First REW Graph - Where from here?

Discussion in 'Subwoofers' started by Ninj, Apr 18, 2007.

  1. Ninj

    Ninj
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    Hi,

    Just got my 309i installed and had a tinker with REW.

    Here is the graph its produced. I understand the sub is brand new so its charateristics may well change but any thoughts or advice gratefully received.

    Im looking specifically at the 2 dips at 61 and the big one about 140hz.

    How bad are the peaks at 46 and 88hz? I have a BFD waiting in the wings.........

    Rgds

    Richie
     
  2. Ninj

    Ninj
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    Graph 1:
     

    Attached Files:

  3. mattkhan

    mattkhan
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    Hi,

    I would say that fairly standard advice is;

    • set the graph limits to 15-200Hz on the x axis & 45-105dB on the y axis
    • take measurements for a variety of different phase settings and work with the 'best' one
    • basically ignore narrow, deep dips as you're unlikely to actually hear them (can be v sensitive to mic position, move it 25cm in one direction and it often changes quite dramatically) nor are you realistically able to do anything about them with a BFD
    • don't worry so much about the response after the crossover as the BFD can only deal with the sub
    • as a starting point look for a natural in room response that is amenable to as many cuts (not boosts) as is needed to get the shape you're after, a quick look at yours say it looks pretty steady already and nothing a few cuts won't do a good job on
    • read up on the advice at the 'official' REW/BFD support forum which you can find here at the Home Theatre Shack
    • once you've done all that, repost your graphs and get everyone to comment :thumbsup:

    Cheers
    Matt
     
  4. AngelEyes

    AngelEyes
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    What he said :)

    That dip at 60 may well be improved with some phase tweaks or even adjusting the crossover. Lots of fun ahead :smashin:

    Adam
     
  5. Ninj

    Ninj
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    Cheers Angel Eyes,

    The crossover is set on the amp to 80Hz. Am I right in thinking the idea would be to get the dips as near to the crossover as pos?

    Is it a better plan to keep the crossover at 80Hz and use some phase tinkering to move the dip, or to lower the crossover down nearer the dip?

    Also, what effect will fiddling with the frequency on the sub itself?

    Thanks again

    Rich
     
  6. chrisgeary

    chrisgeary
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    As Matt has said, ignore the narrow deep dips. There is always one in any given room and its the frequency at which bass bounces around the room and cancels itself out. There is virtually nothing you can do about it. The dip at 60hz is somewhat more in your control, although it too is a result of room acoustics. You will often find that by moving your sub a few inches can have a big effect on the overall response. Unfortunately, also moving your SPL meter mic can have the same effect. Use your ears as well as REW and decide whether the dip is real or not so bad. Remember you have two ears versus one MIC.

    Try a completely different position in room also. Where is it currently in relation to your listening position? The strongest bass is often generated when the sub is in a corner at the opposite end of the room to your listening position.
     
  7. Ninj

    Ninj
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    Hi Chris

    The sub is currently a few inches from the corner of the room, the listening position is the opposite wall in the centre. It sounds nicely part of the system and doesnt stand out. Ill have a move about and have a look with REW and a listen too.

    Is the 60Hz dip the only real problem with the graph then?

    Just off to investigate how to find the recommended BFD filters.


    Thanks

    Rich
     
  8. chrisgeary

    chrisgeary
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    I think so. As it stands, you would do a little cut at 88hz, a cut at 45hz and it wouldn't be half bad. Do try adjusting the phase control and see if the other setting produces a more favourable graph.
    Out of interest, where have you put the MIC?

    Once you have found what you think is the best place, do a graph, apply some filters and then listen. Listen to some music you know well and see if it sounds good. If not (and sometimes I have had a graph that looks great but the sound was weak in the bass dept), then try upping the gain on the sub 3 or 4 db. Half of it is ironing out peaks and troughs, and the other half is getting the overall level right.
     
  9. Ninj

    Ninj
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    Thanks again,

    The mic is sitting on a heap of cushions in the listening position, vertical at ear level.
    Off to read the HTS REW forum, loads of good advice there.
    Rich
     

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