Loudspeaker enclosures for low frequency reproduction face the developer with a goal conflict. Either he achieves a small volume enclosure or he achieves a low cutoff frequency. One approach to overcome this shortcoming is the well-known vented enclosure. However, the commonly utilized resonator ports cause other issues, such as flowing noise and delay differences between driver and port. Due to this delay, vented designs suffer from worse phase response compared with sealed enclosures. To achieve deeper bass reproduction sealed enclosures must comprise chassis with high dynamic mass, high compliance, large linear displacement and a strong and heavy magnet. Typical bass chassis for this application are comparably expensive.
An alternative is the passively augmented sealed enclosure. In comparison to a non-augmented design, the phase response of this design still suffers some actually unwanted changes.
Siegfried Linkwitz encountered the aforementioned issue with his well-known zero point/pole shifting method. Applied to a closed enclosure design the so-called Linkwitz transformer shifts the cutoff frequency to a considerably lower frequency. In addition, the Linkwitz transformer maintains the appreciated flat phase response of closed designs. The used chassis, however, massively consumes electric power and must be capable to perform very high displacements. In addition, the original Linkwitz approach yields comparably poor sound pressure levels as well.
Affordable drivers – in particular for consumer products – do not meet the aforementioned requirements. The common Linkwitz transformer most likely will cause mechanical damages due to collisions of the driver coil with the rear pole plate. There strongly remains a demand for an active augmentation suitable for bass drivers commercially available for consumer applications.
A new solution, recently developed by a German university, avoids the shortcomings and maintains the benefits of the commonly known Linkwitz approach. It considers the properties of the audio input signal and shifts the pair of poles in frequency. Small sealed enclosures achieve deep bass reproduction with smooth roll off and flat phase response without inappropriate loudspeaker diaphragm displacements and excessive power needs.
The technology is applicable in the following devices: car audio, home audio, build in flat screen speakers, miniaturized Bluetooth speakers, smart speakers, smartphones and tablets.
The university offers a license agreement as well as a technical cooperation agreement to jointly work on reaching market readiness to speaker manufacturers.