Adding a Subwoofer

[bearfoot]

I have a good lead on a used , powered subwoofer w/crossover.

Is this the beginning of the end?

Over the last several years, I have found that I am trying to get too much thump out of my modest, mid-range PA cabs (Peavey 15+horns). Eventually, the 20+ year old voice coils went. The replacement woofers sound great, and I'd like to keep them that way.

So, a dedicated subwoofer seems like the answer. But I know this will open up another can of worms.

My general impression is: less is more. I am only looking for a little chest thump. Placement is critical, and from what I've researched around here, a sub placement to one side or the other of the stage, facing across, is often ideal.

Looking for general advice on first PA subwoofer pros and cons - horror stories, religious experiences induced, etc.

 

[Downunderwonder]

Make sure it is turned up before you soundcheck the bass.

 

[musicman7722]

I was in your shoes although I had QSC K10 tops. I bought one of these EV subs and gradually purchased 3 more. They are small and light but give a decent low end. By having 4 I can taylor my sub needs to the gig.

I do a lot of sound jobs and use these along with my Turbosound IP2000's.

 

[Wasnex]

I have a good lead on a used , powered subwoofer w/crossover.

Is this the beginning of the end?

Over the last several years, I have found that I am trying to get too much thump out of my modest, mid-range PA cabs (Peavey 15+horns). Eventually, the 20+ year old voice coils went. The replacement woofers sound great, and I'd like to keep them that way.

So, a dedicated subwoofer seems like the answer. But I know this will open up another can of worms.

My general impression is: less is more. I am only looking for a little chest thump. Placement is critical, and from what I've researched around here, a sub placement to one side or the other of the stage, facing across, is often ideal.

Looking for general advice on first PA subwoofer pros and cons - horror stories, religious experiences induced, etc.

I would be a lot easier to provide answers and give advice if you gave more details and explained your goals.

In my experience, subs are generally less efficient and our ears are less sensitive to low bass, so I am not sure how realistic it is to expect one sub to keep up with a pair of 15s unless it's a really good sub...or the 15s are really crappy.

Personally I like to run subs off an aux. In order to do this you will need some way of high passing your mains and low passing your subs at the same frequency...time delay to align the cabinets would be ideal, but perhaps this is asking too much.

The necessary features are built into some digital boards and also speaker processors. The built in crossovers in active speakers will do part of the job.

The idea with running the subs off an aux is to send only the bass and the bass drum and maybe a few other select instruments to the sub such as the left channel of the keyboard and the low tom. Instruments sent to the subs are dual assigned to the mains. No need to send vocals and guitar to the subs. Extra open mics in the subs will only increase the chance of low frequency feedback and muddy sound.

During sound check, set up the gain structures of the sub aux and mains for a flat response so the bass and bass drum have a natural sound. The balance between subs and mains should be maintained throughout the show. If you need more bass, dial it in at the appropriate channel strip. Unfortunately many audio techs like to reach for the sub aux fader and push it to "11" which makes for muddy mayhem instead of full natural sound.

Sorry if this is seems technical...it is.

 

[Jimbob Jones]

you will need some way of high passing your mains and low passing your subs at the same frequency

This. IMO not reducing the sub frequencies in your tops is the primary cause of 'it sounds muddy'. The subs are there to produce those low lows, so the tops don't have to.

Some great advice in the above, especially running subs off an aux, rather than splitting your desk's main output to the sub. If the system I'm mixing is mismatched (i.e. subs from one manufacturer & tops another) This can be a silver bullet for getting a clean sound out of that system.

As to whether to do it or not, I would say try it. You may find that you need two subs to get the desired effect, but I've run many smaller gigs with 1 and been just fine!

If you do end up getting two subs though, get a matching pair - mismatched subs = world of pain IME!

 

[bearfoot]

Ok that's all interesting, thank you! - I had not considered the possibility of microphones picking up low frequencies and adding mud to the signal. Especially the vocal mic on the bodrhan player I can see needing a high-pass - !

To explain a bit more, I am using two mid-90's Peavey main cabs. These cabs were never given a wattage rating, but they came with Scorpion 15's + horn. I'm fairly sure they are in the 200-watt range of power handling. I drive them with a 500-watt stereo PA amp, usually in mono. (In stereo the power is 180x180watts)

These speakers have served well, even in outdoor venues they have been great at reasonable volume levels.
But, in the last 5 or 6 seasons, I've been getting performers on my stage with kick drum pedals/loopers that throw off a real low thud. Also in my band, we have a wide range of natural skin drums, as well as bass guitar including a low B-string. But it was trying to get the kick drum sound to push a little more air that I weakened the Scorpion speakers, and they eventually broke down. (replaced with Sheffields , which I find do sound warmer than the Scorps)

The subwoofer being considered is a Behringer that claims a 1400-watt power rating. I assume there is some marketing involved in that figure. It is a single 15", with stereo i/o and a crossover that goes up to 150hz at highest.

I will definitely be using an AUX send, for the channels in question then.

The goal is to just get some natural thump (we are a folk-jazz-rock dance band), in frequencies the PA cabs cannot produce at higher levels.

 

[craigie]

It sounds like a good match. We use two EV ELX115’s for mains and two 12” for monitors. I bought a yorkville NX720s sub and it sounds great with the system. It is 720 W program, 1400 W peak or so.

We tried several different subs. One was way too big with a lot of power but too much whump and would have been impossible to move. Tried two double 12” line 6’a but they distorted and sucked.

The 15” Yorkie is perfect. Sounds great. Enough power. Portable. Built in dsp: variable crossover, limiter and protection in case you forget to turn it off first and send a bid transient.

Our board has a sub setting that cuts the low frequencies out of the mains AND the monitors and also boosts the sub signal a bit. It sounds so much better than running everything full range. It’s counter-intuitive because more speakers = more bass right? One source = better bass at least for sub frequencies. Also “I’ve got two mains so I want two subs, one under each.” No. Then you get comb filtering. One sub is best. Centre of stage is probably best location acoustically (depending on the room of course) but off to one side is best so that it’s not a big Stonehenge in the middle of the stage. Pointing forward, not to the side! Place it so that it is time aligned with the speakers.

Now on to aux feed vs main feed:
Does your board have a hpf switch for each channel strip? If yes just engage it on everything you don’t want in the sub. Aux feed is just a nice work around or if you have a powered board and can’t send a hot enough signal to the sub. I’ve read about using left/right outs to do the same thing if you have a mono mix, which you should probably have. These are good solutions if you have a very basic board.

Try our different subs and don’t expect that one will work for your setup based on specs. The proof is in the pudding pops!

I find the bass and music in general sounds worlds better with the sub because it’s well balanced and we have it set up right. Your mains and monitors will sound better and won’t be worked so hard. Also, the peavey XR1212 which is just a fantastic analog powered mixer vita even more bass from the monitors so I’d recommend that. It just seems to work really well.

So you can cut the high frequencies out of the sub using the built in crossover and you can cut the unwanted lows from everything using HPF’s/aux fed sub. How are you going to cut the lows from the mains/monitors?

You can use a GEQ if you have one for the mains and one for monitors that is separate from ty aux sub feed, but it won’t be as good as a crossover. Some subs have a through feed which is post crossover which you can run back to your power amp. Of course that doesn’t take care of your monitors. Another solution is an external crossover but that’s more $$ and another piece of gear to hump/rack/setup/tweak so consider that in your sub purchase.

 

[Wasnex]

Ok that's all interesting, thank you! - I had not considered the possibility of microphones picking up low frequencies and adding mud to the signal. Especially the vocal mic on the bodrhan player I can see needing a high-pass - !

To explain a bit more, I am using two mid-90's Peavey main cabs. These cabs were never given a wattage rating, but they came with Scorpion 15's + horn. I'm fairly sure they are in the 200-watt range of power handling. I drive them with a 500-watt stereo PA amp, usually in mono. (In stereo the power is 180x180watts)

These speakers have served well, even in outdoor venues they have been great at reasonable volume levels.
But, in the last 5 or 6 seasons, I've been getting performers on my stage with kick drum pedals/loopers that throw off a real low thud. Also in my band, we have a wide range of natural skin drums, as well as bass guitar including a low B-string. But it was trying to get the kick drum sound to push a little more air that I weakened the Scorpion speakers, and they eventually broke down. (replaced with Sheffields , which I find do sound warmer than the Scorps)

The subwoofer being considered is a Behringer that claims a 1400-watt power rating. I assume there is some marketing involved in that figure. It is a single 15", with stereo i/o and a crossover that goes up to 150hz at highest.

I will definitely be using an AUX send, for the channels in question then.

The goal is to just get some natural thump (we are a folk-jazz-rock dance band), in frequencies the PA cabs cannot produce at higher levels.

Given the type of music and relatively low power of your mains I believe a single sub should easily do the job. Does your board have an HPF on the channel strips? If yes, I would engage the HPF for all channels that are not sent to the sub.

You can run you mains full range and simply add the sub. This is not ideal as destructive interference can occur because of different phase and group delay errors cause by variation in drivers, box tuning, and the the subs crossover.

Regarding the HPF for your mains, ideally it should be set to interact with the LPF of the subwoofer so that a crossover is formed. Best peformance will be achieved if the HPF is injected before you power amp (active) rather than between the power amp and speakers (passive). A passive HPF will dissipate some of the amp's power so it is not available for your speakers to make sound.

Usually crossovers use the same slope for both LPF and HPF....the slope is pretty important given the nature of your proposed setup. If the LPF and HPF have different slopes and are set to the same frequency, either you will have overlap or a hole in the response. Different slopes can be configured to work with each other, but test equipment and time delay is required for seamless integration. Unfortunately the Behringner documentation doesn't seem to show what crossover slope is used with their subs...their support services are very good, so send them a questions if you are curious.

Options in order of performance (worse to better): 1. Run mains full range, 2. if your PA has EQ between the mixer and mains, engage available HPF on EQ and dial out lows below sub crossover frequency, 3. use a variable HPF filter with same slope as subwoofer crossover, 4. use the HPF section of regular two way crossover with the same slope as the subs built in crossover, 5. use a digital processor with variable filters and time delay.

If you are running a digital board, try to use the functionality of the board instead of buying more gear. I used to mix on several low end Yamaha digital mixers and I configured the output section of each mix rather than using outboard gear.

Luckily the ear is not super sensitive/critical to low frequency phase and frequency response issues. Just do the best you can with the equipment you can afford by tuning the system with your ears. I use downloadable tone generator myself as I can't justify spending the cash on SMAART and the necessary hardware to run it.

A rabbit hole to go down if you are interested. (I am totally lost down here myself). Pro level equipment often uses 24db crossover slopes. One reason is because this slope is "phase coherent." There is a total phase error of ~360 degree across the crossover region; so signal phase error pretty much works out. With 12db crossovers the phase error is 180 degrees so the common fix is to flip the polarity of one of the drivers.

 

[bearfoot]

A rabbit hole to go down if you are interested. (I am totally lost down here myself). Pro level equipment often uses 24db crossover slopes. One reason is because this slope is "phase coherent." There is a total phase error of ~360 degree across the crossover region; so signal phase error pretty much works out. With 12db crossovers the phase error is 180 degrees so the common fix is to flip the polarity of one of the drivers.

Interesting. If I grok any of this (and preceding statements), would this mean that a crossover phase problem would be more noticeable the higher the crossover setting?

Obviously, a lot of experimentation will follow acquiring the subwoofer unit.

My board does have low-cut on the mic preamp channels, and I usually do use the low-cut. I think it cuts at 60hz.

But as you mention, going digital cuts a lot of equipment needs. For the first show using the sub, we will be using a wifi --->laptop/tablet mixer. I might still use the BBE sonic maximizer, just before the PA amps, but otherwise there will be no need for dedicated EQ, compressors, or other effects. (i will probably bring the 31-band EQ, though, just in case)

The main festival I work sound for comes at the end of June, by which time I may acquire a 12 or 16 channel wifi setup myself.

Thanks for the advice, I will be referring to it as I shakedown the system.

 

[Wasnex]

Interesting. If I grok any of this (and preceding statements), would this mean that a crossover phase problem would be more noticeable the higher the crossover setting?

IMHO yes, comb filtering is much more apparent in mid range frequencies than low bass frequencies.

If you work sound regularly, a digital board is a great investment as they provide a lot of processing power for the money. I keep my old analog board because it has only seen a few gigs and is unlikely to see many more as I am pretty much retired. The one issue with a digital board, you do need to spend some time to learn and remain competent on the OS.

Back in the day I mixed on Yamaha 01V, DM1000, LS9/16 and LS9/32. When I transitioned from analog I was amazed by how much better my mixes sounded. The last analog board I regularly used was a Crest XR20 with Klark Teknik and BSS outboard gear. All of this gear was owned by my employer.

 

[craigie]

I love my Soundcraft ui12. It has so many built-in features and you can save all the settings. Would be nice if it had sub crossover built-in.

 

[bearfoot]

well my first impression is, I am surprised how much bass guitar string information is present and very responsive, in the subwoofer, even at the lowest crossover setting.

its as if i have just added a dedicated low cab to the bass guitar rig. though obviously with low drum information, it will sound differently. it's time for a full PA shakedown...show is end of this month...

 

[Wasnex]

well my first impression is, I am surprised how much bass guitar string information is present and very responsive, in the subwoofer, even at the lowest crossover setting.

its as if i have just added a dedicated low cab to the bass guitar rig. though obviously with low drum information, it will sound differently. it's time for a full PA shakedown...show is end of this month...

Hopefully helpful hints:
It sounds like you may have the subwoofer a bit hyped. I suggest you dial the system in using music with the goal of a flat system response. Set your channel tone controls flat and play a high fidelity recording you are very familiar with. Compare the sound to a good set of headphones such as Sony MDR7506 to match levels between the subs and mains. You could also connect to one of the online tone generators and sweep a tone while listening to the levels.

After get the balance about right, set the tone at the crossover frequency and have an assistant flip the polarity on the sub to make sure it is in phase with your mains. Out of phase will decrease the SPL...if it makes no difference the phase is somewhere in the middle. Run the sweep and final time if polarity was wrong the first time.

Physical offset can be used in place of time delay if you want to mess with it. Notice that sound radiates hemispherically from speakers and think about what this means in the time domain with the sub in the middle instead of next to one of the speakers...perhaps this can be helpful in some performance venues.

 

[bearfoot]

Hyped, perhaps.

I don't take it as far as some people.

 

[Wasnex]

Hyped, perhaps.

I don't take it as far as some people.

View attachment 3014823

I have been pretty close to the brown note. Did a gig on a little stage built into a very small trailer (smallest I have ever seen). We tight packed four double 18 Apogee AE12 subs stacked on their sides in front of the stage. The low end gave me a bit of vertigo, but I was able to keep the brown stuff on the inside.

Set the system as you like, just be mindful that mics are prone to feeding back at hyped frequencies.

 

[craigie]

When we tried the “massively powered 18 whumpy” sub my friend had it way too loud so that he could get the kick he wanted (because we have midi tracks where relative levels are all fixed unless I edit every track) and my bass would blast on a low G and below. Very annoying. Didn’t like that sub anyway. With our smaller, tighter, more balanced to the system sub we don’t have that problem and just turn it up or down until we have a nice balance.

P.S. try sitting on it while you play. It’s nice to really feel your bass.

 

[bearfoot]

P.S. try sitting on it while you play. It’s nice to really feel your bass.

Please. This is a family friendly forum.

I believe the issue you cited is why so many recommend using an aux or monitor mix for subwoofer, and not just sending the main mix through it. I'm willing to bet that even guitar strings make all sorts of mud in the subwoofer channel, since it was reactive at bass middle E and above. I'm still a bit goofed to discover how much low frequency "talk" is in mics and instruments and how undesirable that is to amplify the hell out of.

This particular Behringer has stereo i/o. I don't know if that is standard or not, but it seems useful for running pre-recorded music, or for sending keys, synths, or as you mention MIDI through it, and still get your L/R top.

This is definitely a can of worms I've opened up, but it's worth it -

 

[Wasnex]

Please. This is a family friendly forum.

I believe the issue you cited is why so many recommend using an aux or monitor mix for subwoofer, and not just sending the main mix through it. I'm willing to bet that even guitar strings make all sorts of mud in the subwoofer channel, since it was reactive at bass middle E and above. I'm still a bit goofed to discover how much low frequency "talk" is in mics and instruments and how undesirable that is to amplify the hell out of.

This particular Behringer has stereo i/o. I don't know if that is standard or not, but it seems useful for running pre-recorded music, or for sending keys, synths, or as you mention MIDI through it, and still get your L/R top.

This is definitely a can of worms I've opened up, but it's worth it -

In my experience all open mics pickup and amplify subsonic frequencies, so it's best to not route them to the subs unless the mic carries a signal that needs subwoofer support. As you have noted, even instruments such as guitar produce subharmonic garbage that is not particularly useful for most musical styles. Now if you are trying to capture the chugga, chugga of a couple of 412s with a big tube amp pushed into blocking distortion and that sound is characteristic of the style of music, by all means send the signal to the sub.

I guess the point is you need to evaluate and decide what to do...just because a given channel has subsonic information, does not mean the information should be used...in order to make the decision it's most important to consider how the signal will impact the mix, rather than how it will sound solo. Most solo signal sources sound great with a lot of bass, but when you put them all together you get a boomy mess. As a result you may choose an EQ strategy that involves slotting frequency bands for each sound source to minimize the amount of masking that occurs.

Yes the stereo I/O would be useful if you decide to run the full mix through the sub. I believe it has full range thru's and also HPF outputs that could be send to the power amp for you mains. I agree this would be fine for recordings. Running the sub off the aux provides the opportunity for enhanced performance providing you run the system wisely. It can also produce really poor results if run without discretion.

 

[craigie]

In my experience all open mics pickup and amplify subsonic frequencies, so it's best to not route them to the subs unless the mic carries a signal that needs subwoofer support. As you have noted, even instruments such as guitar produce subharmonic garbage that is not particularly useful for most musical styles. Now if you are trying to capture the chugga, chugga of a couple of 412s with a big tube amp pushed into blocking distortion and that sound is characteristic of the style of music, by all means send the signal to the sub.

I guess the point is you need to evaluate and decide what to do...just because a given channel has subsonic information, does not mean the information should be used...in order to make the decision it's most important to consider how the signal will impact the mix, rather than how it will sound solo. Most solo signal sources sound great with a lot of bass, but when you put them all together you get a boomy mess. As a result you may choose an EQ strategy that involves slotting frequency bands for each sound source to minimize the amount of masking that occurs.

Yes the stereo I/O would be useful if you decide to run the full mix through the sub. I believe it has full range thru's and also HPF outputs that could be send to the power amp for you mains. I agree this would be fine for recordings. Running the sub off the aux provides the opportunity for enhanced performance providing you run the system wisely. It can also produce really poor results if run without discretion.

Lots of good advice above.

Crossover in the sub sending high signal to mains as mentioned in the paragraph above is the best case (unless you have external crossovers of course). This is of course assuming you have HFP’s on your channel strips and the aren’t too low.
As an experiment put everything you wouldn’t send to the sub using the aux feed and engage the HPF’s and send just that to the sub. What do you get? If your HPF’s cutoff frequency is at least as high as the sub crossover then not a lot. Just comes down to what gear you have and what’s more convenient.

 

[Wasnex]

Lots of good advice above.

Crossover in the sub sending high signal to mains as mentioned in the paragraph above is the best case (unless you have external crossovers of course). This is of course assuming you have HFP’s on your channel strips and the aren’t too low.
As an experiment put everything you wouldn’t send to the sub using the aux feed and engage the HPF’s and send just that to the sub. What do you get? If your HPF’s cutoff frequency is at least as high as the sub crossover then not a lot. Just comes down to what gear you have and what’s more convenient.

What you have written is 100% true. However, I believe there are benefits to running aux subs with an analog board even when each channel has HPFs. For example, the left hand of the keyboard and the low to medium toms are kinda in the middle....the place where you might not want to run a fixed frequency HPF on the channel strip, but also might not want to send them to the sub.

With an analog board and unpowered speakers, a bit of extra gear is required to reap max benefit from running subs off the aux. At the minimum, it would be good to apply an HPF to the mains that integrates with the LPF of the powered subwoofer to form an effective crossover.

I have a couple of extra crossovers that I can patch in as required. For example I can use a stereo 2-way to provide an HPF for my mains amp rack, and a mono 2-way to provide the LPF for the sub amp rack. With a digital board, I would just configure an appropriate HPF into the mains output of the mixer....or if using powered speakers from the same series, usually compatible HPF and LPF functionality is a provided feature.