| Video Noise August 2006
Home-Theater Bass and
Subwoofers Revisited
Over time, little system-setup tricks and tips come
along. Some I find on my own, others come from another home-theater enthusiast or from a
manufacturer. Dr. Po Ser Hsu of Hsu Research, makers of the extraordinarily affordable and
excellent Ventriloquist surround speaker system and the VTF-2 Mk.II subwoofer (so good at
$500 that it beat the pants off an $1800 imported subwoofer I recently heard), is working
on a new woofer-subwoofer combo in which the woofer is placed close to the main listening
position and the sub is placed at an appropriate location within the room, often in a
corner or near a wall. Hsu contends that the proximity of the bass source (in this case, a
woofer) to the listener helps remove room effects from the overall bass response.
The lower the frequency, the longer its wavelength, and the
more it is affected by room dimensions and surfaces. When a subwoofer or woofer is placed
close to the listener, while the room is still a factor in the overall sound, the sound
from the subwoofer/woofer now reaches the listener first. The result is that fewer room
effects interfere with the sound than in the more typical farfield placement of the
subwoofer/woofer.
Overall, my room is quite good in the bass; its dimensions
were chosen to minimize room-mode reinforcements, and 45-degree surfaces in the corners
inhibit the creation of standing bass waves. Yet even with these advantages, when I used a
test CD or setup DVD to take meter readings of the room’s bass response, it was clear
the room was doing a lot to make its bass response less linear than I like.
So to try Dr. Hsu’s idea, I moved my LFE subwoofer
right behind the couch that is our primary listening position for home theater. This sub
has downward-firing drivers, a large passive radiator on one side, and slots around the
perimeter of its base that allow the sound to radiate into the room. I placed it about
6" behind the couch with the passive radiator facing the rear of the room. I used a
sound-pressure-level meter to rebalance all the channels and subwoofer, and reset the
subwoofer-to-listener distance from 12’ to 2’.
I then screened the Superbit versions of The Fifth
Element and Batman Begins to see if I could hear any difference in LFE quality,
power, impact, and extension. It was obvious that the bass was better with the new LFE
subwoofer placement. I noticed no difference in extension, but the power, impact, and
quality of the subwoofer bass were decidedly better than ever. Impacts were quick and
energetic, moving the entire couch with surprising and realistic-feeling energy. Bass
sounds of longer duration were significantly more sinister and powerful. Indeed, the
familiar bumps and valleys in my room’s bass response seemed to disappear. I doubt
they disappeared entirely, but with the primary source of bass being that close, it was
significantly stronger than the reflected and room-altered bass, and gave the impression
of audible improvement.
This nearfield placement may not be practical for gigantic
subwoofers. If you’re using an 8’-tall subwoofer with multiple 24" drivers,
you might not want that too close to your seating position. And if the sub is
really small -- more a woofer than a subwoofer -- it will better integrate with the other
speakers if it’s in the front-center position. Standalone woofers are used with
really small satellite speakers to fill in frequencies that are quite a bit higher than
those covered by true subwoofers, so you won’t want to place one of these too far
from the speakers. The nearfield-placement trick will work best when the sub is crossed
over at 60-80Hz and is of fairly typical size, with a 10"-18" driver or multiple
8" drivers, and a cabinet volume of 1.0-2.5 cubic feet.
If you want to try this for yourself, don’t forget to
use the speaker-setup function in your surround processor or A/V receiver to adjust the
listener-to-sub distance, and to reset the channel levels. Otherwise, placing the
subwoofer behind your couch or chair will make the bass too loud.
While my testing has gone on for little more than a week,
so far the indications are excellent that this new, nearfield location for the LFE
subwoofer is a winner. It also makes me want to experience the woofer-subwoofer combo Dr.
Hsu is working on.
...Doug Blackburn
db@hometheatersound.com |
