Originally Posted by VWbug08'
Any ideas about why it happened?
Pretty much what others are saying. Even the absolutely best shielded bass ever made is only so-so shielded. It has to let the magnetic field from the pickup(s) interact with the strings and that means that external EM fields can get in. Some venues just have worse interference than others. In a dense urban environment the source of your trouble could be something the occupants next door are doing. If you need to play at this venue a lot then it is worth trying to track down what is being turned on and off when the interference comes and goes. Once you know the source someone may know a solution. If it is a one time deal then ignore it for now and hope that the source is not something that venue was an early adopter of and which is about to become hugely popular....
Originally Posted by Bongolation
Shielding blocks ESI, not EMI.
I realize you are quite firm in your beliefs about this but shields are quite effective against EMI. Shields and filters are the bread and butter of EMI protection. Filters alone will not protect anything against EMI and shields alone will not protect anything that needs to have a wired connection to the outside world. Together they solve all EMI problems if used correctly. Or almost all. Neither one will protect radio gear from interference on the frequencies it is tuned to. You can neither shield nor filter out the frequencies you must transmit and receive. If you have an EMI issue and you cannot use a shield then you most likely will not be able to solve the problem. There is no substitute for a shield.
As far as ESI goes I see no professional engineering references to it. I assume you mean electrostatic interference. I find a few IEEE papers that mention it but they are referring to very exotic situations: corona discharge, orbiting spacecraft, etc. I do find this definition: Electrostatic interference
Music Dictionary Guitar Dictionary
The undesired presence of an electrostatic hum field in signal conductors.
which is pretty much pure nonsense. I also found a nice web site from a recording studio that had a sensible discussion of shielding practices and which used the term ESI in nearly every sentence. I assume you are getting your information about ESI from a source like this. However, what they are calling ESI is a combination of two things: capacitive coupling and EMI and in fact if you drill down into Maxwell's equations in enough depth you will find that capacitive coupling is just another form of EMI. It is very convenient to think of some situations as capacitive coupling from both an analytical and a remediation standpoint but it really is all EMI at its core.
And a shield that has been properly designed for the frequency of the interference and the suppression ratio needed will be death to EMI.