Standard deviation. Every CE certified earplug goes through rigorous tests to comply with high standards. The listening part of the test involves multiple people recording (in dB) when they can hear a certain frequency as shown in the top row of the table.
All these results are collated and an average is produced (row two). The difference between the highest and lowest value for each frequency band is called Standard Deviation (row three).
The lower this number is, the closer each test subjects results were. For example; at 1000 Hz the difference between the highest and lowest test result was 3.0 dB.
A low difference like 3.0 means subjects were achieving a similar universal and accurate fit meaning a more reliable and safer experience.
Other leading earplug manufacturers have a higher standard deviation shown here.
3M™ E-A-R™ UltraFit™ Earplugs
SNR = 32dB. H = 33dB. M = 28dB. L = 25dB.
|Mean Attenuation dB||8,8||10,3||13,2||16,6||20,6||25,4||25,2||19,2|
|Standard Deviation dB||4,4||3,3||3,0||2,4||2,8||3,0||5,0||4,1|
|Assumed Protection in dB (APV)||4,4||7,0||10,2||14,2||17,8||22,4||20,2||15,1|
|EN 352-2: 2002 compliant|
Nominal diameter: 9-12 mm
H=19 M=17 L=12
The attenuation difference between the SNR High/Medium/Low ratings is also just 3 dB whereas the market-leading standard foam earplugs is as much as 10 dB.
By attenuating frequencies more evenly, the user is safely protected from harmful levels of bass, mid and treble whilst enjoying an accurate sound experience.
Just at a much lower volume.