LFE and bass below 80hz (1 Viewer)

[dave alan]

The only pre/pro I'm aware of that allows for mono or stereo RB sub(s), AND a discrete LFE sub, is the Lex MC-12.

Unfortunately, I believe it was configured this way to allow for their proprietary 'Bass Enhance' feature to work properly, and therefore, little is said in the manual about the advantages of a discrete LFE sub system.

At the very least, it lends some proof to what I've been saying for a long while. That is, summing the RB (or, as Lex refers to it, 'derived bass') with the LFE signal alters the end results of reintegration of RB with the sats and, as such, should be kept discrete through playback.

Short of buying the pricey Lex pre/pro, I've decided to design and build an analog version of mono or stereo RB sub(s) + LFE router/processor, and versions thereof.

I will post results when complete, for those interested.

Edward...I was referring to my Dolby Manual where, regarding mixing/monitoring (LFE), it calls for "a 6th or 7th order LP filter at 120 Hz.", by no means a brick wall.

However, after reading your post, I thumbed through to find that it does indeed say that, during encoding, " A
brick wall filter @ 120 Hz. is implemented".

Sorry for the mistake, and thanx for pointing it out.

I was trying to point out that the .1 channel of MC SACD/DVD-A has no such limiter applied as a standard, which fact is not addressed in the BF/Dolby article. Nor does the article address the various effects of combining RB+LFE+10 dB into 1 sub system.

By no means is my intent to dissuade those who 'buy it, place it, EQ it and sit back and enjoy their system'. This is a good thing...for them.

 

[ChrisWiggles]

Dave: I see where keeping all the audio discrete can obviously have it's advantages, especially in making sure any directional bass is coming from the right places, along with sub noises, perhaps rattling, port chuffing, etc, don't screw up the soundspace.

This is why, IDEALLY you'd want a competent sub on EACH channel, or a speaker that really is capable of plumbing the depths of bass.

I don't see how having two subs, one for dedicated LFE, and the other from rerouted bass from the main channels, would help that much. you'd still be getting a mishmash of 5 channels of bass in one sub. Also, placing two subs in different locations is quite hard to pull of, and probably far more degrading(unless you take care and do it right) than sending everything to one sub.

I'm just thinking out loud, though your idea is one I haden't really considered that much.

 

[dave alan]

Chris,

The advantages, as I've tested and documented so far:

1. Above all, you know if and how much LFE content is included in any given source via signal indicator LED and muting the pre/pro while letting only the LFE sub play, which otherwise, you have no idea.

2. You also know if the signal is too hot from the player or pre via clip indicator LED. This is not usually audible, except in very extreme cases, but occurs probably more often than you might think.

3. You can adjust the LFE level independent of the RB, which is not possible if they are summed before the sub(s).

4. Though you are correct in saying that each sub should be able to 'plumb the depths', each sub does not have to be able to reproduce 5 channels of RB PLUS LFE+10 dB at the same time. This significantly expands the design/placement/ parameters governing each sub.

5. Seperate filter/slope options are absolutely necessary for each of the RB and .1 channels of the various MC audio formats that we have now and are soon to come. It's absurd to think that they can somehow be applied seperately and then sum those two signals and send the summed signal to 1 subwoofer system. This is a fairly vast subject of it's own.

6. I have just begun to measure the intermodulation effects of summing a sythesized explosion with the RB from the music soundtrack. Very little info is avalable and I'm no engineer, but I can assure that it's audible.

7. Retaining the entire .1 signal. In fact, in this system, by using a crossover instead of a LP filter, with SACD/DVD-A, the .1 channel is a 6th full range channel, or, allows for a 2-way subwoofer system which is, again, impossible with the summed mono signal system.

8. My HT is by no means optimal for LF reproduction (who's is?), yet I've been able to use simple placement techniques, phase alignment, cascaded filter options and level adjustment to acheive a flat (+/-3 dB) FRC at the primary LP, with no post EQ. Placement is much easier with this system, and IMO, is more a problem of time/phase/filter slope than where the sub sits.

9. Having a musical sub and a movie sub in the same system, each required to do no more than what it's designed to do best, is not only better, there simply is no other way to do it. I would like to think that my 10 cu ft ported sub sounds as good with acoustic bass sources as my sealed sub, but it doesn't. Just the same, I could say that my sealed sub does as well with the LFE/RB of AOTC, but it doesn't.

OTOH, when both are properly connected and setup, I can definitely say that my 'system' does both equally well.

The differences are subtle to huge, depending on the source, your hardware and your prefs. IMHO, this whole hobby is about subtleties, across the entire audio spectrum. The routing scheme/tweaks are not for everyone, but not meant to be.

Still, it's from input like yours that I've gone down this path. I very much appreciate your post. In fact, I've learned more than I could ever say by reading yours and other's posts here for a long while. I visit almost daily, and just read what you all have to say.

I'm just reporting what I think is a fairly significant bit of info.

 

[ChrisWiggles]

I likewise enjoyed reading your posts.

FYI you CAN listen to LFE only if you set all your speakers to large, and unplug them, and listen to just the sub. It should be receiving LFE only.

Also, I'm pretty sure that quite a few receivers can adjust LFE level independantly of overall sub level (lfe plus whatever other channels).

I am also curious as to what equipment you are using?

 

[Zack_R]

I don't have experience with multi-channel music formats so the following deals with HT (movies).

I would think that another way to skin the cat is to use two subs connected normally and placed where you think sounds best.

This should reduce the maximum bass load significantly per sub. I'm gathering that some of the concern with using one sub is with the +10 db LFE on top of the re-directed bass,potentially over taxing the sub. Using two subs should reduce this risk as you are spreading out the workload. I don't think that there are necessarily more bass frequencies in movies versus music but I do agree that bass in movies is typically lower and more dynamic.

I would also think that you want a music sub to at least play strong to 25 hz as there is no way to predict what music is going to present during a movie.

Again with HT, one way I can see using two subs and have one for music and one for LFE is as follows:

Sub A is your LFE sub and is connected to the SW out and placed where you think sounds best. Sub B's amp is connected via main speaker level outs from your receeiver Speaker wire is then run from the sub amp to your left and right mains. You would be using the crossover in your sub's amp. I have a sub amp that has a built in 80 hz crossover.

In this set-up you would set your mains as large and all other speakers as small. This set-up assumes your receiver amp can fully deliver a full range non-LFE signal to the main speakers. The center and surrounds would deliver summed bass to the LFE sub. While this doesn't totally eliminate re-directed bass going to the LFE sub, I'm thinking that there is little bass music coded for the rear surrounds (movies)so you are probably mostly dealing with the center channel's redirected bass.

I'm not endorsing the above combo. It's just a suggestion / idea for people that have two subs but not the other equipment. They can experiment / try this set-up if they are interested in having a sub for re-directed bass and a sub for mostly LFE bass when watching movies.