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Question about adjusting the balance

I'll start out making my question to the point:

which would be better to use to adjust the balance using a sound level meter, a 315 HZ tone or a "uncorrelated (stereo) pink noise 20 Hz to 20 kHz" test tone?

Now I will add the confusion:  I placed my meter about where my head is when I am listening and checked it with the 315 Hz tone and it was WAY off.  So I adjusted by turning the input level knob (Cary SLP05) way down on the strong side.  Then I measured with the 20 Hz to 20 kHz tone and to get an even reading on both sides I had to turn the side I had adjusted way down back quite a ways back up.

Which do I trust if I don't trust my ears?

That is the uncomplicated the version of the question.  To post the full story, the 315 Hz test tone came from a CD that said to use it with an AC voltmeter to test the AC volts at the terminals (I used the speaker terminals) and one side was about 0.2 VAC stronger (if I remember correctly) so I adjusted the strong side down.  (Also I will note that I checked and the voltage imbalance follows the balanced input 6sn7  tubes, and I do actually have tubes that check dead nuts even, but I was playing with some different pairs.)  So no biggy, right?  Now I have the input knob for the strong side turned a bit lower and I put a small piece of making tape by the knob and made a dot with a sharpy so I could remember where I set it in case I moved it.)

BUT:  now I get the idea to test it with the sound level meter, so I position the the meter where my head would be and use the 315 Hz test tone and now the strong side reads EVEN STRONGER!  I am not trusting my ears so I continue to adust the strong side knob down 'til it is pretty far down but both sides read about even on the sound level meter.  BUT then I find a test CD with the "uncorrelated (stereo) pink noise 20 Hz to 20 kHz" test tone and the strong side is NOT nearly as strong!  So I adjust it to get it as close to even as I can using the "uncorrelated (stereo) pink noise 20 Hz to 20 kHz" test tone

and

it turns out it is about BACK WHERE I HAD IT  after I adjusted it using my AC vm at the speaker terminals.

I guess I should add that this is a VERY nearfield environment with my tweeters, and ears (so therefore my sound level meter) making a pretty much eqilateral triangle of 50 some inches and it is a "dirty" untreated room which I can definitely see having a bad effect on the balance on the sound level meter after I had adjusted it using the AC vm, but why would I get  db readings that were inconsistent (balance wise) with the different tones?  I mean if the balance was off--fine, I can understand that and adjust for it on the meter, but I guess my question is why does it show way far off with one tone and not as far off with the other tone--if that question makes sense.

Thanks.

immatthewj
tablejockey
3,916 posts
 

Don't  be put off by "lopsided" speaker placement to achieve center focus of the stereo image.    

Your hearing and gear are not perfect (L/R balance)

Imagine adjusting binoculars.

The alternative is full techie absolute- mic/software, laser pointer and kniffle rod adapter.

Not that there's anything wrong with that. 

 

immatthewj OP
2,073 posts
 

Don’t be put off by "lopsided" speaker placement to achieve center focus of the stereo image.

Your hearing and gear are not perfect (L/R balance)

Imagine adjusting binoculars.

Okay, I just didn’t think that there was anything unreasonable about placing a sound level meter where my head is usually at and then turning one speaker completely off and measuring the level of the other speaker, and then repeating the process on the other side, and then setting the input level knob for the speakers so that the sound level meter was measuring nearly the same db for each speaker.

My only question was why I was getting readings (balance wise) that were way different depending upon which of the afore mentioned test tones that I used.

That’s all.

ghdprentice
7,052 posts
 

My remote has a balance adjustment. If I feel the central image is off center, I’ll adjust it to center. To me some albums seem different. Probably just my hearing creates this illusion. But that is what a balance control is for.

I never thought of thinking deeper on it. Not a problem if you want to. But I would apply this technique to measuring the spl of different frequencies in stereo to identify peaks and troughs and then smooth them out. This is something that could improve the sound of your system. 

Post removed 
immatthewj OP
2,073 posts
 

@carlsbad2

So the question is, how is your tube bias set? I prefer manual tube bias adjustment so I can match any 2 tubes. Theoretically, an auto bias circuit should do this also, but if you’re getting different voltages, then maybe it isn’t.

the bias for my amp is set manually, but I can only bias the left bank of six output tubes and then the right bank of six output tubes (and I have them within a couple of mA, (I believe the last time I checked on bank was about 268 and the other was about 270) and I cannot adjust the bias of the individual tubes.

However, when I was referring to checking AC volts at the speaker terminals (per the instructions on the test CD) and I said the voltage discrepancy was following the tubes in the left and right balanced input sockets (when I switched them back and forth from left to right) I was referring to the preamp. And I assume you swere referring to the amp? I don’t have much of a handle on the circuit topology or circuit functions of components, so does a preamp need to auto bias its tubes? Except for volume and the left and right "input levels" (which was what I was using to adjust for the voltage discrepancy at my speaker terminals) there is NO adjustments whatsoever for bias on my preamp (Cary SLP05 and the tubes are 6SN7s).

But my original question was this:

I put a 20Hz to 20 kHz pink noise in and put my sound level meter where my head is and used the "input level" knobs to get the meter to show that the speakers were at the same level. Then I put in the 315 Hz test tone (which is the one that the instructions said to measure VAC at the terminals with) and using the sound level meter, the settings I achieved with the pink noise tone to adjust the balance with were way off.

I can understand that the meter would show different dbs for the different tones, but I would have thought that once it was balanced with one tone it would be still balanced with the other tone.

And I was just wondering why that would be. That’s all.

 

 

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