An RTA can be used as a tool for finding general modes if you have multiple sources to play in the room that exhibit a wide variety of sounds to "test" the room with. Classical music is a good source because recordings are made with orchestras that have all instruments producing all frequencies and in a manner that provides both low and high pressure outputs through your system and into the room.
Start by listening in your chair with a RTA app on your phone. Look at the energy distribution in the RTA. Use 100 Hz. as your divide line. Look at frequencies below 100 Hz. Look at frequencies above 100 Hz. How do they compare. Do the lower frequencies rise higher than the frequencies above 100 Hz. Do you see certain frequencies stay longer on the graph compare to the other frequencies around it. You can then use the FFT function to get a specific frequency.
Using an RTA in this matter, will help you understand how your room reacts to sound energy. It is a teaching tool in this case. For more accurate, unwanted, frequency data, a sine wave sweep is best.
My question is regarding the level of sound not so much the tool used.
I realize that there is a limit to how much sound you can put into any space before you exceed the ability for the room to dissipate it.
I would like a test to show the point beyond which adding energy to the room becomes unproductive as it exceeds the absorption capability of the surroundings.
I know this is a poor description but that is what I am thinking.
Thanks for your patience and explanations.
The materials I usually work with are pipe organ accompaniment with choir or solo voices. These are really taxing sources as there can be lots of difficulty with understanding the words of the choir through the organ sounds. We have an E. M. Skinner organ that was recently restored and it is one of the most capable organs for this type of accompaniment. The organ can be very powerful and still leave the choir words understandable. My point is that when there is more sound than the room can absorb, the whole thing becomes indistinct because of the sound splashing about in the room. This seems to happen above 80 DB on the meter.
Short of making the room "dead" fully absorbing the sound, how can we make the sound both louder and more intelligible? Normal performances are 90 DB or more.
Diffusion seems to help with the articulation but there is still a building of sound that resolves itself as "noise".
Full range sound systems at these pressure levels requires certain room size and volume. Without knowing that information, I can not assist you. Please fill out the information in this link and I can better advise you.