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Discussion Starter #1 (Edited)
Hello,

I just finished measuring my system :) There seems to be a nasty dip around 300hz :( but otherwise it looks good to me.

The measurement is a nearfield one, measured from ~3 feet away from listening position. Measured sub+l and sub+r then averaged them:


Microphone is Behringer ECM8000. The sound card is bit trickier, as I had to use two; The calibrated one was emu 0404 pci card (which has no preamps for mic). Then I ran the mic thru emu 1616 interface, and connected the mic signal from 1616:s line out to 0404 line in. So there can be a little deviation because of the other soundcard I guess. But other than the 300hz dip (which I'll be trying to tackle next with some acoustics) the graph looks good? Sorry it's not in the 45-105db range, but almost :)

edit: here's a couple of more graphs, with 1/6 oct smoothing and left+sub and right+sub separated:
L+sub

R+sub


thanks for the input in advance,

t
 

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Elite Shackster , HTS Moderator Emeritus
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How tall are your ceilings and what height is the microphone?

I have nulls at 150 and 300 Hz in my room due to floor-to-ceiling standing waves. If the mic falls on a null you get a pretty big drop. Treatment can help, but the best thing is to just make sure ears and the mic aren't in those null regions (1/2 wavelength point).

Just a thought.
 

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Discussion Starter #3
not very tall, and the ceiling is sloped.. might be front to back wall standing waves. I'll know today if some absorbers help. There's little room to reposition, but I'll try to move things as much as I can.
 

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Elite Shackster , HTS Moderator Emeritus
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I doubt that would be front to back standing waves, the wavelengths are too long (unless you have a really small room).

Another option is that something in the room is acting as a broadband absorber, like a panel resonator. What's the construction like? Slab floor? Wood floor? Any half-height walls in the room?

The easiest thing to do is move the mic up or down and see if the response changes greatly. If it does, then you probably have a standing wave. If it does not, it is likely a larger issue like the room or speaker response.
 

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Discussion Starter #5
It's definetly a room problem. And the room is small.. wooden floors, wooden walls, low ceiling height.. Measured near the speakers the response is flatter. I might have to reposition then.. Not an easy task though. I might try some 20cm tight foam for starters. Position, measure, reposition, remeasure.. etc.
 

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Discussion Starter #6 (Edited)


here's a new measurement, moved speakers a little bit. The source of the dip is indeed the ceiling. Now I'll just have to figure out how to attach a 20cm thick foam block on the ceiling..



at least the low end looks good :D
 

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I agree that the low response looks very good on the frequency response. It kind of looks like the mode spacing between them is very close together. Is your room a large one? Is that equalization? Is there a reason that the level is at around 65dB? Sorry for so many questions but these look very interesting.
 

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Discussion Starter #8
Hey,

the room is a small wooden one. The bass response also sounds good :) Only minor BFD applied, few filters from -1 to -4. The absolute spl level is not calibrated so the decibel level is not accurate. That shouldn't affect on the measurement results, right?

edit: how about the full range? it looks pretty good to me now, besides the ~8db dip at 300hz
 

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No that really shouldn't change the results. As long as your measuring higher than noise the meter picks up that isn't what your measuring you should be fine. You also want to be sure that the soundcard or computer isn't picking up noise also but that problem isn't very common.

Since your 300Hz dip has to do with the ceiling, I would say that it probobly very difficult to detect, and probobly does not effect your soundstage much. Since you are able to find it when you walk around, is that a small area, or a large one? I can find nulls in my room that are the difference of walking two steps in any direction, but it is perfectly normal for a room to have dips and peaks. The improtant thing is your not sitting in one. One thing it may have to do with is off axis response of the speaker also. I have been thinking about taking my own outside to measure at different angles to see what might be causing my 200Hz dip. It could very well be my floor also. In my opinion it might be worth looking into fixing the dip, but the rest looks good. If it were my room I would probobly be measuring other locations where people sit also if any, and try improving those for the subwoofer if needed.
 

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Discussion Starter #10
The dip is a small one, if I move few inches upwards, the dip changes into a boost. I have to put the foams on the roof, that solves the problem with the dip (did some quick measurements while holding the acoustic foam in place).

The setup is a nearfield one which I use to listen/mix/produce music and I also do sound design. So it doesn't really matter how the response changes anywhere else in the room :)

I'll have to try to move things around a bit more too, but my space is so full it's going to be a massive task..
 
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