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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Subwoofer Forum => Topic started by: Matt Gordon on September 16, 2013, 12:22:15 pm

Title: QSC KW181 stacking (placement) - NEED ADVICE!
Post by: Matt Gordon on September 16, 2013, 12:22:15 pm
So I DJ at this bar/club every weekend and it has concrete floors.  I have 2 KW181s and 2 Yamaha S115V's (powered off QSC amp).  I am wondering where the best placement of said subs would be. 

Things I have tried:

1. Subs on left and right side with poles for the speakers.  Sounded alright, but not too much bass kick except right in the front.  Also, I can't get my hands on the adjustable pole mounts anyways. 

2. Subs placed side by side right in the middle underneath/in front of my table.  Sounds great, especially where I am, but still not a big kick on the dance floor and also sounds lower than the speaker (i.e. not a hard punch).


So what I am thinking of trying, and need your advice on, is stacking two of the subs to the right side of my table with a pole on top for the speaker.  And the other speaker on a stand on the other side.  My thoughts are that since one sub is higher, it might give that chest punch i was hoping for. 

Please help me out!  I'm open to other options as well.  Thanks!
Title: Re: QSC KW181 stacking (placement) - NEED ADVICE!
Post by: Bill Hornibrook on September 16, 2013, 08:29:21 pm
Stacking your subs will not help their low frequency output, and usually diminishes it whenever I've done it.

I read the responses to your question in another forum (of which I am not a member). As a DJ I actually want a power alley if I can make it happen on the dance floor. I want things to just pound right there but don't want all that LF info around the bar area or the back seating. To do that, I'll usually place my subs right in front of the dance floor on either corner, but I sometimes have to skew them one direction or the other in order to minimize phase cancellations from adjacent walls. The suggestion about keeping subs 8-10 feet from walls is a good one generally, but there's this one room where I get the best LF response when I place one sub right against a side wall and the other on the far end of the dance area. If I placed both subs along that side wall they get too localized, decouple from the tops, and sound weird.

There's no exact science to this because each room is different. 

As mentioned over there, you really need a crossover. But in the meantime you might try a quick and dirty experiment of reversing the polarity of your tops versus your subs to see if that helps at all in the 50-100hz frequency range.
Title: Re: QSC KW181 stacking (placement) - NEED ADVICE!
Post by: Ryan Fontenot on September 16, 2013, 09:34:28 pm
Hi, after reading your post I would like to comment on what you are trying to accomplish. 

First of all, are your subwoofers powered? 

Second, your subs should be crossed over at between 100 and 120 Hertz.  This will mean that they will get everything below the set crossover point. 

Third, you do not need to stack your subs.  The reason why your subs are not pushing out the bass is because the bass is hitting the concrete and reverberating off of it.  Therefore, it never gets to the audience.  My advice would be to stick a piece of carpet under the sub that sticks out about 8-10 feet.  This will allow the bass to actually come out of the enclosure the way entended.

Thanks,
Ryan


So I DJ at this bar/club every weekend and it has concrete floors.  I have 2 KW181s and 2 Yamaha S115V's (powered off QSC amp).  I am wondering where the best placement of said subs would be. 

Things I have tried:

1. Subs on left and right side with poles for the speakers.  Sounded alright, but not too much bass kick except right in the front.  Also, I can't get my hands on the adjustable pole mounts anyways. 

2. Subs placed side by side right in the middle underneath/in front of my table.  Sounds great, especially where I am, but still not a big kick on the dance floor and also sounds lower than the speaker (i.e. not a hard punch).


So what I am thinking of trying, and need your advice on, is stacking two of the subs to the right side of my table with a pole on top for the speaker.  And the other speaker on a stand on the other side.  My thoughts are that since one sub is higher, it might give that chest punch i was hoping for. 

Please help me out!  I'm open to other options as well.  Thanks!
Title: Re: QSC KW181 stacking (placement) - NEED ADVICE!
Post by: Samuel Rees on September 16, 2013, 10:08:25 pm

Hi, after reading your post I would like to comment on what you are trying to accomplish.

First of all, are your subwoofers powered? 

Second, your subs should be crossed over at between 100 and 120 Hertz.  This will mean that they will get everything below the set crossover point. 

Third, you do not need to stack your subs.  The reason why your subs are not pushing out the bass is because the bass is hitting the concrete and reverberating off of it.  Therefore, it never gets to the audience.  My advice would be to stick a piece of carpet under the sub that sticks out about 8-10 feet.  This will allow the bass to actually come out of the enclosure the way entended.

Thanks,
Ryan

His subs are powered, front loaded, and crossed over at 100hz with an 18db / oct filter built into the box.

You need to separate the effects of the rooms you are in with the general properties of the sub deployments you've described.

1- Subs on left and right: will have a "power ally" down the center of the floor along a line equidistant from each sub. Coverage off to each side will be reduced, and interference patterns between the subs will leave cancelations at different frequencies across different points in the room. Clean sight lines.

2 - Centered subs: consistent and wider coverage, no power ally. Possible bad sight lines.

With just 2 subs and no external processing, this is about all you can do. Any other effects you are observing are likely room related.
Title: Re: QSC KW181 stacking (placement) - NEED ADVICE!
Post by: Brian Jones on September 24, 2013, 08:09:04 pm
Depending on the venue, you might get quite a bit extra from your subs by corner loading. Try side by side and stacked, but either way, place them at a 45 degree angle in  corner. The boundary loading will give you extra dBs.  For more information, just google, 'boundary loading subwoofers.' Also, try adjusting your crossover lower. If you're not already using an external active crossover, consider picking one up. Just 10-20 Hz lower on the crossover can have a significant impact, but you won't know until you try it. At some point, as you move lower, the tops won't be able to fill in the gap created properly, or might not be able to produce enough volume without unacceptable distortion/limiting, etc.
Title: Re: QSC KW181 stacking (placement) - NEED ADVICE!
Post by: Doug Fowler on September 24, 2013, 09:31:28 pm
Hi, after reading your post I would like to comment on what you are trying to accomplish. 

First of all, are your subwoofers powered? 

Second, your subs should be crossed over at between 100 and 120 Hertz.  This will mean that they will get everything below the set crossover point. 

Third, you do not need to stack your subs.  The reason why your subs are not pushing out the bass is because the bass is hitting the concrete and reverberating off of it.  Therefore, it never gets to the audience.  My advice would be to stick a piece of carpet under the sub that sticks out about 8-10 feet.  This will allow the bass to actually come out of the enclosure the way entended.

Thanks,
Ryan

Please explain the physics behind this.

Wow.
Title: Re: QSC KW181 stacking (placement) - NEED ADVICE!
Post by: Lee Buckalew on September 25, 2013, 06:47:10 am
Please explain the physics behind this.

Wow.

Thanks Doug,
I was trying to leave that alone.   ::)

Lee
Title: Re: QSC KW181 stacking (placement) - NEED ADVICE!
Post by: Tim McCulloch on September 25, 2013, 10:26:38 am
Hi, after reading your post I would like to comment on what you are trying to accomplish. 

First of all, are your subwoofers powered? 

Second, your subs should be crossed over at between 100 and 120 Hertz.  This will mean that they will get everything below the set crossover point. 

Third, you do not need to stack your subs.  The reason why your subs are not pushing out the bass is because the bass is hitting the concrete and reverberating off of it.  Therefore, it never gets to the audience.  My advice would be to stick a piece of carpet under the sub that sticks out about 8-10 feet.  This will allow the bass to actually come out of the enclosure the way entended.

Thanks,
Ryan

More B.S.

I'm with Fowler... please show your math...
Title: Re: QSC KW181 stacking (placement) - NEED ADVICE!
Post by: Ivan Beaver on September 25, 2013, 09:06:26 pm

Third, you do not need to stack your subs.  The reason why your subs are not pushing out the bass is because the bass is hitting the concrete and reverberating off of it.  Therefore, it never gets to the audience.  My advice would be to stick a piece of carpet under the sub that sticks out about 8-10 feet.  This will allow the bass to actually come out of the enclosure the way entended.

Thanks,
Ryan
This is wrong on every count.

1: By stacking the subs you gain a "mirror" image-so that leaves the horizontal coverage the same as a single sub-but allows for a narrowing of the vertical pattern-which helps to direct the energy forward-towards the audience and away from the ceiling.

2: The carpet is simply not thick (unless you are using carpet that is several feet thick-------------) to do anything at the sub freq.  How is something  1/2" thick going to do anything to a wavelength that is 20'ish long?

3: What does having the extra length out front do?

There are 2 things that putting carpet under subs can accomplish.

1: It can help keep the subs from "walking" around-a good thing.

2: It can help protect the bottom of the sub from being scratched from the floor.

Of course it will "absorb" liquids and keep them around the bottom of the sub-which is a bad thing.

There may be something I am missing.  If so please enlighten me.
Title: Re: QSC KW181 stacking (placement) - NEED ADVICE!
Post by: Tim Perry on December 14, 2013, 01:09:03 am
So I DJ at this bar/club every weekend and it has concrete floors.  I have 2 KW181s and 2 Yamaha S115V's (powered off QSC amp).  I am wondering where the best placement of said subs would be. 


Matt, every one of use like to get the best possible use out of the equipment we invested our hard earned $ in.
The simple answer is: if what ya got doesn't whomp hard enough for you you gotta bring more.

The only thing I can suggest is that the older series QSC amps (the USA series for example) use tip negative on the 1/4 inch inputs. this results in a polarity reversal to the outputs.

If you are using XLR or barrier strip input terminals all is well.

You haven't mentioned which top you use. In some cases, the polarity of the subs or the tops should be reversed to make things nice at the crossover point.



Title: Re: QSC KW181 stacking (placement) - NEED ADVICE!
Post by: john sanders on December 15, 2013, 10:30:23 am
Mixing speaker brands, including subs produces undesired effects. Stick with just the KW's and you should improve your system's performance.
Title: Re: QSC KW181 stacking (placement) - NEED ADVICE!
Post by: Mike Maly on December 15, 2013, 11:31:27 pm
Tim and John, are you guys reading the original post? The Yamaha S115V's are his tops; the subs are powered QSC KW181's. Ivan has nailed this one, quick and easy. Placement and more boxes needed if not enough.


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