Page 14
R.5-MAX, R2-MAX
Installation and Operation Manual
Now, as a thought experiment, imagine that we apply the specified maximum of 63 Volts to the entire loudspeaker before
applying the recom6 dB boost at 70 Hz. The entire bandwidth of the loudspeaker would then be operating at its
2000 watt limit. Now, add the +6 dB boost at 70 Hz into the signal chain. The flat portion of the driver pass band will still be
receiving 63V, but at 70 Hz the voltage will be 6 dB higher, or about 127V, which is the equivalent of about 8000 watts! Clearly,
the LF driver cannot handle 8000 watts continuously, so some compromise must be made.
To protect the LF driver from over excursion or thermal damage, we’ll need to limit the voltage at 70 Hz to the specified
maximum of 63V (2000 watts). Since we’ve boosted 70 Hz with the +6 dB PEQ filter, this is the only frequency that is able to
reach the full 2000 watt input. The remainder of the loudspeaker’s pass band will receive 6 dB less input voltage, or about 32V,
which corresponds to only 500W.
Figure 9
illustrates the situation.
Frequency (Hz)
‐
36
‐
30
‐
24
‐
18
‐
12
‐
6
0
6
12
18
10
100
1000
10
100
1000
-18
-6
0
-12
18
6
12
+6dB
+0dB
32V + 6dB = 63V (2000W)
applied to driver at 70 Hz
Non-boosted portion
of driver has only 32V
(500W) applied
Figure 9.
Generic DSP EQ transfer function with +6 dB @ 70 Hz boost
FREQUENCY RESPONSE
(processed multi-amp*)
70
80
90
100
110
120
10
100
1000
10000
Am
plitu
de
(d
B
SP
L)
Frequency
(Hz)
Frequency
Response
(EQ3)
1/6
Octave
Smoothing
Frequency (Hz)
—
Complete,
—
High Frequency
—
Low Frequency 1/6 Octave Smoothing
100
1000
10000
10
70
80
90
100
110
120
Amplitude (dB SPL)
Figure 10.
R2-64MAX Spec Sheet Frequency Response Graphs
70
80
90
100
110
120
10
100
1000
10000
A
m
p
lit
u
d
e
(dB
SPL)
Frequency
(Hz)
Frequency
Response
High
Frequency
Low
Frequency
Resolution
>180Hz
~ 12Hz,
<180Hz
~
3Hz, 1/6
Octave
Smoothing,
1W
1/6 Octave Smoothing, 1W/1m
Frequency (Hz)
—
High Frequency
—
Low Frequency
100
1000
10000
10
70
80
90
100
110
120
Amplitude (dB SPL)
FREQUENCY RESPONSE
(unprocessed)
LOW FREQUENCY “BOOST” EFFECT (continued)
With any loudspeaker, for every 3 dB of LF boost, the resultant maximum amount of power available to the flat portion of the
pass band is cut in half. And, 6 dB of boost results in one quarter of the original power. For our example loudspeaker, this
means the Maximum Output SPL in the flat portion of the pass band is reduced from 130 dB down to 124 dB.
Most manufacturers’ spec sheets do not discuss the EQ transfer function used to create the frequency response curve and
they may not disclose the LF boost that has been applied. This makes it difficult or impossible to determine the actual Maximum
Output SPL with EQ. Sometimes, the spec sheet will show “unprocessed” and “processed” response curves. These provide
some indication of the LF boost. However, it is still time consuming to calculate the actual LF boost and its effect on Maximum
Output SPL. Complicating matters further, acoustic simulation and coverage prediction software does not usually account
for the differences in real-world output that occur as the result of this LF boost, even when the EQ filters are included in the
loudspeaker source file. Modern acoustic simulation software predicts loudspeaker system results so well that many users
may not realize they have overlooked the effect of EQ boost until the system has been installed and it either cannot reach the
intended output levels, or the LF extension must be reduced in order to achieve the output levels.
COMMUNITY’S ALTERNATE APPROACH
As a contrast to the competitive loudspeaker in our thought experiment,
Figure 10
shows the published response curves, with
notation, for Community’s R2-64MAX.
Note the asterisk after “(processed multi-amp*)”. This refers the reader to the explanation you are now reading. These R-MAX
curves include LF boost to produce the result shown in the frequency response chart. However, other manufacturers may use
much greater boost (in excess of 6 dB) to achieve their published results.