Sam has established that The Californian was 12/13 miles away. The Cotton Powder Co distress signals used by Titanic performed a dual role in emitting a display of white stars very high, and a retort (bang).
Captain Lord specifically stated to the British Inquiry that Stone and Gibson did not report hearing any retort.
At no time was any question asked as to what Stone and Gibson were wearing on their head, and there was evidence of a weather cloth around and over the flying bridge. If (which they were not) in the enclosed wheelhouse below the flying bridge they certainly would have been unlikely to hear any retort.
Around 1956, (I have the exact date somewhere) Groves wrote to
Walter Lord that things on The Californian were not dead quiet in any event.
Leslie Reade in TSTSS was provided with expert advice that even at the closer distance he argued The Californian would not have heard the retorts from Titanic’s distress signals.
I’ve certainly heard modern firework displays explode from a distance of 4 - 6 miles away, so although I understand the physics, I’m not sure that my empirical evidence backs up Leslie Reade. I don’t think that I have exceptional hearing!
I find Boxhall’s assessment of the distance of Titanic to The Californian to be perverse.
Equally, Captain Lord, Stone, and Gibson thought they were seeing a small ship at closer proximity not realising it was a much bigger ship further away and not broadside to them. Groves got it approximately right in a rather tortuous explanation - a passenger steamer with a lot of lights about 10 miles away that then turned to show little of her lights. (I have much simplified Groves’s evidence).