Quick Answer
If the problem is overheard speech, people in the corridor or the next room hearing what’s said in a meeting, sound masking is almost always the cheaper, faster, and less disruptive answer.
If the problem is intrusive noise, traffic, plant rooms, neighbouring tenants, or a noisy gym below, soundproofing is what you actually need. Masking will not help.
For most office speech privacy problems in the South of England, the right answer is masking. Where partitions are unusually thin or doors fit badly, the best result usually comes from both: minor construction repairs plus masking on top.
Soundproofing...
Tries to block sound from passing between two spaces. It does this by adding mass to walls, sealing gaps, decoupling layers, upgrading doors, and fitting heavier glazing. Done well, it reduces the sound level on the listener’s side of the partition by 10–25 dB. Done partially, it often does very little, because sound flanks around the upgraded element and finds the weakest path (typically a door, a vent, or a partition that doesn’t go all the way to the slab).
Sound Masking...
Accepts that some speech will arrive at the listener through whatever construction is in place, and adds a calibrated low-level noise to the listener’s space. The arriving speech now sits at roughly the same level as the masking, so the brain can no longer extract intelligible words from it. The conversation continues; it just becomes indistinguishable from the background. See the science for the physics, and the glossary entry on STI for the metric used to measure the effect.
What it does: Reduces the sound level passing between two spaces using construction.
→ Sound Masking
The clearest sign that you need both is a meeting room where the partition reaches the suspended ceiling but not the structural slab above. Sound from the meeting room rises into the ceiling void and then falls into the corridor or the next room over the top of the partition. Construction can fix this (extend the partition to the slab) but is disruptive. Masking can fix it more cheaply by adding maskers (small ceiling speakers) in the listener’s space, but it does not address the root cause.
The most cost-effective answer is usually a combination: minor construction repairs to seal the worst flanking paths, plus a masking system in the listening space to handle the residual speech that gets through. Done together, the cost is usually lower than the construction-only path needed to achieve the same outcome.
Alternatively, talk to customer service or see five real office layouts.