Listen. It's the only way!
When comparing Public Address & Sound Systems, there is no better way than to listen to them, in their intended environment.
At STG Media Systems, our speciality is to produce mobile and portable PA systems that are loud, clear, and intelligible; systems which accurately amplify and reproduce the human voice with all its various tones and nuances. Whilst we quote the commonly accepted statistics for decibels and effective range, these figures can be misleading - please read on, for full clarification.
The figures we quote for range are the theoretical distance, from the speaker, at which a loud (76dB) voice can be heard - assuming no background noise and perfect environmental conditions.
It is necessary to have approximately 10dBs, over and above the background noise, to be heard clearly. Therefore, if the PA system is to be utilised in situations with a high level of background noise (eg evacuations, crowd control etc), then the system will have to produce around 86dB, at the location of the listener, to be heard effectively. The table below shows the enormous difference this can make to effective range. The effective range of the AHD, for example, is reduced from 6000m to1850m.
| Product ||76db can be heard at:-|| 86dB can be heard at:-|
| Acoustic Hailing Device AHD||6000m||1850m|
| Glock 360||1250m||398m|
| MegaVoice Lite LSAMV2011LW||1000m||315m|
| MegaVox MEGA-7500||315m||99m|
| MiniVox AN-Mini||45m||14m|
NB: The table above assumes a high level of background noise - but that all other environmental conditions are perfect.
Environmental factors affecting performance.
The ability for sound to be heard clearly depends upon a number of environmental factors including temperature, air pressure, humidity, wind speed, wind direction, wind state (ie gusty, smooth etc) & physical obstacles (eg trees, buildings etc).
Clarity, intelligibility & accurate reproduction of sound.
Whilst a sound maybe clear and intelligible it is also important that the amplified sound is an accurate reproduction of the source sound. Public address systems can be loud, clear & intelligible - but if they re-produce a human voice, that sounds like a robot, psychologists have demonstrated that this robotic voice is more likely to be distrusted, ignored or even instil panic!
Technical factors affecting performance.
- Sound Pressure Level (SPL - measured in decibels dB) & the many ways of presenting the results. It is very important to be aware that there are a number of ways of measuring, and expressing SPL. To attempt to compare audio equipment it is usually expressed as the number of decibels measured at 1m from the speaker using a source sound signal having a single frequency of 1000Hz. It is important to note that human speech has a frequency range of 20 to 20000Hz - so the quoted peak recorded dB at 1000Hz may not be an appropriate way of comparing sound levels. Furthermore, sound, being a wave, has peaks and troughs - this wave can be measured at different points in the cycle. The common way is to measure the decibel value at the peak of the wave - as this gives the most impressive sounding value. Another way is to quote the value as Root Mean Squared (RMS), this is the more valid statistical way of measuring the magnitude of a varying quantity, and gives a more meaningful result for sound intensity, but if used to quote the "loudness" of a sound system, may give the impression that the system is quieter than a competitor that is quoting the peak value.
- How much louder is 110dBs than 100dBs? It is also important to note that the decibel scale is logarithmic and not linear eg 110dB is not 10% greater than 100dB. It requires DOUBLE the amplifier power to produce each additional 3dBs. So to produce 103dBs rather than 100dB the amplifier has to be twice the power - and twice the power AGAIN to produce 106dB, and twice the power AGAIN to produce 109dB. So a system delivering 109dB would need EIGHT times the power of a system delivering 100dB! This fact is often overlooked in specifications which commonly state, for example, "we are looking for a system with an SPL of 100 - 110dBs". This range is, of course, far too large to be a useful specification. NB: 6dB are lost with each doubling of the distance from the sound source.
- Amplifier Output Power (measured in Watts W). The "loudness" of consumer HiFi amplifiers is often quoted in Watts. This is the output power of the amplifier. The most efficient speaker designs convert a small amount, of amplifier output power, into a relatively large sound output. The volume of sound coming out of the speakers is dependent upon the sensitivity of the speaker driver and the speaker cone design. It is STG Media Systems' specialism, in the area of driver and cone design, that enables us to produce incredible sound volumes from small power inputs, resulting in some of the loudest, lightest and most portable systems on the market.
- Beam angle (measured in degrees & usually with a vertical & horizontal component). Some systems have the Sound Pressure concentrated into a narrow beam. This can be an advantage if it is really necessary to focus an address on a small or distant target group, but can be a major disadvantage where the speaker or the target is moving - analogous to trying to hit a moving target with a single bullet rifle or a shot gun - a particular problem, for example, when using haling devices in anything but calm seas. In addition, a narrow beam is more easily blown off target by the wind. A narrow beam angle can also be used to conceal a lack of efficiency, output power or coverage. It is, of course, easier to achieve a given volume of sound over a narrow area, than the same volume of sound over a wider area. It is therefore important to carefully consider the units intended operational use before making your choice.