I suspected I had a midbass bloom. Even though I cannot move the speakers more than a few inches (domestic harmony - well I did get the TV!!) I thought I'd use JA's methods to see how bad the problem is in measurements.
Here's the room (19'w x 21'l x 20'h) with cathedral ceiling
Left speaker position with fireplace to left of listening position
Problematic right speaker with rug treatment
Rear of listening room
Having set the reference playback level using 1 KHz tone (track 20) at 75db I recorded the sound level of the track 21 warble tones at intervals from 200Hz down to 20Hz.
I used a digital Radio Shack sound meter.
I created this spreadsheet - hope you can read it!
Having isolated the 50Hz 10db bloom (or should I say boom?)
to the right speaker and attributed it to the box effect created by the TV built-in which is 24" deep, I concentrated on trials to offset:
- Sock as bass plug for front bass port
- Rolled rug as per pic above
- Sofa cushions piled in front and around rug
- moving speaker 10" forward so back is level with front of built-in unit
Plug worked the best as most others were ineffective or killed the 100/80 Hz tone while improving at 50Hz.
I need some more suggestions please and also an indication of how exaggerated these issues are relative to other systems/rooms.
The speakers are Linn AV5140 driven actively by 3 x av5105 200watt power amps. Pre is AV5103 and front end is Ikemi CDP and VPI Scout tt with BenzLP cart.
Speakers have front ported rear facing 8" woofers which may be adding to my problems. However, I have to work with what I've got. Changing speakers is not an option at this time.
Thanks for your help and please ask for clarification / image reposting as necessary.