This is the impedance sweep of an inexpensive 8" DVC woofer that was part of a Buyout on Parts Express. Not a bad woofer for only about $10. I am very curious about the apparent resonance peaks so close to the F[s).
Here are some pictures of the driver for reference:
That huge spider has undampened resonance modes. That doesn't always show up in the CSD or FR, but can elevate HD.
Mechanically exercised to the limits, so it is not a crunchy spider. Frequencies are much too low for cone and frame resonance, even spider/damper resonances would be 250-300 Hz range. It is not rubbing as far as I can tell.
Yes, it can be that low of a mode and possibly a harmonic of Fs. Large spiders can also allow rocking modes and also radial modes. I'd try clamping the frame in a vise and re-measuring.
I also re-state that these resonances often don't show up in the woofers acoustic response when the driver is mounted in a box. Alot of drivers emit various "junk" in sideways or rearward direction that doesn't go out forwards.
I also notice that driver of yours doesn't have a vented pole piece. That can cause airflow restrictions in the magnetic gap which also show up in the impedance. These can be quite audible at higher excursions and lower midrange frequencies.
I also notice that driver of yours doesn't have a vented pole piece. That can cause airflow restrictions in the magnetic gap which also show up in the impedance. These can be quite audible at higher excursions and lower midrange frequencies.
@wolf_teeth. Yes, I see it now looking much closer at the pic. May still be too small for a large excursion woofer like this.
That's usually what I sort of do with drivers that don't have any pole piece vents. If the spider is raised, then I usually choose to put the holes there, around the raised perimeter of the spider. The cone neck is a secondary choice because it can weaken the cone coupling to the VC. Some people prefer venting the dust cap because it can diffuse the cavity resonance in the air space between the dust cap and center pole. That doesn't always work out based on my experiences. One reason is due to the potential increase of air speed through the VC gap caused by the air pressure equalizing from inside the enclosure through dust cap opening. Drivers with phase plugs (open center poles) require special VC ventilation which won't audibly restrict airflow in the VC gap.