Derived from the granted resonator system of Helmholtz type and the RJ decompression system, the peripheral laminar decompression system constitutes an exceptional load of the driver in the very low frequencies improving speaker's braking, so transient rendering.
This system is similar in operation to the bass-reflex by the presence of two resonances framing an anti-resonance adjusted to the resonant frequency of the speaker in open air.
However the enormous progress made on the bass-reflex system is the coloring abscence (barrel's sonority) from 80 Hz to 300 Hz, by :
• Total acoustic filling of the enclosure increasing its apparant volume and avoiding all standing wave (coloring).
• The rear wave quickly exit the enclosure in phase with the front wave rolled through the cavity located immediately behind the speaker, this cavity acting as a low pass filter with very sharp cut (80 Hz to 30 dB per octave).
• The distortion obtained is extremely low compared to that obtained with a closed box.
• The cavity and its second baffle allows the rigorous phase of the tweeter with the boomer by spacial shifting from 3 to 5 cm (depending cutoff frequency).
1- Vent 2- Speaker
• Input impedance : 8 Ω
• Rated power : 60 W
• Maximum power : 80 W
• Sensitivity (for 1 W at 1 m) : 92 dB
• Amplitude frequency response curve : 30 to 35 000 Hz
In this type of loudspeaker the drivers are all connected in the same polarity (the negative poles at the ground).
Music, like speech, is essentially a result of attacks, unbalanced signals, pulses, the drivers all working in the same direction operate in a consistent way when reproducing these signals.
The filter introducing a delay of the woofer relative to the midrange, and this one compared to the tweeter, it becomes necessary to shift the plans of the drivers to catch up acoustically this electrical phase shift. The acoustic shift corresponding varies with crossover frequency of the speakers and complexity of the filter. For example, if we chooses 500 Hz as the crossover frequency between boomer and midrange, the theoretical distance that must separating the speakers with a 6 dB per octave filter (one self and one capacitor) should be 17 cm ! With a 12 dB filter... 34 cm (it's far from the 3 to 5 cm provided in most loudspeakers...).
Moreover, this spatial shift must also consider the position of the acoustic center of each driver from its mounting plane.
The PHASE PLUS also optimizes the amplitude-frequency response of the loudspeaker, the drivers working then in phase around each cutoff frequency (pic. 2).
Conventional systems with little or no spatial shift, imposed to cross the polarities of successive drivers in order to regularize the amplitude-frequency response curve around their cutoff frequency. But this had the effect, firstly poor phasing when moving away from this cutoff frequency, the other unable to correctly reproduce transients (pic. 1).
Art & Acoustique Appliquée
3A patent filed November 25, 1976 n° 76 35 488
