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Taming a room null from 80 to 110 hz

post #1 of 8
3/21/08 at 6:28am
Thread Starter 
When measuring the response of my room, I found that there is an enormous null from about 80hz to 110hz. It's about 10db below the rest of the response. My first thought was that it was a phase problem between my sub and mains because the sub is crossed over at 80hz. But I did a measurement without the sub, and it was still there in the exact same place.

At that frequency, is there any (inexpensive) material I can put in the room to try to absorb any standing waves? Can a null that wide even be explained by standing waves, or am I dealing with something else? Any suggestions are appreciated.

thanks,
greg
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post #2 of 8
3/21/08 at 6:59am

Re: Taming a room null from 80 to 110 hz

Your best solution is probably a Behringer Feedback Destroyer. Just do a search and you will find plenty of info.
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post #3 of 8
3/21/08 at 12:30pm

Re: Taming a room null from 80 to 110 hz

Greg,

And yet, and yet ...
Quote:
But I did a measurement without the sub, and it was still there in the exact same place.
... which only proves you get no 80-110Hz, but it doesn't prove you have a null inside your room.

Did you also measure the spectrum with the sub, but without the mains?

Remember: the cross-over isn't a switch value: output power of the mains will start to go down significantly from 160 Hz on, while the sub is supposed to start outputting it.


I'm certainly not saying you're wrong: just that it looks like you didn't prove it yet. You should also do a few "near-field" measurements: output levels close to the speakers. In other words: is it there but countered by your room's geometry, or isn't it perhaps not fully there at all - which would call for different measures.


Cees
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post #4 of 8
3/22/08 at 9:07am

Re: Taming a room null from 80 to 110 hz

Of course, Cees is right. I seem to be constantly being criticized for questioning the understanding others have of this stuff. I gave you the benefit of the doubt.
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post #5 of 8
3/22/08 at 10:33am
Thread Starter 

Re: Taming a room null from 80 to 110 hz

Quote:
Originally Posted by Cees Alons
Greg,

And yet, and yet ...
... which only proves you get no 80-110Hz, but it doesn't prove you have a null inside your room.

Did you also measure the spectrum with the sub, but without the mains?

Remember: the cross-over isn't a switch value: output power of the mains will start to go down significantly from 160 Hz on, while the sub is supposed to start outputting it.


I'm certainly not saying you're wrong: just that it looks like you didn't prove it yet. You should also do a few "near-field" measurements: output levels close to the speakers. In other words: is it there but countered by your room's geometry, or isn't it perhaps not fully there at all - which would call for different measures.


Cees

Let me clarify. When I tested without the sub, I told my receiver I had no sub so I sent the full signal to the mains. they have good response down to about 55hz, and the response is reasonably flat from 55 to about 80, then there is the dip, there it's reasonably flat again from 110 on up.

I already have a BFD as well, and that has helped significantly in flattening out the peaks. But it doesn't really help at all in bringing up the low points.

Are there any other tests I should run to make sure I understand the source of the low spl in that range?

thanks,
greg
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post #6 of 8
3/24/08 at 10:08am

Re: Taming a room null from 80 to 110 hz

Just shouting vile thoughts here, but, did you check only in your listening spot? It could be that you sit near the middle of the room, or in some other null spot.

As an example: My favorite chair always winds up too close to the center of the room. It's just the way it goes, because the sound (except for bass) is wonderful there. The bass was underwhelming for me, but thunderous on the couch in the back. The bass was downright scary in the corners of the room. So, I moved the sub to right behind my chair. Problem solved.
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post #7 of 8
3/24/08 at 11:04am
Thread Starter 

Re: Taming a room null from 80 to 110 hz

Quote:
Originally Posted by chuckg
Just shouting vile thoughts here, but, did you check only in your listening spot? It could be that you sit near the middle of the room, or in some other null spot.

As an example: My favorite chair always winds up too close to the center of the room. It's just the way it goes, because the sound (except for bass) is wonderful there. The bass was underwhelming for me, but thunderous on the couch in the back. The bass was downright scary in the corners of the room. So, I moved the sub to right behind my chair. Problem solved.
Yes, my chair is right in the center of the room, because I like to be looking straight at the TV and have the left and right speakers be the same distance from me. I don't think I could put the sub right behind my chair because I couldn't get the wires to it (power and signal) without people constantly tripping over them, or having something ugly to cover them (tape or something else). It seems like there must be a way to get decent response in the middle of the room though.

greg
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post #8 of 8
3/24/08 at 1:22pm

Re: Taming a room null from 80 to 110 hz

You've found out that you can't correct a room null in the exact center of the room! Well, not without doing something physical, anyway. No amount of EQ or boosting is really going to make it work - you might get the level right for your chair, but then it would be horribly wrong elsewhere. This stinky situation does have a way out, though. I chose the easiest, since I don't care if I have a sub cable running across the floor.

Try this: put the sub ON your chair, then play something with lots of base - perhaps a test signal. Wander around the room with your soundmeter, and try to find the loudest spot. Now put the subwooofer there, and re-test from your chair. It might work.

There are threads here on the board about "bass traps." These things make your room behave as if it is larger, and might help tame the null, at the expense of some loudness. But, you can just crank up the sub some.

Some folks with plenty of room and unlimited budget might decide to change the actual size and shape of their room... I have a chance to do that with a proposed alteration on the back end of my house, so maybe in a couple years I won't have a subwoofer behind my chair....
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