Best way is to try some tweaks and see if they improve the sound. First, bring the speakers out from the wall using the 38% rule (see realtraps site for details). Also using the realtraps web site calculate the reflection points and see if they are interfering with room nodes. Yes, any glass is a no-no, as all glass 'rings'. Leave it were it is and put a blanket, or two, over it to see if things improve. Others have also suggested some considerations. Also, check out the Toole book, 'Sound Reproduction', it has tons of information that will help you 'listen'. Use the music that is most familiar, Chet is great listening. Finally, hit the 'pillows', placing them at reflection points to see if improvements result.
How to tell if Acoustic Treatment is Needed?
I have a 12x22x8.5 ft room with the audio on the long wall - for various reasons - facing the listening chair 8.5' away from front of speakers. The soundstage is excellent with the center clean and tight. The ceiling slopes from 7.5' to 9' upwards from speaker wall to wall behind chair. I have no complaints; I think the sound is very good, although with 60 year-old ears and not a lot of experience with high-end audio systems I don't know whether MY budget system can be better.
I do know that there are furnishings in the room that people say do create problems, such as a large glass-fronted picture behind the chair, a coffee table in front of the chair. The speakers are older Mission 762s with front ports and thin cabinets (similar to Harbeth/Spendor BBC style) which sound quite nice. They sit with their back edge about 20" from wall.
My question is: How can one tell - or, what do you listen for - in order to determine if acoustic treatments would improve the sound? For example, I've tried moving the coffee table away from the chair but couldn't determine a change in sound.
I do know that there are furnishings in the room that people say do create problems, such as a large glass-fronted picture behind the chair, a coffee table in front of the chair. The speakers are older Mission 762s with front ports and thin cabinets (similar to Harbeth/Spendor BBC style) which sound quite nice. They sit with their back edge about 20" from wall.
My question is: How can one tell - or, what do you listen for - in order to determine if acoustic treatments would improve the sound? For example, I've tried moving the coffee table away from the chair but couldn't determine a change in sound.