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Speaker placement and dB differences

So I’m pretty anal about speaker placement. I use tape measures, along with laser lights and levels to assure proper and equal placement from walls. I was using my new Omni mic and testing software to run some white noise frequency graphs vs db range to see where I stand.  After overlaying the R/L graphs I noticed that there is about a -1db difference in the right channel generally across the entire frequency range and about -5 dB at about 250 hz. 
Also my room is 12’ x 13’. 

I remeasured my speaker distance from the seating position wall and I noticed the left speaker was 96” from the front the chair and the right speaker was 98.5” from the chair. By my calcs that would only account for a .22 dB difference. Not enough to account for the 1 dB drop in the right speaker and certainly not the -5 dB at 250 hz.
Question is, is a 1 dB difference between two speakers normal. My speakers are Thiel CS 2.4’s and I’m using an older ARC tube amp - which can certainly account for 1db.

the bigger questIon is can a 2.5” difference in room placement cause a 5 dB difference at 250 hz?
last_lemming
jjss49's avatar
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jjss49
6,612 posts
 
room is small... tough

semi nearfield listening
erik_squires
16,330 posts
 
2.5" is too small to account for a 1 dB difference.

Swap the speaker cables and see if the effect remains.  If the effect changes, it's your equipment.

If it remains, measure your speakers at 3'
geoffkait's avatar
geoffkait
23,365 posts
 
You would not have had that problem had you followed my advice which is to use the speaker placement track on the XLO Test CD or similar TEST CD or LP. Trying to find the absolute best locations for speakers by lasers, tape measures, trial and error are bound to fail. The speaker placement track allows you to find the absolute best locations for ANY speaker in ANY room and with ANY level of room treatments applied. All other techniques are like trying to solve x simultaneous equations in x + n unknowns, the best they can do is find local maximums. Hint: most speakers are way too far apart. Yes, I know what you’re thinking, but that’s how you get a wider soundstage, right?
erik_squires
16,330 posts
 
Was too tired when I answered this. If you are using OmniMic, use the swept signal with gating/blended results.

This will help you see if the problem is consistently across all frequencies (which would imply an equipment issue) or if it's in the bass for instance, which would imply more room issues...or narrow across 1 driver's range.
rbstehno
1,473 posts
 
why not move your listening chair to make the distance equal from each speaker and take another snapshot?
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