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Low Freq Crackle ... Fixed with a cloth?

Discussion in 'Amps and Cabs [BG]' started by Gabu, Oct 7, 2002.


  1. Gabu

    Gabu

    Jan 2, 2001
    Lake Elsinore, CA
    Hi guys.

    I noticed something kind of funny. I get a crackle sound when I hit certain notes in the lower register. It doesn't drowned out the note or anything, but i can hear it.

    I also noticed the the Ampeg B25 cab. (It's a 215) Vibrates the heck out of my Ampeg SVT400T amp.

    So I took a towel and folded it up, set it imbetween the amp and cab... wala! No more crackle!

    I am going to take my amp in to the shop anyways, to check on it's loud pop, and also to check it's solder connections. Damn, that B25 shakes!! :p
     
  2. Dean_CustomJazz

    Dean_CustomJazz Guest

    Jan 23, 2002
    woburn
    i have a similar story. I was at a practice, and my drummer secretly shoved a tennis ball in one of my rear ports of my goliath jr, without me knowing. I noticed while we played one of our songs, I was getting alot more punch. I looked to see if something maybe got changed on my pedal, but sure enough, it was a tennis ball. I haven't taken it out since:D
     
  3. Call me the What IF Guy, but I don't think it's to healthy over some time to keep that tennis ball there. It may give you the sound your looking for with the punch and all, but those ports are there for a reason. Let's see if some of the people here that really know their stuff, agrees with me...Then again you may not care. :D
     
  4. Brad Johnson

    Brad Johnson Commercial User

    Mar 8, 2000
    Gaithersburg, Md
    Boom Bass Cabinets, DR strings
    Sounds like your drummer is a moron. What would you have done if it damaged the cab?

    Rule #1- don't screw with my gear
    Rule #2- I will not assist in removing my foot from your ___ if you violate rule #1

    I can imagine how a drummer would react if I got curious as to how several small slits would effect the sound of his drums and brought a razor to rehearsal.

    Ha ha.
     
  5. geshel

    geshel

    Oct 2, 2001
    Seattle
    I don't think it'll do any harm. It might lower the power handling of the cab at a certain frequency range, but if you're overdriving the speaker you'll hear it (and it'll improve the power handling in other places).

    One thing though - how tight is that thing wedged in there? I'm just wondering about the possibility that you hit a big slap or something and it goes flying out and hits someone/thing! :D Or, possibly, gets sucked into the speaker and goes right through one of the cones?
     
  6. to answer the first question, it is most likely a cracked solder joint or loose connection in your head (if it has a valve probably its connection), and when you play the vibration of the speakers are making the crackle...
    if u r any good at soldering it is most of the time pretty easy to fix... sometimes it can be hard to find the crack or loose connection, but if you have your amp hooked up as normal with the top off, (or the amp out of the case) and then go around the circuit board with something like a wooden icypole stick, when you bump and rub the connections it should crackle or whatever when you hit the one that is loose.
     
  7. Plugging the port with a tennis ball will not screw up your cab. On the contrary, it will actually protect your speakers by making them run in a sealed cab with that sealed up springy air to keep them from moving as much. The result will be a cab that does not go down to as low a frequency as it did when ported, but instead has a smoother roll off at the low end, and like you said, more punch.

    Porting a cab makes the output go down to a lower frequency, but if you look at the phase response of the speaker as it approaches the tuned frequency, the phase gets nasty because you start to get your sound from the port, not the front of the speaker. And below the tuned frequency, the speaker is basically just flopping loose with no help from the cab.

    Using a sealed cab does not give as low a frequency range, but the response is smooth all the way down to cutoff. The sealed air in the cab keeps the speaker from moving as much at lower frequencies, so it helps protect it.

    40 Hz is not necessary. 80 Hz sounds great. Just listen to an SVT. It uses sealed speakers. I build all my custom cabs with sealed speakers because it gives more punch.

    Chris
     
  8. Gabu

    Gabu

    Jan 2, 2001
    Lake Elsinore, CA
    Bricks.

    They're not just for breakfast anymore...


    Hey, I was wondering. If I put something heavy on my cab to keep it from vibrating as much... would that improve it's performance in some way? I guess the speakers lose something when the cab vibrates along with them.

    Does anyone do this?
     
  9. That brick will get vibrated off and fall on your toe.

    Are you pushing that old B25 cab with 400 Watts? You know the original B25 head only put 55 Watts to that thing, so you may be in danger of frying those speakers if they are the original CTS ones, and maybe even if they are the ultrasweet Altec Lansing 421A's. The Altec's could handle more power, but 200 Watts each will be pushing it. If you've got Altec's in there, don't blow them! They are the best bass speakers ever built.

    Also, that cab was originally 16 ohms, unless you have a later one that is switchable to 4 ohms, or you rewired it.

    What's the scoop, poop? Don't blow up that gem. It may be vibrating like crazy because you're killing it with oodles and oodles of power.

    Chris
     
  10. Gabu

    Gabu

    Jan 2, 2001
    Lake Elsinore, CA
    Howdy Chris,

    I think this is the later one, because it has a sliding switch, which I leave on 16. I bought it with the original speakers blown. I reconed them at Orange County Speaker Repair, and they said the reconed speakers would be able to handle 200w each. (Though at 16 ohms, they should be only getting a max of 100w each) They are the original speakers that came with the B25, other than the recone. :)
     
  11. Okey dokey, Artichokey. Sounds like you got it covered. No sweat. Reconed for higher power, and you're running it so it's only getting about 100 Watts each speaker. Couldn't have done it better myself.

    Just get your girlfriend to sit on the vibrating cab. She'll like it, and it will look cool. :D

    Chris
     
  12. Gabu

    Gabu

    Jan 2, 2001
    Lake Elsinore, CA
    Hmm... I dunno man. My dreams for being a famous rockstar might get squashed by everyone wanting to see the vibrating lady instead.

    I have been gettings some mucho stylin' sounds from this cab... But I have to admit... My P-Bass is what really rocks going through this rig. My Jazzes seem to like the 410s better.
     
  13. Brad Johnson

    Brad Johnson Commercial User

    Mar 8, 2000
    Gaithersburg, Md
    Boom Bass Cabinets, DR strings
    Vibrating ladies are pretty hard to pass up.