SELTECH SOD20722X4CVT Instruction Manual

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Recommended design guideline
for micro speakers
SELTECH –CONFIDENTIAL

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2
Common Application Design Guidelines
Back volume
… why a closed back volume?
… how to connect to the speaker?
… mechanical robustness
… acoustical influence
Sound Port
… opening size vs. Bandwidth
… damping/acoustic load
… turbulence/noise

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Back volume
… to have a well defined acoustical environment behind the speaker
Well defined acoustical performance
… to be able to adjust the resonance frequency of the system
Resonance frequency range is the most efficient range of the speaker
… to avoid acoustical short circuit
Speaker for closed box design needed
… Why a closed back volume?

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Back volume
Using PCB as box-cover
Directly contacting to PCB
Create closed box
Contacting with flex-print
Create closed box
Contacting with contact pin
… How to connect to the speaker?

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Back volume
Create closed box
Contacting with contact spring
Reverse application
Directly contacting to PCB
… How to connect to the speaker?
back volume
Sound port at rear side of the speaker

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Back volume
Min. wall thickness to avoid wall resonating (depends on material)
Avoid « wall-to-wall-design » (e.g. antenna module)
Vibrations can cause rattling noise
Use « sandwich » for applying the speaker (foam-gasket, speaker, hard
support at rear side)
No heat-radiating components inside the back volume
Etc.
… Mechanical robustness

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Back volume
It is possible to put the RA completely down on a PCB or module housing
Venting to the back is provided by 4 venting holes and slits
All 4 holes should lead to a common, closed back volume
Back venting of RA11x15

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Back volume
Speaker surounded on three sides by walls will
influence resonance frequency and sensitivity.
Additional acoustic load will reduce performance
compared to a free scenario
Acoustic load at the rear side of speaker

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Back volume
Channels connecting parts of the
back volume can cause peaks in
frequency response
Shape of volume: high aspect ratio
volume spaces do not constitute
effective volume
Acoustical influence

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Back volume
Leaks can cause damage to the speaker by exceeding maximum membrane excursion
Acoustical influence

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Sound Port
Opening size vs. Bandwidth

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Sound Port
Acoustic load by side venting sound port
Tube dimensions have a dramatic influence
on the acoustic performance.
Tube length: avoid sharp edges or corners that
could result in audible turbulence.
Distance from top of speaker to housing
should be at least 0,5mm to avoid audible
turbulence.
Dimensions:
V1 = V2
V1 + V2 = 0,8ccm
Tube 1: (5x1) x 5 mm
Tube 2: (5x0.5) x 5 mm

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Sound Port
Turbulence/noise
Possible reasons:
Sound port openings too small
Front volume too small
Sharp edges in sound port
Damping mesh on sound port too tight

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THANKS !