Telex DN9848 Loudspeaker Processor, DOC02-DN9848 specifications Phase-adjustment with the DN9848

Application Notes

10.2. Phase-adjustment with the DN9848

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 cross-over filter designs, e.g. Linkwitz-Riley types, are inherently phase-aligned at cross-over, 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 the graph below show the effect of these controls on the filter response when set to a 90 phase shift at references points equivalent to 20Hz, 300Hz, 1kHz and 20kHz. 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
	+150									+150
	+100									+100
	+50									+50
d	+0									+0	d
e											e
g											g
	-50									-50
	-100									-100
	-150									-150
	20	50	100	200	500	1k	2k	5k	10k	20k
						Hz

Color	Line Style	Thick	Data	Axis
Green	Solid	1	Anlr.Phas e	Left
Yellow	Solid	1	Anlr.Phas e	Right
Yellow	Solid	1	Anlr.Phas e	Left

phas e.at1

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

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).

The graph over the page 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 or PEQ section.

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