In the
Monitor
4 project this woofer was used in a sealed box with a large volume to
have a Qtc near to 0.6 in order to obtain the best transient response.
Here I am making an attempt to improve the performance even more by
using an H-frame then a dipole configuration.
The H-frame design has
advantages over the classic flat dipole because it is more compact under the
same conditions and high frequency peaks are generated outside the frequency
band used but in any case a high slope pass low filter low should be
used.
Here there is an article of
Martin J. King about a comparison of the Bass Performance of Open Baffle, U
Frame, and H Frame Speakers.
To compensate the normal loss of efficiency of the dipole it is
necessary to use a filter, in this case an active filter is placed before a
dedicated amplifier.
This active filter increases about 12-15dB at 30Hz
therefore it is necessary to use a high power amplifiers and only woofers
with large excursions and high power are able to support this conditions.
This project born to be combined with the new system with the
Purifi mid-woofer and the Mundorf AMT but it can
be used in any system with mid-woofer able to produce 80Hz.
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Wavecor
SW263WA03
SW263WA03 is a
4 ohm woofer designed for dedicated subwoofer applications.
It works equally well for high-end
hi-fi, high quality home theater systems, and top multimedia
setups.
The extremely stiff aluminium cone,
the long linear throw, exaggerated ventilation, and the special
dynamic linearization short circuiting rings together makes up
for an unusually linear and low-distortion woofer.
Even at very
high signal levels, the unit behaves controlled and without
distortion.
Due to low mechanical losses SW263WA03
masters equally well low level details and extreme dynamic
requirements.
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BOX DESIGN
The box was built using 19mm MDF.
SIMULATION
This H-frame has been simulated using the
Matcad
worksheet
by
Martin King
on a Windows XP virtual machine.
MEASUREMENTS
Follows the frequency response of the loudspeaker
without the active filter, this is like the simulation model.
You can see the typical resonance peak at 300Hz
determined by the length of the case and this will be this will be reduced
significantly with a high slope filter.
Follows the various
frequency response using the active filter with the dipole compensation.
ACTIVE FILTER
I have got on Ebay an active crossover module
to start like base (NE5532
Subwoofer processing circuit).
The original schematic have a big problem, the output voltage change with
the frequency setting.
so I have changed some components and the schematic to obtain a good
low-pass and to add a dipole compensation.
The main problem of this
previous circuit is the 50Kohm potentiometer for frequency change which is
not linear but logarithmic so it is not easy find the right position.
See the new filter module on
The extreme H-frame subwoofer .
FINAL CONSIDERATIONS
AND LISTENING SESSION
PHOTOS
