Sunken Sub, Remote Power, and Speaker Placement

We got a little sick of having to constantly work around the subs and speakers sitting on stage, so decided to finally sink the sub in the stage, and hang the speakers.

With that it becomes a little more difficult to turn everything on and off, so I'll cover a remote power switch (that doesn't require routing the power for the devices through your sound booth or wherever you want your switch) and I'll talk a little bit about speaker placement.

Lets start with the subwoofer, you may ask why sink the sub in the stage rather than flying it? After all I've seen large sound companies fly subs at the top of line arrays or other setups.

Well thats a good question, and It all comes down to money and ease. When you fly a sub you actually have to have more power to have the same results. When a subwoofer is in contact with the ground its like getting free power. In fact you gain 3db just for coupling your sub to the ground, if you where to put it against a wall and on the ground you would've gained 6db, and in a corner touching 2 walls and the ground you'll gain 9db of free volume. (I know that its not an exact number and there are other circumstances that could change your results, but the numbers are close enough for the example)

There are so many different ways to arrange your speakers, but if you're looking for a pretty easy way to know where to place your speakers here's a good option.

Most rooms you'll be working in will be rectangular, and this will be a solid way to get a good even sound without much phasing. You'll Need to measure the width of your room. Your placement for the speakers off the side wall will be 27.6% of the width of the room. W * .276 For the placement off of the back wall will be 44.7% of the width of the back wall. W * .447 Now these numbers didn't come from me, I found this a long time ago while researching and jotted them down and forgot where I got them from. Now if your doing live sound, you don't want your speakers to be behind the band or behind any mics being used. So if your stage happens to be farther out than that speaker placement you are ok to fudge the numbers a little bit and push the speakers out beyond the band.

If your speakers and sub are on different planes (meaning different distances off the back wall) its not the end of the world, but you will want to do a bit of timing correction to make sure that your sound lines up. If you don't, depending on how far off plane they are, it could make the band sound like they're always off tempo, or the sound could be muddy. You can either impulse test the room, or pull out your tape measure and do a bit of math to find out how many milliseconds to delay your speakers by.

For the power, rather than running high voltage lines a long distance to your sound booth, or having to run up front to turn everything on and off you can very easily build a remote power controller. Furman sells units like this but they are very pricey and do nothing different than what this does. (besides sequencing which if you have enough power draw that you need sequencing its not hard to modify the circuit)

I used a 40 amp solid state relay, with a 20 amp breaker to protect the relay. (I originally had a 20 amp relay but burned it up by accident) this will ensure that the breaker for the relay will trip long before the relay can burn up. To activate the relay I used a 12v led driver power supply. Now all you need is to run a low voltage line from the booth up to the relay box. When you turn your switch on it sends 12v to the relay and turns on the circuit that your speakers are plugged into.

WARNING: Be sure to follow all local building codes. If you are at all not sure about the code hold off and verify with an electrician. You don't want to end up with a fine for not doing things the proper way, or even worse having someone get hurt because of an improper wiring job that you did.