I’ve been thinking about this and I think these sustained up and down valleys are cup resonance. I don’t think they are the result of an undamped driver. The HE560v4 and HE6se both have drivers that are moving fast enough and depending on the pads, don’t require driver damping. My mod mostly removes cup resonance though it does damp the driver a bit as well. I believe an underdamped driver would be very hard to see in CSD’s because it’s not sustained. It’s literally the driver just not moving fast and flopping back and forth instead of vibrating quickly. I imagine the burst decays would be a better way to see it. Or one of your overhead views of the CSD’s where we can more easily see decay right after the original note. I’m going to send you a stock LCD-2 Classic and a modded LCD-2 Classic with driver damping. Hopefully we can see the difference in the measurements because the stock LCD-2 Classic is way underdamped. I’m guessing we might see some up and downs in the burst decay of the stock pair as the driver can’t move fast enough but I don’t know for sure.