From the study:

Overall sound quality ratings were then given by 52 guitarists in a dimly lit room who played the different guitars while wearing welder's goggles to prevent visual identification.

They gave similar ratings to all six guitars, while blinded tests by 31 of the same guitarists indicated that they could not easily distinguish the guitars by their sound or feel.

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Even if there were a difference, I don't think anyone is justified in killing rare trees to make guitar backs from them.