Application Note
LFE Channel Management
Daisy-Chaining Subwoofersin Stand-Alone Mode
September 2016

September 2016

LFE Channel Management
Daisy-Chaining Subwoofers in Stand-Alone Mode
The purpose of this Application Note is to provide further insights into the LFE Channel management andthe use of the +10 dB setting when daisy-chaining multiple subwoofers together.
Note: the configurations below concerning Genelec SAM subwoofers only describe their use in standalone mode – meaning without the use of the GLM 2.0 network and software for the 7200 and 7300 SAM
subwoofers.

Table of Contents:A. The LFE (.1) Channel
B. 7000 Series Subwoofers
C. 7200 Series Subwoofers
D. 7300 Series Subwoofers

A. The LFE (.1) Channel
The LFE channel is the space on the medium for a (.1) encoded (and usually band limited) audio channel.
The subwoofer reproduces the LFE channel and / or the low frequencies of the main channels dependingon whether bass management is used and how the system is setup.
In a 5.1 and 7.1 audio productions, all main channels (Left, Center, Right, Surrounds Left and SurroundsRight) have full bandwidth, i.e. 20 Hz to 20 kHz. Before encoding, the LFE channel is not band limited,i.e. it is just another full bandwidth channel. Figure 1 illustrates the audio bandwidth of each channel in a
5.1 production.

Figure 1 - Audio bandwidths of encoded 5.1 channel materials

After the LFE channel is being encoded it usually has a limited bandwidth (hence the label ‘.1’). This
encoded bandwidth will range from 20 Hz up to various upper cut-off frequencies depending on theencoding formats

Headroom in the LFE channel
The LFE channel is recorded at the same nominal level as all main channels, however the monitor chaininserts a +10 dB boost to give the LFE channel a perceptual advantage since it does not include thehigher frequency content of the main channels. The result is often “less level” going to the recording
media, but occasionally the mixer may take advantage of the 10 dB differential and push the LFE content
to the attention of the listener. Subwoofers are challenged as they are now asked to perform additional
SPL requirements.
To deal with this issue some encoding systems – namely Dolby Digital & DTS Digital - require the LFE
channel to be monitored at a level +10 dB higher than the nominal level of the main channels. In doing so,
the audio level recorded to the media will have an additional 10 dB of available headroom as the engineer
will naturally reduce the LFE channel level by 10 dB on the mixing desk output to maintain the sound levelbalance between the channels. Note that this increase in headroom is at the expense of 10 dB of signalto-noise ratio, but as the LFE channel is eventually band limited in the encoder, it is a price worth paying.

How is this achieved in practice?
In Dolby Digital and DTS Digital formats, between the LFE channel monitor section fader and the acoustic
output of the monitoring system, there must be a +10 dB level change - see Figure 3. This can happen invarious places in the audio chain, but it must be implemented during the production stage.
Note that there are no level changes between the console outputs and the inputs to the recording media.
The net effect is that there is a 10 dB additional headroom on the LFE channel level recorded to the media
compared to the main channel levels.

All tracks are then encoded into a single bit-stream and replayed accordingly, including a +10 dB boost on
the decoded output for the LFE channel - see Figure 2.

LFE Channel

Monitoring Systemin the Studio

5 MainChannels+10dB

Mixing Console

Multitrack
5.1 Channels

5.1 Channels

SurroundSound
EncoderCD, DVD etc.
LFE Channel

Speaker Systemin the Listening Room

5 Main Channels+10dB

SurroundSound
Decoder

Figure 2 - Complete Multichannel Audio Production Chain for Dolby Digital and DTS Digital formats

Figure 3 – Mixing console 5.1 monitoring section with LFE channel initial gain structure for both the monitoring and the recording
output busses.

B. 7000 Series Subwoofers
Analogue 7000 Series subwoofers cannot be used with the Genelec Loudspeaker Manager (GLM)
control network and software management system. Hence, they are always used in so-called stand-alone
mode – meaning without possible computer control.
Subwoofer 1••

LFE +10dB: ON or OFF. Note that if the +10 dB is selected, it will be carried on the cable going tosubwoofer 2.
Sensitivity: note that the input sensitivity should be reduced by -6 dB on each subwoofer as afirst action in order to take into account the mutual SPL coupling of multiple subwoofers.
Additional attenuation may be required depending on the level balance to the main monitors, but
at least -6 dB needs consideration.

LFE Channel input

Output toSubwoofer 2

Input/output tomain channels

Subwoofer 2•

The SUM IN DIP switch must be set to ON. It disables at the same time all other DIP switches inthe same switch group, including the LFE +10dB.

Input toSubwoofer 2

C. 7200 Series Subwoofers
7200 SAM Series subwoofers only feature digital AES/EBU inputs and outputs. They can be controlledusing the GLM control network and software management system. The application below documents theiruse without GLM control in the so-called stand-alone mode.
Subwoofer 1••••

LFE IN USE: YES. States that there is a digital LFE channel on the input 4.
LFE +10dB: ON or OFF.
PASS THROUGH: selected. This allows all channels including the LFE channel to be sent to theirrespective outputs in order to feed the second subwoofer adequately.
Sensitivity: note that the input sensitivity should be reduced by -6 dB on each subwoofer as afirst action in order to take into account the mutual SPL coupling of multiple subwoofers.
Additional attenuation may be required depending on the level balance to the main monitors, but
at least -6 dB needs consideration. This can be done via the Acoustic Editor in GLM 2.0.

LFE Channel input +another channel (Center)

Inputs comingfrom audio source

Outputs tosubwoofer 2

Subwoofer 2•••

LFE IN USE: YES. States that there is a digital LFE channel on the input 4.
LFE +10dB: ON or OFFNORMAL: selected. This allows all channels including the LFE channel to be bass managed andsent to their respective main monitors’ outputs.

Inputs tosubwoofer 2

Outputs tomain monitors

D. 7300 Series Subwoofers
7300 SAM Series subwoofers feature analogue and digital AES/EBU connections. They can becontrolled using the GLM control network and software management system. The application below
documents their use without GLM control in the so-called stand-alone mode.

D.1 Using Analogue Signals
Sensitivity: note that the input sensitivity should be reduced by -6 dB on each subwoofer as a first actionin order to take into account the mutual SPL coupling of multiple subwoofers. Additional attenuation may
be required depending on the level balance to the main monitors, but at least -6 dB needs consideration.
This can be done via the Acoustic Editor in GLM 2.0.
Subwoofer 1 – Analogue Signals••

LFE +10dB: ON or OFF.
LFE OUT: the output is an unaltered copy of the LFE IN input.

LFE Channel input

LFE Channel output
to subwoofer 2

Sum of mainchannels output tosubwoofer 2Input/output tomain channels

Subwoofer 2 – Analogue Signals•

LFE +10dB: ON or OFF.
LFE Channel input
for subwoofer 2

Sum of mainchannels inputs
to subwoofer 2D.2 Using Digital Signals
The application detailed below documents the use of daisy-chained subwoofers receiving only the LFEchannel.
Sensitivity: note that the input sensitivity should be reduced by -6 dB on each subwoofer as a first actionin order to take into account the mutual SPL coupling of multiple subwoofers. Additional attenuation may
be required depending on the level balance to the main monitors, but at least -6 dB needs consideration.
This can be done via the Acoustic Editor in GLM 2.0.

Subwoofer 1 – Digital Signals•••

LFE +10dB: ON or OFF.
DIGITAL LFE: ON. Indicates that subwoofer 1 is receiving a digital LFE channel.
LFE CHANNEL: the subframe A or B containing the digital LFE channel has to be selected.

Digital LFEChannel input(subframe A or B)

LFE Channel output
to subwoofer 2(subframe A or B)

Subwoofer 2 – Digital Signals•••

LFE +10dB: ON or OFF.
DIGITAL LFE: ON. Indicates that subwoofer 1 is receiving a digital LFE channel.
LFE CHANNEL: the subframe A or B containing the digital LFE channel has to be selected.

Digital LFE Channel
input (subframe A or B)
from subwoofer 1

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