At what frequencies does this 3db loss appear? As Herman suggests you might just have a difference caused by boundary reinforcement unless the loss is across the bandwidth. Also, are you getting a substantial shift in the center of the soundstage to the stronger speaker? Or do you must detect it with the sound meter and in the frequencies 500hz or lower?
The best way to measure the speakers, if you are not already doing so is to put the meter about three feet in front of the center of each speaker and chart the results there as opposed to the listening position.
You can refine this further to identify which driver is failing, if it is, by measuring each driver with the mike right in front (a couple of inches) of each driver and charting the results. Be sure to use a secure stand. This is not a 'hand held' procedure.
The best way to measure the speakers, if you are not already doing so is to put the meter about three feet in front of the center of each speaker and chart the results there as opposed to the listening position.
You can refine this further to identify which driver is failing, if it is, by measuring each driver with the mike right in front (a couple of inches) of each driver and charting the results. Be sure to use a secure stand. This is not a 'hand held' procedure.