How to connect an active subwoofer to a sound reinforcement system

hello everyone and welcome back to GLB productions my name is Bruno Luce thanks for joining me now in this video we're going to cover how to connect an active subwoofer to your sound reinforcement system this is a video that has been requested many times by my subscribers and I'm very happy to be able to bring it to you now before we get onto the connections let's first find out what we mean by subwoofer and what we mean by active now before we can connect our active subwoofer we need to understand what a subwoofer is a subwoofer in the sound reinforcement context or live sound context is a speaker system that is designed to work in the sub bass region of the audio spectrum as you can see here on my whiteboard I've got the sound spectrum laid out going from 20 Hertz right through to 20 kilohertz now sound engineers will generally divide the spectrum into four broad areas we have lows low mid-range high mid-range and highs now the exact point at which one transitions to the next is dependent on the particular instrument that you look at as well as the types of speaker systems that you're using but in general a subwoofer is a speaker system that is optimized to function in this area here generally 100 Hertz and below now what about specific subwoofer models in order to fulfill their role of operating in this sub base region subwoofers in sound reinforcement generally tend to have fifteen or eighteen inch speaker cones now what I have here is a 10-inch studio subwoofer and I'm using this just for illustration purposes but in sound reinforcement subwoofers tend to be 15 or 18 inch there are some new designs that use a 2 by 10 or 2 by 12 configuration and they can sound excellent there are also larger cones like 21 inch subwoofers that are used for speciality and certain forms of music such as reggae music dub music as well as electronic dance music there are also some very large subwoofers that are used in cinema applications but sound reinforcement generally we're looking at 15 inch and 18 inch cones the other thing about a subwoofer that sets it apart from a full-range speaker which I have here is the fact that a subwoofer has only a single type of driver as you can see here it has only a 10 inch woofer there are no mid-range drivers and there are no high-frequency drivers if you compare it to this the full range speaker you can see that the full range speaker has a woofer and a tweeter in larger sound reinforcement loudspeakers they may have a mid-range driver in addition to this and as a result a subwoofer is a specialized loudspeaker designed to handle only base and sub-base now let's look at the word active we hear the term active speakers passive speakers what's the difference between the two all speakers need amplifiers whether a speaker is active or passive depends on where the amplifier is located so on the left here I have a passive speaker this speaker requires an external amplifier and that amplifier is typically housed in a rack somewhere near the stage if it's an installation it may be housed in an amplifier room somewhere but the point is this speaker will not function without an external amplifier in the case of an active loudspeaker the power amplifier is built into the back of the loudspeaker cabinet itself there are several important differences between active and passive loudspeakers to begin with active loudspeakers such as these require at least two connections they require an AC power connection and they require a line level signal connection with a passive speaker like this all that is needed is a single loudspeaker level connection you can see that there are two connectors on the back one of these is an input and the other one is a parallel output which is used for daisy chaining two other loudspeakers in the case of our active loudspeakers you can see they have an IEC receptacle which takes an IEC power cable also known as a jug plug in the UK and they have XLR connectors for taking a line level signal from a mixing console it's very important that you do not try and run the output of a power amplifier into an active loudspeaker because you will overload the input and you could very well damage the amplifier that is inside of this active speakers have a number of important advantages over passive especially for mobile sound reinforcement use to begin with you don't need a separate amplifier rack all you do is you bring the active loudspeaker your mixing console and whatever peripherals you need that alone save space and it also saves weight with the new d-class amplifiers the digital switching amplifiers an active loudspeaker can be made just slightly heavier than its passive equivalent and that's really important for these days where fuel costs are going up haulage and trucking charges are going up so with with an active system you can actually get rid of quite a bit of gear and quite a bit of wiring secondly active loudspeakers have the amplifier matched to that loudspeaker so with a passive loudspeaker like this very often it's you the end-user who have to decide on what power amplifier works best and how much power do I need how much power can I get away with that sort of thing with an active speaker system all of that has been decided for you the amount of power is just what the designer has determined that is right for that particular speaker system there is also speaker protection in the form of limiters built in which will hopefully stop your loud speaker from blowing although that is not guaranteed especially if you overdrive the system finally it's important to understand that an active speaker system will be more expensive than a passive speaker system however if you put in the costs of a separate power amplifier as well as all of the cabling that is required to connect the amplifier to the loud speaker a active loudspeaker is almost always going to be cheaper than a passive loudspeaker and a separate amplifier now do active loudspeakers have disadvantages yes they definitely do the biggest one is that you need to run both power and signaling to the speaker this means that you need extra power cabling it also means that you need additional power located near the stage and sometimes you'll need power located on the stage itself however in my opinion these trade-offs are worth it because active loudspeakers typically sound better than the equivalent passive system now let's have a brief discussion about whether you need a subwoofer as you can see here speakers come in two general types they come in full range and subwoofers you always need full range loudspeakers without full range loss because your system will be just bass and while that may appeal to some of us it generally does not result in a paycheck at the end of the show so when do you not need a subwoofer I would say that if you do only the reinforcement of speech for example meetings presentations conferences that sort of thing you can generally get away with no subwoofer so speech only no subs necessary this can be extended to light background music where the music itself is not the main attraction classical music reinforcement can often be done with no subwoofer and the reason for this is that classical music reinforcement is often a slightly lower level than pop rock and that sort of thing as well as the fact that classical music audiences often don't expect that sort of thunderous lambing sub bass that is associated with more contemporary types of music so classical music reinforcement often you don't need one but check with the producer know if there is any kind of contemporary music you need to look at whether you have instruments that operate below 100 Hertz for example kick drum floor tom bass guitar keyboard and upright bass just to name a few if you have any of these instruments I strongly recommend that you include a subwoofer in your PA system now there are some exceptions to this such as the club type PA system where the PA system carries the vocals keyboard and acoustic guitar and the other instruments including the drums are simply heard acoustically so this will be applied on a case-by-case basis in my opinion any PA system sounds better with a subwoofer and the reason for this is that you are spreading the load of the audio spectrum among more than one loudspeaker when you're using just a full-range speaker that full range speaker has to handle every it has to do low mid and high when you add a sub the sub handles the low freeing up the full range speaker to concentrate on the mid and high so it's like a team as a result the system sounds cleaner because there is more power available and it's much better able to handle transients things like kick drum Tom hits snare drum hits acoustic guitar that sort of thing all of that sounds much cleaner because the audio spectrum is being divided among these different loudspeakers it's important to understand that the low frequencies contain the most energy and because of this it makes sense to have a separate dedicated speaker system for that part of the audio spectrum finally with a sub woofer you can actually reduce the size of your full range cabinets if you have a subwoofer you can often get away with using 12 or 10 inch full range cabinets because they don't have to carry the bass as well as the mids and the highs so in my opinion if you can afford it and you do contemporary music it's always a good idea to have at least one subwoofer in your system as my mentor and teacher Marty McCann used to say if you want to mic the kick drum if you want to mic the bass guitar you're gonna have a sub baby now let's look at the first method of hooking up an active subwoofer and this is using the crossover that's built into the subwoofer what we're assuming here is that we have an active sub and we also have active full range speakers which are known as tops because they sit above the subwoofer hence top sub and top so what is a crossover a crossover which is also called an X / short-form is an electronic dividing network that splits a full range audio signal into a number of bands and in the case of our example here we have a sub band which contains all the frequencies below a hundred Hertz and then we have a mid high band which contains all of the frequencies above 100 Hertz most active subwoofers nowadays have this built in so the way that we're going to hook this up is from our mixer we're going to come out left and right full range we're going to go in to the active sub the subwoofer crossover will divide the full range signal into lows and mid highs the sub will handle the lows it will then output the mids and highs to our active top speakers and this is how we're going to set it up now so here's the setup that we're going to be using I've got a Macky 802 vlz 4 that is going to act as our signal source we have a small studio subwoofer and we have a full range loudspeaker again just for the purposes of illustration now before we go on we need to take a look at the back of this subwoofer because this is the part that contains the crossover which we're going to connect to now in the case of this subwoofer you can see that it has a pair of inputs left and right it also has a pair of outputs now on a lot of sound reinforcement subs you will have two pairs of outputs you will have a full range output which is basically just a parallel out and it's designed to connect to other subwoofers and you will have a pair of high pass outs and what this is it's the full range signal - the sub base that the sub is handling so basically the sub takes the full range signal splits it up takes the base and it hands the mids and the highs off to our full range speakers in addition to that this particular sub has an input level control as well as the crossover frequency controls now on this sub the crossover frequency is actually variable you can see it's variable from 55 to 110 Hertz on many sound reinforcement subs this frequency is fixed and it's typically fixed around a hundred some maybe a hundred and twenty Hertz and if it's fixed don't worry that's perfectly fine it's what the system designers have said is appropriate for that particular subwoofer to begin with let's hear how the system sounds with just the full range speaker hooked up so we're coming out of the mixer and into our full range speaker sub is not connected now for most people they'd say that sounds pretty good but if you listen carefully you can hear that on the loud bass notes the full range speaker is beginning to break up a little bit and there are some there's a little bit of distortion in the bass simply because it can't handle the level and you know we're only at about 85 decibels here you try and do that at a hundred and ten and see how your full range speakers sound all right now let's get the sub hooked up we're going to come out of our mixer from the XLR outputs and we're going to connect to the left input of our subwoofer if you have two speakers left and right you do both left and right for this illustration I'm only going to do one side just as we've only got one full range speaker after connecting the mixer to the subwoofer you will take another normal microphone cable and connect the high-pass output of the subwoofer to the full range speaker remember make all of these connections with the power turned off all right now we're going to set our crossover frequency if your son doesn't have a crossover adjustment control you can skip this step as I mentioned on this particular sub the crossover frequency goes from 55 to 110 because these are really small speakers I'm going to set it at 110 what that means is the sub will handle everything below 110 and the full range will handle everything above that okay we're now ready to switch on mixer is already on we switch on the sub first and then we switch on the full range speaker what I'm going to do now is I'm going to turn the sub level all the way down so that we can hear the full range speaker without the sub and what you hear is that it now sounds a lot less bass see so the reason that it sounds real thin now is that the sub has taken away all of the low frequencies now you wouldn't want to leave your system like that because it sounds terrible doesn't it so this is where we bring in the subwoofer so what I'm going to do is I'm going to raise the input sensitivity of the subwoofer this particular sub has a detent at the 12 o'clock position because that's sort of nominal right same in same out I've already set the level of the full range speaker to the volume that I won the sub has a polarity switch I have it pushed in just because the sub is facing one way and the full range is facing the other way I face the full range towards the camera so that you can hear the full range as opposed to the muffled sound with it facing away alright now let's hear the same track which I recorded by the way alright enough said now I don't know if you could hear that but when I turn the sub up past the unity gain setting the room actually started vibrating and that's what the subs do so now we have to ask ourselves how do you match the level of the sub to the level of the full range speakers if this were a professional setup what we would do is we would use something like smart life to optimize the system but if you don't have smart life you can use spectrum analyzer or you can just use your ears start with a sub at the unity gain position right if there's a zero on the back if there's a détente 12 o'clock position set it to that then play a track that you know well and listen if there's not enough bass turn up a bit if there's too much bass turn it down but of course there's never too much bass but seriously if you find that the balance is wrong don't be afraid to turn the sub down because every venue has its own acoustic some venues are naturally very basic this is especially true if you have the sub in a corner or if you have the sub next to a wall so sometimes you actually have to bring the sub level down if you are outdoors the opposite is true without these reflecting surfaces you need a lot more sub bass to the same effect as when you're indoors so use your ears and don't be afraid to make adjustments so now we're going to look at the second method which is the group or Oxford sub system now this is a little bit more complex than the first but it gives a lot more control and is favored by many professional engineers myself included so what we have in this situation is the mixer is connected through a high-pass filter to the top or full-range speakers now how you get this high-pass filter can be done in a number of ways you can use an analogue crossover to provide this and not connect the low output to anything you can use a system processor or there are a number of full range speakers available today that have a subwoofer mode and what that does is it inserts a high-pass filter after the input to the speaker which basically takes away the bass because it knows that there's a sub somewhere else handling it then a post fade oxen or a group send is connected to the subwoofer now the advantage of this system is that it allows you to send only specific channels to the subwoofer and this has a number of advantages number one it reduces the load on the sub amp because you're only sending the channels that you choose to that sub woofer ock send good choices are of course kick drum and bass guitar as well as floor tom and certain keyboard patches the other thing is that this technique can actually reduce feedback because you're not sending the vocal mics to the subwoofer and typically the subwoofer is on the floor or ground nearer the the singers then would be a flown or pole mounted full-range speaker system it is best to choose an aux end as long as it's post fade and the reason for that is that the level of the sub will track with your fader movements but if your post fade aux ends are all used typically for effects ends you can also use a group send or a matrix end that you have configured specifically for that purpose all right now let's hook up our oxford subwoofer we have here is we have the same setup our mixer is connected directly to our full range speaker now in reality this connection would have to run through either an external crossover or some kind of digital processor or if you're active full-range speaker has a sub mode you need to engage that now let's connect the sub to connect the sub I'm going to use a TRS two XLR male cable you can also use an adapter and because this particular mixer has only a single aux end we're going to connect to that we're going to make sure that the aux end is set to post and I'm going to connect this to the subwoofer subwoofer settings are the same and we're going to power the system on sub first and then full range and I'm going to play that track and as we play the track I'm going to turn up the Ox and on the channel where my recorder is connected so at first you'll hear no sub and then you'll hear more sub level on the sub is set to unity no sub turning up and thus up more so back to no sub so that's how you implement the Oxford subwoofer technique now what about if you have passive full range speakers meaning that you have an amplifier and loudspeakers this is the case with many existing systems out there and people want to add a subwoofer to a system like this the good news is that it's really easy and you don't necessarily need an external crossover this is how you do it from your mixer you take your left and right connections which would normally go to your system amplifier and you connect them to your active sub you then connect the mid high or high-pass outputs from the sub to your amplifier in exactly the same way as you used to connect your mixer outputs so the sub sits in between your mixer and your amplifier and all of the frequency dividing will happen as we've shown in our instructions and you'll have a subwoofer if you want to use the Oxford technique with full range passive speakers you will generally need to at some kind of filtering before your front-of-house amplifier to cut the base out of your full range speakers and this can sometimes be a crossover it can also sometimes be integrated into the power amplifier many power amplifiers these days have a built-in crossover or filtering function which can be used very very successfully with an additional powered subwoofer and finally a word about larger PA systems with larger PAA or sound reinforcement systems most of these functions will be handled by an external digital signal processor DSP or electronic crossover on your mixer would be connected to the DSP the DSP would do the frequency division and then you would have full range and subwoofer systems these methods that I've shown you today by and large do not require the connection of an electronic crossover because the crossover in the sub is more than sufficient for small PA systems and that's how they are designed so unless you have a larger system you often do not need a separate crossover if you have an active sub so that's how you connect an active subwoofer to a sound reinforcement system I hope this video has been useful as you can see there are a number of different ways to connect an active sub to your sound reinforcement system there's in line there's group fit or aux fit and you can also use an external processor or crossover if you have any questions and I'm sure you do or comments please feel free to leave them below I love to hear from my viewers and I'm more than happy to answer questions on this topic so until the next video this is bro loose for GLB productions I'll see you then bye bye

Channel: GLB Productions

Views: 920,010

Keywords: sound reinforcement, pa system, subwoofer, active, passive, sub, bottom end, sub bass, bass

Id: 548GZAF6fMY

Length: 30min 17sec (1817 seconds)

Published: Thu Oct 20 2016