Pressure at nodes and antinodes

[g.foster]

Greetings Fellow Physies
We have just made a long metallic tube with a loud speaker
at one end and gas entry at the other. This enables us to
light the gas which comes through 1 mm holes 1.0 cm apart
and to produce single frequency sound at the other. The
flame pattern at resonance is one where we see high flames
at the antinodes and small flames at the nodes. Many of you
will have seen similar appartaus in photos. 
However we are discussing why we get high and low flames and
we would appreciate clarification. If the high flames are at
the antinode this is where there is maximum variation in gas
pressure, so sometimes there is low pressure and at other
times a higher pressure than normal. At the nodes the gas
pressure remains constant at normal pressure and we think
that is where we get lower flames.
Question: Is a high flame produced at the antinode? 
Our reasoning: 
For at least half the time there is higher pressure than
'normal'? Since the frquency for the best effect seems to be
1 kHz to 2 kHz this would imply that there is higher than
usual gas pressure for at least 50% of the time and this
pushes more gas out the holes.
Comments please.

Thanks
Graham Foster
EGGS Auckland

Graham Foster
Director of Science, EGGS
AMI Learned Society