The next step (that will probably never happen) would be to refurnish the Hagia Sophia, as it would have been before it was plundered in the fourth crusade, and seat an audience in it, as if for a mass. Then pop another balloon. All those extra furnishings and bodies would have had a significant impact on how the space sounded. The plastered over mosaics might also create a noticeable effect that would need to be compensated for. Even with the impressive work of Abel and Pentcheva we still have something that would likely sound empty and strangely hollow to people familiar with the Hagia Sophia when it was serving as a church.
I don't know that there would be extra furnishings. It's not unheard of for Orthodox churches to only have seating around the perimeter for the sick and elderly. It's common for worshipers to stand during an Orthodox mass.
That could have turned out so much worse for all involved, but I suspect those involved had different perceptions of the risks than we do now. Though there was still some risk of dying, this must have seemed like a cakewalk compared to jumping out of a WWI trench!
Some Greek chanters got permission to go into the Hagia Sophia and record a TV special (for Greek TV) of chant music several years ago. While not a service, it is the music that would have been used at a service. (Either that, or this is another case of convolution reverb and some clever video editing. I'm not sure. But it sounds pretty cool.)
I don't know about it feeling empty and strangely hollow. I've sung in plenty of very large cathedral spaces, and even when they're packed with people they're still immensely resonant, sometimes to the detriment of the music - singers often prefer smaller spaces where the sound doesn't get lost in an acoustic bathtub. And as another commenter pointed out, there never would have been rows of pews in the Hagia Sophia like in a western church.
You don't have to measure it, strictly speaking. When you know the acoustic material properties of the surfaces well enough, you can compute an impulse response with high enough accuracy (getting to one jnd and below). The tricky part is knowing the material properties. These are often just guesses as measuring them in situ is very difficult/impossible.
I find it strange that people and historians are so fixated on the 4th Crusade as the be all end all of the Byzantine's and ignore or minimize as much as possible all that irrelevant side business of the centuries of fighting with the Muslims. You know, the guys that fought them far more often and more brutally and actually took away nearly all their territory and destroyed them? In addition to the above comment and a few others in this thread take this video for example.
Don't forget the Persians before the Muslims or all the self-inflicted damage from coups, inept emperors, etc..
In this case though, the fourth crusade really is important since it was when the Hagia Sophia was first looted during a sack of the city. Nearly seven centuries of accumulated treasures were carted out of the place.
It's totally done on a politically oriented ground to denigrate a religion and culture, and put another in favouring light. If people were more educated about some historical facts (for instance the bloody conquest of India) it would be harder for some people to keep the power and push their agenda.
