/Optimizing passive radiator acoustics using the QF3DFX processor
It is becoming very popular for manufactures to adapt passive radiators as a means of providing bass performance in small-enclosure stereo systems products. Integration of passive radiators requires careful tuning to effectively produce the much needed bass missing in these small systems. A sampling of the currently available products in this market clearly indicates that the tuning requirements are not being met.
Passive radiators respond to frequencies, presented as internal air pressure from the active speakers, on each side of a resonance frequency. Therefore, tuning for optimum performance is significantly more demanding and generally not well supported by the typical audio systems-on-a-chip integrated circuits on the market.
What makes passive radiators unique is that the tuning requirements are below the response range of the system’s active speakers. The active speakers produce less acoustic energy (audible output, air movement) as the frequencies become lower or their volume is lowered. A system with a passive radiator needs to be tuned such that the passive radiator is active at frequencies below the active speaker counterparts and when the volume, air pressure, is less than optimum (maximum).
Passive radiators assume the requirement of producing lower bass frequencies from the generally smaller diameter active speakers. The lower bass frequencies require more air movement to be equally loud therefore, passive radiators are typically larger and are also capable of greater motion; movement in and out.
In addition, the enclosure’s internal acoustic frequency response falls off at 6 dB/octave while the passive radiator performance falls off at 18 dB/octave leading to a requirement to maintain audible bass (internal air pressure) at lower volume levels (lower air pressure from the active speakers).
Additional care must be taken to avoid issues at the resonant frequency of the passive radiator; the displacement of the passive radiator is at a maximum (low volume level) when the active speaker is at a minimum (high volume level). Under these conditions, there can be an audible drop in bass output and unwanted audible harmonic distortion if the system is not properly tuned.
A modern system-on-a-chip audio integrated circuit should provide a means for,
Additional features that systems like this can benefit from,
Additional features that would enhance the end-user experience,