What is haptic feedback, and why does it feel so different between devices?
Haptic feedback is physical sensation produced by a device to communicate information — and the enormous difference in quality between devices comes down to the type of motor used, which is a component decision rather than a software one.
The motor types, in order of capability:
ERM — eccentric rotating mass. A small motor spinning an off-centre weight. Cheap, and the characteristic buzz of older phones and inexpensive devices.
Its limitations are physical: it must spin up and spin down, so it cannot start or stop quickly. That latency means it cannot produce a sharp, precise tap — only a vague buzz that begins after the event it is meant to accompany.
LRA — linear resonant actuator. A mass on a spring driven back and forth along one axis. Much faster to start and stop, so it can produce crisp, short pulses and vary intensity meaningfully.
Because it is resonant, it works best at a specific frequency, which constrains the range of sensations available from a small unit.
Large, well-engineered LRAs — the kind found in premium phones and some game controllers — can produce a genuinely wide range of sensations, including the convincing illusion of a physical click on a surface that does not move.
Piezoelectric actuators, used in some specialised applications, which are very fast and used for fine textures.
Why the difference is so noticeable. The perceived quality depends on timing precision far more than on strength. A sharp, well-timed tap of modest intensity feels deliberate and physical; a delayed buzz feels like a malfunction. This is why haptics cannot be improved much by software on hardware that cannot respond quickly.
Where it is used well: confirming a control has registered when there is no physical travel; conveying different notification types without sound; simulating detents in a scroll or dial; and in game controllers, conveying texture and impact.
Accessibility value is substantial and under-recognised — haptics convey information non-visually and silently.
Over-use is the common design failure, and constant undifferentiated buzzing trains people to ignore it.