APP Acoustic Performance Plug

Report January 1999, ©Mats Andersen, Qln Acoustics AB


This summary is not intended to convince you about the excellence of Qln G3. You are already aware of its virtues and know of the sound quality it is capable of. Instead we would like to give a technical background to how it actually works.

The design philosophy
Our goal was to create a loudspeaker which combines outstanding sound quality with Scandinavian design and excellent finish, but with an appearance possible to integrate into a modern and aesthetically decorated home. Qln G3 is only 11 centimetres wide and the transducer units are strikingly small. Normally, this means limited bass reproduction and a weakened sound. This is not the case with Qln G3. It retains transparency and dynamics also at high sound pressure levels.
The inearity in the low frequency range comes from three co-operating solutions.
First of all the speaker unit itself provides excellent performance in terms ofcontrolled behaviour throughout its frequency range. It has a rigid chassis and a high-precision suspension.

The cabinet
Secondly the cabinet is a quarter-wave pipe. This means that it can be easily tuned to match the resonance frequency of the speaker unit and even extend the range a bit.
The tall and lean proportions combined with the placement of the units also provide for full and controlled damping of harmonics to the pipe resonance.


The secret
This is the little secret of this loudspeaker; our invention APP, the Acoustic Performance Plug. By attaching a defined amount of air to the cone diaphragm we can increase the moving mass at low frequencies. The diaphragm is better coupled to the surrounding air, which increases movement control and the efficiency at low frequencies. The audible result is an agile loudspeaker with a well-defined transient response, hence providing a clean mid-range and a more natural sound reproduction.

The solution
In practice the APP is an open cavity placed behind the low-frequency units. It contains mechanical impedance that can be compared to an RC link. Below the resonance frequency, where the diaphragm would normally operate under poor loading conditions, it adds an acoustic resistance that limits the travel of the cone.
By tuning the dimensions and the mechanical impedance it is matched to the characteristics of the speaker unit. The result is a reduction of intermodulation and doppler distortion products, and the bass reproduction remains clean, tight and controlled.
APP is only active at low frequencies, around the resonance point. The added acoustical mass does not load the diaphragm at higher frequencies, nor does it limit rapid movements of the cone. With this acoustical solution we can combine a deep, and well-controlled bass with high definition and transient response.

Mölndal, January 1999
Mats Andersen