JBL S4Ai, S4HC, S4VC manual An even distribution of them, so that their, Some suggestions

• 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

FINE-TUNING YOUR AUDIO SYSTEM

STANDING-WAVE SOLUTIONS:
ROOM RATIOS
In new construction, the best way to minimize	SUB
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	Low Relative Pressure	Low Relative Pressure
another should also be avoided where possible.	Copyright 2000 Lucasfilm Ltd.
	Figure 27.

STANDING-WAVE SOLUTIONS: SPEAKER PLACEMENT

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				• How to improve a
standing wave depends on its frequency, with
				2nd-order standing
lower frequencies requiring more movement
				wave
owing to their longer wavelengths. As a result,
		Resulting Modal Structure		• The subwoofer
			Listener
minimizing colorations due to standing waves				drives the + and –
often requires significant adjustment of sub-	+	–	+	areas equally,
woofer placement. Leave yourself some latitude				resulting in reduction
				of resonance
with regard to subwoofer placement when plan-
		Subwoofer
ning your system – the final adjustment will
	Copyright 2000 Lucasfilm Ltd.

probably have to be done on something of a	Figure 28.
trial-and-error basis. See Figures 28 and 29 for
some suggestions.

STANDING-WAVE SOLUTIONS: ABSORPTION

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

	Resulting Modal Structure
	Listener
+	–	+

		Subwoofer
		Output
Subwoofer 1	Subwoofer 2
		From

damping. This means a five-foot thickness of fiberglass would be required in order to damp everything down to 100Hz – not very practical.

Mono!

Copyright 2000 Lucasfilm Ltd.

Figure 29.

Controller

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