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My current PA system I use with my band (usually 2 guitars, a bass guitar and drummer - with 3 vocal mics) consists of a powered mixer (Mackie 808S) driving passive speakers with 12" low/mid drivers and high frequency horns in each cabinet. I am using powered speakers as floor monitors.

Often our drummer will use a Roland electronic kit and in some venues it helps to run the Bass through the PA. I am thinking about incorporating a sub-woofer or two into my system to add some low end uummmph to the kick drum and bass guitar.

I suppose I could use passive subwoofers but I am leaning towards powered subs. I am wondering what the best way to run the signal chain is and what things I should consider.

I am thinking I might get a powered sub with a high pass filter and run it from my non powered monitor out jack - and pass the +125 Hz frequencies to my floor wedge monitor line and just run a powered full range signal to my passive 12s.

One reason for favoring powered subs is that in the future I may want to convert to a passive mixer, powered mains system and I would want the sub woofer to survive. Of course if I run powered mains with a passive mixer, I would probably pass the +125 Hz frequencies to my powered mains and run full range to my monitors.

Also, will I get acceptable results from just one powered subwoofer or will I need at least two. I don't have any now.

Finally, will I need a separate crossover or can I just get sub woofers with a high pass filter and use that in lieu of an independent crossover.

Any advice on effective ways to accomplish my goal would be appreciated.

  • In addition to my answer, this sounds like a good time to re-evaluate owning a PA as a band, as opposed to renting one with or without a sound guy. A lot of bars in my area now have their own PAs, partly so they can control the overall volume. If you almost always gig with other bands, splitting up the costs of a PA rental for the whole show can make it very cost-effective. On the other hand, if you're bringing the PA and letting other bands use it, you should get a bigger share of the door or charge them something for the PA. – Todd Wilcox Nov 12 '15 at 15:51
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    Also, once you have subs, one prime candidate for adding to the PA mix is the kick drum, which can often get lost. As a sound guy I've put a lot more kick signal through PAs than bass signal, by a huge factor. I usually take a bass guitar signal but often muted it or only brought the fader up a little. I gave a lot more love to kick mics. Downside is once you have a kick mic you want a snare mic to balance it and then tom mics and - oh god the drum channels! – Todd Wilcox Nov 12 '15 at 15:53
  • @ToddWilcox Most of the Bars/Restaurants I play do not have their own PA and I like to do private parties whenever possible (they pay better and are more fun) so I don't see myself eliminating my PA. And when I've played with other bands, they want to use their PA (I guess they are used to it and trust it) and don't want to let me use it (maybe they want to load out and go home). But I did play once with a house PA and good sound man in the booth and never sounded better. – Rockin Cowboy Nov 12 '15 at 17:06
  • @ToddWilcox good point about the kick drum vs. bass. Definitely want the kick to stand out. And yes, drums are the hardest instrument to EQ -From the kick to the cymbals and everything in between they occupy the entire spectrum. – Rockin Cowboy Nov 12 '15 at 17:08
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I agree that looking at the future configuration you want is a good idea becuase that way you're not spending money on something now and then spending more to replace it later. From that point of view, one piece of advice is to imagine your ideal, complete PA system that you hope to have in the future. Then, when you want to add or change what you currently have, you buy with the ideal future PA in mind.

Regarding subs in general - Subs bring two things to the table: low end frequency extension, and more power to the system overall. The first is a lot less important than one might think (and also more difficult to attain), the second is extremely helpful. I'm not sure of all the technical or acoustic reasons why, but if you had a 1000 Watt system and you wanted to make it a 2000 Watt system, it's better to subdivide the frequency range and have 1000 Watts for lows and 1000 Watts for mids and highs than it is to just add another 1000 Watts to a full-range setup.

The reason that is relevant to you is because if you don't cut the low frequencies to your powered mains when you introduce a sub(s), you're not getting as much benefit from the power boost that you would normally get from adding subs. The other downside to not putting a high pass on the mains/tops is that you're more likely to have destructive interference of low frequencies between the tops and the subs.

Regarding full-range vs. low pass vs. crossover - It might be a challenge to actually high-pass the mains feed when using a powered mixer (unless you have a main out insert), so for now I wouldn't worry too much about it. It's a good thing to plan in advance for if and when you change out your mixer. To that end, you should consider getting a crossover to low pass your sub feed, which you can then use in the future to high-pass your tops. Either a passive EQ-only crossover like these, or if you want to future-proof your rig a lot more and have lots of options, you can go for a speaker management system like these. The speaker managers cost more and offer delay, EQ, and other processing. The delay processing in particular can come in handy for time-aligning subs with tops, which makes a surprisingly huge difference when you get it right. The downside with speaker managers, besides cost, is that they are more complicated and might be overkill for mixing from the stage if you don't have your own sound person to really tweak it out.

Regarding one or two subs - you can divide that question into placement and budget. You don't need two subs for stereo purposes, partly because you don't want to run a non-stadium PA in stereo anyway (and most stadium-sized PAs are run mono also), and partly because even if you did run stereo, the low frequencies are poorly localized by our ears so there's no benefit to stereo spread for subs. That also means that placement is down to time alignment, coverage, beaming, and visuals. Acoustically, the best place for any number of subs is right in the middle of the stage. A lot of club-level venues build a stage tall enough to put the subs under the stage behind a black scrim. If you don't have a tall stage, then you usually want to put the subs near the tops, which are typically off to the sides so they don't block the view of the band. Putting the subs near the tops also helps with time alignment, as mentioned above regarding delay processing. If you only have one sub, and you can't put it in the middle, then you're stuck with choosing a side to put the sub on and that means people closer to one side of the stage will hear more bass than people on the other side. The downside to separating the subs is there can be destructive interference in the middle that creates hot zones and dead zones in the low end (the problem is often called the power alley), but typically that's a necessary compromise for bar-level gigs. If you can afford it, I would say two subs is preferred because you can place them together in the middle if possible, or spread them with the tops for better coverage and time alignment (and just endure the power alley in the latter case).

Regarding powered vs. unpowered - This is a tougher question that probably only you can answer. With the concept of how you want your whole system to look at some point in the future, and assuming if you go powered subs now you'll go for powered tops later, let's look at some bullets.

Using Powered Mains and Subs

  • Overall, a powered system can be more compact. With powered subs and tops available based on 12" drivers, and without the need for a power amp rack on stage, a fairly high-wattage FOH system can fit in a smaller vehicle for bar-sized gigs.
  • Running power to powered systems can be very tedious. A roll-up multi outlet extension cord for each side of the stage is usually perfect for this, but that doesn't change the fact that you have to run both power and two signal cables to both stage right and stage left. Since the signal cables for powered speakers are line level, instead of speaker level, they can be more susceptible to noise.
  • Manufacturers can tune the amp to the enclosure very closely, creating systems with more ideal damping factors and internal bi-amping (for tops).

Using Passive Subs and Tops With Separate Power Amps

  • Usually these systems take up more space than systems based on powered speakers, since the cabinets are usually about the same size and then you add on the amp rack, which has to go somewhere. Usually the amp rack goes on or near the stage to take advantage of snake returns and shorter speaker cable runs.

  • Once you have the amp rack(s) powered up, the only cables that have to run around the stage area are speaker cables, which helps keep stage cabling neater. Also, good quality speaker cables are more durable than line level cables and it's easier to keep the amp rack and power supply out of the way of stray beer spills as opposed to powered speaker power supplies.

  • Separating the amps from the cabinets can save your back, since you are dividing the weight up into separate boxes. On the other hand, the total weight of the amp rack(s) and cabinets of a passive system will usually be more than the total weight of a powered system. So passive is better for your back(s), worse for your vehicle suspension.

  • If you blow the driver in an unpowered speaker, you can more easily and cheaply repair or replace it and/or rent a substitute. Likewise any beer spillage, toppling, or other trauma is less likely to cause a complete failure of an unpowered speaker.

  • You can choose your favorite speakers separately from your favorite power amps, versus a powered system where you might get a great enclosure with a so-so amp or vice versa. Overall I've been more satisfied with the sound from unpowered speakers and separate power amps, and this reason is my favorite theory why.

  • Purchasing and using unpowered speakers with separate power amps does require more understanding, research, and careful product selection to match power and impedance levels appropriate and also to set crossovers, filters, and limiters appropriately to get the best sound and protection of the speakers. Powered systems can be tuned and configured inside the box(es) for the ideal settings, making them a bit more plug-and-play.

Not totally related note about mixers

I want to put a personal recommendation against powered mixers and in favor of at least considering a digital mixer if and when you look at replacing your current mixer. Powered mixers are nice compact ways to build the smallest systems, but they have so many limitations and you can't upgrade power levels without upgrading the whole mixer. Digital mixers are nice because you get effects and more flexible EQ built in without having to build a separate effects rack, making the whole system more powerful and compact at the same time. These days sound quality is not at all an issue with digital mixers.

  • Thanks for your insight. You have mentioned a few things I have not considered. BTW my Mackie 12" passive mains are heavier than the newer Class D powered 12" Mackie SRM V3s. And my powered mixer is heavy too. Currently I am running speaker cables to my passive mains AND speaker cables to my powered monitors. Should I be using a different type cable to my powered speakers since they are getting a "line level" signal? My theory for future - is that since the newer powered speakers are bi-amped with an internal crossover, they might sound better - but my current system sounds great. – Rockin Cowboy Nov 12 '15 at 17:00
  • If you are actually using speaker cables to connect powered speakers I expect they would definitely sound better if you used balanced line level cables instead. I'm sure the SRMs will take XLR balanced inputs. The mixer might only have 1/4" outputs but they should be TRS, so just a TRS male to XLR male cable should do it. In case it's not obvious, never connect a speaker output from a powered mixer to the input of a powered speaker. The SRMs probably have much lighter magnets and maybe lighter baskets and cabinet materials - there are certainly no hard and fast rules. – Todd Wilcox Nov 12 '15 at 18:26
  • Actually I do use a TRS to XLR cable to connect my first powered monitor to the mixer from the non power 1/4 inch output and then chain the other's with XLR mic cables. But there is also a 1/4 inch input on my powered monitors as well. I get better results from the TRS to XLR cable though. – Rockin Cowboy Nov 13 '15 at 6:12
  • What are "the tops" in your section "Regarding one or two subs"? – Dave Dec 7 '15 at 14:18
  • "The tops" means the speakers that are not subwoofers. Usually they are handling all the frequencies the subs are not handling. On larger systems there may be "subs", "mids", and "tops" with separate amps for each part of the frequency range, although the word "tops" may refer to anything that's not a sub. – Todd Wilcox Dec 7 '15 at 14:26
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I would go for an active subwoofer. Most have inputs for full-range signal and outputs for high-pass signals. Get a sub that can divide both left and right. You should be able to find eg a used Mackie SWA 1501.

Connect two cables from mixer out to the sub inputs (Left and Right) and two cables from sub out to the mixer power amp in. As it is signal level, you use shielded signal cable to minimise possible problems. The sub probably has XLR - contacts (same as on microphones), while the mixer has 1/4 inch. This means that you will need to ask for help to get the correct type of unbalanced cables, nothing really difficult for an experienced person, but not all are.

The advantage of not sending the low frequencies to your top speakers is that the tops now will only need to work on high frequency. Often this leads to both higher volume (more decibels) and better clarity of sound.

Start with one sub, it is often enough.

  • I have a Mackie 808S powered mixer. I have two main out's and two powered mixer in's but only one monitor out which I use for powered monitor. I have only volume and effects level control on monitor out vs. 3 band EQ on main outs for each channel. So if I plug a mic into channel one on mixer and run main outs to tops and monitor out to a powered sub and hi pass back to power amp in will the signal to the mains (tops) go from channel one input to mains through the main out or will sending hi pass from sub to power amp in cause the signal chain to flow through the sub before out to mains? – Rockin Cowboy Nov 7 '17 at 2:19
  • It is the main outs you want to pass through the sub. The whole chain is: microphone -- channel input (here you copy signal to the monitors, not part of the chain otherwise) -- out of the mackie (jacks mixer out) - to sub - through sub (now without bass frequencies) - to mixer power amp (jacks on the 808S) - to tops. The sub will now play low frequencies, the tops only higher frequencies. – ghellquist Nov 7 '17 at 12:07
  • I don't think I can run an amplified signal to a powered sub. Do you mean use a passive sub? – Rockin Cowboy Nov 8 '17 at 5:57
  • On the front of the 808s there are four jacks under the heading of MAINS. Two of the jacks carries a line signal (not speaker level) containing the output from the mix, Left and Right. The other two jacks are the inputs to the power amplifier inside the box. Inside the box these are connected in a clever way. If you enter a jack in the Power amplifier input the connection is broken. This is what I suggest you use. You take the signal out from the mixer (it is one level), let it pass through the sub (still line level) into the 808S again to the power amplifier in jacks. Hope this helps. – ghellquist Nov 8 '17 at 7:01

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