Hello , Could tiny cracks have developed at the joints of the support beams under the piano and between inner and outer rim? We've had good success in some older smaller grands turning the piano upside down, and filling these cracks with CA glue. This strenghtened the structure and resulted in a better sustain particularly in the treble. The sustain was not much longer but stronger/fuller during the after sound. I have never attempted this on a concert grand but it's just a thought. -Mike Jorgensen RPT
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