Comparative Hand Dryer Noise Levels Provided by Dr J.Drever
Dr Drever’s recent study into hand dryer sound and in particular how this sound is amplified in situ caused a bit of stir in the mainstream media. His soundscapes study was taken out of context and turned into a totally sensational and untrue piece of journalism about how hand dryers damage your hearing. This is not what Dr Drever’s paper was alluding to and anyone who cares to talk to him on this subject will find out that his issue is related to noise irritation not hearing damage.
Hand Dryers categorically do not cause hearing damage, not unless you strap yourself to one for many hours continuously anyway! Certain models do however cause certain individuals to become unsettled or upset and therefore it is a subject that requires attention.
We were very interested at Intelligent Hand Dryers UK to see what we could learn from Dr Drever as we agreed that some hand dryers are too loud for certain users and they need to be made more inclusive. We also felt that the information available on hand dryer noise levels is very unclear, some manufacturers are using sound measurements that relate to sound power and some that relate to sound pressure but still stating these in decibel levels. Some manufacturers are just blatantly making up their decibel levels.
Dr Drever conducted the testing at the Building Research Establishments (BRE), in an anechoic chamber using his own equipment. An anechoic chamber is essentially a sound proof room. Click here to understand how anechoic chambers work.
In acoustic speak the readings he took were 10 second Laeq at 1 meter, measured in a free field over a reflecting plane. We provided only the samples. For you and I an anechoic chamber essentially removes all echo so the sound measured is purely that generated by the hand dryer and does not include any amplification caused by sound bouncing off surfaces.
These tests are hopefully going to form the first part of a far more comprehensive study into hand dryer sound and how the sound is affected by the environment the product is positioned in and how it affects a spectrum of users. However at this stage the data provided is meant to only provide a more reliable comparison between the sound levels of various models of hand dryer. The tests were carried out based on a 10 second average recording and hands were placed in or under the dryer to replicate the ‘real sound’ a hand dryer makes.
Dr Drever’s Results
• New Xlerator 500 – 87 dB/88 dB (A)
• eXtremeAir CPC with adjustable motor on Max power 86 dB/86 dB (A) on min power 73 dB/ 73 dB (A)
• Air Fury/TurboForce 84 dB/84dB (A)
• New Dyson Airblade AB14 dB – 82 db/80 dB (A)
• Stealthforce with adjustable motor on Max power – 82 db/80 dB (A) on min power 75 db/ 72 dB (A)
• Airforce 79 dB/79 dB (A)
• Jetflow – 81 dB/79 dB (A)
• Mitsubishi Jet Towel – 78 dB/75 dB (A)
• G-Force eco 550– 74db/ 74 dB (A)
• Dryflow Classic Plus – 73db/ 72 dB (A)
• Dryflow Elite – 70 dB/ 67 dB (A)
Source: Dr J.Drever MIOA (firstname.lastname@example.org) 28th Feb 2014
What is the difference between dB and db (A) reading for Hand Dryer sound?
dB sound pressure level is un-weighted, whereas dBA levels are ‘A’ weighted according to the weighted curves (see figure 1 above) to approximate the way the human ear hears. If for example we take a 100 dB level at 100 Hz it will be perceived to have a loudness equal to only 80 dB at 1000 Hz.
We will shortly be updating our website to show Dr Drever’s reading alongside manufacturers and also a methodology for predicting how that sound may be amplified in different room sizes.
We will be publishing videos of the tests and a foreword from Dr Drever on our YouTube channel so please subscribe if you are interested in following the full study.
How significant is a dB difference in hand dryer noise levels?
The table below allows you to assess the relative difference between the hand dryers Dr Drever measured.
|Sound Level Change||Acoustic Energy Loss||Relative Loudness|
|-3 dB||50%||Perceptible Change|
|-10 dB||90%||Half as Loud|
|-20 dB||99%||1/4 as Loud|
|-30 dB||99.9%||1/8 as Loud|
|-40 dB||99.99%||1/16 as Loud|
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