Phase Difference: 0°

Phase Difference: 90°

 

85 Hz

85 Hz

Phase Difference: 180°

Phase Difference: 270°

85 Hz

85 Hz

Figure 4. The effect of phase difference between the subwoofer and the main loudspeakers

Subwoofer placement

Bass Roll-Off

 

setting

 

 

Near to a wall

-2 dB

 

 

In a corner

-6 dB

 

 

Flush mounted

-2 dB

 

 

Table 1. Suggested Bass Roll-Off settings

Figure 5. Flush mounting the subwoofer. Note the clearance needed on the reflex port side.

a drop in the frequency response of the whole system at the crossover frequency. The graphs above (Fig. 4) show the effect of phase difference to the frequency response The phase difference between the main loudspeakers and subwoofer at the listening position is dependent upon the position of the subwoofer, so the phase adjustment should be done only after the preferred position is found. Acoustic measuring equipment is required for accurate system alignment. If this equipment is not available, the following

coarse phase matching can be applied

Coarse phase adjustment

method

Connect an audio frequency signal generator to the “FRONT CENTER” input of the 7050B and set it to feed a 85 Hz signal to the system. Alternatively, you can use a 85 Hz signal fom a suitable audio test recording. Make sure you connect (even temporarily) a main loudspeaker to the "FRONT CENTER" output, so that the test signal is properly reproduced by both subwoofer and main loudspeaker.

Toggle the -180° phase switch (DIP 5 from left) "ON" and "OFF", and set it

to the position which gives the lowest sound level at the listening position

Next toggle the -90° phase switch (DIP 4) "ON" and "OFF", and again set it to the position which gives the lowest sound level

Finally, set the -180° phase switch (DIP 5) to the opposite setting and deactivate the test signal

Phase correction method with

test equipment

The following procedure matches the phase between the subwoofer and the main loudspeakers using a frequency analyser and a pink noise generator. Connect a high grade measuring microphone to the analyser and feed pink noise into the "CENTER IN" input of the subwoofer. Position the microphone at the listening position and adjust the input sensitivity of the subwoofer until frequencies below and above 85 Hz are reproduced at equal level. Then adjust the phase control switches for the maximum dip of at least -6 dB at the crossover frequency (85 Hz).

Change the -180° switch to the opposite setting. The phase should now be set correctly and the frequency analyser should show a smooth response around 85 Hz.

Using the LFE Bandwidth and

LFE +10 dB functions

The “LFE BANDWIDTH” switch allows you to select the upper cutoff frequency of the LFE channel between 85 and 120 Hz. Limiting the LFE bandwidth to 85 Hz can be used to simulate the effect of some consumer decoders that do not replay information above 80 Hz on the LFE channel when the bass management is used. Checking the multichannel mix with this setting on lets you know how it translates in systems with this limitation

The 120 Hz LFE bandwidth setting complies with the replay systems of movie theaters and cinemas. 35 mm movie soundtracks use the LFE channel to reproduce a bandwidth of 20 - 120 Hz through dedicated subwoofers. In this case the LFE and main channel bandwidths overlap between 85 and 120 Hz, which may create unwanted acoustical summing if the same signal is present in both channels. To avoid this, the LFE content should be kept completely different (de-cor- related) from the low frequency content of