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Getting phantom image perfectly centered

This is driving me nuts! I can't get the image centered unless I turn the balance control on the preamp to the 1:30 position. I've tested the system from source to loudspeakers from an electrical standpoint, so I know each speaker is getting the exact same electrical signal with a test tone and each speaker outputs the same dB with the same test tone.

So, it HAS to be the speaker room interaction, right?

I've read http://www.linkwitzlab.com/listening_room.htm and I THINK I understand everything.

All of the following measurements are in inches:
The room is 189 long by 144 wide. (15.75 feet by 12 feet)

The speakers are precisely 45.5 inches from the back wall.
They are each 26.5 inches from the side walls with a caveat. The left speaker is 27.5 inches from the window sash, which is 1 inch deeper than the wall. It's 30 inches to the top panes of glass and 28 inches from the lower panes of glass. But measured from the actual wall, both speakers are exactly 26.5 inches from the wall.

The speakers are precisely 90.5 inches apart.

The listening position is pretty close to 45.5 inches from the back of the room. The back of the room is open to the rest of the house and the wall on either side of the opening is symmetric with each partial wall being 36 inches.

Listening to a recording were I know the voice is dead center, the voice is actually just to the left of centered, and I mean "just". Would you recommend moving the left loudspeaker towards the center an inch or two?

What kinds of techniques to you use to "dial it in" when you've got a really revealing system and you are past the "math" and it's all more art than strict science?

I think you should be able to see a picture of my listening room here: http://orion.quicksytes.com/download/file.php?id=3096

My apologies if this isn't the right sub-forum to post this question to.
marktrav
audiokinesis
2,751 posts
 
It is possible that you have a bit of high frequency loss in the one ear.

A crude but quick test is, rub your fingers together right next to one ear, and then right next to the other. Is the tonal balance exactly the same?

By the way, I use the fingers-rubbing test to gauge ambient sound pressure level. If I can't hear my fingers rubbing together right next to my ear, there's a pair of earplugs in a plastic case in my pants pocket, and unless there's a really compelling reason not to, they go in my ears. I only have one pair of ears and I need them to be fully functional.

Duke
b_limo's avatar
b_limo
2,288 posts
 
I posted a thread about this a few years back also. I've noticed that the image can shift on me daily and I've attributed this to my ears. Some days my left ear is more clogged up, sometimes it's my right ear. I've made cleaning my ears part of my audio hobby. I also value my hearing more than ever and wear ear plugs at times to protect my hearing (15,000 rpm's and 100mph wind is no good for the ears).

I've found that the bay window in my room accentuates the bass in the same way that bass is louder in the corners of the room.

Since you are so exact with speaker placement you ought to do what I do and attach a string to the center of the headrest on your listening chair and make sure that your speakers are equidistant from the listening position. I've found that to be more critical than the speakers being the exact distance from the walls (someone pointed out to me that rooms aren't perfectly square). You still need to "eye" the placement because they can be equidistant but not equally apart from the centerline. I also use a level to level my speakers.
marktrav OP
24 posts
 
Thanks for all of the responses so far! As mentioned in my prior post, I moved the left speaker OUT and inch, and using a string (tape measure) moved the left speaker forward until it was equidistant to my ears as the right speaker.

All is well now.

The reason I don't like to use the balance control unless it's absolutely a last resort is that I got it in my head somewhere that it causes a phase shift/imbalance or something to that effect. Perhaps it was a manufacturer's ad that made a big deal out of the fact that the balance control was "out of the circuit" when at the 12 o'clock position.

The speakers are an dipole, active crossover design from Linkwitz Labs that I built myself. The crossover happens before the amps, so each speaker gets a direct amp connection. The dynamics are amazing. Everything is amazing about this speaker, and I'm glad the only issue I've had so far is the center image problem.

I sold a pair of Vienna Acoustics Beethovens powered by a VTL ST-150, so I was a bit worried going down this path, but it wasn't a mistake at all. A friend of mine who owns a pair of Maggies (the smaller ones), says mine sound just as good as his on the upper and mid-range, but my bass is worlds better than his. As the designer says, it creates a magic window to the recording.

My ears are clean and super sensitive, which I wished sometimes they weren't. :) Then I wouldn't have these problems. :)
larryi
4,106 posts
 
Making the distance between each speaker and your ears different will cause slight phase shift, particularly at higher frequencies, and unequal toe-in will also have an effect on phase. Changing the relative volume (using the balance control will not have a direct effect on phase relationships.

When adjusting speaker position, like you, I still try to make the speakers equidistant to my head. I have found that a cheap laser rangefinder I picked up at Home Depot to be really handy in this regard.
maplegrovemusic's avatar
maplegrovemusic
1,113 posts
 
you state you moved the left speaker in further to compensate for the window making that wall equal to the right . It is the hardness of the glass that is causing the sound waves to reach your ears sooner than from the right side. Try placing something with a more absorptive nature on the sill when listening , perhaps a small piece of sheetrock as a test .
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