Confusing LPF of LFE With Bass Management

Denon Menu For Speaker Crossover & LPF of LFE

Denon Menu For Speaker Crossover & LPF of LFE

I find that many people are confused about the bass management and LFE frequency settings in their surround receiver.   Hopefully, the description below will help clarify this.

Each speaker in these systems can have a frequency set such that sound below that frequency at a 12-24db/oct slope is transferred to a subwoofer when one is present. This is referred to as the crossover frequency.  This frequency is the -3db point that the high pass filter for the speaker is set.  There is a corresponding low pass filter used to send the sound to the subwoofer at this same frequency.  Adjusting this frequency will determine how low that particular speaker is allowed to go versus that supplied by the subwoofer.

These systems also have a LPF for the LFE channel.  This is the low pass filter (LPF) setting of the low frequency effects (LFE) channel.  It is usually included in the crossover settings for bass management, but it has nothing to do with bass management.  This is the high frequency cutoff point for the LFE, also known as the .1 channel in a 5.1/6.1/7.1 surround source.  In practice this should always be set to 120Hz since the LFE channel supports information up to that frequency.  When you set this lower than 120Hz the receiver or preamp will not redirect the LFE information to other channels.  Instead it is not reproduced by the surround system.  It should also be noted that this setting has nothing to do with how bass is managed for the full range channels in a surround system.

Another interesting fact is that some systems cutoff the LFE channel prematurely at 80Hz instead of 120Hz no matter how you setup the product.  There are also software bugs in some systems that will set the LPF of the LFE channel at the crossover frequency clipping the higher frequency content of the LFE channel at the frequency you set for the crossover.

It is amazing how such a simple thing can get so messed  up with software errors or people’s lack of understanding and this is only the tip of the iceberg when it comes to getting good sound from your surround system.  It should also be noted many of the automatic calibration systems get this wrong.

W. Jeff Meier

ISF and THX Certified Home Theater Consultant

1 Comment
MagnumX

Bass should never “really” have been included to 120Hz in the first place as it can be directional at these frequencies. It was included for headroom purposes only (no one wants a brick filter). It should be avoided like the plague, IMO as directionality of a subwoofer is unacceptable to me. Plus some of us like to run our sub levels a bit hotter than normal in the lower frequencies, but above 100Hz it just adds bloat. How various people mix films also varies, with many soundtracks carrying the LFE information in the mains and sometimes vice versa. You can end up with too much or too little bass so in my opinion, it’s good there are adjustments so poorly mixed movies do not overwhelm or underwhelm. Most are fine somewhere in-between but like in everything, some products are better than others. Of course, some will not notice either way (95% of LFE content is not in that range anyway), but the fact is most systems have ONE subwoofer at best and any directional information played in them can lead to localization of the subwoofer (never a good thing, IMO).

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