I think they got location mixed up I have a fairly reliable source "The Fleet Boat Submarine in the US Navy" in its diagram for the GUPPY the sound room is in the space below the control room.I suspect that this was an earlier design and later designs wisely removed the officers mess and use that space as a sound room the Guppys where more about submerged performance and they had one less engine which freed up space not available originally. Those spaces are not too small the crew did go down there to work on the pumps and such and the refrigerator was below the main deck as well it would just not be the ideal place to spend an extended period and on a WWII G,B,T that is where the pumps would be.
link for a WWII Gato diagram if you missed it.My book has much better diagram but it is too large to scan.
http://www.ussflierproject.com/wp-co...ne-Cutaway.jpg