How Important Is the LFE Subwoofer to Home Theater?

Bernal

How Important Is the LFE Subwoofer to Home Theater?

"1.- When you turn LFE on something else happens in the decoder circuitry that causes the midrange and highs to loose air and to sound slightly squashed, gray and dry compared to what you hear when LFE is off.
2.- The problem arises from the fact that LFE on/off is not just turning LFE on or off. The bass management circuit takes a little bass from the main speakers and off loads it to the LFE sub whenever LFE is on -- even if you have selected "large" main speakers.
3.- I find the effect bad enough that I generally prefer to drive the LFE subwoofer from the analog outputs of the DVD player rather than from the LFE output of the receiver or processor.
4.- You may not have the sub setup correctly or you may not think a sub is really needed.
5.- The information here should arm you with the basics to understand and win the Dolby Digital bass wars"

cnh

I haven't heard any of those effects on my system so I can't comment on the author's findings above...I find it hard to believe that a good AVR would interfere with the bass on the mains if you use the LFE out. On a digital recording the LFE is a discrete channel? As are all the other 5 channels?

Perhaps someone else can comment further...?

cnh

tonyb

The way alot of avr's handle bass management differs between make,models,and of coarse price. Just do your homework is all. Wasn't aware of any DD bass wars btw.

kuntasensei

1. I would immediately disagree with 1. When you offload bass duties to the subwoofer, you open up the midrange and highs on the speaker itself because you're giving the speaker more clean power to handle those frequencies. Bass is the hardest to drive, power wise, so moving the power needs for bass off to the subwoofer (which typically has a better amp section than your AVR, with a higher damping factor and more power) is pretty much always going to make your speakers sound clearer and give you more available power for transients.

2. Also incorrect. If you set your other channels to large, only the LFE channel is sent to the subwoofer (and therefore 2-channel sources will send NOTHING to the subwoofer). Doing that would have zero effect on the sound of the speakers.

3. Driving the LFE off of the analog outputs of the DVD player would only get you the LFE, not redirected bass from the other channels, unless you're doing bass management in the DVD player itself. This is not a good idea at all, because the slope of the crossover in the DVD player will almost definitely be different from the slope of the crossover in the AVR, which would cause a gap in frequency response in the crossover range. It's also a problem because the voltage output of the analog outputs on DVD players varies so much from that of AVRs, which will make level matching more difficult (and could be overdriving the input section of the amp on your subwoofer, in worst case scenarios). It's better to let the digital filters in the AVR do the filtering and summing of LFE and redirected bass.

What crazy backwards logic land did you get this information from, Bernal?

Bernal

kuntasensei wrote: »

What crazy backwards logic land did you get this information from, Bernal?

http://www.soundstage.com/video/columns/200003_db_hometheaterbass.htm

Sherardp

I don't get any of that in my setup OP. In the SC-07 I can make numerous adjustments to my setup. I don't lose anything at all. Have you tried or done any tweaking?

NotaSuv

Interesting read..thanks

kuntasensei

Well, thank God none of the equipment I've ever used has acted that way. I'd say that if you have a modern AVR with independently adjustable crossovers, you can pretty much ignore that article (though its tips on subwoofer setup are still applicable). Maybe things were different 10 years ago when that article was written, though I would say that the only thing that has really changed since then is that LFE above 80Hz is no longer thrown out when using bass management. Older AVRs, when speakers were set to SMALL, would sum all of the redirected bass with the LFE channel and then filter it all at 80Hz before output. Newer AVRs let you have separate filters so that you can still redirect bass from the main channels at 80Hz but also pass the full bandwidth of the LFE channel, because the summation doesn't occur until after the filtering. It's all done on a digital level now, using filters designed to mimic analog Linkwitz-Riley crossovers, so you don't have to worry about losing anything due to phase so long as your subwoofer's phase is properly set and your speaker distances are spot on (since distance/delay can alter the phase correlation between each speaker and the subwoofer across the crossover range).

What AVR or pre-pro are you using, Bernal?

Bernal

kuntasensei wrote: »

What AVR or pre-pro are you using, Bernal?

DENON AVR-4308CI + SUNFIRE Grand Signature - Bob Carver's + OPPO BDP-83 + POLKAUDIO LSiC (Center speaker) LSi15 LEFT (Front speaker) LSi15 RIGHT (Front speaker) LSif/x LEFT (Surround speaker) LSif/x RIGHT (Surround speaker) and VELODYNE OPTIMUN 12"

◊ Main speakers - LARGE,
◊ Center - SMALL - crossover to 60 Hz,
◊ Surround - SMALL - crossover to 60 Hz,
◊ Subwoofer - the Subwoofer Direct feature is invoked,
◊ LFE (Low Frequency Effects) channel: crossover to 120Hz.

kuntasensei

Yeah, though I wouldn't be running those LSi mains as Large, your system doesn't suffer from any of the issues this guy was talking about 10 years ago.

Before you ask why I wouldn't run those as large, I'll just go ahead and explain: Typically, if you run your mains as large, you have to consider bass management. With the center and surround crossed at 60Hz, ideally you want the bass below that point to go to the subwoofer. However, some AVRs let you set things so that redirected bass is handled both by your subwoofer and steered to the mains. There is a huge potential for cancellation when reproducing the same bass from multiple point sources, which is why you'll see people with dual subwoofers either co-locate them or run them as stereo subs with different signals (which still can cause cancellation with the LFE channel). Now, if you have them set to large because you do a lot of 2-channel listening... carry on, sir. If you're more on the movie side of the spectrum, I recommend a crossover of 60Hz. This gives you a full octave transition before the speaker's -3dB point of 30Hz. Additionally, since that particular speaker does have a -3dB point of 30Hz, it isn't truly capable of playing back full range audio (i.e. 20Hz-20kHz) as required by digital surround tracks. Your Velodyne, on the other hand, has a -3dB point of 21Hz with extension down to 13Hz. By setting your mains to a 60Hz crossover, you're ensuring that bass from the other channels is redirected only to the subwoofer and you're freeing up headroom from your amp which should give you cleaner reproduction of mids and highs. You're also letting that 8" woofer in the LSi15s handle roughly 60-150Hz, which should give you a more defined sound to mid-bass and maintain directionality.

Another BIG advantage is if you're using Audyssey's MultEQ XT. MultEQ XT does way higher resolution equalization to the subwoofer than it does to the main channels. Therefore, offloading the bass duties to the subwoofer can give you flatter and more consistent bass response overall.

Some interesting reading for you that is far more relevant than the Soundstage article:
http://www.hometheaterhifi.com/technical-articles/156--miscellaneous-ramblings-on-subwoofer-crossover-frequencies.html
http://www.hometheaterhifi.com/technical-articles/163-the-misunderstood-01-lfe-channel-in-51-digital-surround-sound.html

Incidentally, I also would try that LSiC at 80Hz instead of 60. Its -3dB point is 52Hz, meaning you're going to get a frequency gap as the AVR's crossover transitions in the same range as the enclosure's natural rolloff begins. 80Hz would give you a solid octave of transition before the LSiC's 40Hz bottom end, which should prevent any noticeable gaps in response. It also lets the bass driver handle roughly only 80-200Hz, which should give you better mid-bass definition. The same goes for the LSiF/X, which have similar specs as the LSiC. Just a suggestion.

Bernal

kuntasensei wrote: »

Yeah, though I wouldn't be running those LSi mains as Large, your system doesn't suffer from any of the issues this guy was talking about 10 years ago.

Before you ask why I wouldn't run those as large, I'll just go ahead and explain: Typically, if you run your mains as large, you have to consider bass management. With the center and surround crossed at 60Hz, ideally you want the bass below that point to go to the subwoofer. However, some AVRs let you set things so that redirected bass is handled both by your subwoofer and steered to the mains. There is a huge potential for cancellation when reproducing the same bass from multiple point sources, which is why you'll see people with dual subwoofers either co-locate them or run them as stereo subs with different signals (which still can cause cancellation with the LFE channel). Now, if you have them set to large because you do a lot of 2-channel listening... carry on, sir. If you're more on the movie side of the spectrum, I recommend a crossover of 60Hz. This gives you a full octave transition before the speaker's -3dB point of 30Hz. Additionally, since that particular speaker does have a -3dB point of 30Hz, it isn't truly capable of playing back full range audio (i.e. 20Hz-20kHz) as required by digital surround tracks. Your Velodyne, on the other hand, has a -3dB point of 21Hz with extension down to 13Hz. By setting your mains to a 60Hz crossover, you're ensuring that bass from the other channels is redirected only to the subwoofer and you're freeing up headroom from your amp which should give you cleaner reproduction of mids and highs. You're also letting that 8" woofer in the LSi15s handle roughly 60-150Hz, which should give you a more defined sound to mid-bass and maintain directionality.

Another BIG advantage is if you're using Audyssey's MultEQ XT. MultEQ XT does way higher resolution equalization to the subwoofer than it does to the main channels. Therefore, offloading the bass duties to the subwoofer can give you flatter and more consistent bass response overall.

Some interesting reading for you that is far more relevant than the Soundstage article:
http://www.hometheaterhifi.com/technical-articles/156--miscellaneous-ramblings-on-subwoofer-crossover-frequencies.html
http://www.hometheaterhifi.com/technical-articles/163-the-misunderstood-01-lfe-channel-in-51-digital-surround-sound.html

Incidentally, I also would try that LSiC at 80Hz instead of 60. Its -3dB point is 52Hz, meaning you're going to get a frequency gap as the AVR's crossover transitions in the same range as the enclosure's natural rolloff begins. 80Hz would give you a solid octave of transition before the LSiC's 40Hz bottom end, which should prevent any noticeable gaps in response. It also lets the bass driver handle roughly only 80-200Hz, which should give you better mid-bass definition. The same goes for the LSiF/X, which have similar specs as the LSiC. Just a suggestion.

I will keep your suggestion
"LFE + Main" is recommended or LFE only in my Denon.
Thanks friend.

Note: The opening quote is a question of reading. I do not have the problem described.

Bernal

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