chuffing - what is it and what causes it?

Discussion in 'Loudspeakers' started by Methost, Mar 22, 2006.

  1. Methost Full Audioholic

    Methost
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    I think I know what chuffing is because the word sounds like the noise made by my x-sub during some loud, low frequency scenes in certain films.

    Is this caused by volume or my frequencies lower then my sub can handle? Or is it a combination of both?

    Can this be remedied? My room size is in excess of 2500 cu ft and is open to another room. It's not a great room for sound, but it's what I am stuck with.

    Any suggestions on how to curb this noise?
  2. ironlung Banned

    ironlung
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    Chuffing is noise caused by turbulence as air enters and exits the port. I think this is common to ported enclosures and little can be done about it. You may be able to replace the port with one with radiused and tapered openings to minimise the turbulence if the X-sub does not already have them(I am not familiar with x-sub). That would take some carpentry and re-tuning of the box though.

    good luck,
    Ironlung
  3. JennAir Audioholic Intern

    JennAir
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    "Chuffing" is used to describe the sound created by the port tube during periods of high excursion of a bass driver. This can happen in any speaker system, not just subwoofers. Chuffing is created by large movements of air within a speaker port. The solution is to alter the speed at which the air is moving. This can be done by increasing the diameter of the port but this requires a change in the length as well. Another solution is to flare the ends of the port tube. This changes the velocity of portions of the air mass enough to reduce chuffing to an acceptable level. It's similar to bundling several lengths of water hose. When water is fed through them the column of water exiting the other end will be a different length depending on the length of the hose it traveled through. In existing ports suffering from chuffing you can put in a bundle of drinking straws to simulate the "hose analogy" above.
  4. 3db Audioholic Overlord

    3db
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    maybe your sub working too hard because

    its located in a bad spot in the room. My subwoofer chuffed like crazy during intense deep base scenes but iI had to dial it that way becuase of lack of bass response. I did some reading and found out about the intercation of low frequency and room acoustics so I played with the location of my sub. needless to say, once I found the sweet spot, I had to turn the gain wayyyyyyyyyyyy down on my sub and it never chuffed again. Before you listen to anyone in here about getting this sub or that sub, play with the sub location relative to the room 1st. You may get the same results as I did. If, not, then start looking at alternative subs. Good luck
    3db,
  5. Sheep Audioholic Warlord

    Sheep
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    One things that HASN'T been noted is that chuffing usually occurs BELOW the tuning point of an enclosure(ported).

    Some manuf. impliment a subsonic filter to decrease output below the -3dB point. Example, my DPS-12 has a subwonic at 24Hz 1 hert below my -3dB point.

    SheepStar
    Last edited: Mar 22, 2006
  6. Methost Full Audioholic

    Methost
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    The subs location in the room can effect chuffing?

    Will turning down the volume have any effect? Or is that not the best method?
  7. Sheep Audioholic Warlord

    Sheep
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    It will, but your turning down the volume. Assuming your stereo is level matched, now the subwoofer is to quite.

    I think you may have to live with it.

    SheepStar
  8. Sheep Audioholic Warlord

    Sheep
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    That is not possible with the X-Sub. It uses a slot port, and I would not want to mess with its enclosure.

    SheepStar
  9. annunaki Moderator

    annunaki
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    The best advice I have heard so far is to play around with room placement. Seeing as though the enclosure uses a slot port, changing the port is out of the question. Is there anyay to get the Theile-Small Parameters for the sub woofer? If so, get them to me and I can model a new enclosure for you.

    Before we go to that extreme....

    What music, movies or movie passages is this happening on? Where is the gain on your subwoofer set at? What level is the subwoofer output on your receiver set to? You could simply not have enough woofer for your room which would lead to overdriving of the (sub) system.
  10. Methost Full Audioholic

    Methost
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    Wow ... I understand about half of what you just said. ;) Noob here.

    I will look in to the questions you asked and get back to you when I can. Currently my amp is at Cadence having service done, so it will be a few days till I can follow-up.
  11. MacManNM Banned

    MacManNM
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    This is true. The noise will occur when the air velocity reaches anywhere above 20m/s (depending on the port). So it usually will happen just above and just below the tuning of the port. Annunaki or I could model a new box for it, but I have a feeling that 1. you won't be able to find the TS parameters for the woofer and 2. It wont be worth it.

    If I were to do anything, I would prob build a new unit entirely. You could reuse the amp. Next to that would be to find the optimum placement for the unit.
  12. Methost Full Audioholic

    Methost
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    I guess I just don't understand how putting the same driver and amp in a new cabinet would stop the problem. I'm not saying I don't believe you, I'm just saying I can't get my mind wrapped around the problem. My Cadence Xsub is a pretty well regarded sub in the lower end market. Does just the fact that I have it in a room too big for it cause this? And how does the sub no how big the room is anyway? Just by the air pressure?

    Much of my problem is that I don't understand how sound and sound waves work.

    When I get my amp back from Cadence, Ill play with the settings some and try to find a scene that I can use to reproduce the sound everytime.

    Thanks everyone for your input.
  13. 3db Audioholic Overlord

    3db
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    Please read

    Not exactly. What a poor room location gives you is weak bass response RELATIVE to your listening position/location. So one tends to over compensate this by cranking up the volume on the sub. This causes the sub to work much harder than it should, causing it to chuff for the reasons given my sheep. What I would do if I were you is to move the sub where you normally would sit, turn the gain down on the sub a little, put on a cd or DVD with some heavy sustained bass passages and start crawling aeound the room on hands and knees. (I did this and it works all the time.) While crawlng around the room and along the walls, you'll notice the bass very strong and pronounced in one location and weak in most of the others. Where you find the bass the strongest is where you are going to place your sub. Then you get set levels again. Try it and let us know
    3db,
  14. Buckeye_Nut Audioholic Field Marshall

    Buckeye_Nut
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    If you hear obvious chuffing sounds and the above comments dont help reduce the noise, I'd suggest upgrading subwoofers. Chuffing is usually a sign of a grossly overworked and underperforming subwoofer. You should never hear chuffing from ports on a sub that's doing it's job well:)

    If you cant upgrade, I'd suggest turning the gain down because your sub is being pushed beyond it's comfort level.
  15. MacManNM Banned

    MacManNM
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    By building a better enclosure with larger ports you can reduce the air velocity from the port, and improve the output of the unit. That sub is small, and is not really designed to play under 30hz.

    It has nothing to do with the room sixe. It is all about the output level. You need to push the sub harder in a large room than you would to get the same level of SPL in a small room.
  16. ironlung Banned

    ironlung
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    Could a SPL meter be used with the above method to ge a little more tangible info?
  17. MacManNM Banned

    MacManNM
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    I wouldn't say that. I would say that the unit is not really designed to play that low and that's why he is hearing that. Heck, I have made an SVS PB12/ultra2 chuff by plugging 2 of the ports to tune it low. I wouldn't call that sub a slouch.
  18. Ron Temple Senior Audioholic

    Ron Temple
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    Methost,

    The XSub works very hard and trys to play beyond it's capability. How do you have it calibrated? In my room 2000 cube with an opening, I drove it to distress many times, but no chuffing or bottoming (it did try to walk a few times). I always was on the minus side on receiver trim and about 11:00 on the sub gain, calibrated to 75-78db @ -10 MV (playback rarely more than -21). Something like Hitchhikers or WotW with subsonic content was a stretch for the little guy. I'd say you probably need to back off the volume a bit, maybe drop the crossover and trim the 50hz filter. Basically, run lean so it doesn't work as hard.
  19. 3db Audioholic Overlord

    3db
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    Sure it would help

    but its notreally needed. The location in the rooms where the bass is strongest is really noticeable. A SPL meter to find that isn't really necessary. It only becomes necessary when calibrating it with the rest of the system
    3db,
  20. Johnd Audioholic Samurai

    Johnd
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    3db: What a novel suggestion. I never heard of that before. I'll have to give it a try sometime (even though I'm not lacking bass).

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