I hold barometric pressure, humidity, temperature, ventilation and density as key factors for quality sound in a rehearsal space. Not especially scientific but based on actual experience. Years ago, we (BG & TSC) shared a rental rehearsal space in a big complex with a trio of hoarders. Way too many of their amps, gear etc and things hanging from the relatively high ceiling. Very claustrophobic ~
but... the sound was always good. We moved to another similar sized space in the same complex but it was way more sparse/uncluttered, and I had huge difficulty getting the same bass rig to sound good. Luckily it was short lived. Our current space under our guitarists home goes back & forth from sounding
sooo good to sounding just ok. All settings the same. Same bass, same drums, same keyboards, PA & guitars - but different sounding depending on the day. I refer to the difference as shifting "molecules in the air" - and I'm convinced it's more that than anything else. As in, nothing inherently changes but one rehearsal sounds awesome (levels/sound quality) and another... just ok. When we first moved there we did some acoustic work on the space but by no means like a recording studio would. So all I'm saying is we can attempt to control a space optimally in as many ways as possible on a budget - and the rest comes down to the molecules in the air.