Anyone who has ever bought consumer Hi-Fi will be familiar with signage and packaging offering thousands of watts of power for low prices, and incredible figures quoted by sales staff. But what does it all mean in the real world, and what lessons can we learn from this when it comes to selecting the correct equipment for commercial purposes?
As anyone who has worked in the electrical industry would know, power is calculated and that calculation results in a ‘wattage’ figure which indicates the power consumption of a piece of equipment or a system. This is a critical concept to understand when it comes to audio! In terms of a speaker, wattage indicates how much power a speaker consumes, and for an amplifier how much power it can generate on its outputs. In neither case does this give any indication of acoustic performance which is our primary concern when selecting equipment.
In this article we will look at speakers and where power is used to indicate consumption. These figures are often rated at PMPO (peak max power output), which is a theoretical maximum value a speaker driver can attain before it physically fails due to heat or “over excursion”. In reality, listening to a speaker at its PMPO would not be appealing. It would sound distorted, and the frequency response would be far from flat or musical. A more realistic figure is the maximum power the speaker can handle at the point it is best reproducing its source tonally i.e. before the onset of distortion. Unfortunately, a speaker’s power rating does not necessarily relate directly to its acoustic output. A speaker should be selected based on the space it is covering, and how ‘loud’ the reproduction needs to be in the space. How loud a speaker can be clearly depends on not only how much power it can take, but also its ability to reproduce that power as acoustic output (and not heat) referred to as sensitivity, and the area it needs to cover in the room. Sensitivity figures are rated in decibels, which read as a sensitivity in the format of “xx dB SPL, 1W, 1M” with the xx being the figure unique to the speaker, and an SPL meter reading decibels at 1 meter’s distance when the speaker is provided 1watt of power.
This in turn shows us how efficient a speaker is and how well it converts those watts coming in to sound going out. We have to judge how loud a speaker should be in a space for its intended purpose. Coupled to this is the consideration of how much power is going to have to be fed into the speakers to achieve this output level. Amplifier equipment increases in cost as its output wattage increases, and more efficient speakers also increase in cost, so correct speaker selection is often a compromise of both with a view to the budget available. We have only touched on the issues of sensitivity here – and there is much more to it – but suffice to say that just because the power rating is higher, does not mean that the output will be greater, or more musical…
