Anatomy of a speaker fart

Discussion in 'Amps and Cabs [BG]' started by Gabu, Feb 16, 2002.

  1. Gabu


    Jan 2, 2001
    Woodland Hills, CA
    When a speaker cabinet produces a distorted output at certain volumes, and at certain frequencies, I am wondering what the true culprit is.

    If your speaker has a usable range of say 60 hz to 5khz, with -3db at 50hz and -10db at 40hz... (seems to be common for many 10s) then would you be more likely to produce a speaker fart if the cabinet was tuned lower than the speakers could go? Or perhaps if the cabinet was too small for the speakers would that produce the distortion? Or is it more of a case where the speaker is pour quality so it distorts instead of just attenuating a clean signal?

  2. FalsehoodBass


    Jul 22, 2001
    Denver, CO
    my assumption was that the speaker wasn't good enough to produce the low frequencies.... at high volumes i needs to go all the way out and back in the allotted time. When the volume goes up, the speaker needs to go out farther, and therefore move faster to do it in the same time... when it can't do that, it farts..

    that's only my educated guess though...
  3. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    Usually that sort of sound is produced when you have insufficient power available from your power amp to produce the notes at loud volume. Bass frequencies require lots of power to prevent clipping in the power amp at higher volume.

    Clipping the power amp is the most common cause of driver failure and not "overpowering the speakers" as many suppose. The power amp runs out of headroom and the top of the waveform becomes flattened (clipped). This overheats and distorts the voice coil and the speaker will fail if you drive it for very long this way.

    If, however, turning down the amp does not make the notes become clear (assuming your speakers are not blown) then you may have a distorted signal coming from your bass or the preamp section of your amp.

  4. fleetwood


    Aug 29, 2001
    Swansea UK
    Well, you guys, I'm glad someone else is having similar problems. Here's my story:
    I cut down my combo ages ago and boxed up the head and made the 15" speaker cab smaller by doing away with the original side porting. This has worked fine for years using an Aria Pro 2 Cardinal Series Bass. Last May I bought a Fleetwood 5 String and things seemed OK. However, last December I bought an Aria TAB60 Semi-Acoustic with humbuckers. Now the problems started. Low G, F and open E produce horrible rasping from the speaker but only at higher volumes. I didn't notice in rehearsals but when we go on a gig I'm unable to turn up the volume very far. This makes it impossible to use that bass out anywhere.
    I took the cab to a repairer who said I was expecting too much of the cab since it had been made smaller. I then got in touch with a person at Celestion Speakers who gave me details on how to tune the cab. This meant inserting a port of a certain diameter and length. This I did, and although it improves the quality of the sound of the speaker, it doesn't stop the rasping at high volumes. So, does anyone know where that leaves me. Is it the speaker? Is it the cab still not OK?
    Should I try my amp head on another cab somewhere ( I would if I could find one).
    I've tried the TAB60 on a new Laney 300watt head + 2 X 10 and 1 X 15. and there's no rasping there - just lovely bass sounds. Sounds like new gear needed.
  5. New gear is needed. Speaker's don't last forever.
    Some touring pro's replace/recone them once a year.
  6. chucko58


    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    Ported cabs are notorious for excessive cone travel below the box resonance. This is a likely source of "farting" noises.
  7. cassanova


    Sep 4, 2000
    I agree with chuck m here.

    especially if your using the carvins gabby. they're inefficent to begin with, and if you dont have enough power your going to distort rather quickly. This happens to me alot whenever i have to really drive my amp. I run out of headroom and start to clip.

    you are talking about your carvin distorting right??
  8. Gabu


    Jan 2, 2001
    Woodland Hills, CA
    No, my new 210 was sounding kind of ugly going lower than G on the E string.

    I was powering it with 175 watts (one side of the Carvin R600 @ 8 ohms) , which might be a bit low for these speakers, rated at 150 watts each.

    The speakers are rated 50hz to 4khz. I tuned the cabinet to ~ 41hz.

    I am going to give em more juice and see what happens. :D
  9. Tightanic

    Tightanic Supporting Member

    Oct 26, 2000
    Well, I've recently purchased a Glockenklang Double 2x12" cab, and noticed, that the speakers are moving like crazy. Even at moderate Volumes, you could notice the woofers following every pluck of the strings, eventhough I'm not digging in very hard, but now farting or clipping could be heard. As you can imagine, I was a little bit excited, especially concerning the fact that I was driving it with a 280 Watts head, and the cab should take 500. I wrote a mail to Glockenklang, and the very quick reply said, that I should not worry, that's a normal thing for a enclosure which is linear down to 36 Hz. But what about all those Acme cabs? I've heard, that their speakers don't move that much. Are they less linear?

  10. This isn't quite right. Speakers get blown in two ways: First, they can be destroyed by being driven beyond their excursion limits (Xmax), which can tear surrounds or permanently alter where the coil sits in the gap. This is the most common type of cone driver failure. This happens when a speaker is massively overpowered, or given a lot of low frequency information, especially if the frequencies are below box-tuning frequency. Speakers will fart if driven beyond Xmax.

    Second, they can be destroyed by overpowering, for lack of a better word. This can be but isn't necessarily because of clipping. Basically, if a speaker is given more energy than it can dissipate, the voice coil will overheat and damage the driver. So, even if your power is totally clean but is way more than the speaker is rated for it will damage the speaker. That being said, when amps clip they produce considerably more power than their clean rated power, so a 300 watt amp driven hard into clipping could concievably produce twice that or more. This is more the culprit behind blown speakers than the actual distortion is. For example say you have a 100 watt speaker and a 1 watt amp. If you drive that 1 watt amp way into clipping will it blow the 100 watt speaker? Not a chance, because the speaker can dissipate the heat easily. Anyway, there have been some in depth discussions of this on the boards (with some very knowledgeable people like Bgavin, Bob Lee from QSC amps, MikeyD and Joris, etc) so I'll shut up about it now..:D
  11. fleetwood


    Aug 29, 2001
    Swansea UK
    Well, all this worrying talk of damaging speakers leads me to another point. Should you therefore, when looking for a new amp head, have one with a limiter on it. Would this prevent the overloading of the speakers?
  12. Tom Crofts

    Tom Crofts

    Mar 15, 2001
    Do you mean like a compressor? I have one of those but all it does is make it a lot quieter. Apparently it's good for studio use though...