Sudden Mid-Panel Disparity

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Doug Ravizza

Sudden Mid-Panel Disparity
« on: 26 Nov 2022, 02:30 pm »
Recently, all three mid-panels on one of my RM30 Series IIs’ (CDWG, OXO, TRT) comparative output dropped ~5dB lower than the other. Driver output was measured with a Radio Shack meter placed 8” away from the driver, vertically centered. I  bought them new back in 2011 and they’ve always performed beautifully up until now.

Before measurements were taken, I tried swapping crossovers, cables and speakers from side to side and the output deficit always followed the same speaker. Now extreme settings on the “MID” L-pads (weak side turned way up and the strong side way down) are required in order to “balance” the left and right outputs.

Has anyone had a similar experience and were you able to find a solution?

Thanks For Reading,
-Doug

GeorgeAb

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Re: Sudden Mid-Panel Disparity
« Reply #1 on: 28 Nov 2022, 10:32 pm »
Have not had that experience. I would suspect the L pad first and the panels second. Panels are fairly easy to check by removing the - wire from the top panel and then measure the 2.8 ohms across each panel. For the L pad you need to remove a couple wires (else 3.6m H inductor is in parrallel and you will read 0 ohms) to measure the resistance to verify proper operation. Discussion on L pads. https://www.diyaudio.com/community/threads/8-ohm-l-pad-total-resistance.130760/ From memory I believe it is 150 ohms between pins 1 and 2. When/if you find it is the L pad, I would replace both. The L pad may be tacked down with hot glue to prevent their rotation, so when replacing, it may help to heat up the enitre body so MDF doesn't come off with the L pad when you pop it out. Hope you get it sorted soon. 







Doug Ravizza

Re: Sudden Mid-Panel Disparity
« Reply #2 on: 1 Dec 2022, 08:10 pm »
Thanks for the reply George,

It seems there's a resistive coupling between the positive binding post (the OXO, "MID" connection) and the plus terminal of the bottom mid-panel at the ring lug connector. It measured 1.3 ohms higher than on the other (good) speaker. I applied a drop of WD-40 and carefully wiggled the hex nut on the front of the driver and that managed to cut the resistance reading in half. Not perfect but it made a significant improvement.