Silent Mice - White paper
By Logitech, August 2016
Executive summary
Several studies have shown that noise can affect human health and productivity in a negative
manner (Banbury & Berry, 1998; Maxwell 2001). To reduce the disturbance induced by
computer mice, Logitech has launched new models integrating technology that lowers the noise
level.
New click switches, new gliding feet and new internal construction are all part of the solution to
make the new mice quieter. As a result, independent tests commissioned by Logitech have
shown that the noise emitted by the clicks has decreased by more than 90%. As evidence of
this achievement, Logitech is the first mouse company in the world to receive the Quiet Mark
certification, an international mark of approval award program from the UK Noise Abatement
Society recognizing technology that has been designed to reduce noise.
1
Introduction
According to Julian Treasure, renowned sound expert, noise affects us physiologically,
psychologically, cognitively and behaviorally (Treasure, J. 2009). Most of the sound around us is
unintentional and unpleasant. Although, unfortunately, many people are unaware of the possible
negative effects of noise, being unable to get away from it can be extremely damaging for health
and productivity .
According to a study published by Banbury and Berry (1998), productivity is reduced by 66% in
open-plan offices, a massive decrease that is mainly due to the negative effects of sound.
With a goal of improving health and productivity, Logitech has decided to tackle the irksome
sounds of one of the most used computer companions by introducing “Silent Mice”.
Problem
Besides affecting the health and productivity of its user (Maxwell, 2001), the sound of a mouse
also impacts people in the vicinity. With the prevalence of open-space office layouts and
conference calls, the clicking sound can be highly disturbing to a large number of people. In a
home environment, using a loud clicking mouse when partners, children or roommates are
going to bed can actually prevent them from falling asleep.
1
Noise Abatement Society official website: www.noiseabatementsociety.com
1
Solution
In computer mice, the sound comes from three distinct sets of components: 1) the feet, when
gliding the mouse on a mousepad or table, 2) the wheel module, when scrolling up and down,
and especially 3) the switches, when clicking on the left, right or middle button.
Figure 1: Bottom and side views of Logitech M330
Through technological advancements, Logitech has considerably reduced the sound emitted by
these components.
Technological advancements
Switches
The switches used in Logitech Silent Mice are made of a rubber actuator that dampens both the
vibration and the sound. A red plastic cap covers the rubber actuator to improve the switch’s
tactile feedback and lengthen its lifespan. The switches used by Logitech have a lifespan of
5 million cycles, on par or often better than most of the non-silent mice found on the market
today.
2
Figure 2: Assembled silent switches - Figure 3: Dismantled silent switches
The new switches significantly reduce the clicking sound while keeping a tactile feedback similar
to that found in non-silent models.
Scrolling
Logitech used a mechanical encoder for its M330 Silent Plus Mouse model. As compared to an
optical module, the mechanical encoder has the advantage of considerably reducing the sound
level while maintaining a satisfying feeling of ratchets when scrolling the wheel up and down.
Feet
Logitech normally uses gliding feet made of Unsaturated Polyester (UPE) material for its lower-
and middle-range mice, and Polytetrafluoroethylene (PTFE) for its higher-end range. UPE feet
provide good performance at a reasonable price, while PTFE feet provide a better gliding
performance.
For its Silent Mice, Logitech opted for Plastic Lumber (PL) material, which proves quieter and
more durable than other materials such as UPE and PTFE.
Plastic part design
Most mice have a large empty cavity under the keyplate. While it is often necessary to give the
mouse a certain volume to achieve the desired comfort level, this empty chamber also amplifies
the noise created by the clicking switches, scrolling wheel and gliding feet. To further reduce the
noise level, Logitech added plastic ribs within its Silent Mice. Like a noise barrier on the side of
the highway, these inner walls dampen the sound and reduce the echo created within the
mouse.
3
Figure 4: Red parts show noise-dampening ribs inside M330 Silent Plus top case
Methodology and results
Acoustic measurements of Logitech Silent and Non-Silent models were conducted by an
independent lab, Foxconn CMC, located in Suzhou, China. The sound equipment was placed
1 meter from the center of the mouse and measurements were taken at four different angles
around the mouse.
4
Figure 5: Testing setup at Foxconn CMC anechoic chamber with < 6 dBA background noise
Sound pressure level (SPL) or acoustic pressure level is a logarithmic measure of the effective
pressure of a sound relative to a reference value. It is measured in dB. Below is the Noise
Abatement Society’s description of what a difference in dBA represents for the average human
ear:
● 1 dB difference – imperceptible
● 2 dB difference – you can just about convince yourself there’s a difference
● 3 dB difference – yes, I can definitely tell there’s a slight difference
● 4 dB difference – the difference is clearly noticeable
● 5 dB difference – quite a big difference there
● 6 dB difference – wow it’s getting towards twice as loud!
● 7 dB difference – yes, I think almost twice as loud
● 8 dB difference – around twice as loud
● 9 dB difference – more than twice as loud!
● 10 dB difference – massive difference between these levels!
5
A-weighted sound measurements (dBA) are filtered to reduce the effect of very low and very
high frequencies, better representing human hearing. With A-weighting, sound monitoring
equipment approximates the human ear's sensitivity to the different frequencies of sound.
The results for the left click as measured by the independent lab show a maximum Sound
Pressure Level (SPL) of 25 dBA for Logitech M330 Silent Plus and 26.4 dBA for Logitech M220
Silent, while the minimum measurement for the Logitech M170 was 36.1 dBA, which represents
a difference of more than 11 dBA in the case of the M330.
The following formula puts in relation the measured SPL level to a source radiating a certain
acoustic power level (Lw), assuming a directivity factor Q=2 (half spherical, for a device laid on a
table):
where Lwis the Sound Power Level of the source, Lpis the measured Sound Pressure Level and
r = 1 m, the distance to the sound source.
The noise reduction is then computed with the following relationship:
Noise reduction = [1 - 10^(Δ
/10)]*100
SWL
where Δ
is the difference between the Logitech M330 Silent Mouse’s maximum SWL and the
SWL
Logitech M170’s minimum SWL. The measured noise reduction was thus of 93.3%.
6
Figure 6 - Results of the acoustic test for the left click
The sound pressure level from the feet was measured by gliding one model of mouse with
different foot material 200 mm horizontally and vertically on a melamine board. The results
showed an improvement of 1.7 to 2.9 dBA when using Plastic Lumber, the material selected for
the silent mice.
7
Figure 7 - Results of the acoustic test for different foot material
Conclusion
By studying the sources and nature of the noise made by a computer mouse, Logitech was able
to single out the components that needed changing to tune down their level of decibels. With
new gliding feet material, new types of clicking switches, and a new plastic case construction,
Logitech is able to produce much quieter mice.
As an evidence of this achievement, Logitech is the first mouse company in the world to receive
the Quiet Mark certification. This international mark of approval award program from the UK
Noise Abatement Society recognizes technology designed to reduce noise.
Logitech is resolved to reduce unpleasant sounds around us and be part of the solution to
improve health and productivity at home and the office.
Reference
Banbury, S. and Berry, D.C. (1998), The disruption of speech and office-related tasks by speed
and office noise. British Journal of Psychology
Maxwell, L. E. (2001), Noise in the Office Workplace, Cornell University Facility Planning and
Management Notes
Treasure, J. (2009), The 4 ways sound affects us, TEDGlobal 2009
, Volume 1, Number 11
, 89, 499-517
8
Loading...