For city apartment dweller audiophiles. Have you ever had neighbors banging on your walls?

Are you talking about spikes under your speakers or under an electrical component.  If it is an electrical component, I think the complaint is a coincidence.  It might be a real phenomenon with spikes under a speaker.

Spikes are intended to couple the speaker to the floor and will transmit MORE energy to the structure.  Most footers are intended to dissipate that energy and would reduce transmission to the structure.  If you somehow, by using both the spikes and footers, created a particular tuning of the resonance of your speaker set up such that the system is resonating at a frequency that is easily transmitted by the structure of the apartment and is particularly loud in the music you are playing, this might be the cause.  Try taking off the spikes and going with just the footers.  I still think it is somewhat unlikely that the spikes caused such a change that it was a cause of the complaint.  It is more likely a coincidence—your music playing happened to annoy your neighbor more than usually (she might have had a rough night trying to sleep and you woke her just as she was getting some shut eye).

I live in an apartment and my experience with speakers and spikes is that spikes definitely transmit more bass energy through the floor. I have wall-to-wall carpeting and there is a foot of cement between floors, so I've lived here for 33 years and never heard anything from upstairs (except when contact is being made with their floor) or downstairs neighbors or the one wall that borders on another, and nobody has ever asked me to turn it down.

The spikes supporting the wooden base the speakers sit on. 

It's a pretty big coincidence because I had been playing music at that level for a few years from when she first moved in, early morning and in the evening, and it never had been a problem. If she had mentioned it to the super I would definitely have received a letter.

I never lived in any apartment really.

I was lucky.😊

But i worked when young in a store...

I read books between customers.

The neighbour above make some much noise with a rockband...

I did not know if it was a real one or playback...

I go up banging his door...

I only make the sign of cutting a throat...He close the door.

I go back and the silence i was used too go back...

I only make noise with my speakers when i was 15 years old...

No neigbours came for cutting my thoat... After this critical year i never listen window open at 100 decibels and more ...

i am pretty sure that my own isolation coupling decoupling sandwich is better than footers to control vibrations then bass sound level in the floor and ceilings ...

Tough guy, huh? 😉

I go up banging his door...I only make the sign of cutting a throat...He close the door.