First of all, what is the cause of the noise?
You may not have many people in the office or boardroom, but flat reflective surfaces will reflect the sound enough to make it sound louder than it is. It is sound reflections that make the room echo and sound loud.
Offices that suffer from boardroom or office echo are just as difficult to hold meeting, with two people as twenty people.
The teleconference speakerphone is often blamed for the poor quality during a conference call. Quite often the problem is room echo caused by sound reflections.
Acoustic panels are the most economical solution.
Acoustic diffusors can help scatter the sound, but they don't look professional and they can get expensive. Acoustic panels can blend in, be installed on walls or ceilings.
What else will reduce noise?
Any material, that has a soft porous texture will absorb sound, such as couches, chairs, curtains and carpet.
Will sound masking help?
Sound masking is designed for areas where people need privacy in an open area. Sound is broadcasted at special frequency to mask conversation. This is great for call centers, where you don't want voices to carry across the room. Unfortunately it won't help with reducing the noise level in a room.
Why are offices so loud?
Office rooms and boardrooms have become quite simple and stark in the last 10 years. With Polished concrete floors becoming popular, offices have become loud, with the reflected sounds of voices.