# Low Midrange Null Fix



## vettett15 (Jul 1, 2009)

Guys,

I've finally gotten some time to try and hunt down my rather large null in the 250-500Hz range.

Here is the graph of the left and right full range response (1/3 octave smoothing):









As you can see there is about a 10db drop in the 250-500hz range.

I have done close speaker measurements to ensure that this isn't the speaker.

I did an ETC to see what reflections I have going on, this is left and right overlayed:









As you can see there are a good amount of reflections.

So I went ahead and looked at filtered reflections:

Left:










Right:









Looks like a large reflection in the 500Hz band, so I took a closer look.

Here is the 500Hz band using the distance function:










I used the timing back loop reference to ensure the distance is meaningful.

Here is the room layout:











So I took some string, measured the distance between the right speaker and mic and added 13'. 

Taped the string at the seat and at the right speaker, and manipulated the middle of the string to see what I hit.

Well, it turns on the string hits perfectly on the window you see on the right hand side. Furthermore I looked at the 500Hz band ETC for the left speaker and sure enough there seems to be a nice reflection that is about 20-21', which makes sense as the speaker are about 8' apart. 

So currently this window (kinda large at 5' wide by 6' tall) has those fake wood blinds and curtains. One thing I noticed is my fiance has moved the curtains to the side so all I really have are the blinds blocking the window.

My real question is what is the best way to get rid of this null? I'm guessing it will be a combination between moving speaker, furniture and room treatments. I was wondering if I moved the couch on the right towards the window if that would help me.

I know it will take some actual movements and measurements to know for sure, I would just like to go about it a smart way.

Thanks,
Pete


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

This is basically a speaker placement / seating location issue. The easiest thing to do is use REW’s real-time analysis feature. That way you can immediately see what changes speaker and/or seating re-location has on the 300 Hz hole. If you can at least reduce the size of it, you should be able to improve it further with equalization, if you have that option in the upper frequencies.

Regards,
Wayne A. Pflughaupt


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## vettett15 (Jul 1, 2009)

Wayne,

Thanks for the reply, perhaps I went into Columbo mode too fast. Is there an "easy" way to determine which way to move the speakers and/or couch?


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

I’m not aware of any method that will tell you what to expect before you actually move any speakers or seating. But the RTA can give you instant feedback on the results of any changes you make.

Regards,
Wayne


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