Dec 16, 2012

Hybrid Networks

Before I proceed further, it is important to note that this is a hybrid design. By that, I mean the crossover is active (from the Synergy) while passive components are used to contour the frequency response of the drivers.

Some may argue that it makes more sense to go active all the way. Surely 1/3 octave graphic EQs have finer control than passive networks. This is a valid argument but for the sake of sonic purity, I prefer to keep the electronics minimal. Graphic EQs are extremely intrusive. While they are indispensable for prosound, they have no place in HiFi.

Acoustic Crossover

Fig 4 shows the Gated Response of the RS108s and the PDS382/H07E combo. Though the Synergy 18dB/oct crossover was set for 2,250Hz, the final acoustic slope of the RS180s is about 20dB/oct. The PDS382, on the other hand, is about 22dB/oct.

Fig 4 - RS180s LP with H07E HP (Gated)
click picture to enlarge
Fig 5 - H07E In Phase (Gated)
click picture to enlarge
Fig 6 - H07E Reverse Phase (Gated)
click picture to enlarge
Fig 7 - H07E In and Reverse Phase
click picture to enlarge

In-Phase Summing

Fig 5 shows the resultant response (Blue Plot) when the two drivers are in-phase.

It is interesting to note that there's cancellation before the crossover and addition after.

Reverse Phase Summing

Fig 6 shows the resultant response (Green Plot) when the compression driver is in reverse phase.

Now, the opposite happens. There's addition before the crossover and cancellation after.

Time Alignment

Fig 7 shows the superimposition of the In and Reverse Phase of the compression driver.

One can infer from these plots that the addition and cancellation around the crossover region can be resolved by time-aligning the two drivers. That is indeed a tempting idea which I shall leave for another day.

next > In-Room Frequency Response

60 Downes Street | Calais | ME 04619 | USA