Port noise with my PB10!

Discussion in 'Speakers & Subwoofers' started by Vaughan Odendaal, Sep 29, 2005.

  1. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    Hi guys,

    I just want to say that I have been very happy with my subwoofer so far. Alright. I put in Matrix Revolutions the other day and I put the master volume at -10.

    On the scene when Neo and Smith make that massive water explosion (the final one) and it went all slo-mo, there was excessive port noise! I mean, the sounds were very distracting.

    At first I thought I had bottomed the subwoofer out but then I knew that was impossible. Is there a reason why I am getting this port noise? Could anyone tell me what kind of frequencies are listed in the scene from Matrix Revolutions that I described above?

    I mean, I have played many films with my subwoofer, and this film (that sequence), is the only film (alright, besides ROTK the "heart beat scene" at the end) that had excessive port noise.

    I also found that if I play the same scene over a few seconds after I heard the noise, it doesn't play as loud as it did before. As in the port noise is actually reduced because the bass is actually lowered. But then if I let my subwoofer "rest" for a two or three minutes, it's back at full strength.

    I don't know. Even if I backed the volume down by 4-5 dB's, I still get the port noise. Up to that point in the film, my subwoofer was amazing. So what's going on here?

    Anyone else with the same problem (with that specific scene)?

    --Sincerely,
     
  2. TimJC

    TimJC Stunt Coordinator

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    What does the noise sound like? Try to be as specifically descriptive as possible.

    Thanks,

    Tim
    [​IMG]
     
  3. BrianWoerndle

    BrianWoerndle Supporting Actor

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    Trying to move that much air with only 1 3" port is going to cause port noise. It is just plain physics. I used to have a 20-39CS cylinder with a single 4" port and it had port noise. When I upgraded to a CS+ with tri 3" ports I no longer have the problem. It is just something you have to live with.

    While the PB-10 is a killer sub for $400, you have to realize the comprimises that were made to get it to that price. Otherwise you need to upgrade to a bigger, badder sub, or multiple subs.
     
  4. Edward J M

    Edward J M Cinematographer

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    Yeah, what he said. [​IMG]

    That scene has tripped up more than a few subwoofers. IIRC, it has very strong content around 20-25 Hz - close enough to Fb on the PB10-ISD to cause some port chuffing at high playback levels.

    For the Ultra/2 review, I played that scene at Reference Level (on a single Ultra/2) in the 25 Hz tune, and the amount of air blowing out all three 4" ports was enough to rearrange Dolly Parton's latest hair-do. There was no chuffing though.

    If you drop the level from -10 to -16, does the port noise go away? If it does, then you can expect no port noise at -10 with dual PB10-ISD (because duals give you 6 dB of headroom). I think that was your plan, last I read?
     
  5. AlanZ

    AlanZ Screenwriter

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    I'd like to know what port noise sounds like, too....I've never heard that, nor have I ever heard what it sounds like to bottom out the driver. I know about the 'clack', but I'd like to hear a description of port noise. Thanks!
     
  6. Ilkka R

    Ilkka R Second Unit

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    Here it is. Quite strong content around 16 - 32 Hz. Also the actual sound effect is quite interesting. I can easily see PB10 chuffing quite easily on this one. I'll have to fire my duals one day.

    [​IMG]
     
  7. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    If you drop the level from -10 to -16, does the port noise go away?

    Hi Ed, nice to hear from you again.

    No, if I drop the level to -16 the port noise doesn't go away completely, but it is significantly reduced.

    If I drop the level to -18, there is no port noise to speak of, but it's such a low level that it's kind of underwhelming.

    Throughout the film, I was feeling all kinds of bass. I assume that there are scenes from Revolutions that go down even lower than the water explosion scene? Because my subwoofer played them all with no problem at it's limits.

    Strong and deep, until, of course, that water explosion. In fact, every film with deep bass content I've been feeling, and this is in a big 3600 cubic foot room.

    The funny thing is this; I am sitting 2.5 meters away from my sub. If I sit another meter away, the bass is even stronger. The subsonic bass hits me harder. I always thought that the further away you sit, the less bass output you would get.

    Not in my case.

    The sound I get is definitely port noise. It's like a "wwwhooossh" sound. If I put my head next to the port, it's blowing so damn hard and I can hear it.

    If it does, then you can expect no port noise at -10 with dual PB10-ISD (because duals give you 6 dB of headroom). I think that was your plan, last I read?

    Definitely. I plan on purchasing my next PB-10 next month. I plan on having a total of 4 (co-located) in the upcoming months. Another PB-10 would be close to ideal for me.

    You see, my ideal listening level is -10 to -7. I will not go higher than that level.

    So I think in order for me to reach those levels without any compression, or port noise, I would need another 2 (to reach uncompressed levels at -7).

    But yeah, if someone has duel PB-10's, please do me a favor and try that scene out and tell me what you think. I don't know why my subwoofer has a more difficult time playing the upper bass frequencies than it does subsonic. Although I could be wrong on that.

    I mean, I put in LOTR FOTR the other day. When I listen to when Sauron hits the soldiers (which I've been told has a lot of 16hz bass in the swings), my subwoofer is flawless.

    When Frodo's heart beats in ROTK (towards the end when he is about to throw the ring into the fire but doesn't), the entire room is throbbing. There is very little port noise on that scene, and I think you said that it has major 20hz content in it.

    But when there is a lot of output in the 25-30hz range, I have slight problems. Perhaps "someone" can tell me why that is.[​IMG]

    Guys, thank you all for the feedback, I really appreciate it.

    --Sincerely,
     
  8. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    Is the water explosion scene from the Matrix Revolutions supposed to have loud bass in the 16-30 hz range? Because I just played it on a system using the M&K MX-5000, and I didn't think it was loud at all.

    This was at -10 from reference. The bass on that scene with the M&K was actually quite soft. So, yeah. Perhaps someone with more capable equipment could explain what kind of effect I would be getting.

    Remember, the equipment we use is calibrated correctly.[​IMG]

    --Sincerely,
     
  9. Edward J M

    Edward J M Cinematographer

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    Your port is tuned to about 18 Hz. While it will start to shoulder some of the load at higher bass frequencies (probably starting around 25 Hz), it will be doing the most work at 18-20 Hz.

    If you look at the water bubble chart, there is a big red blotch at 18-20 Hz. At -10 RL, that is simply too much for a single 3" port to handle - so you heard some chuffing. The 25-35 Hz stuff won't bother your subwoofer at all, and the port contribution at those frequencies is minimal - it's all coming from the woofer.

    If the chuffing goes away completely at -18, then you will be able to play that scene at -12 without chuffing once you get the duals. With four PB10-ISD, you can push that to -6 without chuffing. [​IMG]

    Considering that is the only scene in the entire movie that gave your sub problems at -10 RL in a pretty large room, that is impressive for a single 10" woofer with a single 3" port. This is especially true considering the darn thing actually does play flat to 20 Hz at high volumes with low distortion, unlike other brick and mortar subs in this price class which lop off the entire 20-40 Hz octave and won't even bother trying to play half the stuff in this movie.

    The reason your bass is stronger in certain parts of the room (despite being farther from the subwoofer) is that room modes become the predominant influence output as you move farther away from the sub. If you were outdoors, the inverse SPL law would certainly apply and it would get weaker as you move farther away.

    Inside, you just happen to be sitting in a peak at that location, so it sounds louder despite being farther away. Bass traps and a PEQ will help to flatten the in-room response and also provide a more uniform FR at more listening locations.
     
  10. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    I think it's possible that either I am sitting in a null, as far as low bass is concerned, or I am sitting in a position where the room nodes are giving me some healthy bass peaks.[​IMG]

    Ed, since you have far more capable equipment than I do, perhaps you can give me some feedback on certain scenes in Revolutions. Which is the loudest and lowest bass scene in Revolutions?

    I put in Reloaded yesterday, and I was pleasantly surprised at the different kinds of bass sounds in the Burly Brawl. I haven't really heard many people comment on it but it's fun. There is a scene when Neo kicks Smith before being picked up and thrown into the bench. That kick gave me an ultra low bass hit.

    Could someone plot the response of the Burly Brawl so that I know what I'm experiencing here? Ilkka?

    Ed, just a quick question; if I put a sock in my PB-10, heh, and play the scene over again at the same volume, -10, could that work?

    What kind of SPL drop would I expect? Just a thought, because I haven't tried it out yet.

    --Sincerely,
     
  11. Edward J M

    Edward J M Cinematographer

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    Ilkka is the king of spectral charts. He told me how to make them, but I haven't had the time yet. Be aware these take some time to generate, and Ilkka is quite busy right now.

    Regardless, I listed some scenes from both of those Matrix movies in my Ultra/2 review. I think the loudest scene in Reloaded (at least on my system) was the Trinity Falling (take 2) scene. It's probably not the deepest though - maybe 25-30 Hz.

    If you plug the port, you will lose quite a bit of extension and output below 30 Hz. I don't recommend it, but you can certainly experiment.

    I do recommend enough subwoofers so that you are artifact-free (compression, port noise, woofer cry, etc.) at your preferred playback level. This will be a far more satisfying option that simply stuffing a sock in the port because the sub is being overdriven on a given scene.

    It would be hard to pinpoint why the M&K 5000 lacks impact on that scene without measuring the in-room FR and compression/distortion limits. It's possible it simply isn't very capable in the 18-25 Hz region.
     
  12. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    Ed, you could be right about the big M&K. In fact, I tried the scene on Reloaded (Burly Brawl) when Neo kicks Smith before smashing into the bench, and the big M&K makes a big "flop" sound.

    This was at -15 from reference.[​IMG] So I'm wondering if that specific kick has ultra low bass information in it to cause the bottoming on the M&K. Of course, there is no bottoming on my subwoofer. It plays to around -10 perfectly with no major compression.

    About the sock thing; I could be wrong, but I thought that sticking a sock in the port would lower bass extension below the tuning point.

    Am I correct?

    --Sincerely,
     
  13. Edward J M

    Edward J M Cinematographer

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    No, sticking a sock in the port would create a sealed subwoofer.

    A sealed subwoofer will start to roll-off at 12 dB/octave (2nd order) below the natural system resonance frequency (undetermined at this point). But sealed subwoofers don't have a "tuning point" per se - they just have an F3 point where they start to naturally roll-off.

    Jack Gilvey could probably model it, but if I was to hazard a guess (and it's just a guess), a "sealed" PB10-ISD would start rolling off around 30 Hz (maybe a bit deeper).

    The electronic high pass filter at 19 Hz will still remain obviously, so that will cascade with the natural 2nd order roll-off at that point, creating a much steeper curve.

    Again, I don't recommend it, and it certainly won't give you deeper extension or more output. I do recommend dual PB10-ISD at least in that size room - that alone will solve many of your problems.

    The "flop" sound from the M&K 5000 on that scene could be soft bottoming or cone cry or a limiter kicking in, etc. Hard bottoming would be a harsh clacking sound. Regardless, you are clearly reaching the limits of that sub at that playback level in that particular room.
     
  14. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    I need those charts posted. . . pronto![​IMG]

    Thanks Ed. Excellent points as usual. The thing is, I can play most bass heavy scenes from the Burly Brawl perfectly fine with the M&K (their reference sub), but that one kick gives a bottoming out kind of sound.

    If I lower the volume to -18, it goes away. It just seems strange for that one kick to bottom the sub out but all other bass in the film which you would expect to mess the subwoofer up ([​IMG])plays just fine.

    Strange.

    --Sincerely,
     
  15. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    Jack are you trying to be funny here?

    --Sincerely,
     
  16. steve nn

    steve nn Cinematographer

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    Wow! 4 PB10-ISD's! I think you would be the first and only to do so. A very nice option and would certainly take care of any headroom issue that you have experienced (although very seldom) with the single. Going collocated dual will definitely give you quite a boost (+5+6dB) in headroom though. Four PB10-ISD's in your size room and listening level should more than whip any port chuffing into submission no matter what the scene.
     
  17. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    Whatever.

    --Sincerely,
     

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