No one has reported inaccurate information here.
Both views are right but which question is being asked has been obscured. I'll try taking another stab at this at the risk of falling short of a complete (technical) explanation.
1) Does a same size speaker in a small room vs. a larger room have higher or lesser SPL at the same listening distance?
No. Gena measured this and is supported by sound principles (pardon the pun).
2) Does a small vs large speaker have higher or lesser SPL at the same listening distance in a small vs. a larger room?
In a linear distance sitting in front of a speaker, small or large room, Gena is correct. The SPL will still be the same. That is an undebated fact. Mdrew (and earlier myself) has also tried to point out the change that occurs in using a smaller vs. a large speaker in a small vs. a large room is where room volume plays a role.
So, question 3) Will the sound from a small vs. a larger speaker be different in a small vs. a larger room? (the idea of 'filling the room'). This question now depends on more variables which throughout this thread have been presented, but have perhaps gone beyond what Gena was originally investigating.
To me, filling the room with sound does not equate to straight dB but rather, the ability of a speaker to provide good imaging across a larger area (and again, volume since more than one linear direction, such as listening only directly in front of a speaker, is being suggested; up, down left or right).
With a larger room there are greater distances to side walls, ceilings, certainly. Will SPL differ between a small and large speaker at a 9' distance sitting directly in front of the speakers in that room? No, not within the dB range already noted by Gena and JohnK.
However, sit off axis, left, right, up, down from a large speaker driver compared to a small speaker driver, and room volume (again directly related to linear distances) makes a difference, primarily b/c in a small room, one cannot move that far off-axis (or very far period) from a speaker. Some of the largest sound changes occur by shifting even slightly left or right, up or down and with a larger room, more spread in the speaker spacing, the issue of smaller and larger drivers now comes into play. Straight SPL does not say anything about the sound dispersion (e.g. imaging).
If i can go back to my rubber ducky idea of a spoon vs an ice cream pail lid to make waves in water, yes, at 3m the wave amplitude may be the same in a tub or in the sea, but how wide is the spoon produced wave compared to the pail lid produced wave?
Perhaps the specs of off-axis response should be brought into this thread since i believe it is more the topic of discussion when referring to "filling the room with sound", but that is my interpretation of the expression..
I was playing around with off-axis dispersion when i first bought my large Tannoy speakers. I could move something like 2 feet to the left or right of the speaker and receive a pretty equal sound quality. If i move only a foot to the right of my M60, the sound begins to change. Don't quote me on the distances (try it yourself and see), it was awhile back that i played with this, but the conclusion is the same.
Electrostatic speakers are good examples of 'larger' units that provide an amazingly wide dispersion in this regard.
Another fun test i did was to play pink noise and then squat down and slowly stand up in front of a speaker. Listen to the sound change as your ear becomes level with each distinct driver. Find a speaker that reduces the change in noise over a wider distance and you have a 'better' room filling speaker IMO. The only way i know to do that is by using a larger driver.
