Subwoofer crossovers

I should being this by saying I am from the pro side. Pros feel the best way is always to run the mains full range, use a Low Pass filter on the sub that's being fed the same full range signal. However, for movies, the correct movie set up uses a dedicated Low Frequency Effects channel, with the caveat being different studios have used different LFE crossover freq's in their mixes. The correct one is 120Hz for THX style but some have used 80Hz. This is also a summed mono channel. This whole area of LFE and crossovers etc is what's called "bass management", which many of us hate for lack of a universal standard. The idea of rolling off mains sucks! Inserting a crossover into mains at such an audible point leaves a good sized "hole" to sort out, a artifact you cannot fix.

Obviously this is a common problem so there is an entire class of product out there for it. Being that this 5.1, 7.1 processing is typically all digital, there will be a wide range of performance differences between processors.

The main point to make is DO NOT rolloff the mains or insert any type of crossover on the mains for anything but movies. It makes a big [audio] mess.

Brad

Brad, glad there is professional confirmation for what my amateur intuition told me. I am running mains at full range and use a low pass filter for my discrete stereo sub signal. For MCH 5.1 I also sum the unfiltered LFE channel to the discrete stereo signal of my 2 subs. The only (non-pro, and non custom made) device I found that can do this is the NHT-X2 Xover. Now discontinued.

You mention cross-over frequency for LFE channel, but I presume this is only relevant is you cross over mains, center of surround to the LFE channel. If you don't you will simply get on the LFE channel what was mixed to that channel in the studio.

Hi Edorr
Yes the crossover applies to the mains and a lot of speaker manufacturers (like ATC) dislike the idea. Others do it out of compliance if they plan to sell a lot of small 5.1 systems in post-the customers (in this case post production engineers) need to hear exactly what the 5.1 mix will sound like.

Brad

The posts in this thread suggest you folks are knowledgable about bass management. It seems as though SACD discs output as DSD from my Sony XA5400ES or Oppo BDP-93 to my Cary Cinema 11a lack bass management. The subs are not invoked. OTOH, HDCD discs from the BDP-93 do invoke the subs. I read one of Kal Rubinson's remarks to suggest DSD might not carry bass management information. Do I need to output LPCM to get the subs to fire? Is it endemic to DSD or is it a problem with the Cinema 11a? I'm trying to understand this.

db

In case it's relevant to my previous post, the sub output from the Cinema 11a goes through a Velodyne SMS-1 to a pair of HGS-15s using XLR connectors. The 11a has movie and music modes. I use 80 Hz crossover to the mains for movies and 60 Hz or none for music.

db