Subwoofer experts please..again !!

Discussion in 'Archived Threads 2001-2004' started by Jon Slater, May 7, 2002.

  1. Jon Slater

    Jon Slater Extra

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    [​IMG]
    Above is a graph taken using my spl meter (adjusted values) .
    Using frount speakers and paradigm pdr-10 subwoofer, Using a pioneer amp ..crossover set to 80hz and subwoofer also set to handle bass from 80hz down..speakers set to small.
    any opinions on this chart would be most welcome..i am striving to get my home cinema sound as 'level' as possible..
    cheers
     
  2. Ned

    Ned Supporting Actor

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    Could you make a drawing of your room showing the sub location? With a curve like that I envision a room with lots of doorways and the sub placed somewhere unideal.
     
  3. Jon Slater

    Jon Slater Extra

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    Nope..cant get diagram to work..

    i have 2 doors in my room, and my frount speakers are either side of the tv with sub just behind...
     
  4. Ned

    Ned Supporting Actor

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    You can use Paintbrush if you have a PC. Just hold Shift when using the line tool to get accurate angles.
     
  5. Jon Slater

    Jon Slater Extra

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    [​IMG]
    OK, here is my room layout..the frount speakers are either side of the tv on stands, the subwoofer is behind the right speaker..but not obscured because of the stand..
    cheers
     
  6. Neil Joseph

    Neil Joseph Lead Actor

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    Turn the crossover of the sub all the way up to maximum. Looks like you have a null, centred around 55Hz according to the diagram. Let the receiver handle the crossover, especially since you have the sub at the front location and retry the graph if you can.
     
  7. Ned

    Ned Supporting Actor

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    Try moving the sub to the front left corner. Sitting mid-wall near a window is a poor position. The bottom left corner is another option as long as the sub can't be localized (dependant on the cross-over setting and any resonance problems). Basically anywhere along the left wall will probably perform better than where it is now.
     
  8. Jon Slater

    Jon Slater Extra

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    Thanks for the replys..i will try repositioning the sub later this week..
     
  9. Neil Joseph

    Neil Joseph Lead Actor

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    Yes, I forgot to mention that the sub location is another likely suspect. A corner placement will give you a boost of a few dB. Please try these things and let us know what the effects are on the response.
     
  10. Jon Slater

    Jon Slater Extra

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    [​IMG]
    Set crossover on sub to full..here is the results..
    still seems to be a problem at 50hz ?? Do you think moving it to the top left corner as you sugested will get rid of this ?
    cheers
     
  11. ling_w

    ling_w Second Unit

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    Do you have the room dimensions and location of where your seating position relative to that?

    Try to put the sub right behind the sofa or right to the left of it. This would provide nearfield listening where you hear more of the direct bass and less of the boundary effects.
     
  12. Jon Slater

    Jon Slater Extra

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    [​IMG]
    OK guys..moved sub to bottom left of room behind seating area, port at rear of sub pointing into corner.
    I havnt altered the subs settings so it may be too loud as the sub is alot nearer to the listning position now.
    What do you think now ? any better ?
    How many db's should i lower the subs setting to alow for the new position ?
    cheers..I apreciate the help...
     
  13. brucek

    brucek Second Unit

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    Jon,

    A few questions.

    Is this a "sub only" response curve or do you have your other speakers turned on at the same time? If it's a sub only, it would seem odd that the output at 160Hz is about the same as at 80Hz. If your receiver is dropping the level at 24dB/octave above 80Hz crossover, then we should see that drop off?

    Is this response curve taken at your normal listening position - i.e. the couch?

    The blue line certainly looks better since you corner loaded the sub - does it sound any better?

    Use your internal test tones or a test disk like AVIA or VE to set the overall level of the sub in relation to the other speakers. That wholesale level is a matter of individual preference once you've found the optimum positioning to produce the best response.

    Many people simply corner load their sub and then use an EQ to remove a few resonant peaks.

    brucek
     
  14. Ned

    Ned Supporting Actor

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    are these results raw or corrected values?
     
  15. Jon Slater

    Jon Slater Extra

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    Hi there, thanks for the replys...The tests were with sub and frount speakers. The graph shows corrected values.

    The measurements were taken from the listning position.

    Im not too sure if it sounds any better..i am having to use a basic phono cable as i dont have a lead long enough (10m) for my sub in its new position.

    Any further advise is much apreciated...

    Cheers
     
  16. Michael R Price

    Michael R Price Screenwriter

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    Stick with that position. Your response above 40Hz is much, much flatter now and if I recall correctly, the PDR-10 isn't the best at super low frequencies anyway. I'd personally keep the flat midbass response and sacrifice a few decibels below 40Hz.
     
  17. brucek

    brucek Second Unit

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    Jon,

    Why don't you try the front corner behind your left speaker for your sub. This would shorten the cable considerably. It might provide an even better response (although the response isn't too bad now).

    You might also want to try a "sub only" response, so as to remove the influence of your other speakers interacting with the sub. It will give you a truer picture of the subs response in the room. Then after that you can deal with the mains combined with the sub.

    Your 40Hz peak would indicate a room dimension somewhere of about 14ft. I see your room is fairly square. According to modal design theory, a cube is the worst possible dimensions for a room. The next worst is a room where all dimensions are multiples of the height. A perfect example is a room 8-ft high, 16-ft wide, and 16 ft long. I don't know your dimensions. Maybe you could tell us..

    brucek
     
  18. JohnSC

    JohnSC Stunt Coordinator

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    I read somewhere that there is potential for speaker damage when using pink noise in this fashion. Is this true or should I ignore it?
     
  19. Wayne A. Pflughaupt

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    Jon,

    Brucek is right; I don’t understand why you moved the sub all the way across the room when you had an ideal corner right by the system...?

    Re Ling’s suggestion to move the sub by the couch: There is no escaping boundary effects. Nearfield placement is usually the worse because it allows interaction with so many more boundaries, compared to corner placement.

    Just for grins, though, I’d be interested what kind of readings you got at the couch, if you’re inclined to take the trouble. That would certainly help put this controversy to bed.

    John SC,

    Any signal played loud enough can damage a speaker. However, this usually applies to sine waves, with are pure tones and as such generate very little cone movement. Pink noise is more random in nature and therefore generates a lot of come movement. The cone movement is what keeps the voice coil cool, so pink noise is less likely to damage a speaker – up to a point, of course.

    Regards,

    Wayne A. Pflughaupt
     
  20. Manuel Delaflor

    Manuel Delaflor Supporting Actor

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    Jon

    Another possibility is that the polarity is wrong. Try to change it (being this the only variable) and show us another graph.

    Also, if you can, try to play with the position of your couch. I would say that it will sound better if you put it as far as you can from the center of the room, that movement alone should give you more dB on the 30's.
     

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