# Large dip at 200hz



## Eotas (Jan 27, 2014)

Hello gentlemen

I have a problem with a large dip around 200hz that i would like to get rid off.

The only method i have found working is to take all 5 auto EQ measurements with my anthem arc in the same position but unfortunatly it totally ruins the frequenzy respons for the side chairs (see picture below)

My room dimensions are (in millimeters)

4500x2900X2300

I have 100mm absorbtion in first reflection, bass traps in the 2 rear conors and the front wall with 200mm absorbtion.

My front speakers are in a partial screen wall and the side speakers are placed 710mm from the side walls. My center does not have this dip so i am thinking that it might be a side wall problem.

Can anyone give me some pointers to what the problem might be and how to get rid of it without EQ?


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## bpape (Sep 14, 2006)

If you move the mic forward or backward from the current ear position does the center of the null change? Could easily be off the wall behind you.


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## Eotas (Jan 27, 2014)

Hi Bryan

I have taken some new measurements about 30 cm in front and 30 cm behind my seating position

Here the dip is gone so it is only in my actual seating position. Unfortunately it is not possible to move either the seats or the speakers :-(

red is in seating position


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## bpape (Sep 14, 2006)

As wide as that is, it's more than just one thing - likely a combination of hte wall behind you, coupled with SBIR from the front wall and side walls.


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## Eotas (Jan 27, 2014)

Thanks Bryan

I will try and replace my QRD diffuser on the backwall with absorbtion and see if that can help


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## bpape (Sep 14, 2006)

Like I said, the nulled area is so wide that it's pretty much sure it's more than one thing in more than one place in the room. Back wall could be a piece.


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## Eotas (Jan 27, 2014)

I did try various tests without any good result. The thing that had the most impact was adding a lot of absorbtion on the wall next to the left speaker. This pulled down my peak between 100 and 150hz just before the dip.

I do have a wish of getting a larger screen going from 90" to 105. So my next step is to change the screen wall from a partial baffle wall to a full baffle wall. 

Like this http://www.acousticfrontiers.com/2013322baffle-walls/

This way i will be able to move the speakers approx 20 cm closer to the back wall and the front speakers closer to the side walls.

Do you think that would be the right approach?


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## bpape (Sep 14, 2006)

It will just shift where some of the peaks and dips happen. Treating the front and side walls is the best wy to help fix it in stead of just moving it to different frequencies.


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