Subwoofer Optimizer System
Michael McKelvy
http://www.speakercity.com/Sos/SubwooferOptimizer.shtml
According to them:
The Automated Controlled Environments, inc. Subwoofer Optimizer System (SOS)
is an automatically calibrating, subwoofer optimization component, that acts
to attenuate an audio system's major room mode resonance to provide
significant improvement in measured and subjective bass system performance.
After installation and calibration, your system will have a more linear
frequency response, bass evenness, tightness, extension, and improved sound
clarity.
Anybody ever try anything like this?
Comments, criticisms?
Kalman Rubinson
extended one some time back in Guide to Home Theater (now Ultimate
A/V). The key issue is that it is a single band EQ and will do great
if(!) all you need is a single band of correction. Worked for me.
Kal
On 25 Nov 2004 15:59:33 GMT, "Michael McKelvy" <desk...@peoplepc.com>
wrote:
Nousaine
Part of the thinking behnd Harman's RABOS system (a single band parametric EQ
with cut-only) was the idea that the single most often encountered low
frequency room mode problem, that can be fixed with EQ, is a single peak due to
stacked room modes.
In general this is a good idea but IMO the single most commonly encountered low
frequency modal problem is a deep notch in the 30-50 Hz range caused by failure
to excite one or more of the primary modes due to sub-optimal woofer placement.
Kalman Rubinson
>Part of the thinking behnd Harman's RABOS system (a single band parametric EQ
>with cut-only) was the idea that the single most often encountered low
>frequency room mode problem, that can be fixed with EQ, is a single peak due to
>stacked room modes.
>
>In general this is a good idea but IMO the single most commonly encountered low
>frequency modal problem is a deep notch in the 30-50 Hz range caused by failure
>to excite one or more of the primary modes due to sub-optimal woofer placement.
Absolutely. One should not be using electronic
correction/compensation until after the acoustics and placement issues
have been optimized.
Kal
>
---MIKE---
one of my sub woofers in my usual listening position. I then played the
bass tones from a Stereophile test CD and using my trusty Radio Shack
meter, moved around the room. I found that at 40 hz, the corner
position (where I had two of the subs) had a big suck-out. The side
wall (next to my listening position) had the best response. At 60 hz,
the corners were best. So, it seems you really need several subs to get
the best results! A 1/3 octave equalizer could best be used to smooth
out peaks caused by room resonances.
---MIKE---
Nousaine
A number of years ago I response mapped 13 rooms with a MLSSA system as to
subwoofer location relative to the primary listening position using the
reciprocal microphone technique (woofer in listening position; microphone in
possible subwoofer locations) used by the owners. In every case except one a
closed corner (at least 5-feet of wall to each side of the corner) provided
the smoothest in-room response.
In that case (an unusual listening room that was a loft open to 2 floors of a
stick frame house) the best subwoofer location(s) were 2-3 feet from both of
the in-room corners.
I also discovered that not all closed corners are equal. For example; one
corner that was kitty corner to a single large opening, 5-foot wide
floor-ceiling doorway, in a room that was otherwise a perfect shoebox had an
anomaly, a response notch near 40 Hz, where apparently the room would be trying
to act symmetrically .... sound was being allowed to escape through the opening
... so the room may have been behaving in a anomalous manner in the symmetrical
location. On the other hand ordinary doorway openings seemed essentially
unimportant.
There is an apparent reason for this. Standing wave modes exist at all
frequencies between any 2 set of parallel walls. However at frequencies above
2-300 Hz the wavelengths are short enough that the pressure distribution is
essentially the same everywhere in the room. For example play a 1000 Hz tone
(wave-length of about a foot) in any room and you'll hear the sound pressure
change as you move your head by a few inches. This is due to a standing wave.
However because the wavelength is relatively short and thus statistically dense
you'll get exactly the same effect everywhere in the room.
Try this at low frequencies where the wavelength is measured in feet (for
example 10-feet at 100 Hz and 20 feet at 50 Hz and 50 feet at 20 Hz) you'll get
significant changes in pressure at any given location relative to another. And
because most nominal sized rooms have a volume that allows only the development
of 5 modes below 100 Hz you'll find that the real problem is that there aren't
enough modes at low frequencies to deliver even sound pressure distribution.
Isn't the solution mode-cancellation? Well, that would seem to be so at first
glance but its more complicated than that. The modes in any space carry the
energy and while it's fairly easy to attain adequate loudness at high
frequencies it gets progressively more difficult to do so at low frequencies.
For example the speaker displacement required to attain a given SPL quadruples
for every octave lower.
For example to obtain a maximum SPL of 105 dB at 100 Hz (the reference THX
level) might require an 8-inch speaker with 12 cubic inches of peak-peak
displacement. To maintain this level at 25 Hz will require 195 cubic inches and
12 Hz requires 780 cubic inches or about the same as 2.2 small block Chevy V8s.
What's the displacement of a 12mm clean stroke 12-inch woofer? About 44 cubic
inches assumimg the amplifier will drive the soeaker to full displacement at
any given frequency. So it becomes pretty to see that speaker displacement is a
major issue with subwoofers. This gets really problematic if you start
cancelling modes that are maintaining the energy.
The best alternative with a single subwoofer is to maximize the excitation of
all possible modes and the only location that will do that is closed corner.
Even then Sound Pressure won't be perfectly even in most listening locations
but it will allow you to put less energy selectively into the room at offending
frequencies where there may be peaks instead of in large low frequency blocks.
In all, with a single subwoofer corner placement will nearly always be optimal.
Michael McKelvy
news:coj1e...@news2.newsguy.com...
should really have 3 subs for best bass.
Stu-R
same time, you have to account for their interaction, which gives you
new set of anomalies. FWIW In the room I currrently use, I have to
use a 200hz crossover frequency because the room has nodes around
160hz that are excited to intolerable masking by the non-subwoofer
channels. I never considered such a high crossover frequency until
now, but it seems to clear up many of my problems.
On 30 Nov 2004 23:58:02 GMT, twinmo...@webtv.net (---MIKE---)
wrote:
Steven Sullivan
Harman-Kardon has studied the use and placement of single and multiple subs systematically
-- see http://www.harman.com/wp/index.jsp?articleId=1003
--
-S
Your a boring little troll. How does it feel? Go blow your bad breath elsewhere.
Ban
I do not support this statement. For me the room corners are the optimal
place to put absorbers for those few low frequency room modes. These can be
either Helmholtz- or plate-absorbers.
I move the subs 1/4 of the short and 1/3 of the longer side into the room,
my listening position is almost in the middle. In the corners the sound
becomes too boomy IMHO. Important is also a symmetrical placement. I find
two subs to be sufficient, but 4 are a bit better if you like music with low
frequency content.
--
ciao Ban
Bordighera, Italy
Jim Cate
orient or "aim" the sub in a particular direction? Also, is it
recommended that the sub be spaced from cabinets and other components of
the system, or that no component be positioned between the sub and the
listener?, or is that not a critical factor?
Jim Cate
Nousaine
>If a sub is placed in a corner, is it important or advantageous to
>orient or "aim" the sub in a particular direction? Also, is it
>recommended that the sub be spaced from cabinets and other components of
>the system, or that no component be positioned between the sub and the
>listener?, or is that not a critical factor?
>
>Jim Cate
If you think about it, at these wavelengths where sound is being radiated
omnidirectionally its impossible to "aim" a subwoofer and sound blocking
objects smaller than a half-wall or so are not an issue.
However is the subwoofer has out-of-band artifacts (such as port noises and
turbulence, suspension noise and the like) there can be some advantage to
facing the driver and/or port away from the listener because it may reduce the
audbility of the artifact which is often manifest in the midrange.
There are certain cases, but usually best implemented in the design stage,
where placing a driver or port close to a boundary the air between the boundary
or radiating element will be added to the moving mass and lower system tuning.
The latter is most usually seen in subwoofers that have a downward facing port
of driver.
Buster Mudd
>
> A number of years ago I response mapped 13 rooms with a MLSSA system
as to
> subwoofer location relative to the primary listening position using
the
> reciprocal microphone technique (woofer in listening position;
microphone in
> possible subwoofer locations) used by the owners. In every case
except one a
> closed corner (at least 5-feet of wall to each side of the corner)
provided
> The best alternative with a single subwoofer is to maximize the
excitation of
> all possible modes and the only location that will do that is closed
corner.
> Even then Sound Pressure won't be perfectly even in most listening
locations
> but it will allow you to put less energy selectively into the room at
offending
> frequencies where there may be peaks instead of in large low
frequency blocks.
>
> In all, with a single subwoofer corner placement will nearly always
be optimal.
I'm curious, Tom whether you've had the opportunity to perform similar
response mapping of rooms with multiple subs? Reason I ask is not only
because your description above seems almost conspicuously focussed on
single subwoofer systems, but also because I've had at least three
separate acoustic consultants (none of whom had a vested interest in
selling subwoofers) tell me that the best way to overcome modal-induced
anomalies & get smooth low frequency response is via multiple subs
distributed around the room.
Note also that none of these professionals advocated the 1/4 distance
or 1/3 distance from the walls or corners that I've seen various folks
on Usenet or other internet discussion groups advocate. They instead
recommended four subs located in either the center of each wall
(equidistant between corners), or directly in each corner.
Nousaine
Yes I have but to a much smaller degree (fewer rooms.) In my original work I
discovered that subwoofers at standard left and right stereo locations all had
serious problems because apparently they failed to excite the width mode in the
room causing a serious suck-out between 45-55 Hz (room size 22x12x8.)
In a similar fashion the placement of subwoofers in what is now known at the
ITU multi-channel locations had even more serious problems, such that 5
subwoofers in that placement were worse in frequency response and SPL than a
single subwoofer in the corner.
You might check out the Harman web-site and investigate the Todd Welti
modelling work on multiple subwoofers. In that work he suggests that mulitple
subwoofers can optimize in-room response over a fairly wide range of seating
positions BUT serious adjustment balancing EQ, Level and Polarity is required
at EACH subwoofer location...meaning that unless you have his model there is no
way to figure location and individual sub set-up relative to level, EQ and
polarity from scratch. And the 1/3, 1/4 rules of thumb don't work.
He also suggested that the most improvement is gained by using 4 subwoofers. He
also suggested that one good approach is placing a subwoofer half way down each
of the 4 walls as a good starting point in a shoebox shaped room.
I tried this approach in my new room (irregular shape with open foyer and
staircase with 18-foot catherdral ceiling) with a 13x23 basic footprint and
discovered that such placement was problematic (introduced significant
frequency response errors at basic listening area) and if you evaluated maximum
SPL at 1/3octave frequencies compared to a single (same model) subwoofer in the
best corner of that room that you get a couple dB-SPL less output with the 4
subwoofers.
I'm looking for a 15 x 20 x 8 foot shoebox to conduct more experiments on this
line. I chose thi ssize room because a study of 251 North American Listenin
Rooms conducted by one speaker manufacturer shows that 15x20x8 is the modal and
mean average room size. Therefore experiments can be expected to affect more
users in a meaningful way.
So as far as I can tell as of today there seems to be little reason to use
multiple subwoofers until we have some more data on what might work and what
might not.
If you check back from time to time I'll keep you updated but I must warn you
that progress isn't speeding along at breakneck speed. It's hard to find an
unfurnished room (conference room or lie) for rent which is that size.