I've gotten similar charts sometimes when there were sounds at the same time as the frequency sweep. What's difficult is to find an explanation for this particular result which looks like some kind of acoustic interference with the measurement. I suppose if multiple damping resistors lost their ground connection it could create a series of peaks and/or dips. But then I would expect much larger errors in the response. I notice the treble is also raised in that measurement, could be from speaker axis change.
If there was really nothing changed between measurements, my only other crazy conspiracy theory is that the coils were interacting with something magnetic nearby which had resonances at those frequencies.
If there was really nothing changed between measurements, my only other crazy conspiracy theory is that the coils were interacting with something magnetic nearby which had resonances at those frequencies.
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I think the general shape of that hard falloff below 100 Hz was there on raw (no resistors or anything) - and it was measured using the steel terminal block in place because that was how the female bullet connectors were attached for the speaker cable connects. So not the components but literally the connector block itself. It is puzzling and I wonder how I can measure the effect by impedance sweep of connector?
I waited for quiet time so no external noises to contribute.
I waited for quiet time so no external noises to contribute.
Sure. But what's wrong with gating? Just kill those room echoes and then we can all be sure we're looking at the driver only.
That's a good point... something like a neighbours washing machine. I get some 50Hz wobble on one of my mics from mains wiring under the floor (but not other mics... output impedance maybe?).
Otherwise yeah... I'm going to buy copper alligator clips now lol.
Would you be able to repeat the test with extreme near-field measurements of the woofer to see if that bump around 450 Hz comes and goes?
These are the clips I use (used for 0.0001% THD 100W+). Be sure to get the L size clips as the M size have bad teeth meshing. Or maybe you already know of something better. 20KV, I have indeed used these with a taser with reduced spark gap.
https://www.amazon.com/Alligator-DROK-Electrical-Connectors-Experiment/dp/B07B2PDZ8F
https://www.amazon.com/Alligator-DROK-Electrical-Connectors-Experiment/dp/B07B2PDZ8F
I've been using these ones that go on the end of banana plugs. So my test leads have 4 mm banana plugs that can interface with amps or speaker binding posts then convert to alligator clips. However I dislike that they are kind of large and only have conductive teeth on one side. I also have some general small and cheap ones. I actually like the small ones practicality wise, just they are sh*t quality.
Here's an idea. Connect a medium size inductor to a terminal block that is screwed down, so the inductor resonates mechanically. Put a speaker magnet nearby. See how the impedance of the inductor is affected at it's mechanical resonance. It might take a smaller inductor to raise the frequency to audio. I'm not sure what situation would be required for 400 and 1k resonances though.
I’ll try as time allows. It’s a good thing to do anyway to estimate the anechoic response for the bass without an anechoic chamber.
I happened across something relevant on youtube today, the video should play about 8 minutes in: