I took nearfield measurements, which is standard
practice to properly measure subwoofers, to help
negate room reflections. I was looking for the
lowest f3 with the flattest frequency response. I
first wanted to get a starting point (reference) so I
measured the response of the driver-amp system
with the crossover setting at maximum and no
equalization. Looking at the graph below the f3 was
around 40Hz.
Nearfield Measurement
A little known but useful feature of the Dayton HP
(high power) amplifiers is the 6 dB notch filter,
which was added for the Titanic kits to help flatten
their frequency response.
Note: The default factory setting of the notch filter
is “disabled”. To enable the notch filter, simply
switch the position of this jumper (connect left
and middle pins.)
Here are the measurements of the amplifier's
output with the notch filter enabled (Blue) and
disabled (Red).
Amp Measurement
Next I measured the system output after adjusting
the amplifier settings to create the lowest f3
and flattest response curve, with the notch
filter disabled (Red). I achieved a relatively flat
response with an f3 of 30 Hz. I noticed a peak in
the 50-60 Hz range and because of this peak I
thought the complete system might also benefit
by enabling the notch filter. I measured again with
the notch filter enabled and after some tweaking
was able to achieve a relatively flat response with
an f3 of 25 Hz (Blue).
Nearfield Measurement
Red Response - Output of the amp-driver
combination with notch filter disabled, crossover
set at 100 Hz, and with parametric EQ settings of:
Frequency = 25 Hz
Bandwidth = 0.20
Level = +6 dB
Blue Response - Output of the amp-driver
combination with notch filter enabled, crossover
set at 85 Hz, and with parametric EQ settings of:
Frequency = 25 Hz
Bandwidth = 0.27
Level = +6 dB
Note: To compare measurements of notch fi lter
enabling vs. disabling, I found it easier to remove
the rear enclosure from the amp and mount it
separately in the cabinet. This allows easy access
to the jumper while maintaining the integrity of the
cabinet for measurements.
The choice is yours-to notch, or not to notch.
With plenty of power available, I feel the tradeoff
of a little efficiency for a lower f3 is worth it, so my
choice is with the notch filter activated.
