[Phil Allison[_4_]]

Phil Allison wrote:



** In a portable PA system, this can be risky when you allow for simple mistakes made during set up. The risk is supersonic oscillation, induced by crosstalk.

Running balanced and speaker lines tied together is commonly done with amp racks. It works fine until someone powers the rack up without connections being made at the far end of the cables and advances the amp gain controls.. The unterminated balanced line couples capacitively to the hot speaker wire and oscillation is possible. Usually at a frequency like 50 or 100kHz.

The risk is higher if you are using a powered desk since so much more gain is available.



** I should point out that supersonic oscillations, while inaudible, will destroy high frequency drivers and seriously damage most power amplifiers in a few seconds.


..... Phil