Setting the center subwoofer to mono or as LFE?

[danielb]

How should the subwoofer be configured in a 5.1 system, as mono or as LFE?

- I have a 5.1 system with front speakers set to large

- Center and surround speakers set to small.



Measurement procedure/settings:

- I have selected the subwoofer as the center subwoofer and set it to mono

- then measured each speaker individually (center and surrounds without subwoofer)
- Created the user filters for all speakers and imported them into the RMC-1L.



If I now carry out a control measurement with the subwoofer activated, everything looks not bad as long as the subwoofer is defined as mono.

If I now configure the subwoofer as LFE, the center and surrounds show almost the uncorrected front speaker(s) during the measurement. As an example here on the LS, the behavior with Center and RS is identical


Picture:

1. Left front - uncorrected

2. Left front - corrected

3. Left surround - Subwoofer set as mono

4. Left surround - Subwoofer set as LFE



What am I doing wrong, or is wrong, or am I interpreting wrong?

[ttocs]

Dec 11, 2023 8:41:26 GMT -5 danielb said:

How should the subwoofer be configured in a 5.1 system, as mono or as LFE?
- I have a 5.1 system with front speakers set to large
- Center and surround speakers set to small.

With your system speaker channels setup the way you describe, here is what happens with the Center Sub setup with each setting.

Center Sub: MONO
This will send all bass below the crossover settings for the Small Channels to the Center Subwoofer Channel.
This will also send the .1 LFE Channel bass to the Center Subwoofer Channel.

Center Sub: LFE
This will send all bass below the crossover settings for the Small Channels to the LARGE FRONTS.
This will ONLY send the .1 LFE Channel bass to the Center Subwoofer Channel.

[ttocs]

Dec 11, 2023 8:41:26 GMT -5 danielb said:

Measurement procedure/settings:

- I have selected the subwoofer as the center subwoofer and set it to mono

- then measured each speaker individually (center and surrounds without subwoofer)
- Created the user filters for all speakers and imported them into the RMC-1L.

If I now carry out a control measurement with the subwoofer activated, everything looks not bad as long as the subwoofer is defined as mono.

If I now configure the subwoofer as LFE, the center and surrounds show almost the uncorrected front speaker(s) during the measurement. As an example here on the LS, the behavior with Center and RS is identical


Picture:

1. Left front - uncorrected

2. Left front - corrected

3. Left surround - Subwoofer set as mono

4. Left surround - Subwoofer set as LFE

View Attachment

What am I doing wrong, or is wrong, or am I interpreting wrong?

When Center Sub is LFE you can see that the trace follows pretty well with the Left Front Large, which is what is supplying half the Bass Management Bass for the Small Channels. Both Large Fronts supply the BM when the Center Sub is setup as LFE.

What I need to see is just the LFE Channel in REW, which will always be a subwoofer no matter how we setup our subwoofer channels. But here's the kicker, when the sub channel is setup as MONO the XO (crossover) will limit the frequency range that shows up in the plot. But when the sub channel is setup as LFE, then the frequency range is limited by the LFE spec.

So Trace #3 is showing the subwoofer and LS. Check by measuring LFE in REW to see how it compares with #3. It should look similar, but having more info about your system would help, like model of speaker and XO setting.

[danielb]

Dec 11, 2023 9:21:40 GMT -5 ttocs said:

Center Sub: MONO
This will send all bass below the crossover settings for the Small Channels to the Center Subwoofer Channel.
This will also send the .1 LFE Channel bass to the Center Subwoofer Channel.

Center Sub: LFE
This will send all bass below the crossover settings for the Small Channels to the LARGE FRONTS.
This will ONLY send the .1 LFE Channel bass to the Center Subwoofer Channel.

Yes, I agree with that. But why is it that the user filters that are set on the large fronts are not applied/used - but ignored?

I think that's what the measurement shows - see image.



The range between 25 and 40hz should look like in curve 2, not like in curve 4 - at least that's what I would expect.

[danielb]

Dec 11, 2023 9:37:54 GMT -5 ttocs said:

When Center Sub is LFE you can see that the trace follows pretty well with the Left Front Large, which is what is supplying half the Bass Management Bass for the Small Channels. Both Large Fronts supply the BM when the Center Sub is setup as LFE.

What I need to see is just the LFE Channel in REW, which will always be a subwoofer no matter how we setup our subwoofer channels. But here's the kicker, when the sub channel is setup as MONO the XO (crossover) will limit the frequency range that shows up in the plot. But when the sub channel is setup as LFE, then the frequency range is limited by the LFE spec.

So Trace #3 is showing the subwoofer and LS. Check by measuring LFE in REW to see how it compares with #3. It should look similar, but having more info about your system would help, like model of speaker and XO setting.

The speakers are:
- Front: B&W Nautilus 802
- Center: B&W Nautilus HTM1
- Surrounds: B&W Nautilus 805
- Subwoofer: Velodyne DD-12

XO: 80Hz/24dB

[ttocs]

Dec 11, 2023 9:41:19 GMT -5 danielb said:

Dec 11, 2023 9:21:40 GMT -5 ttocs said:

Center Sub: MONO
This will send all bass below the crossover settings for the Small Channels to the Center Subwoofer Channel.
This will also send the .1 LFE Channel bass to the Center Subwoofer Channel.

Center Sub: LFE
This will send all bass below the crossover settings for the Small Channels to the LARGE FRONTS.
This will ONLY send the .1 LFE Channel bass to the Center Subwoofer Channel.

Yes, I agree with that. But why is it that the user filters that are set on the large fronts are not applied/used - but ignored?

I think that's what the measurement shows - see image.

The range between 25 and 40hz should look like in curve 2, not like in curve 4 - at least that's what I would expect.

To know more you will need to Measure L+R in REW, then measure LS again, back to back. The BM for LS should look similar to L+R when Center Sub LFE.

[KeithL]

I haven't been following this closely but I'm going to interject one or two (possibly) useful comments anyway...

Mainly, when you have two or more speakers making the same bass, like a sub AND large fronts, they ALL interact with each other and the room.
So you have three sources, each of which can have room interactions, and each of which can interact with one or more of the others...
(If you recall... one of the main benefits of having a single sub was avoiding so many complex interactions... which is still a thing.)
This means that you need to take a lot more measurements and average them because, with all those interactions, there are potentially a LOT more "local nulls" and "local peaks".
(This is why you would definitely want to be taking electrical measurements rather than in-room microphone measurements if you want to know what the filters are actually doing.)

Dec 11, 2023 9:37:54 GMT -5 ttocs said:

Dec 11, 2023 8:41:26 GMT -5 danielb said:

Measurement procedure/settings:

- I have selected the subwoofer as the center subwoofer and set it to mono

- then measured each speaker individually (center and surrounds without subwoofer)
- Created the user filters for all speakers and imported them into the RMC-1L.

If I now carry out a control measurement with the subwoofer activated, everything looks not bad as long as the subwoofer is defined as mono.

If I now configure the subwoofer as LFE, the center and surrounds show almost the uncorrected front speaker(s) during the measurement. As an example here on the LS, the behavior with Center and RS is identical


Picture:

1. Left front - uncorrected

2. Left front - corrected

3. Left surround - Subwoofer set as mono

4. Left surround - Subwoofer set as LFE

View Attachment

What am I doing wrong, or is wrong, or am I interpreting wrong?

When Center Sub is LFE you can see that the trace follows pretty well with the Left Front Large, which is what is supplying half the Bass Management Bass for the Small Channels. Both Large Fronts supply the BM when the Center Sub is setup as LFE.

What I need to see is just the LFE Channel in REW, which will always be a subwoofer no matter how we setup our subwoofer channels. But here's the kicker, when the sub channel is setup as MONO the XO (crossover) will limit the frequency range that shows up in the plot. But when the sub channel is setup as LFE, then the frequency range is limited by the LFE spec.

So Trace #3 is showing the subwoofer and LS. Check by measuring LFE in REW to see how it compares with #3. It should look similar, but having more info about your system would help, like model of speaker and XO setting.

[ttocs]

Dec 11, 2023 12:22:29 GMT -5 KeithL said:

I haven't been following this closely but I'm going to interject one or two (possibly) useful comments anyway...

Mainly, when you have two or more speakers making the same bass, like a sub AND large fronts, they ALL interact with each other and the room.
So you have three sources, each of which can have room interactions, and each of which can interact with one or more of the others...

Let's look at something here Keith.

When the Center Sub is setup as LFE, it will only produce the signal from the .1 LFE channel, IF one is present. ALL of the BM signals will flow to the two Large Fronts. So the bass is being produced by the two Large Fronts and whatever is being made by the LS below the XO as it rolls off. So YES, there are THREE speakers making bass together but none of these three is a subwoofer channel.

But, you are absolutely correct that any and all speakers involved in producing a signal must be investigated. It's the only way to track down the interaction(s) causing summing or nulling.

When I get a null, I invert the phase of a speaker to see how the null is affected, if at all. This is just one tool to use in diagnosing what's going on.

Another very useful tool is REW's Alignment Tool. Setup every speaker channel as Large and then measure each individual channel, and measure each individual subwoofer output, but make certain that no other channel is active other than the single output being measured. Then use the Alignment Tool to make new traces by combining pairs of traces, one pair of traces at a time. This tool is so amazingly accurate!! Can't stress this enough! This will show interactions between two or more speakers very easily.

[danielb]

Dec 11, 2023 10:35:46 GMT -5 ttocs said:

To know more you will need to Measure L+R in REW, then measure LS again, back to back. The BM for LS should look similar to L+R when Center Sub LFE.

You're right :-)

1. left + right front
2. LS + Sub as LFE
3. left front
4. LS + Sub as mono


If only the graph were considered, which would be the "better" variant, sub as mono or as LFE?
The listening test is still pending.

An additional question, does the mono/LFE setting also influence the measurement or correction behavior of dirac?

[ttocs]

Dec 12, 2023 10:37:45 GMT -5 danielb said:

Dec 11, 2023 10:35:46 GMT -5 ttocs said:

To know more you will need to Measure L+R in REW, then measure LS again, back to back. The BM for LS should look similar to L+R when Center Sub LFE.

You're right :-)

1. left + right front
2. LS + Sub as LFE
3. left front
4. LS + Sub as mono

If only the graph were considered, which would be the "better" variant, sub as mono or as LFE?
The listening test is still pending.

An additional question, does the mono/LFE setting also influence the measurement or correction behavior of dirac?

Well, with Center Sub MONO the level is down a bit from the LS level once it's out of range of the impact of the XO, and then it drops off below about 35Hz. So I'd use LFE as the setting for Center Sub and let the BM to to the Large Fronts, this would be a light rise in level from the nominal level of the LS and would be close enough.

The settings of LFE/MONO do not affect how Dirac does correction.

[danielb]

Dec 12, 2023 11:00:45 GMT -5 ttocs said:

Well, with Center Sub MONO the level is down a bit from the LS level once it's out of range of the impact of the XO, and then it drops off below about 35Hz. So I'd use LFE as the setting for Center Sub and let the BM to to the Large Fronts, this would be a light rise in level from the nominal level of the LS and would be close enough.

The settings of LFE/MONO do not affect how Dirac does correction.

Thank you very much for your answers! I have learned a lot.

[danielb]

Dec 12, 2023 11:00:45 GMT -5 ttocs said:

.... this would be a light rise in level from the nominal level of the LS and would be close enough.

This can possibly be corrected. I will test/measure it as soon as possible. From User Manual

LFE Level
The LFE Level control allows you to adjust the level for the LFE channel for all inputs from 0 dB to -20 dB in 0.5 dB increments.

[ttocs]

Dec 12, 2023 13:02:50 GMT -5 danielb said:

Dec 12, 2023 11:00:45 GMT -5 ttocs said:

.... this would be a light rise in level from the nominal level of the LS and would be close enough.

This can possibly be corrected. I will test/measure it as soon as possible. From User Manual

LFE Level
The LFE Level control allows you to adjust the level for the LFE channel for all inputs from 0 dB to -20 dB in 0.5 dB increments.

Myself and another Lounge member both have experience with Large Fronts for BM and Center Sub for LFE, there have been others but I'm not sure if they still use this setup. I'm currently using it, but I've gone back and forth with it over the last few years.

Each channel can be corrected, no issue. It's how it's put back together that can have some interesting results when using the Large Fronts for BM. The BM will not be able to be adjusted SEPARATELY. Depending on your main speakers, you could end up with +3dB of BM due to your Large Fronts summing the BM, so this would be at a higher level than your Small Channels. You could adjust the small channels up by the same amount, but then the fronts would be at a lower level than the small channels. Then you could raise the level for the fronts and be right back where you started with +3dB of BM, but this would then mean that the LFE would only be at +7dB vs the rest of the system. Never ending spiral.

The way it would look in REW is like this,
LFE = +10dB
BM in Lg Fronts = +3dB (This is due to summing and cannot be adjusted away.)
Each Large Front and each Small Channel = 0dB

This isn't objectionable to me in my system even though I actually get closer to +4dB BM in my Large Fronts (every system and room are unique). Since it just affects the small channels it's no big deal to me.

[danielb]

Dec 12, 2023 13:34:24 GMT -5 ttocs said:

Myself and another Lounge member both have experience with Large Fronts for BM and Center Sub for LFE, there have been others but I'm not sure if they still use this setup. I'm currently using it, but I've gone back and forth with it over the last few years.

Each channel can be corrected, no issue. It's how it's put back together that can have some interesting results when using the Large Fronts for BM. The BM will not be able to be adjusted SEPARATELY. Depending on your main speakers, you could end up with +3dB of BM due to your Large Fronts summing the BM, so this would be at a higher level than your Small Channels. You could adjust the small channels up by the same amount, but then the fronts would be at a lower level than the small channels. Then you could raise the level for the fronts and be right back where you started with +3dB of BM, but this would then mean that the LFE would only be at +7dB vs the rest of the system. Never ending spiral.

The way it would look in REW is like this,
LFE = +10dB
BM in Lg Fronts = +3dB (This is due to summing and cannot be adjusted away.)
Each Large Front and each Small Channel = 0dB

This isn't objectionable to me in my system even though I actually get closer to +4dB BM in my Large Fronts (every system and room are unique). Since it just affects the small channels it's no big deal to me.

I have now measured and tried a lot, the new version of REW has also helped to achieve better results (and filters).
Then I skimmed the thread "G3P Elevated BM & LFE Issue". This and the new measurement results have now led me to abandon LFE and set the subwoofer as mono again.

1. left surround - REW, subwoofer as LFE
2. left surround - REW, subwoofer as Mono
3. left surround - Dirac (as a comparison)

Red lines - REW, left and right speaker (as reference)

Attachments:

[Lsc]

For 5.1 as you said, mono is the right choice.