Start with what the room has to do
There are three different jobs that get called soundproofing. Privacy is stopping words being understood next door. Separation is letting two activities run at once without either being a nuisance. Isolation is stopping amplified sound reaching a quiet room. Each needs a different amount of wall, and the price rises steeply from the first to the third.
The honest first question is whether both sides of the partition will be in use at the same time. If not, an unrated door that closes the opening visually is all the room needs.
What an accordion door does
A bare accordion door gives visual separation and takes the edge off conversation. A sealed version with an insulated core, sweep seals at the head and floor and a seal down the lead post does noticeably better, enough for privacy between a consulting room and a waiting area. Neither is an acoustic wall. If one room has to be quiet while the other is in use, the answer is a rated operable wall, and it is better to hear that at quote stage than after install.
What an acoustic operable wall does
A rated operable wall has mass in the panels and retractable seals that drop from the top and bottom of each panel when it is set, pressing against the head and the floor. The panels do part of the work and the seals do the rest. Ratings are given as an Rw number from a laboratory test, and typical operable walls are specified somewhere between the mid thirties and the mid fifties depending on what the room has to do.
A wall run with the seals left up is not a rated wall. Operating instructions matter as much as the specification.
Where sound actually gets through
The wall is rarely the weak point. Sound goes over the top through a ceiling void, under the bottom across an uneven floor, and around the sides through the jambs. A suspended ceiling with a continuous void above it is an open path between the two halves of the room no matter what the partition does, and a wall rated Rw 50 installed over one can behave like Rw 35.
- Ceiling void: needs a barrier above the wall line, usually a builder item
- Floor: needs to be flat enough for the bottom seal to meet it along the whole run
- Jambs: need a proper closure at each end, not a panel edge against plaster
- Doors and ducts: any opening in the surrounding walls leaks whatever the partition saves
Picking a target without over-specifying
Over-specifying costs money and makes the panels heavier to move. Under-specifying costs the room. Speech next to speech in occasional use sits at the lower end of the range; meetings that must not be overheard, in regular use, sit in the middle; amplified sound next to quiet work sits at the top, and only works if the ceiling void is sealed. The Rw selector on the operable walls page asks three questions and gives you a band to write into a specification.
The short version
An accordion door for privacy. An operable wall for separation. A rated operable wall with a sealed ceiling void for isolation. And in every case, the building around the partition decides whether the number on the datasheet arrives in the room.