# Subwoofer Measurements



## vanderschel (Dec 27, 2012)

I'm using two SVS 16-46 passive subwoofers w/ a QSC RMX 850 amplifier. I measured the subwoofers individually, and then together as a single unit. 

Green = left sub measurement
Red = right sub measurement
Black = both subs measured as one unit

I've played around w/ the automatic REW filter settings, but it doesn't seem to adjust anything below 45 Hz.
I'm a newbie at this, so I feel like I'm drinking out of a fire hose trying to get a handle on it. I'm not even sure I'm posting in the right place.


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## ALMFamily (Oct 19, 2011)

I moved this to the REW forum - should get a quicker response here.


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## The Yeti (Jan 23, 2013)

vanderschel said:


> I'm using two SVS 16-46 passive subwoofers w/ a QSC RMX 850 amplifier. I measured the subwoofers individually, and then together as a single unit.
> 
> Green = left sub measurement
> Red = right sub measurement
> ...


In order to get a better handle on what's going on here, set your graphs to the following settings and re-post:
Top = 105db
Bottom = 45db
Left = 15hz
Right = 200hz

5db steps on the left hand side (click the +/- in the upper left corner)


From the graph you posted, it looks like you're getting some phase cancellation with both subs running. We'll be able to see better once you re-post your graph.


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## vanderschel (Dec 27, 2012)

I've reset the graph, hope this helps. I suspected phase cancellation, but I have no way of adjusting phase w/ this amplifier. Also, the room's ceiling height is 17'-6" which probably doesn't help.

Green = left sub measurement
Red = right sub measurement
Black = both subs measured as one unit


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## MJE (Feb 26, 2013)

vanderschel said:


> I've reset the graph, hope this helps. I suspected phase cancellation, but I have no way of adjusting phase w/ this amplifier. Also, the room's ceiling height is 17'-6" which probably doesn't help.


By doing a quick judgement out of those graphs and with 2 subs.....seems you have quite a problematic room. I would suggest as a starter to:
a.) Switch off 1 sub. Depending on where you have them located, start with the one closest to a wall and do a measurement again (either by ear or by mic)
b.) Switch off the other sub and repeat the measurement.
c.) If you know where you have your cancelling spots (either by ear or by measured and calculated results) try moving one of the subs to such a spot and repeat the steps above.
d.)....go on in this manner. you will have some tediuos work as you're using two subs there are many "places" where things may go wrong. Good luck!

edit: Also you have a lot of harmonic disturbance from 15Hz multiples, so maybe some damping in the room could help.


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## vanderschel (Dec 27, 2012)

I measured each subwoofer individually and located them w/ the best response before I measured them together, but I don't have much space for rearrangement. Also, it's a transitional floor plan which means this room *communicates* w/ adjacent rooms and complicates the acoustical treatment application.

This is the current setup. I may place the subwoofers in the same corner and remeasure.

This photo was taken from the approximate viewing/listening position.


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## MJE (Feb 26, 2013)

vanderschel said:


> I measured each subwoofer individually and located them w/ the best response before I measured them together, but I don't have much space for rearrangement. Also, it's a transitional floor plan which means this room *communicates* w/ adjacent rooms and complicates the acoustical treatment application.
> 
> This is the current setup. I may place the subwoofers in the same corner and remeasure.
> 
> This photo was taken from the approximate viewing/listening position.


Seems you have a rather "clean" room judging by the picture looking at the floor and walls, there is not much that can take care of the damping/absorbing of LF. Am I correct when I say that the room is rather long and narrow? What's the length and width of this room? In my opnion I think you are a victim of some standing waves. If you have the possibility to set a rather steep lowcut filter of let's say 30-35Hz (or even higher for testing) and see if that helps. Then you can try decreasing the lowcut frequency until you start seeing/hearing the problems again. That's what I would do, but it's only my opinion.


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## vanderschel (Dec 27, 2012)

The room width is 15'-0", and the viewing position is approximately 18'-0" from the front array. However, the floor plan is relatively open, so the distance to the rear reflection is probably closer to 45'-0".

The subwoofer amp has 30Hz filters that were turned off. The filters are either "off" or "on", there is no adjustment that I know of. Also, I had one port on each subwoofer plugged to lower the bass extension.

I'm using the Xenyx502 for a signal level boost b/w the AVR and the subwoofer amp. I'm using the CD/Tape input/output for now. I couldn't get the SLM to register above 45 decibels w/o the level boost.


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## MJE (Feb 26, 2013)

vanderschel said:


> The room width is 15'-0", and the viewing position is approximately 18'-0" from the front array. However, the floor plan is relatively open, so the distance to the rear reflection is probably closer to 45'-0".
> 
> The subwoofer amp has 30Hz filters that were turned off. The filters are either "off" or "on", there is no adjustment that I know of. Also, I had one port on each subwoofer plugged to lower the bass extension.
> 
> I'm using the Xenyx502 for a signal level boost b/w the AVR and the subwoofer amp. I'm using the CD/Tape input/output for now. I couldn't get the SLM to register above 45 decibels w/o the level boost.


OK, it all comes down to how serious you are about "fixing" this issue. It's really hard to give a quick fix in a forum like this, but based on the info you've given already it comes down to sorting out the issues as described earlier. Of course if you're really hardcore you can always try out any of the room measurement systems to give you an idea of where most of the problems are.
It's a bit off topic and biased maybe but my personal liking is the XTZ Room Analyzer II or Pro. These guys will give you a lot of data about the room itself also with plots for found room-modes, etc. Check out the link if you're interested in what it does: http://www.xtzsound.com/en/products/measurements/room-analyzer-ii-pro

There are so many different devices for this on the market but I like the price/performance with this one and I have used it so I know what I get from it + the company is located here in my country so it facilitates things a bit for me. :bigsmile:


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## vanderschel (Dec 27, 2012)

Well, either I'm lucky or I measured something incorrectly. I reset my AVR's LFE crossover to 60 Hz and remeasured:
 

I utilized REW's automatic filter adjustment and came up with this:

 

I transferred the settings to the FBQ1000 via a M-Audio USB/MIDI interface and then remeasured:


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## JohnM (Apr 11, 2006)

That final plot is a measurement of a loopback connection.


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## vanderschel (Dec 27, 2012)

Oops! I know I need to remeasure in *bypass mode* and then in *filters activated* mode for a better comparison, but this gives some idea of the results. I had no problem w/ REW communicating w/ the FBQ1000 via the USB/midi interface (I have DSP1124 selected in REW).


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