Furniture - Most furniture is designed to be functional or aesthetically pleasing rather than to be a good sound absorber. In many types of offices, screening has been purchased in an effort to improve visual and acoustic privacy. To have any impact at all the screening needs to be at least 5 feet high and one needs solid mass in this screening to block sound energy. When steps have been taken to reduce the signal strength, then measures to increase noise can be adopted. Background music or musak is not an effective way of doing this because the frequency range is too wide.
Speech tends to be particularly distracting when understandable - one strains to ignore the sound.
Unexpected sounds and uncontrollable sounds tend to be especially disturbing. These intruding noises are especially severe in open office type designs.