Putting Sub Against Back Wall

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djtunes

Checking Reality
I've seen a couple people putting their sub somewhat behind them on the back wall with the side of the box against the wall and saying they get good sound like that (member: Maestro?) instead of next to the table to take full advantage of all the technical aspects of boundary cancellation and keep the area clean etc. - etc. - etc.

I have a QSC181 and the port is vertical along the left side if facing the front of the box. Google an img if it don't make sense.

Am I better off having the port close to the wall or opposite? Anyone... anyone?

The answer will determine if I want to put the sub on my right (as I stand behind my mixer) which will put the port close to the wall, or on my left which puts the port on the opposite side from against the wall.

Or is it best with the back of the sub facing the wall??? :/

This is all born from my idea of jobs using my small EV ZX1 tops and the sub... trying to be minimalist - as a clean, neat and discreet set up that packs a punch at the same time.

I do soooo many jobs where I'm getting MEGA bass overload behind/beside the sub only to find it just ok out in front. You prob all know what it's like. But coupling against walls and in corners helps change that.

Please don't tell me to just carry more subs. :) This one sub is doing fine for my little venues. Not many in my area reaching 200. If they do it's too many and the dance floor ends up being the size of a checkers board. Haha!

So.. port close to the wall or opposite... technically which makes more sense?

Thanks to all of you super smart people.
 

bb

Well-Known Member
Just a thought. Get the new EVs EKX, they are lighter than the QSC and use the Cardiod Mode. You'll need two but it will accomplish your goal.
 

Conanski

Active Member
It won't matter which way you orient the sub, sound wavelengths at the frequencies where the port is active are hugh so you'll get the same results either way.
 

maestro

Well-Known Member
I do soooo many jobs where I'm getting MEGA bass overload behind/beside the sub only to find it just ok out in front. You prob all know what it's like. But coupling against walls and in corners helps change that.
If you are not placing the sub against a wall, then it should be at least 8 feet from the wall to avoid the problem you are experiencing. Coupling with the wall using the side or rear of the sub works well for me. You DON'T need another sub. :)
 

bb

Well-Known Member
Cardiod mode is what concerts pros generally use. Eventually DJs will catch on if they want less bass in their face :)
 

NickyB

Gear and Equipment Moderator
Using the back wall to enhance bass increases the db output .... known as a corner reflector. It'll make the bass sound deeper because it partially uses the room walls to enhance the acoustic bass affect. However, sound loses roughly (i.e. minus) -3db as the distance increases by 10 feet, therefore any increase gained most likely will be lost due to the increased distance.

Another thing to remember is that the majority of subs are built to use the floor to improve projection of the bass. If you're setup on a riser or stage, you might want to locate your subs on the floor in front of you, side-by-side to get a +3db gain via acoustic coupling. This is why you don't see concert sound contractors "flying" bass bins. You might also remember that the large majority of sound contractors use four and five way systems for efficiency as opposed to a normal DJ who uses two or three way systems. The true way to get more bass, especially for school dances, is to add bass cabinets but the price to be paid is usually an aching back!

At one point in my past (like 20 yrs ago), I used four EV MTL-1x sub cabinets and two EV T-251 tops, each with its own PLX-3402 amp in bridged mono mode. Now at age 70, when I think about it (while getting my lower back epidural steroid injections), I must have been nuts! I still DJ on my terms but have three complete ZXA-1 systems which I mix 'n match as needed.
 
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bb

Well-Known Member
I hear ya! I use to bring (4) JBL SR4719A dual 18 subs to well paying school dances. Nowadays the thought of that is not so high on my mind. The young Djs can do that for the puny pay that is offered by schools nowadays.

Just to note: some concerts do fly subs and ground stack too.
 

NickyB

Gear and Equipment Moderator
I'd be willing to bet those "flying subs" are not really subs but probably are low-mid horns which would be part of a five way system that sound contractors use. Low-Mid cabinets look a lot like subs but are not true subs.
 

bb

Well-Known Member
I will agree to that. Floor coupling is way most do it for the thundering lows. A cardiod mode can be sweeter yet.
 

djtunes

Checking Reality
Thanks for all of the input. I've known a lot of this about boundaries etc. forgot the number of feet from the wall that was mentioned but I do remember that the cancellations can occur. Some jobs I have the sub against the wall I get a lot better results then other times I'm in the typical 3 feet from the wall with the edge of the dance floor about 5 feet from me. That's the times when on the floor the balance of bass to the tops isn't as nice on the floor as it is farther out into the room. Thanks again everyone.
 

Bob Dietrich

Active Member
Keep in mind, if the sub is several feet behind your mains, you may well end up with a time alignment issue as well. As Nicky noted, you might also lose any boundry output gained for the greater distance to the dance floor...in fact you could actually lose output in the nearfield depending on the distance.

Ideally, your subs and mid/hi cabinets should be on the same plane if both are direct radiating designs. Bent horn subs may need a slight tweak on time alignment to make sure they sound their best as well.
 

maestro

Well-Known Member
Exactly what Bob said! So many DJs run their tops and sub(s) on different planes; drives me nuts! :hp4:

In this photo you'll see my RCF ART705AS subs coupled in the middle with my FBT 4a's running along the same plane. Subs are way more than 8 feet from the rear wall AND I am set up in the corner to cut down on slap-back echo in the gym. :hp5:

full set up wide 600 pixels.jpg
 

djtunes

Checking Reality
Yup! :) I learned a lot for some of you guys' posts quite a few years back when these subjects came up in the past. Also went through a lot of educational papers etc.
Just didn't know if the port along the side made a difference one way of another. Thank you for your willingness to help.
 

jturk1000

And WHERE is Alma MI ?!
djtunes: I, too, have a QSC KW181, and I'm glad to hear you're getting blasted behind the table - me too! But just like you said, the sound out front is just fine. I put mine right in the middle/front of me for aesthetics (wish I could afford and haul two so I had them on either side of me and under my tops). I tried near the wall a couple of times, and despite what I know I've read, personally I think I preferred the sub out front.
 

Bob Dietrich

Active Member
Keep in mind, a subwoofer generally has an omni-directional output, so you could have it pointed backwards and doesn't really make any difference. Some bent horn designs when clustered can achieve some directionality above 60Hz or so.

Many tines I observe a DJ who has a good system, but as the evening progresses, since the highs are very directional and facing away from them, they're being overwhelmed by bass and start cranking up the highs so it sounds better to them. Unfortunately, the highs are now piercing the ears of those out front. If you're running a system capable of some big bass output, I recommend using a monitor of some type so the DJ is getting a better balanced sound without resorting to killing the guests.
 
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