# Initial measurements...opinions requested



## g3kko (Jul 8, 2006)

Hello all. Long-time lurker, first time poster.

So this weekend I sat down with my Ratshack Digital SPL, RoomEQ and my BFD that's been gathering dust on a shelf since I picked it up on eBay 2 years ago. Long story short, my laptop seems to hate RoomEQ, so I fell back on the "subtest" XLS and some 1/6th octave tones. Check it out:










These three measurements were for the left, right & center cushions of the sofa. The 63hz suckout in the "sweet spot" was mighty strange to hear. I placed my head there after running the measurement, and I could literally hear the null come and go moving my head side-to-side by 6". Don't know how worried I am about that one, but if I can get rid of it, I want to. That's where I sit. :bigsmile:

All in all, I'm pretty pleased with how things turned out just as they are. A bit depressed that I don't have more below 25hz, but I'll cope. Do I even bother with the BFD? I'm thinking "maybe", just to pull down the 50hz region a bit. Makes sense that there's a hump; my sub has an Le of 3.5mH and a peak there is common with high-inductance subs. Otherwise, I have the ability to place the sub directly behind the sofa. I know that, for higher frequencies, one can swamp room interactions by being extremely nearfield. Does the same thing apply for purely pistonic subwoofers?

Here's the room layout if anyone has bright ideas. Basement with a 7-1/2' ceiling. The left wall is a half-wall in the front half of the room and that "wall" to the right of the TV is actually a 25" high box that hides the water main. I wouldn't trust my 150LB sub not to shake the thing apart, so no putting it up there. 










Again, I think I'm actually doing fairly well right now as it is. But maybe you guys see something blatant that I've missed. Any help or ideas are greatly appreciated. 

Thanks!


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## brucek (Apr 11, 2006)

> Do I even bother with the BFD? I'm thinking "maybe",


I would say no, but I'd sure like to see an REW plot.

The dip at 63 Hz may display as a much sharper spike in REW rather than the dip you're showing, simply becuase of the difference in resolution from the manual method.

I wouldn't consider 3.5mH that high an Le, and suggest the 50Hz peak is more likely a standard room mode resonance.

I would try a bit of movement with the sub along that wall if possible and take a few measurements. Certainly painful using the manual method, but easy with REW.

I would work on getting REW working (unless of course that laptop is MAC). Hopefully you had a line-in connection or an external USB soundcard and weren't using 'mic-in'..... Some people also have a bit of trouble with Vista.

brucek


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## g3kko (Jul 8, 2006)

brucek said:


> I would work on getting REW working (unless of course that laptop is MAC). Hopefully you had a line-in connection or an external USB soundcard and weren't using 'mic-in'..... Some people also have a bit of trouble with Vista.


Thanks, Bruce. 

It's an HP nc6220 (HP's "business" line). I checked the manual for it, and while _labeled_ "mic in", it is stereo-capable and warns that certain microphones will have insufficient signal. I initially took that to mean that it was as good as a line-in. Seems not.

I just couldn't get the thing to calibrate. I couldn't get the IN & OUT levels to match, and when I got them close, the resulting calibration measurement was clipped. No worries; I may be able to get a sufficiently quiet PC within range.


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## brucek (Apr 11, 2006)

> I checked the manual for it, and while labeled "mic in",


Yeah, your description of how it went for you says that it was a mic-in and shouldn't be used. You need a line-in.

brucek


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