Rock wool & fiberglass are the most efficient absorbent materials
Most absorbent materials do a good job absorbing frequencies over 1000Hz. However, the only materials known to date to absorb under 100Hz are fiberglass, rockwool, and geopannel.
Corners are the most effective location to absorb low frequencies
The corners of any room are where most sound waves end up at a certain point. If you need to reduce reverberation, this is a great location to place your absorbent panels and turn them into bass traps. An absorbent panel placed in a corner will be 95% as efficient as a triangle bass trap made of the same material.
The best sound quality is the one you like
You are the only person who can judge if you like the sound of a given space. Sometimes, we want a very dry room, but other times, we like to record in a big cathedral.
When to measure?
You can measure after you have installed your bass traps and your first-reflection absorbent panels. You always have to do those first steps anyway, so it makes sense to measure after them to find which acoustic cancellations or reverberations still remain after the basic sound treatment has been done.
Measuring an empty room will give you a very chaotic reading and will not help you make any decisions.
Four simple steps for professional results
1. Absorb the first reflections
Place absorbent panels where the first reflections happen, in both walls and roof if possible.
2. Set up bass traps
Place your absorbent material in the corners of your room.
3. Reduce reverberation time
Add absorbent panels in the empty spaces until you have the reverberation time you like.
4. Scatter the remaining energy
Fill the remaining surface with diffusers to reduce the remaining resonant frequencies.
Bonus: The last step to a perfect room
Make specific Helmholtz resonators to trap any remaining resonant frequencies.
Icon credits: Simon Child, Ben Davis, Ali Ali, Sergey Demushkin, Jonathan Li