Aux feed subs?

Re: Aux feed subs?

Spenser Hamilton said:
Paging Art, Paging Ivan...
Click to expand...
Spenser,

I have not used aux fed subs since 1978.
Wait, there was that one Gang of Four tour in 1983 when Kevin Harvey wanted aux fed subs with a foot volume pedal control like he'd heard the Police used.
After looking through the baskets of eight 15" drivers that were blown to bits the first show, the subs went back to normal once eight replacement speakers had been bought.

Later, Kevin told me he had heard Clair had gone through a boatload of 18" on that Police tour...

Art
 
Re: Aux feed subs?

What would the difference be in using aux fed subs versus using high pass filters on channels that you didn't want to get into the subs? Wouldn't that be essentially the same thing?

I could see aux fed subs to be used when there are additional subs needed for an effect, but the added complexity for most applications doesn't appeal to me at all.

With today's digital boards, you can get a pretty accurate high pass filter, and adjust the frequency where you want it to be. I could see maybe with older consoles that didn't have that flexibility, but not now.

I'll actually often do a high pass and a low pass filter on instruments to match their range needed, and keep the unwanted sounds out of the system. Each type of instrument is going to be different, but once set up, it can really help keep noise levels down.
 
Brian jojade said:
What would the difference be in using aux fed subs versus using high pass filters on channels that you didn't want to get into the subs? Wouldn't that be essentially the same thing?

I could see aux fed subs to be used when there are additional subs needed for an effect, but the added complexity for most applications doesn't appeal to me at all.

With today's digital boards, you can get a pretty accurate high pass filter, and adjust the frequency where you want it to be. I could see maybe with older consoles that didn't have that flexibility, but not now.

I'll actually often do a high pass and a low pass filter on instruments to match their range needed, and keep the unwanted sounds out of the system. Each type of instrument is going to be different, but once set up, it can really help keep noise levels down.
Click to expand...

The big thing is a HP is not a cut off but is a slope. So, some energy gets through.
For example, you may have a mic set for a male vocal with a 120hz HP but it is going to pick up lots of stage wash at low freq and out of time with the direct inputs for lows resulting in a muddy bottom end.
If those sources are never sent to the subs, you get a much cleaner low end.


Sent from my iPad HD
 
Re: Aux feed subs?

Gert-
So, basically, what you are saying is that if I put a 6dB boost at 50hz on my kick drum, my phase alignment will no longer be correct? Because, the way you put it, any change in level will result in phase issues. Which is completely incorrect.

Phase and amplitude really have nothing to do with each other. Because if they did, the phase response would change on every kick hit, every guitar solo and every break between songs. Phase has to do with time, and wavelengths more than anything. Once you have everything electronically aligned, it will remain aligned until some other physical condition comes in to play.

Yes, driving your aux subs hotter will move your acoustic crossover points, and potentially add unwanted energy in certain areas, but the electronic crossover and phase alignments will remain the same. I'm ok with cutting a little extra 90-110hz out of the rig if it means more control down low.



Evan
 
Re: Aux feed subs?

Art Welter said:
Spenser,

I have not used aux fed subs since 1978.
Wait, there was that one Gang of Four tour in 1983 when Kevin Harvey wanted aux fed subs with a foot volume pedal control like he'd heard the Police used.
After looking through the baskets of eight 15" drivers that were blown to bits the first show, the subs went back to normal once eight replacement speakers had been bought.

Later, Kevin told me he had heard Clair had gone through a boatload of 18" on that Police tour...

Art
Click to expand...

I was hoping you or Ivan could comment on Gert's statements in post 19. You guys are my go to Bass Gurus around these parts ;)
 
Re: Aux feed subs?

Evan Kirkendall said:
Gert-
So, basically, what you are saying is that if I put a 6dB boost at 50hz on my kick drum, my phase alignment will no longer be correct? Because, the way you put it, any change in level will result in phase issues. Which is completely incorrect.

Phase and amplitude really have nothing to do with each other. Because if they did, the phase response would change on every kick hit, every guitar solo and every break between songs. Phase has to do with time, and wavelengths more than anything. Once you have everything electronically aligned, it will remain aligned until some other physical condition comes in to play.

Yes, driving your aux subs hotter will move your acoustic crossover points, and potentially add unwanted energy in certain areas, but the electronic crossover and phase alignments will remain the same. I'm ok with cutting a little extra 90-110hz out of the rig if it means more control down low.



Evan
Click to expand...

Hi Evan,
No thats not what I am saying at all. Sorry for the confusion. What I am referring to is strictly the relationship between two components in a PA System. Because the question was about sub on aux. So lets say I have a System flown in the Air and Subs on the ground. If I control the Subvolume separate from the Main Pa Volume and turn them down for example. A certain point on the slope of the crossover filter will now move down on the frequency scale. David named that the acoustical crossover earlier on. This must have an effect on my phase alignment and time alignment between the Subs and the flown PA. So once I have tuned the system and aligned all components with each other I should not move this relationship between the cabinets anymore. So to me it seems wrong to have the subs on a separate Fader and to move them up and down during a show. Changes should, in my opinion, then only be made by EQ and to the entire System. But I am aware that the negative effects depend on many factors. What filters are used and the ideal crossoverpoint for the cabinet. But I would like to stress that I was not refering to any channel eq or Low cuts in desk channels. I am also aware that opinions here vary and some people swear by SUB on AUX. :razz:
 
Last edited:
Re: Aux feed subs?

Gert Sanner said:
This is almost correct, what actually happens is that the slope ( which can be quite shallow ) moves position. So lets say the -6db point moves lower and therefore is in a slightly different place on the frequency scale. The actual chosen crossover frequency does not move. Here is to remember that the steeper the slope ( or Filter) the smaller this artefact becomes. On a LR24 this is not a major problem. So depending on the applied Filter this Problem can be fairly big.
[/B]
Click to expand...

So 4 posts later, Chris was 100% correct.

Acoustical Crossover is not some term I made up, but rather a term that is widely used in the industry. I can almost guarantee Chris was referring to the acoustical crossover in his post.
 
Re: Aux feed subs?

Rob Spence said:
The big thing is a HP is not a cut off but is a slope. So, some energy gets through.
For example, you may have a mic set for a male vocal with a 120hz HP but it is going to pick up lots of stage wash at low freq and out of time with the direct inputs for lows resulting in a muddy bottom end.
If those sources are never sent to the subs, you get a much cleaner low end.


Sent from my iPad HD
Click to expand...

O.K, that sounds like a reasonable explanation. Still, if you have a HPF set at 120hz, and your crossover point is at 80 hz, that's going to be a 20db reduction in signal. The stage wash that the mic is picking up is probably going to be 20db down or more from the signal you are trying to pick up, unless you are using distant micing, or have extremely poor mic placement. So that means a 40db drop in sound compared to what you're working with. That's very little energy that would be going to the sub, even at rock and roll volumes.

When I've tried aux fed subs, I've heard very little real difference in the way it sounds. If you are running aux fed subs, you can test to see what the difference is by turning on your high pass filters, and then also turning on the aux for that channel.
 
Re: Aux feed subs?

Brian jojade said:
O.K, that sounds like a reasonable explanation. Still, if you have a HPF set at 120hz, and your crossover point is at 80 hz, that's going to be a 20db reduction in signal. The stage wash that the mic is picking up is probably going to be 20db down or more from the signal you are trying to pick up, unless you are using distant micing, or have extremely poor mic placement. So that means a 40db drop in sound compared to what you're working with. That's very little energy that would be going to the sub, even at rock and roll volumes.

When I've tried aux fed subs, I've heard very little real difference in the way it sounds. If you are running aux fed subs, you can test to see what the difference is by turning on your high pass filters, and then also turning on the aux for that channel.
Click to expand...

Let's try this again. We have a HPF set on an input channel at 120 hz (so 120hz will be about 3db down). So 60hz on the input channel will be about 15db down(12db per octave) in the mains. But, if we run the subs 20db hotter than the mains, the 60hz information from that input coming out of the subs will 5db-ish hotter than they would be with no highpass in the mains. Does that make sense?

Running the subs 20db hotter than the mains may be on the extreme side of the spectrum, but helps clarify the point.
 
Last edited:
Re: Aux feed subs?

Evan Kirkendall said:
Gert-
So, basically, what you are saying is that if I put a 6dB boost at 50hz on my kick drum, my phase alignment will no longer be correct? Because, the way you put it, any change in level will result in phase issues. Which is completely incorrect.

Phase and amplitude really have nothing to do with each other. Because if they did, the phase response would change on every kick hit, every guitar solo and every break between songs. Phase has to do with time, and wavelengths more than anything. Once you have everything electronically aligned, it will remain aligned until some other physical condition comes in to play.

Yes, driving your aux subs hotter will move your acoustic crossover points, and potentially add unwanted energy in certain areas, but the electronic crossover and phase alignments will remain the same. I'm ok with cutting a little extra 90-110hz out of the rig if it means more control down low.



Evan
Click to expand...

Hey Evan,

Let me take a stab at what Gert is trying to say. Usually we try to align phase at the acoustic crossover point for a smooth level transition from mains to subs. Above and below that point it is less of a concern because of the relative level differences between the two sources. Now for those of us who use aux fed subs, that acoustic crossover point is moving, and phase differences at the new acoustic crossover may cause unwanted cancellation. Ideally, we would be able to align phase all the way from 50-200hz eliminating the problem, but this usually isn't possible.
 
Re: Aux feed subs?

David Sturzenbecher said:
So 4 posts later, Chris was 100% correct.

Acoustical Crossover is not some term I made up, but rather a term that is widely used in the industry. I can almost guarantee Chris was referring to the acoustical crossover in his post.
Click to expand...

Yup I just tried to clarify that as I felt the previous statement could be misunderstood by some. To then only proceed to make myself misunderstood. Sorry for that.
Brandon explained exactly what I tried to say. Thanks for that. Reading your own thinking appears to be easier then writing it so others understand it too.
 
Re: Aux feed subs?

Brian jojade said:
When I've tried aux fed subs, I've heard very little real difference in the way it sounds. If you are running aux fed subs, you can test to see what the difference is by turning on your high pass filters, and then also turning on the aux for that channel.
Click to expand...

A lot of bigger rigs are running with the subs 6-10dB hotter than the tops, sometimes even more. I find that without using aux subs, getting rid of vocal plosives in the subs without destroying the low mid response as a whole can be nearly impossible. With a more standard old school setup where the subs aren't run that hot or don't go down that low, it's not so much of an issue. But in today's world of really high powered systems with deep subs running good and hot, it's a problem that's easily solvable with aux subs.

I have my rig installed in a venue where other people can plug in their boards and go. One fairly regular user with an SL24 opts to do non-aux subs run off the non-assignable mono out (L+R sum). Every one of those shows has super boomy plosives in the vocal mics and drives me crazy. But the balance of kick and bass is good because the system itself is setup and tuned well. If he were to run the high pass up to where that issue goes away, the vocals sound to thin in the tops.

Just my $.02.
 
Re: Aux feed subs?

Brian jojade said:
O.K, that sounds like a reasonable explanation. Still, if you have a HPF set at 120hz, and your crossover point is at 80 hz, that's going to be a 20db reduction in signal. The stage wash that the mic is picking up is probably going to be 20db down or more from the signal you are trying to pick up, unless you are using distant micing, or have extremely poor mic placement. So that means a 40db drop in sound compared to what you're working with. That's very little energy that would be going to the sub, even at rock and roll volumes.

When I've tried aux fed subs, I've heard very little real difference in the way it sounds. If you are running aux fed subs, you can test to see what the difference is by turning on your high pass filters, and then also turning on the aux for that channel.
Click to expand...

Of course how many open vocal and other microphones on stage there is and how loud the bass on stage is has to be considered as well. Subs close to the stage not setup well. Loud bass rig on a small stage. Loud drum monitor or just loud monitors with a lot of bass content , keys , kick , bass guitar, etc.
All that bass bleeding into all those microphones makes the bass additive in the overall mix.
The best thing to try is record just your subwoofer sends post crossover. Do one show the "normal" way with just the boards low cut filters. The next night record the subwoofer sends post crossover with an Aux Fed Subs setup. See if you can hear a difference.
Everything you hear in the Low Cut mix that the Aux Fed subwoofer mix doesn't have is stuff that could be adding mud to the mix.
Also the less unwanted sounds the subs have to reproduce leaves more power available to be used on the sounds that need to be reproduced.

Douglas R. Allen
 
Re: Aux feed subs?

Years ago I changed from Aux subs to dual PA for larger shows. One PA is full range including subs tuned for instruments (read flat or neutral) and is taken from my main LR out. The other PA is just top boxes tuned for vocals and is taken from the highest sub-master or 2. Any delays or secondary feeds are from a matrix mixer. I find this leads to a nice sound with lots of head room, simplified wiring, and an easy to mix on system for “brother of the drummer is our sound guy” who have no clue about aux subs and other such magical audio things.
 
Re: Aux feed subs?

Brian jojade said:
O.K, that sounds like a reasonable explanation. Still, if you have a HPF set at 120hz, and your crossover point is at 80 hz, that's going to be a 20db reduction in signal. The stage wash that the mic is picking up is probably going to be 20db down or more from the signal you are trying to pick up, unless you are using distant micing, or have extremely poor mic placement. So that means a 40db drop in sound compared to what you're working with. That's very little energy that would be going to the sub, even at rock and roll volumes.

When I've tried aux fed subs, I've heard very little real difference in the way it sounds. If you are running aux fed subs, you can test to see what the difference is by turning on your high pass filters, and then also turning on the aux for that channel.
Click to expand...

Here's a better test: Talk into any microphone, set the channel controls like you normally would for a show. Switch off your high/mid-speakers. Can you hear a muddy version of your voice coming from the subs? This would be gone if going AUX-fed :)

Now imagine the vocal mic is a lav, sitting on a high-profile-client. And he decides to "walk the floor" and he's standing right in front of one of the subwoofer systems...

Edit: It seems to me that many of the younger techs who absolutely love AUX-fed subs, almost felling like it's necessary to use that technique to put on a good show, previously had some "bad habits" when running normal L/R-feeds: Instead of addressing those, they decided to go the AUX-fed route to fix their issues.

What I'm talking about is boosting the subs in a L/R-system so much that the playback test music CD has chest-punching bass with all EQs set to flat. Even with the HPF engaged a vocal mic channel is essentially a "flat" channel when run through a L/R-setup like this.

Also, many techs have read and heard so many places that EQs should be used to cut ony, and never boost anything - so they forget that it's entirely possible to tune the L/R-system a little "thin" and just boost the low end on those channels that need it.
 
Last edited:
Re: Aux feed subs?

Some people refuse to boost the low end on ch1 and uses it as a basis for their whole system tuning. I'm looking forward to the day when someone can explain to me why boosting the low end of a kick drum is wrong, but running your subs at +10 dB relative to the rest is correct.

I like a solid low end as much as anybody else, but not if it messes up the whole sound system.
 
Helge Dr. Bentsen said:
Some people refuse to boost the low end on ch1 and uses it as a basis for their whole system tuning. I'm looking forward to the day when someone can explain to me why boosting the low end of a kick drum is wrong, but running your subs at +10 dB relative to the rest is correct.

I like a solid low end as much as anybody else, but not if it messes up the whole sound system.
Click to expand...

I think this type of incomplete understanding is the crux of the matter. I also think how aux fed subs are applied is a big indicator of varsity vs. Jr. varsity behavior.

At the JV level I often encounter systems and techs who treat aux feed subs as an excuse for having no idea how the subs and tops interact and who throw some sort of filter on each to limit the bands but never consider those filters together as a crossover. On these systems the octave or two above the sub usually has some flake stuff going on.

On the other hand, on the varsity system the aux fed subs are integrated into the entire system which is measured and tuned as a whole.

I feel if the system is correctly set up, whether flat or with a haystack, with equal levels of pink noise for a signal, I should never have to touch any gain other than what is on the channel.

For the record, I like to make a kick boom as much as anyone, but I really dislike when instruments such as keys and bass have tonal differences in their range because of varying amounts of low end in their signal. I.e. the first note of the bass that has its fundamental above the crossover should not be significantly lower in level than the lower notes. This means to me a full range system augmented by aux fed subs would probably be the best.

Or I will just boost the low end of the kick channel.
 
Re: Aux feed subs?

Helge Dr. Bentsen said:
Some people refuse to boost the low end on ch1 and uses it as a basis for their whole system tuning. I'm looking forward to the day when someone can explain to me why boosting the low end of a kick drum is wrong, but running your subs at +10 dB relative to the rest is correct.

I like a solid low end as much as anybody else, but not if it messes up the whole sound system.
Click to expand...

Some installs are like that, the house array comes with a massive sub boost and other weird things. Only way to connect is main L+R inputs, no access to the processor and not even a hint of a spec saying anything about nominal and max input level or anything else.
Then of course there are installs that have no low end courtesy of saving money in the sub department, but still crossing over at 90-100 Hz. :cry:

So what does the visiting engineer do? Assume that the system is tuned properly for when there is a full audience, or try to make it right for the sound check?
 
Last edited:
Top Bottom