Paper 2: Phase adjustment on the Klark Teknik DN9848 Loudspeaker Processor
To meet the demands of a wide range of situations, the Klark Teknik DN9848 provides two all-pass
filters with complementary control parameters for fine-tuning the phase response on each output.
Although some crossover filter designs, e.g. Linkwitz-Riley types, are inherently phase-aligned at
crossover, others such as Butterworth or Bessel responses may require manual phase alignment.
Even Linkwitz-Riley filters may not produce accurate phase coherence when HPF and LPF are
combined to produce a band-pass output. In addition, the phase response of the drive units and
cabinets (especially horn-loaded types) may require compensation to achieve correct acoustic phase,
even if the electrical phase is correct. The DN9848 filters provide straightforward tuning control in all
cases.
The first filter of the DN9848 is presented as a “phase shifter” for which you can specify a particular
phase shift at a reference frequency, namely a HPF or LPF (typically the cross-over point) or one of
the 6 PEQs. The plots in Fig. 1 show the effect of these controls on the filter response when set to a
90 phase shift at references points equivalent to 20 Hz, 300 Hz, 1 kHz and 20 kHz. Referring to the
figure, the overall response always remains the same shape i.e. tending from +180 at low frequencies
to 0 at high frequencies, but is shifted along the frequency axis to achieve the required phase shift at
the specified reference point.

Audio Precision 90 deg phase shift @ 20, 300, 1K, 20K 01/19/01 15:52:45

Figure 1. Response of the Phase Shifter filter for a phase shift of 90 at reference points equivalent to 20 Hz, 300 Hz, 1 kHz and 20 kHz

The second filter, presented to the user as an “all-pass filter”, enables the user to set the Order and Q
of the phase shift, at a particular Frequency. The Order can be switched to Off (no filter), 1st order
(90 shift) or 2nd Order (180 shift).

Fig. 2 shows the response of the filter for a 1st order shift. In this mode, the Q control is disabled. As
can be seen, the filter behaves in an identical manner to the phase shifter i.e. the response tends from
+180 at low frequencies to 0 at high frequencies, shifted along the frequency axis according to the
chosen frequency. In effect, this is a phase shifter for which the frequency is entered directly, rather
than being referred to a HPF/LPF etc.

Audio Precision 1st order allpass @ 300, 1K, 10K 01/19/01 16:00:02

Figure 2: Response of the All Pass Filter for 1st Order phase shift at frequencies of 300Hz, 1kHz and 10kHz

Fig. 3 shows the response of the filter for a 2nd order shift, with the Q control set to 1, at frequencies
of 300Hz, 1kHz, and 10kHz, and also Q set to 6 (max) and 0.4 (min) at 1kHz. As can be seen, the
filter response now tends from 360 at low frequencies to 0 at high frequencies, and Q controls the
rate at which the phase changes (i.e. the slope) around the transition point. With low Q, the phase
changes gradually across the whole frequency range. With high Q, the phase changes rapidly in the
transition area, and is unchanging at 360°/0° over the remainder of the frequency spectrum. . Hence,
the 2nd order all-pass provides the user the additional control of shaping the phase shift ‘window’.

Audio Precision 2nd order allpass Q=1 @ 300, 1K, 10K + Q=6 Q=0.4 01/19/01 16:09:11 @ 1K

Figure 3: Response of the All Pass Filter for 2nd Order phase shift with Q=1 at frequencies of 300Hz, 1kHz and
10kHz and also with Q=6 at (max) and Q=0.4 (min) at 1kHz

Note: Both filters are all-pass with a flat amplitude response between 20Hz and 20kHz; only the phase response
changes with frequency.