The first detail is the joint between acoustic boards. Boards are stacked in the cavity, and where two boards meet there is a line that will leak sound if it is left as a hard butt joint. The system uses an H-shaped EPDM seal at the overlap, so the joint is flexible: it damps vibration, allows for slight movement, and closes the gap that would otherwise short-circuit the cavity. The material is flame retardant to V-0 under GB/T 10707.
The second detail is the service hole. Cables and pipes have to cross the wall, and the usual site answer is to drill or cut a hole on the spot. That leaves ragged edges, and worse, it leaves an open path for sound. The studs are pre-punched for services, and the middle acoustic board is set out so that the holes line up into a service-separated layer: the cable runs inside the wall but not through the acoustic barrier.
The third detail is the through-hole in the stud. The QU38 cross rail passes through the square hole in the vertical stud and is limited by it, so the two parts lock together at every crossing. This is not only a stiffness measure: a wall that moves under load opens its joints, and an open joint is an acoustic leak. Locking the frame keeps the sealed joints sealed.
None of the three details is expensive on its own. What they have in common is that they are decided at design stage, not on site. A partition that is specified as a system — stud, rail, seal, board, service path — arrives with those decisions already made; a partition specified as separate materials gets them made by whoever is on the scaffold that morning.