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Anyone plug the port on your JBL L-36 speakers?

Discussion in 'The Lansing Legacy' started by cartop, Jan 25, 2018.

  1. cartop

    cartop Super Member

    Messages:
    1,078
    Location:
    Worcester Mass.
    OK, Another question for you L36 owners. I really like these speakers but I noticed that when playing LP's I am getting some woofer flutter or maybe it is called rumble. It is slight but it is happening. I made sure my TT's which consit of a Technics SL-Q3, that uses a Shure M91-ED with proper stylus and a Kenwood KD-550 useing a QLM MKIII with correct stylus, are set up correctley depending on which one I am useing at the time. After making sure everything is set up correctley I decided to try some cheese cloth, which is very pourus, in the ports to see if it helped and to my surprize it stopped all of the rumble and actually seemed to snug up the bass. Now my question is will this hurt the speaker over the long run or is it safe to do this? I did a search here and could not find any answers so I either missed the thread on the subject or it just wasn't talked about which I find strange. So what do you guy's think. TC.
     

     

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  2. Mike Stehr

    Mike Stehr Poverty Audio

    Messages:
    1,646
    Location:
    East Wa.
    Does any of the electronics your using have a rumble filter?

    A friend when he lived up here at the time had a pair of Horizons, and he stuffed socks in the ports and liked the difference in bass response. A bit tighter if I recall...
    I doubt blocking the port would hurt anything...just don't overdrive it with heavy bass.
     
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  3. cartop

    cartop Super Member

    Messages:
    1,078
    Location:
    Worcester Mass.
    I have a Mitsubishi DA-P20 pre-amp with a subsonic filter but even when it is on I still get slight woofer pulse. I am running all tone controls flat so no way I am over driving with too much bass and it sounds pretty good. I was giving it 50w peak according to the meters on my Onkyo M-504 amp and it was pretty loud..:rockon:
     
  4. cartop

    cartop Super Member

    Messages:
    1,078
    Location:
    Worcester Mass.
    The filter on my pre-amp only filters from 18hz and below so I think the freq's that are causing the slight rumble are obviously above that. I know that warped records can cause the problem also but the LP's all seem to be level when playing them. Maybe a record clamp might help?
     
  5. cartop

    cartop Super Member

    Messages:
    1,078
    Location:
    Worcester Mass.
    Wow, Nobody,,,,,,,,,,,,,,,,,,,....................:no:
     
    Last edited: Jan 28, 2018
  6. johnlcnm

    johnlcnm Active Member

    Messages:
    107
    Location:
    Las Cruces, NM
    Cartop. Welcome to the world of LPs. That is pretty normal for record play equipment. The analog filters in most of the old electronics are not very sharp. Probably 6dB per octave. Back in the day it was normal to see a lot of woofer excursion especially with vented speakers, as there is no cone loading below the port/box frequency.
     
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  7. cartop

    cartop Super Member

    Messages:
    1,078
    Location:
    Worcester Mass.
    I didn't realize that. Thanks for the info....:bigok:
     
  8. DavidF

    DavidF Active Member

    Messages:
    343
    Location:
    San Jose, CA
    A ducted port system "tuned" to load the woofer with some amount of resistance in order to get the bass support as intended. Bass energy that is well below the tuning of the system (woofer/enclosure/port combined) will cause the woofer to become unloaded, meaning it is about the same as being on an open baffle. Sounds like that, yes, you have some sub sonic energy coming out of the turntable through to the speaker. The added resistance from the cheesecloth MAY be providing some amount of damping that reduces the visible woofer movement.
     
    cartop likes this.
  9. cartop

    cartop Super Member

    Messages:
    1,078
    Location:
    Worcester Mass.
    Thanks, Do you think in the long run doing this will harm the speakers in any way? I haven't had anyone tell me doing this is bad. I think blocking them completely would not be a good idea but the cheesecloth still allows some air to come out of the port.
     
  10. DavidF

    DavidF Active Member

    Messages:
    343
    Location:
    San Jose, CA
    No, restricting the port air flow, even up completely blocking it, will not harm the system. It will change the bass response, though. Mostly and usually in a bad way.
     
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  11. cartop

    cartop Super Member

    Messages:
    1,078
    Location:
    Worcester Mass.
    Thanks DavidF, I didn't think it would hurt them. The bass still sounds nice, a little tighter sounding.
     

     

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  12. Olddavid

    Olddavid AK Subscriber Subscriber

    Messages:
    20
    You are using the wrong cartridge for the speaker. Shure is a very high compliance and output cart. I use Stanton on high efficiency speakers.
     
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  13. cartop

    cartop Super Member

    Messages:
    1,078
    Location:
    Worcester Mass.
    Thanks for the advice Olddavid. I have tried 2 different carts on this TT. The Shure M91-ed that you mentioned and a QLM 30MKIII on an ADC cart with the same results. Is the ADC a high output cart also?
     
    Last edited: Feb 4, 2018
  14. cartop

    cartop Super Member

    Messages:
    1,078
    Location:
    Worcester Mass.
    OK, I have been tinkering with the settings on my Technics tt again and I was not only getting the rumble in the woofers that I mentioned I also was now getting distortion in the right channel. After loseing more hair going nuts over this I decided to put my original Shure 5x stylus back on and not
    only did the distortion go away most of the rumble is gone also. It just does it very slightly and is almost not noticable. You might say to yourselves, and I can hear some of you now, Why didn't he check the needle first... :dunno: Well the needle is only a few months old because I bought it when I first got the table and figured it couldn't be that but the needle I bought for it was a cheep .3 x .7 Bonded Elliptical Needle and it didn't last so lesson learned. Also the 5x is a diamond stylus so now I will just spend a little more money the next time and get a good stylus for a replacement. Thanks for all the help guy's.:thumbsup:
     
  15. Olddavid

    Olddavid AK Subscriber Subscriber

    Messages:
    20
    Everyone who ever reads has done the same thing, whether it's a bad ground or out of phase wires, everyone is guilty. I would still stay away from Shure with JBL. Just an old man ears problem?
     
    cartop likes this.
  16. MCM_Fan

    MCM_Fan AK Subscriber

    Messages:
    2,661
    Location:
    Oregon
    A few questions:

    Have you tried any other source besides your turntable, like a CD player, FM tuner or DAC?
    If so, do you still get the "rumble" sound with the ports unblocked?

    How are your speakers isolated from your turntable?
    Are they on speaker stands?
    How/where is your turntable mounted?
    Are you using any kind of isolation platform?

    I'm asking these questions because I wonder of the "rumble" you are hearing is actually feedback from the speakers, either airborn or mechanically coupled feeding back through your cartridge. In my current setup my L36 Decades (or 4301B Control Monitorss, or L19As) are mounted on sand filled steel stands, with sorbothane bumbers betweem the spekers and the stands and between the stands and the floor.

    The floor at my current pace is vinyl flooring over concrete. So, there is really no possibility of mechanical feedback even though the turntable sits atop a teak credenza between the two speakers.

    My old place had a wood floor, and while I never had any feedback problems with the L36 Decades mounted on the same stands, I did have some mechanical issues with a pair or Rectilinear III HIghboys that sat directly on the floor.

    Before you spend too much time, or any more money, fiddling with cartridges, you may want to rule out other possibilities. The differences you are hearing between your cartridges could just be due to one being more sensitive to feedback.
     
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  17. cartop

    cartop Super Member

    Messages:
    1,078
    Location:
    Worcester Mass.
    Hi MCM_Fan, I only have the problem when using the TT, Not with any other source. Here is a pic of they way my system is set up. Unfortunately this is really my only option due to space issues. I did move the speakers further away then in the pics but they are only about another foot apart on each side then you see in the pic.

    100_2101 (1).JPG
     
  18. galactus2

    galactus2 Member

    Messages:
    54
    Location:
    Virginia
    Car top, I can’t tell from that pic, but are the speakers sitting directly on top of the stools? Is there anything underneath?

    If they’re sitting on the wooden stools, are you getting vibrations at certain volume?

    By the way, nice speakers. I like my L-26’s, their little brother. :beerchug:
     
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  19. cartop

    cartop Super Member

    Messages:
    1,078
    Location:
    Worcester Mass.
    Hi galactus2, Yes they are sitting directly on top with nothing underneath. I don't notice any vibrations out of the ordinary. I do need to get some proper stands but for now the stools will have to do. Like I mentioned a couple of posts back since I put the Shure 5x needle back on the rumble is almost gone. What would you recommend putting under the speakers? Maybe some kind of rubber mats or similar?
     
  20. galactus2

    galactus2 Member

    Messages:
    54
    Location:
    Virginia
    Something like a rubber mat, or similar, I would think should help. It may sound crazy, but for a thrifty solution, try hockey pucks at the corners. They're very solid rubber, and since you're up in Mass, I know they're not hard to come by.
     

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