FG Wilson, a generator set manufacturer in Larne, UK, (part of the CAT Electric Power Division), has an acoustics facility for obtaining noise emission of current products, future developments and research. A wall between a hemi-anechoic chamber and a reverberation room contains an aperture which is used for testing canopy panels to determine their sound transmission loss. Two different standard procedures for transmission loss testing are compared; the J1400, and ISO 15186. Tests were carried out on both to determine which is most feasible for the company to use. The J1400 is a variation of the ASTM E90 which uses the same method but is specifically for a reverberation room to hemi-anechoic chamber. A known 'limp' material, chosen to be lead, is used to obtain a transmission loss correction. ISO 15186 is based on a sound intensity method. A microphone on the source side recorded the sound pressure levels, and an intensity mapping was done on the receiving side, from which transmission loss was calculated. Two tests were completed; a lead sheet, and a steel plate. Both standards showed an acceptable accuracy in relation to the mass law.