The reason i run a small woofer in free air is because i dont want the neighbours, my landlord and the police kicking my door in for beeing too loud while i do a power output test,
My first BIG classD amplifier, I used car headlights as a load. Head lights do not shake the earth. very quite. You can still parallel with a speaker + pad resistor.
Well same goes with a power resistor as it heats up, not to the same extent as a light bulb, but still. My dummyload is i think six 25 ohm 50W DALE resistors in parallel for around 4 ohms total, and i use to dunk it in a pot of water for higher power tests.
The only reason for my woofercooker videos is to have a bit of fun, see of much power random junk woofers i find on the side of the street can take. Yea i know whats the point of shooting video of such thing when youtube is already flooded with these car audio bassheads doing it, or using the wall outlet on even their brand new woofers they bought just to destroy.
Getting rid of 1000s of watts of heat is a problem. I have large heat sinks with 100 watt resistors and fan. I have buckets of oil with resistors in them. I have tried buckets with water but the water boils and leaves hard water deposits on the resistors. Light bulbs is a cost effective means to dump power. I know the load is not temperature stable.
Now that it is hard to get old light bulbs I may have to change my plans. I hope headlights will be available for a while.
I can see that. If you reduce your time base it might reveal the frequency(s) of the noise and possibly lead you to the component(s)/layout area that's causing the ringing (some manner of coil field collapse and a nearby trace created capacitance tank thing going on, perhaps)...
Although, it doesn't seem to affect the audio out, so not a biggy...
It could be bad capacitors as if i take one and hook it across the speaker output, the resulting carrier residual gets alot bigger, so im gonna replace those caps with better ones.