VI and eveness of scale or tone

[BobD]

I was playing my recently aquired VI last night and I noticed that when I play softly and I go from middle G(G with octave key) to middle A(A with octave key) there is a change in tone. It gets more airy sounding. The pitch is ok tuning wise but I can hear more air coming thru. If I tighten up the emboucher it tends to go away some. Is this change the eveness of scale that I hear people talk about? Or could my octave vent need cleaning perhaps?

[MBushaw]

I've found that's usually just the neck octave vent opening. Only the player hears it.

[Gregg W. Jackson]

It could also be that the lower octave key isn't closing completely, either because of the pad not sealing or an over compressed cork or felt in the linkage.

[beezer]

You will notice that the A pad is closed by the A lever via a small piece of cork packing. If this is missing or not thick enough, the A pad will not close fully and you will experience the symptoms that you describe.
Cheers, Dave