Overview

LGRP Phase 1
Between 2012 and 2014, we organised blind and non-blind comparative playing and listening tests with 15 guitars, in room and concert hall conditions, involving 3 guitarists. See LGRP#1

LGRP Phase 2
Between 2014 and 2017, we organised blind and non-blind comparative playing and listening tests with 44 guitars, made by 22 builders and tested by 20 guitarists in 3 countries. At the end of that period, we also conducted an online listening test with 16 guitars, in which 226 respondents participated.
See LGRP#2 and Online listening test

End of 2017, we conducted tests to assess the long-term stability of alternative wood species for classical guitar necks. This study inspired researchers at the Laboratory for Wood Technology (UGent-Woodlab) to conduct a similar experiment using the same LGRP setup and measurement method plus a new setup method thanks to which the two setups were compared in terms of workability and reliability.
The UGent paper co-authored by LGRP and entitled “Monitoring the long-term stability of classical guitar necks: evaluating the potential of European-grown wood species in musical instrument manufacturing” was published in June 2025 in “Springer Nature, Wood Science and Technology”. See: Related research

Comparative tests / Tropical versus non-tropical 

All comparative tests between guitars built with common tropical woods and alternative non-tropical woods, in which all comparisons were made with a same guitar model and with European spruce tops, show that, in blind test conditions, players and listeners cannot distinguish between the two types of guitars. The preferences for one type over the other can be considered equivalent and did not result in statistically significant differences at the 5% significance level. At times, preferences slightly favour tropical woods, and at other times, they favour non-tropical woods. All in all, the preference ratio is 50/50.
In non-blind conditions, on the other hand, the prevailing bias in favour of tropical woods versus unusual local woods was strongly confirmed, especially in our first study (2013/2014).

This leads to a twofold conclusion:

1) Alternative non-tropical woods can be used to build guitars that sound just as good as those made from the commonly used exotic woods. 

2) Since the blind playing and listening tests showed that no significant distinction could be made between the two types of guitars, this suggest that it is mainly the model, the top plate and the bracing system (as the only constant factors) that determine the sound, and much less the back, sides or other parts, contrary to what is generally believed. This explains, of course, why it is difficult to distinguish between the two types of guitars or between guitars whose backs and sides are made from a specific timber regardless of whether those species of wood are tropical or non-tropical in origin.
This takes us to questions beyond the tropical versus non-tropical issue.

Note: above conclusion was also confirmed by other studies (see the paper by Lincoln university).
More details: Research report LGRP#1, LGRP#2, Online listening test, Related research.

Discussion and questions:

Despite the fact that perceptions and thus assessments of different guitar sounds are subjective, varying from assessor to assessor and often inconsistent for the same assessor (when one thinks that different guitars are being assessed when in fact it is the same one), there are indeed small (sometimes difficult to perceive) differences in sound, timbre and volume, both between tropical and non-tropical types and also between guitars within the same group, whether they are “tropical” or not.

Over all guitars the tops are, of course, as identical as possible, but they are not 'perfectly' identical, as they are made of organic material. Sometimes, for example, a particular top board is slightly denser or less quarter-sawn than another, resulting in differences in stiffness and other parameters, which in turn effects the sound.

The questions we currently have no answer to are the following:
• Are the (small) differences in sound between the guitars used for the tests, apart from the fact that they belong to the tropical or non-tropical group, the result of using different types of wood for back and sides or are they the result of inevitable differences in the different spruce tops? (or in both?).
•Which factors play a role, and to what extent?
•Could luthiers build differently (techniques, materials) and in a more targeted way if they knew the answer?

Further research

One way to investigate the above questions would be to build a series of guitars with different types of wood for back and sides and with truly identical tops made from a material that can be controlled such as carbon-based composite materials or more ecological alternatives such as flax fibre, with which various builders, both for bowed instruments and guitars, have already achieved promising results.