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Does a backline bass rig cancel frequencies in the PA?
- Thread starter caballero59
- Start date
If no one in the audience can hear the bass then isn't it as good as it just being turned off?
I wasn't thinking about 'blasting away', I was just thinking of having my bass amp back at the normal stage volume I used to play at before we went In Ears (we reduced the backline volume once we started using IEM's).
You were talking about raising your level to make yourself more audible in the audience. That means your bass amp's output will be comparable to the bass output of the PA. That's the worst case for comb filtering - your sound will be very inconsistent in the audience.
In Ears and a silent stage (or more realistically, a quiet stage) is how you give the FOH person a fighting chance of doing a good mix. What you're proposing is a big step in the wrong direction.
If you think your FOH person isn't good at mixing, the solution is either more training for them, or a different sound person.
For a fun test, maybe not so fun after you hear the results get a sine wave generator, connect the output to an input on your PA, start off maybe at 70hz, the volume need not to be crazy loud. About 30 feet in front the PA walk from side to side, in a normal Left Right PA stack system you will hear the peaks and nulls of comb filtering, change the frequency and note where the peaks and nulls are now.
There's no way to truly eliminate it, except maybe using just one speaker outside!
With full range music the peaks and nulls are all over the place but if someone
is standing in a very pronounced low frequency null area they may not feel/hear much bass at all.
If FOH is mixing in a null area, the low end may be way too much in other areas or if their standing in a peak the low end could tend to too low in other areas.
No excuse today, grab your iPad and take a walk around.
There's no way to truly eliminate it, except maybe using just one speaker outside!
With full range music the peaks and nulls are all over the place but if someone
is standing in a very pronounced low frequency null area they may not feel/hear much bass at all.
If FOH is mixing in a null area, the low end may be way too much in other areas or if their standing in a peak the low end could tend to too low in other areas.
No excuse today, grab your iPad and take a walk around.
Could you comment more on why this would be? Would it also be true if going direct with no bass amp?
s0c9
Supporting Member
As someone who has been exclusively IEM for at least 10 yrs (bass and guitar) and work freelance for a local soundco doing FOH/Live stream mixing for a number of churches and bands/festivals....
I have to ask... when using IEM's how does one tell what the FOH bass sounds like to the audience?
Are you getting an FOH mix to your IEM's, or ?
In most cases the PA needs to be significantly louder than the stage wash in order to produce nice clear lows. I certainly could have mixed loud enough where it would have been beneficial to use the subs. But this was not really the right strategy to use with our audience.
To be honest, I don't really like it that loud anymore either. I normally wore ear plugs when I was playing bass. I don't like mixing in situations where it's loud enough to require ear plugs.
I also mixed a few pop shows where the musicians where in IEMs. There were no amps or monitors on stage, and the PA had subs. No problem here as there was no stage wash to fight with the PA.
Quick answer: yes
What to do?
With digital consoles, it has now become pretty commonplace to time align each channel with sound sources, as most have delay per input. Obviously, once you reach a certain offset in volume of backline vs. PA this doesn't impact as much, but I've found is most obvious in rooms of 1k cap or less. A couple rooms I mix regularly are full pa support, but have max cap of 250, and in both of those it absolutely makes a huge difference to get things aligned. It is just an additional step added to checking each channel.
In professional live mixing, it is one small thing in a standard to-do list of small things, that really add up to definitive improvements.
Do you need to worry about going this far if you are hucking your own rig and PA around?
Depends on the level of nerd you want to go to, and if you got the time. Plenty of great sounding shows before this could ever be a consideration (trying to just get a PA in phase with itself in the early 80's was hard enough).
What to do?
With digital consoles, it has now become pretty commonplace to time align each channel with sound sources, as most have delay per input. Obviously, once you reach a certain offset in volume of backline vs. PA this doesn't impact as much, but I've found is most obvious in rooms of 1k cap or less. A couple rooms I mix regularly are full pa support, but have max cap of 250, and in both of those it absolutely makes a huge difference to get things aligned. It is just an additional step added to checking each channel.
In professional live mixing, it is one small thing in a standard to-do list of small things, that really add up to definitive improvements.
Do you need to worry about going this far if you are hucking your own rig and PA around?
Depends on the level of nerd you want to go to, and if you got the time. Plenty of great sounding shows before this could ever be a consideration (trying to just get a PA in phase with itself in the early 80's was hard enough).
If adding subs to a mix makes it sound worse, something in the setup (time alignment, crossovers, physical placements) is probably not right. Either that, or you're putting the wrong signals in the subs. With aux fed subs, you can keep stuff that shouldn't be there (rumble from dynamic mics for example) out of there - usually, only the kick and bass guitar get fed to the subs.
Through a well set up PA, if you and the FOH person know what you're doing, your bass guitar will sound much better than it will through a bass amp. An SVT is no match for a dozen 18's and 20kW.
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They will if you have the crossovers set right. Any decent PA setup has crossovers to split the signal to the mains and subs. Just because you've decided to drive the subs with an aux signal, that doesn't mean you yank the high pass to the mains out of the signal path.
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My crossovers are built into the subs. If I feed the subs from aux, the tops will get full range (at least the way I understand it).
Yes they would....or should be if set up correctly!!!
With a powered speaker system the top boxes from maybe 60% of manufactures have some form of selectable mode to operate with a sub applying a high pass around 100hz.
If they don't then you would need some form of external crossover/high pass to drive them with.
Same goes for powered subs, though more often than not they have built in high pass and low pass filtering.
For non powered systems your going to need external crossovers or DSP's or on board processing in the power amps any way.
If they don't understand the extra setup steps needed they should stay with standard full range system operation.
If I'm going to be providing for all acoustic acts at a show with a larger system I almost always set up for aux fed subs.
You need another high pass for your system. Big PA's do things differently than the rig you have - yours are convenient for a modest sized system, but you can do things better if you steal an idea from the big rigs. Line arrays have multiple feeds to each line, and often, but not always just one feed for all subs - that depends on other factors.
I ran aux-fed subs and only assigned appropriate low frequency instruments. The mains, subs, and front fills were time aligned with each other, and also delayed back into the ensemble.
The system sounded very good with program material. I was not completely happy with the sound of the bass guitar or upright during the show, but IMHO the biggest problem was the stage wash was too loud. As I have mentioned, I could have easily mixed at a volume loud enough to make the low end sound decent, but not without pushing more SPL than I wanted to use.
Another fairly significant problem is the acoustics were often not well suited for live amplified music.
The quality of the speakers was not a factor. Subs were either a pair of Apogee AE10s (215) or a pair of Apogee AE12s (218). I preferred to run them in the center, but this was not practical for many venues, so frequently I ran them under the mains. Mains for most of my career were usually four Apogee AE5s or Meyer UPA-1Ps on tripod stands. Front fills were two to four Meyer UPM-1Ps spaced along the lip of the stage. The digital mixers I used were Yamaha LS9-32 and Yamaha 01V. These were relatively small systems, but I rarely pushed any of the elements close to their limits.
Although I was not happy with the low end, I was generally happy with the overall mix and the overall SPL.
I like the concept but my RCF boxes don't have a high pass option so I would need an extra crossover. It wouldn't be as clean of a system as feeding them from the subs. With a digital console, I could do low cuts on the mics, etc.
Yes RCF is one those who do not put a high pass for use with subs function on a lot of their boxes.
A good basic stereo two way analog crossover would do it, used ones sell cheap these days.
The crossover inputs connect to the mixer main L R outputs, the high outputs go to the inputs on your powered speakers.
You would not notice any difference with an analog crossover inline.
What mixer do you have.
It depends on the speakers, mixer, and how you configure everything. If you are using powered mains from the same series as the subs, typically the mains and subs will have presets with complimentary crossover filters. Many cabs provide at least two frequencies to chose from.
In the event, your mains do not have built-in, selectable HPFs, then see what your mixer has. Some mixers have built-in crossover capabilities, so you can assign a complimentary HPF on the main outputs. Even if the board does not have crossover presets, it may have a selectable HPF and parametric EQ available on the output of each mix...meaning you can fake it.
A lot of people think aux-fed subs are passe. I still think it's useful approach, but YMMV.
I've had the A&H QU-16 and Soundcraft ui24. Now I'm getting by with a small analog until I choose the next digital mixer.
