Low Fog Machines were made extremely popular with live music performances and videos in the 80s. It was only a short time ago that realising the low fog effect was still only possible through the use of traditional dry ice fog machine systems, which were a rental-only option due to their prohibitive cost.
Added in with the hazardous nature of buying, storing and handling the dry ice itself, these systems remained the realm of theatres and film studios only, with no real equivalent until now.
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Low fog machines work in several ways depending on their overall size and cost, with the designs varying slightly to suit the requirements of different sized venues.
Most DJs and performers will already be using a smoke machine or haze machine as part of their lighting rig, which will be fine for general room-filling duties and overall ambience. However, these units are all designed for maximum smoke dispersion into an area, and simply won't produce a controlled low fog effect.
Smoke and fog fluid is all water-based and environmentally friendly these days (it was originally oil-based), and works by the machine heating the liquid until it turns to a vapour. The additives to the water are there to help increase the ‘hang time’ of the smoke in the air and to add some density to the mixture for better visual effect.
This heating process obviously means that the smoke output is warm from the machine, which in normal circumstances is irrelevant to its performance, but becomes a big negative when you're wanting to create a low-level fog effect.
The trick to creating a ground covering layer of fog is all about temperature, with the smoke that's exiting the machine needing to be cooler than the air in the room. This requires some form of cooling system to be built into the machine itself.
These low lying fog machines start off with the variants that are known as ice foggers, which are perfect for mobile DJs and venues looking for a convenient and cheap to operate floor fog system.
Ice Fogger Machine
Working in an identical way to a normal smoke machine, using the same low cost, water-based smoke fluids, the ice fogger is a simple yet highly effective design that bridges the gap between the budget and professional ground fog machines.
These systems feature a compartment which is filled with ice cubes prior to use. The warm smoke being produced by the machine is pushed across the ice before it exits, which adds moisture to the vapour to increase its density, and lowers its temperature, making it colder than the air in the room. This allows the cooled smoke to be held underneath the warmer room air temporarily.
This simple solution provides excellent results and has the huge benefit of being both cost-effective and completely safe to handle and operate, with both the fog fluid and ice compartments being easy to keep topped up during an event.
Larger capacity low fog machines will often include electric fans to help force the smoke through the dense icebox, ensuring there is a powerful enough output to allow good room coverage from a fixed position.
Ultrasonic Fog Machines
Designed for large volume output of ground-level fog, these professional machines operate on a unique ultrasonic technology which replaces the standard pump and heater system used in smoke machines and ice foggers.
Rows of small sonic agitators, which are piezoelectric transducers, vibrate at extremely high frequency, which upsets the water's natural surface state and turns it into vapour (think of it as boiling without heating).
It's actually a technology that's been borrowed from industrial greenhouses where similar systems are used for moisture control purposes.
For ground fog use, these high-tech machines use a mixture of distilled water and standard smoke machine fluid, which is generated into the fog with little to no heat, which leaves a damp and cold misted output that will naturally keep low in the air.
A further benefit of this near cold process is that the machines can be run continuously for long periods, producing a dense floor level smoke that rivals professional dry ice units in its coverage, without the huge cost and hazards.
Another noticeable feature of these units is the long hose attachment to the front of the machines. With the systems being physically larger than a smoke machine, this extension to the firing port allows you to hide the machine behind curtains or under skirted tables while retaining full functionality.