LFE and bass below 80hz

SteveCallas · 01-03-2004, 03:57 PM

When setting a crossover to 80hz, and then using the sub for the LFE channel, are you missing the bass that would be going to the speakers that is below 80hz, or does the LFE channel include this?

If this bass is being missed, would it be logical to use two subs, maybe one in the front left corner for the below 80hz material, and then one in the back right for the LFE?

I know dual subs should usually be placed together, but if they are next to each other and one is doing the LFE and one is doing the below 80hz stuff, wouldn't it sound muddy?

Also, wouldn't making the preamp send a signal to the sub that combines the LFE and below 80hz material make the sound coming from the subwoofer seem not very defined?

Or is the below 80hz material that is being sent to the speakers not very important?

Edward J M · 01-03-2004, 04:06 PM

http://www.hometheaterhifi.com/volum...pril-2000.html

http://www.hometheaterhifi.com/volum...rs-9-2002.html

Read these articles. Then read them again. Really good stuff.

WayneO · 01-03-2004, 04:10 PM

Though the LFE and Front L/R low frequency material does differ many times, usually when you enable a crossover, all the under 80hz material should then be redirected to the LFE, but it can depend on what recevier or pre/proc. you have and would require reading the manual. This doesn't mean it'll be muddy, it may actually sound better with a good sub, letting your amp have cleaner/more power for your mids and highs. Material below 80hz is important and a clean output is just as desireable as any other frequencies.

ChrisWiggles · 01-03-2004, 06:10 PM

First, read those great articles that Ed linked you to.

Quote:

When setting a crossover to 80hz, and then using the sub for the LFE channel, are you missing the bass that would be going to the speakers that is below 80hz, or does the LFE channel include this?

SteveCallas · 01-03-2004, 08:34 PM

Thanks for the explainations, I was unaware that the frontal bass was added to the LFE.

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Lewis Besze · 01-04-2004, 04:02 AM

Quote:

Thanks for the explainations, I was unaware that the frontal bass was added to the LFE.

Not just the front, but any speaker's selected as "small".

dave alan · 01-04-2004, 01:41 PM

It's interesting to me how logical thinking:

["Also, wouldn't making the preamp send a signal to the sub that combines the LFE and below 80 Hz material make the sound coming from the subwoofer seem not very defined?"]

Is wiped away by pointing to an article that, though it contains some useful facts, is rather dated and is by no means the definitive 5.1 audio resource.

The answer to your question is absolutely yes. The single, summed digital bass signal renders impossible the task of properly reintegrating redirected bass into the soundfield from which it's derived, lops off a potentially full range .1 channel at whatever crossover setting is selected and asks an impossible task of a single (or whatever number, if they are all playing the same signal) subwoofer.

This has led to two things. The endless 'music vs movie' sub debate and the design and production of impratically larger and more powerful subs.

The 'musical' sub and the boom channel sub have diverged down 2 seperate paths, each designer claiming that their sub is good at both, yet no one, to date, has seen the logic of combining the 2 in a single system.

EQ should be the last option employed, yet it's become the first option. ('Place the sub in the corner and EQ it flat. Better yet, convert the signal to digital, EQ it to taste for a given format, save settings and store as many preset curves as need be to satisfy all MC sources, convert back to analog and bingo, the ideal, technical acheivement award winning solution')

If that were really the case, I think you'd see plenty of single-driver, 1-way satellite speakers out there getting rave reviews.

ChrisWiggles · 01-04-2004, 03:15 PM

Quote:

This has led to two things. The endless 'music vs movie' sub debate and the
design and production of impratically larger and more powerful subs.

The 'musical' sub and the boom channel sub have diverged down 2 seperate paths,
each designer claiming that their sub is good at both, yet no one, to date, has
seen the logic of combining the 2 in a single system.

Zack_R · 01-04-2004, 03:58 PM

IMO, the validity of the article depends on what receiver / pre-pro you are using.

For example, with my Sony 4ES receiver, the crossover is totally independent of the .1 channel. I can set my speakers crossover at 40 hz. and set the LFE cut at 90 hz and I lose no LFE. LFE is not lopped off nor are the mains speakers now crossed at 90 hz.

I verified this through Avia's LFE 100-20 hz frequency sweep. I set my crossover on all speakers to 40 hz and the LFE at 90 hz. When the Avia tone starts at 100, the LFE from the sub is muted around 10 dbs so and then it kicks in fully at 90 and takes it all the way to 20. I also experimented by putting the center crossover at 120 hz and the surrounds at 150 and left the mains at 40. I then set the LFE cut to 80 hz, played the Avia signal and got the same result. The sub kicks in at 80hz regardless of the crossover setting for the other speakers.

I can't adequately measure the phase effect of using the different crossovers when playing strictly re-directed music bass and what the summing effect constitutes. The only phase issues I may have would be between my mains and my sub if I cross my mains at 80 and my center at 120. But since I don't listen to multi-channel music, the potential phase problem is not a big issue.

For movies, I'd much rather have my less bass capable surrounds and center speaker crossed higher and not subject them to boosted non-LFE bass and live with any potential bass phase issues between 80 and 120 hz.

I took this phase part of the article as being theoretically slanted and may not apply equally in different room / listener settings. In other words, I think you'd have to measure this occurence in a room before determining that there is actually a problem.

SteveCallas · 01-04-2004, 05:23 PM

Dave, would you then agree that two subs, one in front for the redirected bass, and one somewhere else, say in a back corner, would be good for the LFE?

If redirected bass and LFE are sent to a sub, no matter how good or bad a sub it is, the sub would have to try and reproduce two distninct sounds at one time.

Without extended knowledge of how drivers recreate sounds besides them creating pressurized air waves, I wonder if the following example would be true?

If there is an explosion going on on the screen, and the LFE track calls for a frequency that is in the 20-28Hz range for a couple seconds, but the redirected bass is calling for a frequency in the 55-65Hz range at those same couple of seconds, how can the single driver of the sub output both frequencies at the same time without it sounding kind of blah?

Wouldn't this be similar to having one of your speakers recieve two seperate inputs at once? Can drivers reproduce this?