# Null below first room mode?



## atledreier (Mar 2, 2007)

Hello!

I have a serious null at around 20hz in my listening position. It's about 12-15dB down, and it's not very narrow either. The problem I have is that my first room mode is at 33Hz. So where does this null come from? If I know how it's created it would be easier to fix it.

Other positions in the room have strong 20Hz, so it acts like a room mode.

Edit:
Just realized something:
The back wall in my room is a light wall with a double glass door into my office. This door is closed permanently, and sealed with rubber. But if I add the length of the office behind it to the length of the room, the first room node is 21,7Hz, almost exactly the problem frequency. Could that be the issue I'm having, that too much 20hz energy escapes and interacts with the wall/door? My listening position is almost right smack in the middle of the 20Hz null if I include the office in the room dimensions...


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## bpape (Sep 14, 2006)

It's possible that the room is acting more like the combination of the 2 rooms together. Glass certainly passes more energy than a drywall wall (in both directions). Another possibility is that it's a combination of 2nd and 3rd order modes (tangential and oblique). These are normally lower in intensity but can build on each other as there are many more of them.

Bryan


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## acoustat6 (Mar 7, 2008)

Hi Atle, I dont believe it is the room behind the glass doors that is giving you the problem freq response. And besides it does not matter where your problem comes from, it only matters that you address it. Can you post a 10 to 200hz REW with one octave smoothing and with no smoothing? Also a 10 to at least 1000hz with one octave smmothing. Please do this so the 75db target line is present.

In your thread "Acoustic tips and help please" this dip is not present in your REW graphs, what changed?


Bob
PHP143


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## atledreier (Mar 2, 2007)

All the graphs in that thread is with different equipment and listening position, and with Audussey enabled.

I'll try to get some fresh, unsmoothed and un-EQ'd measurements of the subs.

Edit: Some measurements from the sub build thread that shows the issue a little bit. this was in a slightly different position, both subs and LP, but the trend is similar, just lower frequency now.


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## acoustat6 (Mar 7, 2008)

Hi Atle, You said, "Some measurements from the sub build thread that shows the issue a little bit. this was in a slightly different position, both subs and LP, but the trend is similar, just lower frequency now."


Sure the null points move around the room. Thats why you cant tune your subs using music, that is a moving target. Some albums sound better a foot or two forwards or backwards because of the key they are playing in or the way it was mixed. The only way to tune your system is with fixed targets.

Have you chosen a seating position that you like as far as imaging and "smooth" sound is, do you like where the speakers and seat are located? If so keep them there or move everything to where you like it best and EQ from there. Its not a moving target as some people suggest.

That would be great to see a graph of the subs with the same one octave and no smoothing 10 to 200hz when you get a chance. Dont forget to include the 75db or house curve target line!

Thanks, 
Bob

Bob


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