Digital mono summing for Subwoofer?

[revyth]

Hey guys, at the moment my setup consists of:
• Laptop + Ableton
• RME UCX audio interface
• Yamaha DXS18XLF subwoofer
• Two Yamaha DZR12 tops

For my first live performance, I used a basic configuration: Ableton’s stereo signal goes out via outputs 1/2 of the audio interface, then through two balanced cables to the subwoofer. From the subwoofer (set to THRU mode to keep independent volume control), the signal is sent via two more balanced cables to the tops. I set the crossover at 100 Hz on both the subwoofer and the tops. No complaints with this setup—everything sounded great.

However, I was wondering if I could do the following: instead of sending separate L and R signals to the subwoofer, I could first sum them to mono in Ableton (for example, by enabling mono mode on an Utility plugin in a stereo track) and send the summed mono signal from one output of the audio interface to the subwoofer.

There are two reasons why I’d like to do this:

• I would use only one cable instead of two to connect the subwoofer.

• I could control the entire subwoofer volume with a single knob instead of two (which I found a bit inconvenient).

For the tops, I would use two additional outputs of the audio interface to send the unaltered L and R signals separately. The crossover settings would remain at 100 Hz on both the subwoofer and the tops.

What do you think about this solution? Is there any difference between summing to mono in Ableton before sending the signal to the subwoofer versus letting the sub handle the summing internally? Anything else I might not be considering?

[AlecSp]

Not sure why you didn't just try it - you know how it would be set up.

One of my frustrations with people in this game is that they don't seem to be interested in learning by experimentation which, as long as you're not doing anything actively dangerous, is the best way to learn through experience.

[revyth]

Not sure why you didn't just try it - you know how it would be set up.

One of my frustrations with people in this game is that they don't seem to be interested in learning by experimentation which, as long as you're not doing anything actively dangerous, is the best way to learn through experience.

I would love to, but it is impossible to experiment with a system like this in my home at proper volumes. I can usually experiment a bit before the live event directly at the place, but it is helpful to know from more experienced people if what I am trying to do makes sense or it is a waste of time

[Aled Hughes]

You could… but why do you need control over what’s sent the subwoofer?

A sub should be properly calibrated to be an integrated part of your monitoring system- you shouldn’t need to adjust its level after this, same way as you don’t turn the volume of your tweeters up and down! It should be viewed as one system that works together.

If you start adjusting the sub volume when mixing, you’re just turning the bass up in your monitoring system, not the track itself. If the track needs more bass, then turn the bass up, but leave the sub alone!

This article is quite old - https://www.soundonsound.com/techniques ... -subwoofer

I’m almost certain I’ve something more recent by Hugh Robjohns, but I can’t find it.

[Aled Hughes]

My apologies, just noticed that you’re talking about a live performance.

To me, the point still stands though - the sub is part of a larger system that should be set up to give an accurate response over the whole frequency spectrum.

Having said that, there is a trend for ‘aux fed subs’ in live systems, which sounds a bit silly to me, but some people like it! That in essence gives control over what’s sent independently to sub - rather more like an LFE channel in TV/film work, and closer to what you’re describing.

To me it still makes more sense to treat the sub/tops as one integrated system, and adjust your mix balances at source, but go ahead and try!

Aled

[Drew Stephenson]

I think you may be misunderstanding the situation slightly Aled, we're talking live sound here not studio monitoring. And if setting up in a room with compromised acoustics and a less-than-ideal option for sub positioning then having a bit of separate control might be useful.

I think Hugh did a Q&A answer in the mag on subs a bit more recently as well.

EDIT - crossed in the ether!

[Murray B]

I don't know the capabilities for Ableton's routing options, and I'm not sure if this is actually helpful, but having typed all of the below I'm posting it anyway

If you could do a post fader send in Ableton routed to one of the outputs, you might not need to do and overall left right summing and have a separate level control for the sub.

You could also then choose what you want to send to the sub if there are some sources you don't sending to the subs - one of the attractions of the subs on aux send idea.

I don't see why mono sum would cause you significant problems, unless it's a very wide stereo instrument - they can sometime sound a bit strange or even disappear when you sum them to mono - a harsh lesson I learnt when checking mono compatibly for tune I made.

You might be able to test this at home at low volume - or use some headphones to monitor the various output paths to check for any potential problems. As to whether it's worth the effort - there are arguments for and against aux fed subs all over the internet.

It seems like main reasons you want to do this set is so you can use one less cable and have real time influence over the sub level? I'm not sure how would you judge if the sub level is right from the performance position and if you are stood in an unhelpful place with the room modes then you could end up making very ill informed choices. It's a job probably best done in a sound check walking the room, where you could just turn down the sub on the back of the cab.

If you want to test for sure at volume - hire a rehearsal space for a couple of hours and have an experiment. A couple of hours messing at volume would probably help you work out the best plan for you.

[revyth]

I don't know the capabilities for Ableton's routing options, and I'm not sure if this is actually helpful, but having typed all of the below I'm posting it anyway

If you could do a post fader send in Ableton routed to one of the outputs, you might not need to do and overall left right summing and have a separate level control for the sub.

[...]

Good points, thank you!
Yes it is defintely possible to have a mono post-send in Ableton, it is one way of doing it. I searched around for aux fed sub and you are right, what I am trying to do is basically it but the difference is that I am trying to do it directly from the source (Ableton) instead from the PA mixer. But at least I see that this idea makes sense, so I would experiment with it.

[revyth]

You could… but why do you need control over what’s sent the subwoofer?

A sub should be properly calibrated to be an integrated part of your monitoring system- you shouldn’t need to adjust its level after this, same way as you don’t turn the volume of your tweeters up and down! It should be viewed as one system that works together.

If you start adjusting the sub volume when mixing, you’re just turning the bass up in your monitoring system, not the track itself. If the track needs more bass, then turn the bass up, but leave the sub alone!

This article is quite old - https://www.soundonsound.com/techniques ... -subwoofer

I’m almost certain I’ve something more recent by Hugh Robjohns, but I can’t find it.

Yeah that is what was confusing me a bit, consider sub+tops as a single system or as separate components that you can control indipendently during the show. I guess there are different schools of thought about it. I am still considering which one to choose

[Murray B]

Yeah that is what was confusing me a bit, consider sub+tops as a single system or as separate components that you can control indipendently during the show. I guess there are different schools of thought about it. I am still considering which one to choose

Mixing individual instruments / stems in the show and using the channel eq as an effect- all good

Changing the fundamental balance of the PA system during the show? - I think that's a bad plan.

Edit to add - have a closer look at how subs on aux is used in live sound.

[Sam Spoons]

This article explains the benefits... https://www.prosoundweb.com/a-detailed- ... chnique/3/

[revyth]

This article explains the benefits... https://www.prosoundweb.com/a-detailed- ... chnique/3/

Very informative, thanks!

[Dave Rowles]

I get why "aux fed subs" is a thing, and for me it's all genre and sound design dependant. I think for 70% of shows, it's of no benefit. A further 10% it's nice to play with, and then maybe 20% of show it's actually worth the effort.

You can do it, but do you have a sound engineer with you? If you're running this from a performer perspective then I worry about over complicating things.

[resistorman]

Sub on aux fan here, no reason to send vocals and most guitars to the subs. I like the control and headroom, though I'm not a stickler, HPF filters will do the job on a "standard" setup just fine.

[revyth]

You could… but why do you need control over what’s sent the subwoofer?

A sub should be properly calibrated to be an integrated part of your monitoring system- you shouldn’t need to adjust its level after this, same way as you don’t turn the volume of your tweeters up and down! It should be viewed as one system that works together.

If you start adjusting the sub volume when mixing, you’re just turning the bass up in your monitoring system, not the track itself. If the track needs more bass, then turn the bass up, but leave the sub alone!

This article is quite old - https://www.soundonsound.com/techniques ... -subwoofer

I’m almost certain I’ve something more recent by Hugh Robjohns, but I can’t find it.

Thinking it over, I’d like to give a more detailed explanation of why I decided to have independent volume control for the subwoofer and tops.

The first time I was able to test the system at high volumes, I had connected the audio interface to the sub (2 XLR cables for the L and R channels) and from the sub, the DSP outputs of both channels to the tops. By using the DSP outputs, the tops receive the signal with the crossover applied by the sub, and in addition, the volume they receive also depends on the level set on the corresponding channel of the sub.

What I noticed was that, when setting the tops volume to unity, I wasn’t able to push them to their maximum because the subwoofer would saturate first (the limiter LED would light up). Essentially, even though the tops still had some headroom, I couldn’t send them a stronger signal because the subwoofer was already at saturation (and since the sub’s channel volume also controls the tops when working in DSP mode, I couldn’t increase their volume independently). The only way to further push the tops would have been to turn their gain knob past unity, but I thought (perhaps mistakenly?) that doing so might degrade the signal quality.

So I told myself: since they’re both Yamaha and designed to work together, I’ll set the crossover independently on both the sub and tops at 100 Hz and set the sub’s output mode to THRU (unprocessed signal). This way, I can push the tops to their maximum (always set to unity) by sending a stronger signal from the audio interface (or mixer) while managing the sub independently.

Not sure if this all makes sense to you

[AlecSp]

What I noticed was that, when setting the tops volume to unity, I wasn’t able to push them to their maximum because the subwoofer would saturate first (the limiter LED would light up).

The root cause of your percieved problem is having insufficient rig for the gig.

While the subs and tops in a "matched" rig should typically work well together, a lot will depend on what you're trying to do with them. If you're up towards max output, genres like EDM or reggae will *need* additional sub output, which may well be by adding more subs (or, better still, upgrading the kit)

The only way to further push the tops would have been to turn their gain knob past unity, but I thought (perhaps mistakenly?) that doing so might degrade the signal quality.

Why would you think that? As long as you don't turn them up so far that you run out of headroom on the tops, there's no problem.

This approach is the far simpler way to achieve what you're describing. Just be aware that, by drinving the tops higher, you'll have relatively less sub in the overall mix. But, given that your speaker setup sounds as if it's not capable of producing the overall SPL you want, it's a compromise that may get you where you need to be.

Ultimately, just remember that, however much you'd like to, you can't overcome the rules of physics.

[Sam Spoons]

Reading your last post it appears you are missing the actual benefit of aux fed subs which is not to give you separate volume control over the subs but to allow you to not send channels which don't have any wanted LF content to the subs in the first place. So if you don't have multiple live mics on vocals or instruments which don't have any LF there is no real benefit.

[Dave Rowles]

The root cause of your percieved problem is having insufficient rig for the gig.

......

Ultimately, just remember that, however much you'd like to, you can't overcome the rules of physics.

Quoted for emphasis. You want to run the tops hotter so you've got more level on the tops you can do that without any problems. If you don't hit the limiters on the speakers then go as high as you want.

Sub on aux fan here, no reason to send vocals and most guitars to the subs. I like the control and headroom, though I'm not a stickler, HPF filters will do the job on a "standard" setup just fine.

I understand and if you're using the subs effectively as an FX then it can work well. I've tried it both ways on large systems and for me it made no difference to the sound at all.

[Hugh Robjohns]

Reading your last post it appears you are missing the actual benefit of aux fed subs which is not to give you separate volume control over the subs but to allow you to not send channels which don't have any wanted LF content to the subs in the first place.

How is this a benefit that can't be equalled by simply high-pass 'bracket' filtering those sources that don't need sub support?

[Sam Spoons]

That is how I always used to deal with it but there is a school of thought that says it's better to simply keep any sources that don't need LF reinforcement out of the subs completely, the argument being that even with channel HPFs a certain amount of unwanted LF could get through.

We tried it a couple of times and I can't say I heard any useful difference but he OP seems committed to trying it but has only considered the ability to adjust the volume of the subs independently of the tops which most of the replies suggest is a bad idea.

[resistorman]

How is this a benefit that can't be equalled by simply high-pass 'bracket' filtering those sources that don't need sub support?

I feel like I can more effectively push the low end of the tops and granularly tailor the amount (if any) of sub content of things like keyboards and electric guitars. I'm usually working with small to medium systems in a hurried setup at imperfect sounding venues In any case, I'm happy to work both ways.

[revyth]

What I noticed was that, when setting the tops volume to unity, I wasn’t able to push them to their maximum because the subwoofer would saturate first (the limiter LED would light up).

The root cause of your percieved problem is having insufficient rig for the gig.

While the subs and tops in a "matched" rig should typically work well together, a lot will depend on what you're trying to do with them. If you're up towards max output, genres like EDM or reggae will *need* additional sub output, which may well be by adding more subs (or, better still, upgrading the kit)

The only way to further push the tops would have been to turn their gain knob past unity, but I thought (perhaps mistakenly?) that doing so might degrade the signal quality.

Why would you think that? As long as you don't turn them up so far that you run out of headroom on the tops, there's no problem.

This approach is the far simpler way to achieve what you're describing. Just be aware that, by drinving the tops higher, you'll have relatively less sub in the overall mix. But, given that your speaker setup sounds as if it's not capable of producing the overall SPL you want, it's a compromise that may get you where you need to be.

Ultimately, just remember that, however much you'd like to, you can't overcome the rules of physics.

The issue here is that even with "more subs" I would get the same problem with this specific system and configuration (sub dsp output to tops), because the sub channels gains affect also the input volume on the tops. Ideally I would have preferred to get the dsp output of the sub (crossover filter applied) but without the gain stage, so I can control that directly on the tops and I am free to push them as much as I want, independently from the sub limit.

[Sam Spoons]

In you OP you say you run the sub in thru mode? The the block diagram in manual shows that the volume controls don't control the outputs in thru mode.

Adding extra subs will mean you will be able to get more LF output, maybe for your desired sound, one sub is not enough to balance with the tops. TBF those DZR 12s are seriously loud at 139dB SPL each.

[revyth]

In you OP you say you run the sub in thru mode? The the block diagram in manual shows that the volume controls don't control the outputs in thru mode.

Adding extra subs will mean you will be able to get more LF output, maybe for your desired sound, one sub is not enough to balance with the tops. TBF those DZR 12s are seriously loud at 139dB SPL each.

Yes I have switched to THRU because in DSP mode I didn't like that sub gain also affecting tops gain. I would like to add another sub in the future, but that it is not in the scope of this topic.

My question was more about operational strategies handling subs+tops.

So my idea was to use a mono bus directly on the DAW (Ableton) for handling the sub, while sending L+R separately to the tops. I learned that this is a sort-of emulation of the aux-fed subwoofers strategy that is generally done on the PA mixer. I was asking this because sometimes if I have to do a solo show I wouldn't probably use a mixer at all, I would just go directly from the audio interface to the speakers. So basically I am applying the aux-fed strategy on the audio interface instead of the mixer.