Standing -Wave Solutions Room Ratios; Tanding Ave Olutions Peaker Lacement; Standing -Wave Solutions Absorption - JBL SYNTHESIS FOUR S4Ai Owner's And Installer's Manual

F -T Y
INE UNING OUR
S -W S
TANDING AVE OLUTIONS
R R
OOM ATIOS
In new construction, the best way to minimize
the audibility of standing waves is to plan for
an even distribution of them, so that their
effects do not "pile up" on top of each other. In
this regard, the ratios of room dimensions are
the critical factor. Rooms having equal dimen-
sions are the worst, since the standing waves
in all directions reinforce one another. Room
dimensions that are even multiples of one
another should also be avoided where possible.
S -W S
TANDING AVE OLUTIONS
Speaker placement also has an effect on standing waves and their audibility. In particular, placement of any speaker
(including subwoofers) where two walls and the floor meet will tend to stimulate all of the available standing waves,
causing the most irregular response. The dis-
placement required to minimize a particular
standing wave depends on its frequency, with
lower frequencies requiring more movement
owing to their longer wavelengths. As a result,
minimizing colorations due to standing waves
often requires significant adjustment of sub-
woofer placement. Leave yourself some latitude
with regard to subwoofer placement when plan-
ning your system – the final adjustment will
probably have to be done on something of a
trial-and-error basis. See Figures 28 and 29 for
some suggestions.
S -W S
TANDING AVE OLUTIONS
A
BSORPTION
In theory, it is possible to dampen standing
waves with absorptive material. The difficulty
is that the thickness of the absorptive material
would have to be approximately one-half the
wavelength of the lowest frequency requiring
damping. This means a five-foot thickness of
fiberglass would be required in order to damp
everything down to 100Hz – not very practical.
A S
UDIO YSTEM
:
Low Relative Pressure
Copyright 2000 Lucasfilm Ltd.
Figure 27.
: S P
PEAKER LACEMENT
+
Copyright 2000 Lucasfilm Ltd.
Figure 28.
:
+
Subwoofer 1
Copyright 2000 Lucasfilm Ltd.
Figure 29.
Resulting Modal Structure
Listener
–
Subwoofer
Resulting Modal Structure
Listener
–
+
Subwoofer 2
Mono!
19
Low Relative Pressure
• How to improve a
2nd-order standing
wave
•
The subwoofer
drives the + and –
+
areas equally,
resulting in reduction
of resonance
• Improving a 2nd-order
standing wave
– Connect the 2
subwoofers together as
"in-phase"
– The 2 subwoofers drive
the + and – areas
equally, resulting in
reduction of resonance
– Experiment a lot
Subwoofer
Output
From
Controller
SUB