There is nothing safe about building any of the common types of air speaker around. You need to be very aware of
the disadvantages of these transducers before you start any work on them. It is possible to address all of these
safety issues and create a perfectly safe end product.
The most obvious disadvantage. Most designs use quite high voltages - typically a few thousand and sometimes in
the 10's of thousands of volts. Not only is there high voltage, but some designs also have the power available to
deliver considerable current into you. If you don't know how to behave when working on high voltage circuitry do
not attempt to build or use these devices.
All high voltage designs have the capacity to produce Ozone. Corona Wind designs are particularly efficient at
producing it. Ozone is an unstable form of oxygen (O3) which lasts around 20 minutes after being
produced. It smells quite refreshing, like a thunderstorm has been through the room, and is invisible. It is highly
reactive and in high concentrations will degrade the cell walls of living things, including those in your lungs. An
often quoted reference is that designer Nelson Pass successfully damaged his
lungs and needed a visit to hospital after trying to perfect his ion cloud loudspeaker.
Ozone is the most commonly cited form of gas produced, but there is a much more toxic gas produced that is
harder to detect and remove.
Plasma arcs are very efficient at producing Nitrogen Oxides (the
plasma combines the nitrogen and oxygen in the air), known as NOx and includes Nitrogen Oxide (NO) and Nitrogen
Dioxide (NO2), NOT Nitrous Oxide (N2O). These are far worse than ozone. Amongst its
effects are that it converts in to nitric acid in the moisture of your lungs and eats them away, as well as
entering the bloodstream and causing cancer. NOx is one of the emissions that is now restricted on cars by using
catalytic converters - you don't want it in your house. The larger and more powerful the plasma arc, the more NOx
is produced and in a small room the levels can build up quite quickly. You can't smell it or see it but it will
stream upwards from a hot plasma. I have used a digital NOx meter to detect levels around a large plasma and it is
off the scale above the plasma, and after 15 minutes concentrations are above safe levels in a small room. Designs
like the Hill Plasmatronic use an inert gas to try and get around the gas
problems, with no oxygen or nitrogen to combine no NOx is produced.
The plasma arcs can emit ultraviolet light. I have measured this on standard plasma discharges with a UV light
meter and found it to be at a very low level (barely registering) even on a large arc and so would not find it a
worry. On an arc discharge, the UV levels can be dangerous in the same way as arc welding.
High voltage sources can be used as X-ray emitters. However, there has to be very special circumstances,
including specific electrodes and the use of a vacuum, for X-rays to be produced. I have also measured various
forms of these speakers with a Geiger counter with no result, so would not worry about these either.