot to save the couple measurements I did do), but with the crossover in place (no C1), more or less on axis, roughly 18" from the CD diaphragm, the freq resp from 3K-20KHz is actually tipped up!
More measurements tomorrow. In the meantime, I'll resist the urge to throw my USB mic pre in the lake.
Wayne Parham Messages: 18787 Registered: January 2001
Illuminati (33rd Degree)
Interesting. The response from the SEOS12 is as I would expect between 1kHz and 6kHz, but above that, it has more rolloff than it should have just from mass. There's 20dB drop from 6kHz and 10kHz, more than 18dB/octave. This would only happen if voice-coil inductance and the front chamber conspired to rolloff at the same point, and they're usually staggered, with mass starting around 4kHz, inductance around 12-16kHz and front chamber just above that.
Could be that the phase plug is blocked with debris, or maybe the diaphragm is misaligned. You might open the compression driver and check it out. Sometimes just taking it apart and putting it back together fixes that kind of thing.
Tried the other CD I had on hand, and the results floored me:
While I have some work to do on the cabinets (bracing, damping of standing waves, etc.) and perhaps more traps in the room, I think we're done here. That said, I'm always open to suggestions...
Wayne Parham Messages: 18787 Registered: January 2001
Illuminati (33rd Degree)
Yes, that looks good. The other driver must be messed up.
Can you send it back for a warranty replacement? If not, you might want to take it apart and see if there is debris in the phase plug. Make sure it is clear and free of dust. Sometimes just taking it apart and putting it back together recenters the voice coil and fixes problems like these too.
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