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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
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
16,373 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
1,478 posts
 
why not move your listening chair to make the distance equal from each speaker and take another snapshot?
audiokinesis
2,750 posts
 
Unless you are using time-gated curves, windowed to avoid room reflections, what you are picking up is speakers + room.   In that case, unless your room is acoustically symmetrical across the spectrum (which never happens), some measured difference between the two speakers is virtually inevitable.   And also totally okay.  What matters is that the first-arrival sound be the same from both speakers, and you can't measure that without time gating, and even then you can't measure it down very low in frequency.   

In particular, that 5 dB difference at 250 Hz is not the result of "a 2.5 inch difference in room placement".  Your two speakers are much farther apart than that.  The room starts to dominate below about 500 Hz, and from there on down each speaker interacts with the room somewhat differently.   

None of this PRECLUDES the possibility of other factors being the cause of the issues you see, but they could just be normal room interactions. 

Duke
larry5729's avatar
larry5729
1,009 posts
 
Sounds like you measured things the way I did.

Call Soundings in Denver.  They specialize in Master Setting.  This is the best way to set things up.  After doing so, you will enjoy the sound in different sitting positions in the room.  Nice when having people over to listen over a few glasses of wine.  The more you drink, the better the sound.
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