Anyone can do plain ‘loud’ – but how do you project a super compact cone of the clearest sound over hundreds of metres? Here Superhailer’s acoustics expert Matt Henry talks technical.
Anyone who has driven a pre-1960s car will know how bad the headlights are. The 12-volt incandescent bulbs spill out a weak yellow light in seemingly every direction than the straight ahead. The energy is wasted in directions it’s not needed. Fast forward to today’s laser powered headlights and the beams they cut through the darkness for over 100m are brilliantly clear, with no spillage of light to scare any animal lurking in the hedgerows.
The ability to direct clearly and efficiently is just as important with sound, especially in emergency situations. Imagine being able to beam ‘Don’t panic, help is on its way’ to a floundering, out-of-their-depth swimmer hundreds of feet off a beach. Or tell the people at the back of a crowded sporting event to ‘Stop pushing forward, you’re crushing the people at the front’. Or beam a ‘Don’t do it, let’s just talk for a while’ to a distressed person on a building top or bridge thinking of taking their own life. Clear messaging projected with precise directional accuracy can save lives.
Accurate, loud, safe and clear
Saving lives was the impetus for me to put my acoustics training to good effect. Being able to focus a crystal-clear message in a tight cone for long distances lies at the heart of the state-of-the-art loud hailer I invented – Superhailer.
The core functionality of Superhailer is to create a narrow beam of sound that can be used to selectively target an individual or individuals over hundreds of metres. Creating a narrow beam is very challenging but being able to do so enables the user to broadcast to a chosen target without exposing themselves, their colleagues or bystanders to high sound levels. This means you can be highly discriminating in how you project the chosen sound.
Figure 1 shows a polar plot on a decibel scale at a key output frequency of 4kHz. This shows an extremely narrow sound cone with a core beam of only +/-7.5 degrees (-3dB) and a very rapid rate of drop-off at the edges. It also demonstrates minimal off-axis intensity outside the core beam.The effect on the listener is stark. Outside the main beam the acoustic signal is audible but the intensity is relatively low. But the moment you move into the main beam the onset of loud clear sound is very rapid.
Figure 2 shows an alternative representation of the device output directionality, in this case as a function of relative intensity by angular position. As can be seen, the intensity experienced by any bystander is extremely low by comparison with the target and those parallel or behind the device experience less than 1% of that experienced by the target at a same range.
This very high level of directionality must be experienced to be appreciated.
Accurate, loud, safe and clear
The two key benefits of this directionality are 1. Users can accurately and selectively target individuals or groups over hundreds of metres and 2. Bystanders and the device operator themselves experience much lower sound levels – ensuring the device is used selectivity and safely by minimising inadvertent exposure to non-targets. For example, the user can talk at a comfortable level to those nearby even when the device they are holding is running at full power.
Loud – but not too loud
Even those within the cone don’t experience harmful levels of sound. I designed Superhailer so that the operator need not decide upon the volume level required. They simply aim the device at the target individuals and press the button – at which point an inbuilt eye-safe laser range finder instantly measures the distance to the target. This information is fed to the onboard safety limiter that ensures the maximum volume the target hears does not exceed 112dB LAeq – well within sound levels generally accepted as being legally permitted. (A lower maximum limit can be set if the user prefers.) The objective is to communicate effectively without hurting anyone, it only needs to be loud enough to achieve that. Superhailer is believed to be the only device of its type to work within current workplace sound legislation –louder volumes can constitute a ‘use of force’.
Just as modern car lighting has improved road safety and saved the lives of thousands, so too do cutting-edge loud hailers that are loud, safe, clear and – importantly – accurate – have the potential to save lives in a wide range of emergency circumstances.