Adding a sub to an existing setup

[mjriley]

Hi everyone.

 

I have been asked to add a subwoofer to my schools system. At the moment it is a mixer connected via XLR to an amp then through speakon to two speakers.

How would I add a subwoofer to this system?

 

Michael

Have a great Christmas.

 

 

Moderation: Moved from "Sound" to "The Next Generation" because it's a pretty basic question....

[grahamdking]

Hi Michael,

 

There are several ways you could do this, first of all you need to find an output for your signal to the sub. This could be the mono output of your desk, from the link output of the amp, from a subgroup output, etc. This signal would be at line level as opposed to an amplified speaker signal.

 

Then the sub, you could go for a powered sub (this for example, don't worry cheaper ones are available!), which would require mains power and the signal. (i.e. no amp).

Or a passive sub (like this), which would require a separate amplifier. To connect up the passive sub you would send the signal to the amplifier (probably via XLR3), and then the amplified signal to the sub via speakon. If you only have one sub, the output of the amplifier could be linked (or bridged) so that both amplifier channels power the sub, giving you more headroom.

 

Alternatively you could run your system in mono, ie both your existing speakers playing the same sound. By linking them to one of the amplifiers outputs, and connect a passive sub to the the output. This however would not be as good as the previous set ups.

 

Hope that helps

 

Graham

[tolley1466]

Whats the system at your school? Also what are its main uses?

 

If you were to add a sub on you would need to run the signal from the mixer through a crossover into your amps. If you don't know what a crossover is its basically a device that separates the high frequencies from the low frequencies. This will help you get a clearer sound.

 

But depending on the application, you may not need a sub or a sub as big as 18"

[mjriley]

Thanks for this.

 

Michael

[Killyp]

Could you post what system your school has? What model are the speakers, the amp and the mixer etc...?

 

Also, what is it mainly used for?

[Bobbsy]

Okay, everybody is demanding more information but let's see if I can do a general reply to at least get you started:

 

To add a sub to an existing setup, one way or another you'll need three things:

 

1. A crossover to separate the low notes from the rest and feed the low bass to the sub and the rest of the audio spectrum to your existing speakers.

 

2. An amplifier to drive the sub.

 

3. The sub speaker itself.

 

No matter how you do it, you will need to have these three components.

 

Where the "there are lots of ways to do this" part comes in is that, quite often some or all of the above can be combined in one box. It's entirely possible to get a sub that contains its own crossover and amp--you just plug the output of you mixer into the sub, then take the output to you existing amp. The sub will have electronics inside that feed the sub-bass notes to an internal amp then the speaker driver while passing the rest of the frequency range onto your existing system.

 

Even more common are self powered subs that have a built in amp along with the speaker. In this case you'd have to have a separate crossover--you feed your mixer output into the crossover and it gives you two outputs, one filtered for the sub and the other suitable for the tops.

 

Finally, you can have three separate boxes, the crossover as above, a separate amp for the sub and an unpowered sub.

 

Clearly there are different advantages and disadvantages to each of these alternatives but any of the three can work.

 

Some people have mentioned that it may be possible to re-jig your existing system so the one amp can drive both your tops and the new sub. Yes, maybe...but this will take some calculations of the power you have avaiable and the impedance of the existing speakers. Yes, it's worth checking but (if the existing system was properly specced) you might not have the necessary power available.

 

Since we have no idea of your needs or budget I'll stop short of suggesting any specific gear but hope the above gives you some information to be thinking about.

 

Bob