General Question about using subwoofers with AVR's

  • Thread starter Deleted member 39241
  • Start date
D

Deleted member 39241

Guest
I have been puzzling about this, and wonder what other people think.

If a subwoofer is playing back the .1 LFE channel PLUS the bass below the crossover setting from the speakers that are set to small, at the same time, is that audio compromised?

In an action film, for example, there could be a frenetic scene where there is a lot of .1 LFE audio detail plus a lot of bass audio in the mix for all of the other speakers. Can one sub reproduce all of that audio at exactly the same time without it getting jumbled and detail lost?
 
In short, yes. A subwoofer plays the 10-120 Hz range, but consider a speaker, the mid-range drivers will cover from 80-500/1000Hz range and a tweeter up to at least the 20kHz range. A subwoofer provides the muscle in a system, but it actually gets asked to play back less content than any other speaker.

In addition, the LFE track is largely a replication of sub bass in the main channels anyway, so most of what it plays out is redirected bass, and LFE bass that is identical, so you're not really asking the subwoofer to play more content at all. The only additional content in the LFE channel is what ever bits get added as part of the LFE soundtrack that can only really be properly produced by a subwoofer, and that's the whole point in subwoofer, its what they're designed to do and why they were invented in the first place.
 
Interesting. Thanks for your input.

I get that a driver in a speaker is able to cover a large frequency range, but usually it is only sent audio that has been mixed for that one channel. Whereas a sub connected to an AVR could be being sent audio that has been mixed for multiple channels, all at the same time!

AVRs don't give an option to redirect different bass to different subs though. That would be good for my room as I have one sub at the front, and one sub at the rear, right behind and close to the MLP, and I don't want centre channel content emanating from that sub. So, bass management has got a bit complicated.
 
Sub bass can't be pinpointed by your ears, we just can't detect the source of low frequency sounds. All the directional cues come from the speakers, which is why subwoofers exist and all bass content it produced by a single signal and can be reproduced by a single subwoofer. Adding in a second subwoofer anywhere isn't an issue, even behind you seat, but you do need to take care when setting two subwoofers up to ensure they're working in perfect harmony, and that's harder to do when they're in different positions in the room and at very different distances from your seating position.
 
Yes, so I understand. Unfortunately that theory doesn't work for me in practice. If I have the centre channel set to small and the bass redirected to both subs, I can hear the lower frequencies of dialogue emanating from the rear sub and it sounds very wrong and drives me nuts!

I don't know how you have things configured in your room, but if you have something similar, try putting your hand (gently) on the sub driver when someone with a deep voice is speaking and you will probably feel it vibrating in time to the voice. Not a problem if all of your subs are at the front of the room, but mine are split, one at the front and one at the back.

I have a nice space behind the sofa where I can fit in a decent sized sub and get a fairly decent flat response, possibly helped by a bit of room treatment on the back wall, so I don't want to not have a sub there, but I need to re-think what audio it is playing.

Which also got me thinking if there were any other advantages to separating out the LFE channel audio from the bass redirects from the other speakers.
 
Yes, so I understand. Unfortunately that theory doesn't work for me in practice. If I have the centre channel set to small and the bass redirected to both subs, I can hear the lower frequencies of dialogue emanating from the rear sub and it sounds very wrong and drives me nuts!

I don't know how you have things configured in your room, but if you have something similar, try putting your hand (gently) on the sub driver when someone with a deep voice is speaking and you will probably feel it vibrating in time to the voice. Not a problem if all of your subs are at the front of the room, but mine are split, one at the front and one at the back.

I have a nice space behind the sofa where I can fit in a decent sized sub and get a fairly decent flat response, possibly helped by a bit of room treatment on the back wall, so I don't want to not have a sub there, but I need to re-think what audio it is playing.

Which also got me thinking if there were any other advantages to separating out the LFE channel audio from the bass redirects from the other speakers.

Pardon the pun but it sounds like you've got something setup wrong if you are hearing vocals through the sub since speech frequency range should all be above 80hz?

Jim
 
Pardon the pun but it sounds like you've got something setup wrong if you are hearing vocals through the sub since speech frequency range should all be above 80hz?

Jim
I know. Many people say that, but my experience is that even with the crossover at 80hz, some of the lower octaves of dialogue do bleed through. It's not that you can hear what the people are actually saying from the sub, but the sub is vibrating in time to people's voices, usually deep male voices. Try it!

The other complication is that my AVR has a global crossover for the base layer speakers, and my rear surrounds would ideally be set higher than 80hz.
 
Patrice Congard at Audio Excellence has worked on the problem of using limited range speakers plus a Sub (which also has to handle the LFE).

They include an additional processor and amplification to separate out the LCR Bass from the LFE.

Audio Excellence :: Home Cinema High-end Screen Loudspeakers

Joe
Hurrah! Thanks very much for this Joe, at least I now know that I am not the only person thinking this way :smashin:

My workaround at the moment is to use the BK200 sub at the front of the room to take the high level input for the front left and right speakers, and the low level input for the centre channel via the AVR pre-out.

This leaves the sub at the back doing the LFE channel plus the bass from the atmos and surround speakers.

I do have access to another slimline sub which I could use exclusively for the centre channel, this would free up the low level input on the BK200 so it can be used as a second LFE channel, along with the sub at the back. But I am not sure if this would bring more problems than benefits.

I am about to upgrade the sub at the back, but want to get all of these options decided upon before pushing the 'buy' button.

I think I will just have to try out each option with the equipment I currently have and decide which sounds best.
 
Yes, so I understand. Unfortunately that theory doesn't work for me in practice. If I have the centre channel set to small and the bass redirected to both subs, I can hear the lower frequencies of dialogue emanating from the rear sub and it sounds very wrong and drives me nuts!

I don't know how you have things configured in your room, but if you have something similar, try putting your hand (gently) on the sub driver when someone with a deep voice is speaking and you will probably feel it vibrating in time to the voice. Not a problem if all of your subs are at the front of the room, but mine are split, one at the front and one at the back.

I have a nice space behind the sofa where I can fit in a decent sized sub and get a fairly decent flat response, possibly helped by a bit of room treatment on the back wall, so I don't want to not have a sub there, but I need to re-think what audio it is playing.

Which also got me thinking if there were any other advantages to separating out the LFE channel audio from the bass redirects from the other speakers.
I've played with putting subs at the backs of rooms without issue. Where the centre channel dialogue has low frequency content any sub will play that content. If you can hear voices from that sub, I'd experiment with lowering the crossover on that sub alone.
 
Hi @D1gita1 Good to hear that you have never had an issue, unfortunately, I cannot say the same!

Obviously, the sub will only play the centre channel low frequency content if the centre speaker is set to small, and the sub is configured to take audio from the LFE input. So, my workaround is doing what I need to, so far, so good.

This has confused me:
If you can hear voices from that sub, I'd experiment with lowering the crossover on that sub alone
That's not an option, as I would lose a lot of the LFE channel, and a lot of the bass from the other speakers that are set as small.
 
Hi

That's not an option, as I would lose a lot of the LFE channel, and a lot of the bass from the other speakers that are set as small.
You would need to do it on the subwoofer itself by setting the LPF. I cant remember if the xls200 has this capability. By reducing the frequency that sub extends up to you could experiment with how that sounds in relation to the problem you are experiencing. Essentially you would run the entire system in the traditional manner and remove some of the higher frequencies from the subwoofer directly behind you. To set it up properly however you would need to use an SPL meter and REW, and if you don't have a low pass filter on the rear sub, something like a mini dsp. I'd be interested in the results and in your situation it's certainly something I would play around with.
 
Last edited:
You would need to do it on the subwoofer itself by setting the LPF. I cant remember if the xls200 has this capability. By reducing the frequency that sub extends up to you could experiment with how that sounds in relation to the problem you are experiencing. Essentially you would run the entire system in the traditional manner and remove some of the higher frequencies from the subwoofer directly behind you. To set it up properly however you would need to use an SPL meter and REW, and if you don't have a low pass filter on the rear sub, something like a mini dsp. I'd be interested in the results and in your situation it's certainly something I would play around with.
Hi, as I explained above, in post 9, the BK XLS200 is at the front. I have an MS309W at the rear, which I want to upgrade, but I am holding off on the upgrade whilst I experiment with different bass management options in the room.

I have to say your suggestion is confusing me enormously, or am I misunderstanding you?

You seem to be saying that in order to remove the problematic centre channel content from the rear sub, I massively cut all of the bass going into that sub, so that a huge amount of the LFE channel and the majority of the bass from the surround and atmos speakers below whatever crossover I set for them on the AVR would be completely lost from that sub.

Don't you think that is a bit nuclear?? o_O

Rather than mess up the LFE channel and all of the bass from the surround and atmos speakers, isn't my workaround better, and just remove the centre channel content from the rear sub, and re-direct it to the front sub only?
 
Last edited by a moderator:
Does the rear sub have a built in(variable) crossover control? If so you can use that and "cascade" an extra filter to establish a steeper attenuation above 80hz.

Tom V.
Hi Tom, thanks, yes it does. I've not heard of cascading an extra filter. Would that filter out the LFE channel above 80hz also, as well as the bass redirects from the surround and atmos speakers?

I'm trying to fix the centre channel bass issue without breaking all of the other bass at the same time!
 
Hi Tom, thanks, yes it does. I've not heard of cascading an extra filter. Would that filter out the LFE channel above 80hz also, as well as the bass redirects from the surround and atmos speakers?

I'm trying to fix the centre channel bass issue without breaking all of the other bass at the same time!

It will filter anything being sent to the subwoofer. Remember though you aren't doing anything <80hz all you will be doing it increasing the rate of attenuation(slope) >80hz. I wouldn't expect this to make any audible difference with the LFE channel itself. Measurable? sure. But home audio is ALL about finding the best compromise for each listening environment+personal preference. What you're hearing isn't uncommon at all and the "goto" fix is adding more attenuation as described.

Also, this may have been suggested already but you can always reset the center crossover(in the avr) to 60hz or 70hz instead of 80hz.

Tom V.
 
@Tom @ PSA Good to know that what I am describing isn't uncommon, I'm a bit relieved to hear that!

My AVR is an Arcam AVR550 and has a global crossover for the base layer speakers, and as my surrounds don't go that low, lowering the crossover on the AVR is regrettably not an option. What is even more annoying is that the Arcam is supposed to send the centre channel bass to the front mains, if they are set to large, but it isn't, it's sending it to the subs. I have reported this to Arcam. If they fix it, that would be a good solution as I have the fronts connected to the BK 200 via high level.

Is it common for a small subwoofer at the front of the room to only be used to take the bass from the front LCR speakers which are set to large? That is what I am doing now and it seems okay.

What I need to decide is whether to leave it like that and get a bigger sub at the rear to use for the LFE channel, or, to get a second BK200 for the rear and use them both for the LFE channel, maybe via a mixer / minidsp to add the centre channel in to the front sub only.

Or, even use this other slimline sub to do the bass for the centre channel and then have the 2 other subs doing the LFE.

This brings me back to my original question, of whether it is better to have multiple subs playing the same audio to even out the room response, but then battle with the difficulties of phase and timing.

Or, have the different subs playing different audio, which is starting to sound like an easier option, and my logic is thinking that it might even sound better, in terms of not feeding multiple channels of audio into essentially one speaker and asking it to play them all at the same time.

I'm very open to suggestions and guidance on this though! The room is acoustically not too bad, and approx 6m x 4.5m.
 
Hi, as I explained above, in post 9, the BK XLS200 is at the front. I have an MS309W at the rear, which I want to upgrade, but I am holding off on the upgrade whilst I experiment with different bass management options in the room.

I have to say your suggestion is confusing me enormously, or am I misunderstanding you?

You seem to be saying that in order to remove the problematic centre channel content from the rear sub, I massively cut all of the bass going into that sub, so that a huge amount of the LFE channel and the majority of the bass from the surround and atmos speakers below whatever crossover I set for them on the AVR would be completely lost from that sub.

Don't you think that is a bit nuclear?? o_O

Rather than mess up the LFE channel and all of the bass from the surround and atmos speakers, isn't my workaround better, and just remove the centre channel content from the rear sub, and re-direct it to the front sub only?
Honestly I think the problem is that your rear sub is an MS sub. The suggestion I've made wouldn't remove much LFE content and would only remove upp frequencies from the rear sub, but would ensure you remove the problematic upper frequencies. Toms suggestion is a good one as well. Filters are stackable and employing the crossover on the sub and the AVR will increase the cut off slope of the upper frequencies to the rear sub. In your position I'd experiment with both. I'm not overly keen on the method you have used personally, but if it works for you then that's all that really matters. I'm also not the biggest fan of using really steep crossover slopes, but again if it's the lesser of two evils and it works then it's a possible solution.

When you have a problem like yours then you need to experiment and explore the solution.
The BK is likely the better sub, so another option might be to swap your subs around and see if there is any difference just as an information gathering excersise. One other question that I don't think has been covered, did you set up your two subs with an SPL meter before running any EQ, ensuring they individually measured the same SPL at the listening position?
 
Last edited:
Hi @D1gita1 thanks for your input, I'll address your questions / points one at a time.

I think the problem is that your rear sub is an MS sub.
The BK XLS200 sub behaves in exactly the same way.
The suggestion I've made wouldn't remove much LFE content and would only remove upp frequencies from the rear sub, but would ensure you remove the problematic upper frequencies. Toms suggestion is a good one as well. Filters are stackable and employing the crossover on the sub and the AVR will increase the cut off slope of the upper frequencies to the rear sub.
The things is, removing upper frequencies from the rear sub is the opposite of what I want to do. I am going to change the rear sub for one that is more capable in the upper frequencies, as I want to raise the crossover setting for my four rear speakers, as they don't go very low. They are also located behind the sofa and very close to the rear sub, so it would work very well to have that rear sub picking up the bass from those as they roll off. Also, I definitely want to enjoy the full volume, full frequency bandwidth of the LFE channel, ie up to 120hz.
I'm not overly keen on the method you have used personally, but if it works for you then that's all that really matters.
Interesting, so you have you tried it? It would be good to hear about those set-ups and in what way it went wrong, or that you didn't like it, that would be helpful.

Have you read the article that Joe linked to above? This bit is interesting:

in a production studio during the downmixing, the LFE channel is mixed separately from the others. This means that it is not due to be phase coherent with the L,C,R channels. As a result, playing back the L,C,R low frequency content mixed with the LFE is not a good idea.

I might have accidentally hit upon something that could improve my system more than I thought!

The BK is likely the better sub, so another option might be to swap your subs around and see if there is any difference just as an information gathering excersise
Yep, done that, The BK works really well in the rear position, lots of bass extension in the upper and lower frequencies, and a much flatter curve than the MS sub. The reason that I got the BK200 was because of it's size and features. It just fits into a small space at the front of the room, and I use if for stereo music playback to support the Kef R300's, that part of it works really well and sounds lush, I don't even use any EQ for music.
One other question that I don't think has been covered, did you set up your two subs with an SPL meter before running any EQ, ensuring they individually measured the same SPL at the listening position?
Indeed I did. I am all set-up with REW and a UMIK-1 and Dirac version 2, so I have good knowledge of what is going on in my room.
 
Last edited by a moderator:
You seem to have a good handle on what you're doing and what you want to achieve. I've played around with more subwoofer combinations in more rooms/scenarios than you're likely to believe and covered just about every conceivable scenario.

I'd be interested in seeing the 2 REW graphs for your subwoofers. If you have them available, a graph of the front sub, one of the rear sub, and a combined repose all overlayed would be useful. If you can measure your front sub only at 80dB then measure your rear sub without changing the level, and then the same for the combined responses again without changing the level, it will give a good view of what's going on in that room. If you have the harmonic distortion figures as well that would also be interesting to see.

With respect to the mixing of the LFE and the normal channels, I'm not sure I would completely agree with the phase misalignment assessment.
 
Of course I believe you! :)

Have you tried the set-up that I am having a go at here? That is a separate sub located near the LCR channels, just taking the bass from those three speakers, and those speakers set as large in the AVR. Then a separate sub(s) located elsewhere for the LFE channel and the bass re-directs from the surround and atmos speakers?

I have a whole ton of measurements saved in various places, I'll dig some out and upload them. I don't have time to take new ones as per your exact specifications, but I am sure the ones I have already will give you an idea. Although the curves are very different depending where on the sofa that I situate the microphone. And, remember I use Dirac V2 to correct.
 
Here are a couple of screens @D1gita1
 

Attachments

  • bk200 at front.PNG
    bk200 at front.PNG
    186.9 KB · Views: 63
  • MS 309W at rear.PNG
    MS 309W at rear.PNG
    199.5 KB · Views: 69
I've probably not done your exact setup scenario, but I did once have a Rel Q100e running high-level connection with an SVS PB13U running LFE with the subs split about the room. I also experimented adding in a pair of MK MX125 subs in the mix as well so was running 4 subs at once point at 3 different locations. I've played with a with a whole bunch of other configurations over the years as well. Including running floor standing front with high-level connections but LFE running on other subs.

Your REW graph above doesn't really tell me anything, I would need to see the individual overlays of the 2 subs and the combined ones, all run with the mic at the same position and the levels untouched between the measurements. I would also change your graph limits and ignore anything below 20Hz as your subs just won't be of use down there and you dont need to worry about sub 20Hz content.

It does look at through your target setting needs a little work in Dirac though as you have areas where your target appears a though it would require more than 6dB boost, and really that's too much and will rob you of dynamics. Theres a good series of Dirac videos by Arcam available here.
 
Last edited:
@D1gita1 Okay, so you have never tried using a sub, located at the front of the room just for bass for the LCR channels then? I thought you had as you said earlier that you were not keen on it. So is it just the idea of it that you are not keen on? You should give it a go, you might find you like it, I could have hit upon a new trend here!

What is it that you are looking for in the graphs that the ones I posted didn't tell you? I might know the information anyway as I have measured every possible combination of everything in that room.

Yes, you are preaching to the converted with the Dirac videos. I have seen them all. They are pretty good to get you going, but trial and error is where it's at, and I've certainly put the hours in.

I'm aware of over stretching the MS309W, remember it is a very old sub that I am on the cusp of replacing, so I'm just squeezing out of it what I can whilst I decide what to buy next.

What set up do you have now, I remember you wrote a review of the Arcam 850, do you still have that? I think you said you were struggling a bit with Dirac, did you try version 2 yet?
 
Last edited by a moderator:
Sorry, got bored halfway through the thread so you may have eventually realised this but just to say LFE is a separate channel that only goes to the sub so not sure where you're getting hung up on losing any of it by setting anything to large.

If you set the centre to large nothing will go to the sub from that channel so all you'd lose is anything in the centre channel below the range that the speaker can handle, no LFE. If you want to be really weird you could then connect a second sub across the centre terminals and use the hi level filter on the sub to balance it into the system.
 

The latest video from AVForums

TV Buying Guide - Which TV Is Best For You?
Subscribe to our YouTube channel
Back
Top Bottom