How much ozone is produced by ionization of air and how turn ozone into oxygen
Even if the UV light idea doesn't work out very well I still want a way to do this


With some photochemical background, I suggest to forget about running such a UV lamp 


Remember that your plasma will be formed in air. For every molecule of ozone formed, there are much more harm- and odourless $\ce{O2}$ molecules around. If you cleave $\ce{O3}$


\[\ce{O3 + O2->[\mathrm{h}\nu][\lambda\ \lt\ \mathrm{300\ nm}] [O2 + O* + O2] -> O2 + O3}\]

the resulting oxygen atom will be captured by the next $\ce{O2}$ to form ozone again. 

The overall process will not reduce the number of ozone molecules, unless $\ce{O*}$ reacts with $\ce{N2}$, which might lead to some other unpleasant species ;)

Note that these processes are fortunately effective in the ozone to protect us from short wave UV radiation, which brings us to the next aspect of the setup.


In order to photolyze ozone, you'll neeed a light source that emits UV at $\lambda\lt300\,\mathrm{nm}$. It's not that these light sources would not be available, but this UV range is not that of a tanning booth lamp! Remember that the ozone layer protects our DNA from running havoc! The least you can expect from short-wave irradtion is the sun burn of your life! Consequently, you will have to shield the whole setup properly!


In summary, I absolutely like the idea of building a plasma speaker yourself and there even seem to be some DIY kits around, but I suggest to forget about the UV part, which can be much more dangerous than the ozone formed.

UPDATE

Burak Ulgut brought up a very interesting point. Back in the days, plasma speakers using other gases (or gas mixtures) were tried, and even went commerical.

This site in German describes a helium driven plasma speaker system :)