Complex sentence: In 1971, the hammer tips were changed to neoprene rubber instead of felt, to avoid the excessive need for regular maintenance, while in 1975, harp supports were changed from wood to aluminum.
Split into simpler sentences: In 1971, the hammer tips were changed to neoprene rubber instead of felt, to avoid the excessive need for regular maintanace. In 1975, harp supports were changed from wood to aluminum.