Klein + Hummel O 300 Operating Manual page 9

The mid control is used to compensate for the acoustical loading experienced when the loudspeaker cabinet is
placed near a large reflecting surface, such as a mixing console. Four settings are available: +2, 0, -2, and -4 dB.
The treble control affects the treble driver output level and can be used to compensate for insufficient or
excessive high frequency damping in the room. The treble control is often set to suit the listener's taste, although
in well-controlled environments there should be little reason to adjust it away from 0 dB. Four settings are
available: +2, +1, 0, and -1 dB.
It is advised that an acoustical measurement system be used to set these controls in the most appropriate way
for the loudspeaker's location. In the absence of appropriate equipment the following settings are recommended
as a good starting point for further adjustment:
Loudspeaker Location
In a corner
Next to or flush mounted in a solid wall
Next to or flush mounted in a soft wall
Free standing in an untreated room
Free standing in a well-treated room
In small room with strong side-wall reflections
Near a desktop or an a meter bridge
1.Setting should be used in addition to the one of the top five settings.
The input attenuator control allows the loudspeaker to be matched to a wide range of equipment outputs whilst
maintaining the desired acoustical output. In the O 300 D, the attenuator affects the output level as it is
positioned after the DAC. As with any other component in the audio chain, it is best to use the lowest gain for the
application so as to minimize amplification of the preceding equipment's source noise. To check this, if the noise
drops dramatically when the input cable is unplugged, the noise is coming from the source not the loudspeaker.
The default setting is "0 dB", and this gives an output level of 96 dB SPL at 1 m when the input signal is
0 dBu (0.775 V), which is the same as 100 dB SPL at 1 m when the input signal is +4 dBu (1.23 V). Below are
some examples of how to calculate the output level:
Input signal [dBu]
Input attenuator setting [dB]
Loudspeaker output for 0 dBu input [dB SPL]
Sound output of loudspeaker [dB SPL at 1m]
In Europe 0 dBu is -18 dBFS (EBU standard R68). In the US +4 dBu is -20 dBFS (SMPTE standard RP155). These
dBu values should equate to 85 dB SPL at the listening position. It is typical in the broadcast industry to use a
reference level of 79 dB SPL at the listening position. Near field loudspeakers can be as close as 1 m from the
listening position, whereas loudspeakers in a Dolby certified movie mixing room should be at least 5 m from the
listening position. In the examples below, it is assumed that the listener is inside the room radius and thus the
sound field decays according to 20 log
O 300 (D) Operating Manual
Acoustical Controls
1
1
O 300 (D) Acoustical Controls
0 (0.775 V)
0
96
96
(r), however this may not always be the case.
10
Bass Mid
-9 dB -2 dB
-6 dB
-3 dB
-3 dB -2 dB
-
- +2 dB
- -2 dB
0 (0.775 V) +4 (1.23 V)
-24 0
96 96
72 100
Klein + Hummel
Treble
-
- -
- -
-1 dB
- -
-
-
-20 (77.5 mV)
0
96
76
7