# Oh my, this room looks bad :(



## swatkins (Nov 26, 2013)

Here are the first complete sets of my rooms graphs.. I used 1/6 smoothing and took a measurement of every speaker except the sub. I was getting clipping warnings on the sub..

There are no treatments on the walls or ceiling, thick carpet and pad on the floor. Room is 19' wide 24' deep with a 9' ceiling. Walls and ceiling are painted double 5/8" sheetrock with green glue. No windows and only one 3' wide door 9' from the screen wall and it was closed during measurements. 

The mic was located at 15' from the screen and centered on the screen. USB mic into a laptop with calibration file loaded. HDMI out to my Onkyo 818 and each measurement was taken with the mic pointed directly at the center of each speaker from the main listening position. 

From what I can tell I have some bad ringing and decay problems. 

















Here I see both mains are dropping down ( why I have no idea) below the surrounds and center.
Does anything else stand out?


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## natescriven (Jan 12, 2011)

On the bright side, your frequency response is fairly flat. How does it sound to you? Does the bass sound boomy? If so, adding bass traps to the corners would be the most effective treatment to start with.


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## Wayne A. Pflughaupt (Apr 13, 2006)

swatkins said:


> ...each measurement was taken with the mic pointed directly at the center of each speaker from the main listening position.


Finally, people are figuring out the correct way to take a measurement!



> From what I can tell I have some bad ringing and decay problems.


Waterfall graphs are only useful below about 3-400 Hz. One reason things “look” so bad there is because of the high signal levels – see this post for more information.

Regards, 
Wayne


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## swatkins (Nov 26, 2013)

Wayne A. Pflughaupt said:


> One reason things “look” so bad there is because of the high signal levels – see this post for more information.
> 
> Regards,
> Wayne


Hi Wayne, 

After reading your link I understand the concept much better.. What I'm not too sure about is the"signal Level" Does simply lowering the volume reduce the signal level?


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## JohnM (Apr 11, 2006)

The plots are not so flat when shown on the correct scaling:








There are some pretty substantial low frequency resonances to deal with.


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## Wayne A. Pflughaupt (Apr 13, 2006)

swatkins said:


> Does simply lowering the volume reduce the signal level?


Yup, sure does. :T Getting the level down to a more normal 75-80 dB would make the waterfall not look as scary as it does. Still, John is right, it will still show some resonance problems in the 50-70 Hz range. A parametric EQ can help this.

Regards, 
Wayne


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## swatkins (Nov 26, 2013)

First off, thanks for the help guys! 

John, I see now see what is meant by "correct scaling". I hope to never be guilty of that again  

Could someone give me a few pointers on what the resonance problems look like on those graphs? I see three major peaks in the 50 to 100 area. The 50 to 70 area has two peaks that are close together and only have a slight dip between them. Am I correct in thinking "Peaks" = BAD and my goal should be to reduce all peaks to base line?

Wayne, you mention a parametric EQ to "fix " the 50 to 70 area.. I was not familiar with that type of equalizer and once again had to look it up  Would you happen to know of a parametric EQ that is affordable and you could recommend? 

I have been reading about problems in the areas from 20 to 100 and it seems that I would need a couple of feet of insulation to tame things below 50 but the area from 50 to 100 would respond to lesser amounts of absorption. Do you guys think that Bass Traps would help with the problems I have? 

After several weeks of reading I think I have a "plan" and a goal to work towards. For starters I think I should place floor to ceiling Bass Traps in all 4 corners. I can easily place triangle shaped traps that are 24" x 24" on the walls and 36" across the faces. The most economical filling, that I have found so far, is roxul safe and sound insulation which I plan to cut into triangular shapes and stack. For the screen and back wall I plan on covering the area between the corner traps with a layer of 1.5" rigid fiberglass duct board. Side walls and ceiling will each have panels at the first reflection points. 

After further reading I now understand why 1.5 inches is probably not enough but I think I'm going to start with that thickness then test and see where I need to go from there.. I'm hoping that the large corner traps help, a lot :bigsmile: My goal is to end up with all the walls covered in a framed panel style, similar to block paneling. By covering the back and screen walls with 1.5 first I can then apply my wood furring strips and hide another 1.5 inches in the paneling if I need it.. 

Maybe as last resort before a EQ, to tame the 50 to 100 area, I could always install soffit traps.


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## Wayne A. Pflughaupt (Apr 13, 2006)

The cheapest equalizer for subwoofer purposes is the Behringer DSP1124 (currently FBQ1000, I think). It’s not especially intuitive, but you can find a guide on how to operate it at our Equalizers Forum. It’s supported by REW, and the program will give you the exact parameters to plug into it. AFAIK it takes some serious bass trapping to tame the lower frequencies. You might run your plans pass the guys on our Acoustics Forum to get their feedback.

Regards, 
Wayne


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## sdurani (Oct 28, 2010)

swatkins said:


> Could someone give me a few pointers on what the resonance problems look like on those graphs?


Simple calculations for resonances show that your room's width modes will be at 30Hz, 59Hz and 89Hz; length modes will be at 24Hz, 47Hz, 71Hz and 94Hz. Use those as a starting point to see if there are peaks & dips at or near those frequencies in your measurements (will also depend on where the mic was placed). 

It is difficult for a room mode to resonate when the source of bass is in the null of that room mode. If you can move your subs to some of those null locations in the room, you might be able to tame some of those resonances, leaving you with less to equalize afterwards.


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## swatkins (Nov 26, 2013)

Ok I understand about the room nodes now and how moving the sub could help with that problem. I also understand about using an EQ to help also..

What I'm having a little problem understanding is whats going to happen when I take a measurement with the subwoofer included  The graphs were take without the subwoofer included because of the clipping warning I saw... 

IS including the subwoofer just going to make it worse?


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## sdurani (Oct 28, 2010)

Can you measure just the subs (no speakers)?


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## swatkins (Nov 26, 2013)

sdurani said:


> Can you measure just the subs (no speakers)?


I think so... I'll give it a shot


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## swatkins (Nov 26, 2013)

Well it looks almost the same. 








Is it worthwhile to start moving the sub around now, before any treatments, to determine if that would help?


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## sdurani (Oct 28, 2010)

swatkins said:


> Is it worthwhile to start moving the sub around now, before any treatments, to determine if that would help?


Do you have a single sub? If so, can you temporarily move it to the midpoint of room width and re-measure?


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## JohnM (Apr 11, 2006)

I thought you said you understood "correct scaling" now  bottom of that plot should really be 45 dB rather than -40.


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