12
12. Acoustic set-up procedure (continued)
Phase Compensation
In any speaker system there will always be inherent phases shifts between
of the main speakers and subwoofer at the crossover point. These are
caused by the actions of the crossovers and the response characteristics
of the speaker systems themselves.
Because of this it is normal to find that the responses don’t add together
accurately as might be expected and some cancellation can instead take
place at the crossover region.
The effect can be similar to when the crossover of the subwoofer is set too
low and a ‘hole’ appears in the overall response as below, although less
pronounced.
The Mezzo 9 features variable phase that allows you to adjust the phase
until the subwoofer and main speaker outputs are in phase at the
crossover region and the two responses sum evenly.
Performing the acoustic set-up
A. Notch filter
Make sure all filters in the sub are turned off (low pass, filter 1, filter 2,
phase) the first time you perform this setup routine (if desired, perform
a factory reset as previously described to reset all parameters).
1.
Disable all speakers in your system except the subwoofer by
disconnecting one of or - leads at the back of each speaker:
2.
Load the supplied set-up CD:
3.
Sit in the listening position and set the SPL meter to 2dB range:
4.
Play track 1 (wide band noise), adjust the amplifier volume until the
SPL REF LED is lit green:
5.
Play the rest of the tracks one by one, noting the readings for each
track. Plot your frequency response or a copy of the supplied graph.
6.
If the response looks like it needs equalisation by a notch/boost filter
you can calculate the best notch filter settings, using the set-up
application supplied on the Mezzo 9 set-up CD or by visually
inspecting the graph. To use the CD simply load it into your computer
and follow the on-screen instructions:
To set up the notch filter by hand:
a)
Find the track with the highest reading and set the notch filter
frequency to this value.
b)
Set the depth to the value that best cancels the peak.
c)
Set the width to the narrowest setting (1).
d) Repeat step 5.
e)
If peaks are measured on either side of the track located in a), set
the width to medium (2) and repeat d).
7.
If there is another peak in the response after applying notch filter 1,
this peak can be addressed with notch filter 2. Follow the above steps
1 through 7 to set this filter. Additionally, if there is a dip in the
response of the sub, try setting the second filter to a boost filter at the
frequency of the dip to give a flatter overall response.
B. Low Pass
1.
If you are using the LFE input, there is no need to set the low pass
filter. The low pass is usually implemented in the AV receiver. However
if your AV receiver features an adjustable crossover frequency you
may wish to adjust that (consult your AV Receivers manual) and use
the Mezzo 9’s SPL meter and test disc to confirm the response in the
same way as you would if you were adjusting the Mezzo 9’s own
crossover.
2.
Re-connect your main speakers and set the crossover to a sensible
starting position.
As a guide for setting the low pass filter here are some typical settings
for different types of speakers to start with:
Tower: 35Hz – 50Hz
Bookshelf: 50Hz – 65Hz
Satellite/mini: 80Hz - 120Hz
3.
Now re-measure the frequency response of your system at the
listening position. In particular pay attention to the response where the
main and subwoofer responses meet (usually around 80-120Hz).
Adjust the crossover frequency to achieve the flattest response.
The sets a
reference
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Ideal match
but phase issue causes dip
