Is the crossover network still existing and fully mounted? Otherwise ist could be a bypass for the crossover... But it looks like a standard work of B&O... ??? Check, wether this cap manufacturer is also used on the board.

Thnx for responding Die_Bogener! Answering your questions ...

• Yes, the crossover network is existing and fully mounted.
• I am not sure if this is the standard work of B&O. I showed a picture to a former B&O repair engineer. He did not recognize this.
• The cap manufacturer I believe is different than what's used on the PCB's.

Probably the crossover ist defect or the one who did this wanted to change the sound. Either more bass or treble... but without filter this is senseless and will destroy the speakers. If it is treble: very nice to send low frequencies to a tweeter, this will extend lifetime... to some minutes. And if it is bass: ok, this will kill the amp...

Thanks again for your comments! I have removed the capacitor, to check if this made a difference. Result = no difference. Sound is the same, functioning of the speaker system is the same. I will just leave it as is, without the capacitor. Probably better to avoid damage.

Came across this old post. This modification was also applied ex works to my 1995 1155 xxxx speakers. ( same construction) Checking the PCB02 schematic shows that this capacitor 4.7 uF has been applied as an additional interference suppression and smoothing on the negative supply of - 15 volts. I think that de reason for this modification was discovered during the final test of the product. Maybe interference or voltage dips. So leave it as it was  or rebuild it. The manufacturer did this for a reason and is not a hobbyist's invention.