APPENDIX 4: THE VALUE OF THE ACOUSTIC HOOD IN THE EXPERIMENT
This graph shows the recorded far field signal from a soundhole with (blue) and without (red) the hood in place:
The effect of the acoustic hood on recorded response from a 45.4mm radius round soundhole
Without the hood in place there are strong resonances at 170Hz, 461Hz, and 494Hz (2.00m, 0.74m, and 0.69m wavelengths). These are present for all four holes tested without the hood, and correspond to dimensions in the room close to the apparatus, indicating that they are most likely room standing wave resonances. The hood is quite effective at suppressing these.