Nokia Portable Wireless Speaker: sound science
How bending the law of physics allows this compact speaker to seem huge.
When the Nokia Portable Wireless Speaker was announced earlier this year, it left a lasting impression. Employing an ‘actuator’ to boost bass, this tiny puck-like noise maker is louder than it looks. But how does this new technology actually work?
We spoke to Matthew Bramble, a leading audio specialist, to explain all.
In its simplest terms what is sound actuation?
As well as a conventional speaker driver on top for high frequencies the Nokia Portable Wireless Speaker incorporates a ‘sound actuator’ on the bottom for low frequencies.
The actuator is like a speaker driver unit but without a cone. It drives a pad on the bottom that rests on the mounting surface. It’s the mounting surface itself that then becomes the cone of the speaker.
Why is this good?
There is a law of physics that says that the lowest frequency a speaker can reproduce is directly related to the size (radiating area) of the speaker cone.
Using an actuator negates the need to build in a large speaker, reducing the size of the unit.
But, doesn’t every action have an equal and opposite reaction? Why doesn’t the large and heavy table just stay still and the unit moves up and down?
Good question. Most surfaces that the unit is resting on will actually bend very slightly under the force of the actuator. With such a large radiating area the flexing of the surface only needs to be very small for quite large sound pressure waves to be created.
Plus, by careful control of resonance, it’s possible to ‘bend the laws of physics’ and optimise the energy transfer from the actuator to the surface for a certain range of frequencies. In this case the engineers have optimised for the bass frequencies they want to reproduce.
So are there any surfaces that produce sound better than others?
Yes, ideally the surface needs to be able to bend very slightly and have low internal damping. i.e. something that is fairly stiff, not too soft and that springs back when very slightly flexed.
This suits the usual use case of table tops. A highly damped soft surface might bend but would lose the energy the actuator puts in as a tiny amount of heat rather than sound.
What are the possibilities of this technology in the future – what’s stopping it from being more prevalent?
The technology particularly suits small portable products but does require both an actuator and a normal drive unit, plus a fair amount of acoustic know-how to make it work well.
What surface do you think the Nokia Portable Wireless Speaker will sound great on?
Matthew Bramble is the CEO of Musaic and owner of Subtectum. Previoulsy, he was the Technical Director at Audio Partnership (Cambridge Audio)