Woofer Pumping--anything to worry about?

Discussion in 'Audio Hardware' started by riddlemay, Jun 19, 2015.

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  1. jupiterboy

    jupiterboy Forum Residue

    Buffalo, NY
    Could be cart/arm resonance as well, because when that is low it amplifies any input in that range. Obviously, they need a shelf or rack or something else to help as well.
  2. chervokas

    chervokas Forum Resident

    No doubt, if it's being excited and and it starts too osciallate, but if it's not being excited by a record playing, even a warped record playing, but is being excited by footfalls, well, then the resonant frequency may be in the right low spot to not be excited by record warps. I mean, there's going to be a frequency at which the mass/compliance spring system of cart and arm are going to resonate. You aren't going to get away from that, but you can get to a frequency at which its unlikely to be excited by normal record playing, and you can damp it at that frequency to knock down its amplitude and duration. But if footfalls, even gentle ones, are causing a problem, well, not only is there that resonant problem, but there's probably other breakthrough problems at other frequencies affecting audible clarity.
    The Pinhead likes this.
  3. head_unit

    head_unit Senior Member

    Los Angeles CA USA
    Your turntable just is (was) not isolated enough. And I too doubt a subsonic filter will fix it totally-the footfalls are a kind of transient event and the filters more a steady-state thing. I don't have access to a handy simulator to check, but I think the pumping will still pump "before the filter can cut in."

    Personally, I wouldn't want to stress a nice and fairly expensive setup like yours with this kind of pumping.

    And, 37 Hz seems quite high for a cutoff frequency.

    So if you are going to do a 'table, chervokas is right, you need a totally different mounting somehow.
  4. chervokas

    chervokas Forum Resident

    This is a good point, that's too high. That's above the lowest fundamental on a piano and just below the lowest fundamental on a standard tuned four string bass guitar. And don't forget, whenever you have a filter rolling off frequencies you also have attendant phase shift. It's best to minimize filtering near, or in this case IN the audible range, particularly since, in this case, given the cause, we know the problem is floor borne vibration. Treat the problem -- floor borne vibration -- with appropriate isolation, instead of just treating this particular visible symptom.
  5. ggergm

    ggergm I don't believe in Santa Claus or MoFi

    Huh? Footfalls are under 10 Hz in their frequency, often significantly under. And waiting for the filter can cut in? Double huh? It's always in the circuit. It's not an on or off thing. It will roll off energy at those lower frequencies all the time. The speaker will probably register some of the initial transient from the footfall but the excursion of the driver will be way down. Continued ringing should be greatly if not totally eliminated.

    Problems like footfalls are exactly what subsonic filters cut out.

    But then I think you recommending the OP make changes for no good reason. As I've said upthread, I wouldn't worry about this if it was my system. In fact, I now have this exact situation in my system and I don't worry about it. After recently changing my turntable's isolation (thread here), making it resonate healthily at 4Hz and as a result, killing any kind of resonance problems at higher frequencies where there is music, my turntable has become sensitive to footfalls. It wasn't before but then, footfalls can cause a 4Hz resonance to kick in. I now have to be careful walking in front of it. Oh, shucky darn. It's a big who cares? I certainly don't.

    I agree the OP could improve his turntable's isolation. It will result in better sound. I hear the difference better isolation made in my system. But do it to improve the music, not because of footfalls (this is chervokas' point). Footfalls are a non-issue. And whether the OP wants to spend time and money addressing his turntable's isolation as opposed to other faults in his stereo is a question only he can answer.
    Last edited: Jun 22, 2015
  6. VinylSoul

    VinylSoul Forum Resident

    Lake Erie
    If your wife or girlfriend doesn't have a problem with it its probably ok.
  7. Captain Wiggette

    Captain Wiggette Forum Resident

    No, it just means that your woofers are producing bass, which is their purpose, what they are designed to do, and shouldn't be an issue unless you turn the volume up very high, in which case the bass is just as much of a 'stress' on the woofers as any of the bass in the music you're listening to.

    The only serious risk would be turning it up so loud, using primarily ported speakers, such that you max out the woofer's excursion and the VC hits the back of the magnet structure. You should be able to hear that pretty clearly as metallic clacking when that happens. That could quickly do physical damage to the driver, but this is unlikely to happen unless you REALLY turn it up and mostly only with the really big drivers which can move that far anyway.

    As I said before, I wouldn't worry about it.
  8. Doug Sclar

    Doug Sclar Forum Legend

    The OC
    A filter would surely help, but it makes much more sense to try isolation or other methods. Yes a filter would work, but OTOH we've spent years trying to improve the ultra low frequency response of our systems, so a filter would be counter productive towards that effort. There can be some very cool super low end sounds on music and it makes no sense to cut them off if you don't have to.

    For example, a few years ago we switched to the King Cello phono preamp and all of a sudden we discovered all kinds of low end stability and impact which would not be there with a filter. It's like we discovered a missing octave in some recordings that we knew well.
    chervokas likes this.
  9. BKphoto

    BKphoto JazzAllDay

    i use a Harrisons 24hz filters no problem...since my speakers don't go any lower than that i'm not missing anything...
  10. head_unit

    head_unit Senior Member

    Los Angeles CA USA
    Well, yes, but not completely. "Frequency" really applies to steady-state phenomena. Transient phenomena (like a footfall or a drum hit) are not steady-state, though they can be considered in a way to be "made up of" a variety of frequencies lasting for a bit of time. A filters' filtering spec (XX Hertz, YY db/octave) applies in the steady-state, it is not a transient specification. So I might rephrase what I said to include
    - A footfall has higher frequencies that the filter perhaps won't filter (more a conceptual statement than a technically correct one)
    - Until the filter reaches steady state, significant energy could still hit the woofers.
    I wish I had access to a simulator like LEAP/LMS to actually look at this definitively, but I am traveling right now. Anyone?

    Except in extreme cases, unless some really nasty sound is heard along with a footfall, you're probably right it's not the end of the world. If the feedback is strong enough, it could make the needle jump which would not be good. And if the 'table isolation is so poor, I wonder if there is not feedback going on at audio frequencies as well and muddying the sound.* That would really be my concern more than the footfalls. Does anyone still sell a low-frequency test tone record which the OP could use to check this?

    *from http://www.ecoustics.com/articles/streamlined-vibration-isolation-improves-sound/
    "by Jim McMahon, Zebra Communications

    The impact of external vibrations plays a critical role in the sound quality produced by turntables and tube amps within high-end audio systems. Capacitors, resistors, transistors and other electronic components used in many audio systems are likewise sensitive to vibration.

    Vibration isolation in the playback process is crucial to experiencing a high-quality audio. Any external vibration, no matter how slight, even someone walking near the turntable or vibration from floor-mounted speakers, is sensed by the turntable's stylus and affects the sound being played back from the record.

    With recorded discs, sound waveforms are captured in the disc grooves with microscopic undulations. The turntable's cartridge and stylus trace these minute wave forms, play them back with very sensitive low voltages and convert them into an audio signal. This is how the sound captured in the record grooves is reproduced. But this process is extremely sensitive to movement and vibration." [because the stylus motions are so tiny]
  11. Electric

    Electric The Medium is the Massage

    I believe that, but was nevertheless surprised and initially concerned to see it today for the first time. I only have an SACD player so was listening to a CD that came in the mail today, and WOW those woofers started pumping and I didn't have the volume loud at all. I'll assume, as you say, they're doing what they're supposed to do and nothing to worry about.

    Here's the CD:

    Last edited: Sep 3, 2015
  12. The Pinhead


    Is your player properly isolated ? I have gel cushions under the OEM feet since it's a '92 model and I listen to loud music with a sub. I never experienced the cone trouble your speakers seem to be though, just feedback prior to the gel feet. Is it possible something in your rig is generating an inaudible frequency(ies) that may be causing this ?
  13. Electric

    Electric The Medium is the Massage

    It's only on this one CD and not on all tracks. The player has decent isolating feet and I have it on a 3" cutting board with three cones underneath. I guess I'm not seeing the pumping as cone trouble, per se., only as doing what they need to do to produce the sound that's on the CD. Is that plausible?
  14. The Pinhead


    Yes, it is. Without the longer cone excursions there'd be no bass. What if you press pause and there's comlete silence ? Do the woofers still move ? (like by themselves ? ) If they don't, get those grilles on and stop worrying !:edthumbs:
  15. Electric

    Electric The Medium is the Massage

    They stop moving on pause. Don't have grills. No worries. :)
    The Pinhead likes this.
  16. jupiterboy

    jupiterboy Forum Residue

    Buffalo, NY
    What is the mastering source?
  17. Electric

    Electric The Medium is the Massage

  18. jupiterboy

    jupiterboy Forum Residue

    Buffalo, NY
  19. james

    james Summon The Queen

    If a CD player not "properly" isolated could cause woofer pumping...I might just give up o the hobby. I can't explain that to myself.
  20. Electric

    Electric The Medium is the Massage

    Again, is it a problem if the woofers are pumping? Aren't they supposed to do that?

    I have 4000 CDs and SACDs. This pumping is only happening with this one CD. I assume it has a lot of 'bass information'.
  21. tim185

    tim185 Forum Resident

    It will do your amp absolutely no favours either.
  22. blakep

    blakep Forum Resident

    It has a lot of subsonic information.

    It's likely because of one of three reasons:

    1) When the original LP was cut there was subsonic information cut onto the LP or
    2) When the transfer was done from LP to CD the playback equipment (arm/cartridge) were not sympathetically matched up or the turntable itself was not isolated properly with respect to either structure borne or air borne vibrations which resulted in subsonic information being transferred at that time to the digital media.
    3) When the transfer was done from LP to CD the record was warped and the playback equipment (Table, Arm, Cartridge) had trouble with it resulting in the transfer of subsonics to the CD.

    Or possibly the table used to do the transfer had main bearing/rumble problems. But my bet would be on one of the 3 above and probably one of the first two.
    james, jupiterboy and The Pinhead like this.
  23. The Pinhead


    Whoa ! That's what I call a lousy transfer ! Hadn't thought the cd could be a needledrop (although I have a couple of those in my collection. But I don't think the OP needs to worry or stop playing that particular CD. I remember the problem as a common occurrence back when no cds existed and never saw any speaker or amps damaged by it.
  24. missan

    missan Forum Resident

    As I see it the woofers should not be pumping for anything but the real music, for really loud playing. If they do for footfalls or when playing a record without any particular loud level, there is a problem that needs solving. Using a high pass filter can solve the symptoms but it´s much better to look into the cause(s) of the problem. The effect these types of resonances have on the music cannot be solved with a filter as the frequency modulations of the music have already happened. The degradations of the music content can only be removed by looking at the real problems, not by a filter.
    Tim 2 likes this.
  25. Electric

    Electric The Medium is the Massage

    Here's a reply I got from my speaker manufacturer:

    "Driver movement is quite normal, especially on deep bass passages. With that said there is an optimal range and volume , at no time should you hear any mechanical noise or distortion coming from the driver. It is quite important that your associated equipment (amplifier) meets your loudspeakers requirements for power, impedance and distortion levels."
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