- Will the decibel value of a sound meter change when you walk from one corner of the room to another? And can I use this sound meter to determine where I can best place my acoustic sound absorbing panels (eg. placing more panels at corners where decibels are highest)?
In a very approximate way, yes, kind of.
I'm assuming you have little more than a phone with a meter app, so this is a simplistic, DIY, experimental method.
You need to be transmitting white noise & you need a meter that can show you a frequency spectrum. That way you can track humps & dips in the spectrum as you traverse the space.
Your acoustic panels will need to be tuned to the frequencies that resonate. Bass traps need more than just a panel on a wall, and if your space generates standing waves anywhere away from the corners you might need some trial & error to discover which pair of surfaces is responsible.
A cheap meter or phone app will not be able to properly measure very low frequencies, so some of the low end compensation will be little more than guesswork.
If you get odd bass lifts against walls or in corners, then so long as no-one is ever going to be monitoring from there, you will probably have to just live with it.
This is one of my favourite tests. I use a software bass synth and play tones going lower and lower using monitors going low (not the computer speakers). There are probably sound files you can find doing similar. I "lock" the sound when I hear a big difference and walk around in the room.
On the "room resonant frequencys" the sound volume can be quite different in different places in the room. Not unusual is a difference of 30-40dB in different places only a foot (3 dm) away.
Doing a test like this in a non-treated room will show the importance of acoustic treatment.
The next step is to create a good plan on how to attack the problem you have found. Budget and experience are two important factors. Often in my experience a good solution is to not try to fix the very lowest frequencies below about 75Hz. Maybe using speakers not going as low in freqencys, say a 5 inch bass instead of 8 inch. The reason is that treating the really low frequencys is both difficult (meaning you need how to do it) and expensive.
Use a decent measurement microphone (should be an omni microphone in order to catch low freqencies) and a program allowing you to make an audio waterfall chart. It will show both the difference in volume as well as in the decay time. Start by attacking the low freqencys below, say, 300 Hz. There is where the large and difficult to select bass traps are needed. Next you can attack reverb times higher up in frequencies.