Nasty dip around 30 Hz, what from?

[mpompey]

I've been doing some measurements and moving my sub around to optimize placement. I've got a couple of nasty dips centered around 30hz and 80 Hz. I'm not sure if these are related to my height or length of the room. These nulls stay regardless of where I place the sub along the front wall.

Because of my room layout, the front wall is the only place for the sub. The best response location came between the front right and center speaker, about 1/4 total front wall width (25") from the side wall. HEre is a post of the sub response.

The 80 Hz dip I'm not worried about, as I've changed the crossover in my amp to 60 Hz, to get around it. The room definitely sounds alot better with the changes in location, BFD (Behringer Feedback Destroyer) and receiver x-over settings. I'm just wondering if there is anything I can do with the dip in the 30Hz range.

 

[sparky77]

This will help you find the room modes which can help explain the dips and peaks in response.

http://www.bobgolds.com/Mode/RoomModes.htm

I honestly don't know a lot about room treatments, but it sounds like you may need some bass traps.

 

[avaserfi]

There are a couple of things you can do to try and help increase these nulls. Since you have a BFD any peaks will not be an issue so try to get as many peaks as you can trading off for minimal (3dB or less) nulls.

One question - are these graphs of your subwoofer alone or your sub and mains? If they are your subs and mains the 80Hz issue is probably your crossover (as you noticed) so you should play with that also it would be helpful to see a measurement of your sub alone.

Remember you should first get an ideal location and set up for your subwoofer than hook the mains back up and tweak slightly from there.

Does your sub have phase control? If so, play with that and see if it helps the situation. Same thing with gain control, some subs have that.

Have you contemplated moving the listening position around if possible?

Room treatments can be another alternative, but they are more likely to help any standing wave issues (see your waterfall) and possibly the the 80Hz issue. The 30Hz issue most likely won't be helped too much from treatments.

Another option would be adding another like subwoofer if possible. With proper set up you could flatten your frequency response using this method.

Posting your room layout would be beneficial as well.

 

[mpompey]

This is a graph of the sub alone, as I was feeding the test signal through the BFD and into the sub. Here's a pic of my room setup, I don't have much room to play with the layout. My guess is that the 30Hz dip is because of my walls. The walls behind the paneling are solid cement.

I'll try the phase control and see if that helps. I was planning on adding panels down the right wall to tame the 1st reflections and even out the room response in the high and mid levels.

I've also been thinking about adding another sub. The only other location is left of the center speaker. I saw the same dip at that location prior to moving it to its current location. So I doubt that another at the same place will cancel out that null.

 

[Highbar]

Any way you can get that image a little bigger? It's an odd shaped room for sure but I'm sure it can be worked out.

T

 

[mtrycrafts]

As was suggested, if you pull those peaks down, using a broader width on the BFD, say 1/6 as a starter, around 20Hz, 40, 50, 60Hz, and see what happens when you boost the overall level back to 80.

 

[mpompey]

Here's another post of the room layout.