Center speaker problem

Discussion in 'Archived Threads 2001-2004' started by Shad R, Oct 29, 2001.

  1. Shad R

    Shad R Supporting Actor

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    I have a Polk Audio center speaker(not sure which model,$200 price range). I've noticed that it can't handle bass very well. Even though I have my Center set to small on my Onkyo reviever, I still hear it distort when bass hits (noticeably on Jurassic Park and the opening theme to Tomorow Never Dies) What gives? It's rated down to 52 HZ, and I KNOW it's not my reviever, I hooked up another speaker to it. Any ideas?
     
  2. Wayne A. Pflughaupt

    Moderator

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    Shad,
    This can be a real problem with certain movies if you play at loud volumes and have a center speaker with a single small driver, like 6” or less. Even though the receiver rolls out the bass, it is typically only at 12dB/octave. For instance if the receiver is high passed at 90Hz, the signal at 45Hz (one octave below) is only 12dB less than it was at 90dB.
    The problem is that some movies have severely elevated levels of low bass signal, to the point that it can effectively flatten the high pass filter to well below its setting. For instance, if the signal had a peak of 12dB centered on 40Hz it would effectively eliminate the high pass filter, shifting the roll off point to below 40Hz. Even worse, if it was a 15dB peak at 40Hz, then not only would the receiver’s 90Hz high pass filter be eliminated, but you would actually see a 3dB boost at 40Hz.
    Keep in mind, just because a speaker is rated down to a certain frequency that doesn’t mean it can handle the extremities at high levels.
    Also, check your menu. Some receivers allow the front L/R, center and rear speakers to each be set as small or large. If this the case with yours, you might have the center set to large and the rest to small.
    Cheers,
    Wayne A. Pflughaupt
    ------------------
    My Equipment List
    [Edited last by Wayne A. Pflughaupt on October 29, 2001 at 10:10 PM]
     
  3. Shad R

    Shad R Supporting Actor

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    Wayne,
    Thanks. My reciever is set to SMALL for the center, but it is still trying to handle the bass! It is dual 5 1/2 woofs and a (REALLY NICE) tweeter. It's clean and clear most of the time, but on certain bass-heavy scenes, the bass tries to come out the center, even though it's set to small. I can't figure this out. My reciever's crossover(I believe) is at 80 Hz, so I don't understand why my center would have trouble with 80 HZ! Any other reply from you would be helpful. Thanks again!
    shad
     
  4. Sean Conklin

    Sean Conklin Screenwriter

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    Maybe your Large/Small setting on your receiver is not working. Also maybe you have a bad woofer that shows itself during 80hz.
    Are your speaker cables/connections good?
    Maybe a defective speaker?
    Oh you have ruled out the receiver OK, you may have to face the fact that the speaker is defective or just can't hack it, although being a Polk it should be able to handle it.
    With what kind of speaker did you rule your receiver out with?
    ------------------
    Sean
    "I was thinking of the immortal words of Socrates who said.......I drank what?"
     
  5. Charles J P

    Charles J P Cinematographer

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  6. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    I had this problem with my Polk CS175i (on an Onkyo 595 receiver, 12'x16'x8' room). Stuff like Titan AE and SPR would make the woofer sound like it was fluttering, and I thought it was just that the center channel couldn't handle the bass worth a damn. I ran the bass frequency sweeps on my Avia disc and the center channel was making that noise with certain frequency ranges, even well below reference level.
    I posted about this on the Club Polk forum at www.polkaudio.com and customer service rep. Ken Swauger told me I probably had a bad woofer, then immediately shipped me a new one to swap them out. Two days later, I put the new woof in and the problem went away. You might want to go to their website and e-mail your problem to the customer service e-mail address. They can give you some stuff to try to verify the problem and then take care of any replacements you need. Polk's customer service kicks much ass!
     
  7. Shad R

    Shad R Supporting Actor

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    Thanks for your help, I will send Polk an email tomarow. Only problem...I've had it for two years, and I've only been able to listen to it loudly lately, since I moved. Before,I had to listen to movies at low volumes, but I moved, so now I can listen to my system at moderately loud volumes. That's why I just now noticed it. I will email them though.
     
  8. Chris PC

    Chris PC Producer

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    Whats the power rating of the center channel Polk speaker?
     
  9. Shad R

    Shad R Supporting Actor

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    Chris,
    it's rated 10-160 watts, but my Onkyo receiver is only 75 watts per channel
     
  10. Wayne A. Pflughaupt

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    quote: My reciever is set to SMALL for the center, but it is still trying to handle the bass! My reciever's crossover(I believe) is at 80 Hz, so I don't understand why my center would have trouble with 80 HZ![/quote]Shad,
    The 80Hz (or whatever it is) setting you refer to is not a brick wall. It does not mean that everything below 80Hz ceases to exist for that speaker. The receiver’s “Small” setting merely engages a high-pass filter. A high pass filter passes all frequencies above a designated point (80Hz in your case), but below that point the signal does not simply end. It starts to reduce in intensity (or level), a gradual roll-off at a specified rate or “slope,” typically expressed as dB/octave, or decibels per octave.
    In the case of most receivers the slope is only 12dB/octave. This means that one octave below the 80Hz filter (i.e., 40Hz), a signal with uniform or flat characteristics has dropped 12dB. In the real world only test signals are truly flat, so in reality the actual cut off frequency and slope is dependant on the frequency response of the incoming signal. As I noted in my first post, the boosted bass signal in many movies can effectively eliminate the slope and send flat (or even boosted) response down to 40Hz, or even below, directly to the speakers.
    Therefore, Shad, your center speaker is not really “having trouble with 80Hz.” In the scenes you mention, it is actually trying to reproduce frequencies much lower than a pair of tiny 5¼” speakers are capable of reproducing (a small speaker's power rating has little to do with its ability to handle powerful low frequencies). Your observation “…but it is still trying to handle the bass” is absolutely correct. That is exactly what is happening. And that’s why your speaker is struggling to keep up.
    If it turns out that both your woofers are in good condition, then you have only a few options:
    1. Turn the volume down
    2. Get a larger speaker capable of handling lower frequencies
    3. Connect a high-quality electronic crossover that has steeper 24dB/octave slopes between the center channel pre-out and amplifier[/list=a]
      Regards,
      Wayne A. Pflughaupt
      ------------------
      My Equipment List
      [Edited last by Wayne A. Pflughaupt on October 30, 2001 at 10:20 PM]
     
  11. Shad R

    Shad R Supporting Actor

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    Wayne,
    If I had the $$ I'd have a better speaker..I guess I'll have to turn the volume down if Polk doesn't reply to my email I'm going to send them.
    You guys ROCK! I LOVE this place, thanks to everyone who replied and gave me suggestions, it's much appreciated!
     
  12. Luis A

    Luis A Second Unit

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    Shad, have you calibrated your speakers to 75db with VE or 85db w/ AVIA? Is your center channel running hotter than the rest of your speakers? Just a thought.
    Wayne is correct, but I've tested many small speakers @ work and have only come across this problem when the woofer was blown.
    Just one more question, at what level are you listening to movies at? Higher than ref. maybe? GL
    L [​IMG]
     
  13. Karim Nogas

    Karim Nogas Stunt Coordinator

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    Ok, I have to ask...
    Wayne,
    How do you get that funky font going? [​IMG]
     
  14. Shad R

    Shad R Supporting Actor

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    Luis,
    I'm kinda new here, so where/how do I get equipment to measure how many Decibals I'm listening at? If it helps, I have an Onkyo, 75 wattsX5 Dolby Digital reciever. I listen to the volume at half way up, with the individual speakers set at L/R +3, C +5, L/R SURROUND +4, LFE 0.
     

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