A Problem

Discussion in 'Cabinets & Speakers' started by Rockcity, Mar 13, 2018.

  1. Rockcity

    Rockcity Member

    Joined:
    May 24, 2012
    Messages:
    130
    Likes Received:
    23
    I have a 2x12 cab. On the back there are two inputs "16 Ohms stereo - 8 Ohms mono" and a switch "left - right".
    I found out that actually when the switch in "16 Ohms stereo" position, each input is for each speaker. So you can play thru left or thru right speaker.
    If you switch to "8 Ohms mono" you turn both speakers in.
    upload_2018-3-13_9-27-12.jpeg
    I have also found that each speaker plays better for itself then both blended together. Let this stays as a matter of personal taste.
    Now, it becomes interesting: I wanted to play each speaker with each amp. So, I have 1987x and 2203 and I wanted to connect 1987x to left and 2203 to right speaker. In theory it is very simple: since each speaker is 16 Ohms and cab has that possibility, I turn output switch on each amp to 16 Ohms and cab switch to 16 Ohms and connect each amp to one input; 1987x to left and 2203 to right. Right?
    But, here's the problem: I connected all that, put guitar cable into a splitter and one cable out to one amp and other to the other amp. When I turn standby switch on 1987x/2003 I can hear it playing thru one speaker. But when I turn on other standby switch, I instantly get feed back and I must switch it off.
    Each amp turned on works fine on each speaker, but turned on both together it just don't.
    Has any of you any idea what could go wrong?
    At first I thought maybe this happens since both speakers are in the same cab, few inches distance of each other. I just don't have a clue...
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    8,122
    Likes Received:
    3,179
    Location:
    On the wrong side of the tracks.
    Yes
    "stereo" position of switch allows 2 separate amps connecting to 2 separate speakers (located in 1 cabinet).
    Two separate amps was the intended application.
    Just make sure the switch is in the correct 16 ohm stereo position.

    "Each amp turned on works fine on each speaker, but turned on both together it just don't."

    Open the cabinet and start checking the wiring.
    As far as I know, the 2 speakers should be isolated in the "stereo" position...

    But maybe not.
    Maybe one input on the cabinet is out of phase to the other one...(?)
    Maybe the grounding of both speaker inputs is tied together, and one is out of phase(?)
    Maybe it's been re-wired(?)

    Post pictures of the insides.
     
    Last edited: Mar 13, 2018
  3. ampeq

    ampeq Active Member

    Joined:
    Sep 14, 2017
    Messages:
    206
    Likes Received:
    83
    Mine is bass ackwards. Mine is the same set up but the 2 speakers are 8 ohm each so both playing on mono is 16 ohm. To play stereo and 2 amps you must switch the little switch to stereo and set each amp to 8 ohm's 1 wire to each speaker. I will test it tonight and see what I get, I'll let you know.
     
  4. RLW59

    RLW59 Active Member

    Joined:
    Nov 30, 2017
    Messages:
    364
    Likes Received:
    170
    I've gone through phases where I slightly preferred the drier, purer, more focused tone of single speakers. But like most people, most of the time multiple speakers just sound "bigger" and "fuller" to me.

    It could just be "personal taste", but it could also be because there's something wrong with the way they're wired.

    Amp Mad Scientist mentioned phase issues. When you run it in mono -- one amp driving both speakers -- is there significantly less bass than when you run one speaker by itself?
     
  5. Rock city

    Rock city New Member

    Joined:
    Feb 7, 2018
    Messages:
    6
    Likes Received:
    0
    No. There is less bass when both run together. I tried several combos with g12h-100, V30, g12h-30 and g12-65. It always sounds best one speaker at the time. Even V30 sounds nice by itself. I did some recording just to listen it after and still one speaker sounds way better then two. Even on loud band rehearsal one speaker has nice punch and bass while blended two together lack of these two above.
     
  6. Rock city

    Rock city New Member

    Joined:
    Feb 7, 2018
    Messages:
    6
    Likes Received:
    0
    Well, enough for me was when I played one amp, turned switch to 16 Ohms and changed inputs few times. I could clearly hear left and right speaker each at the time specially when I had two different ones in the cab. They are not isolated inside, you got that right.
    I did the "9v battery" test to see if they were "out of phase" and they were not. Also, cab is not rewired, I got it new and never touched it except changed speakers few times.
     
  7. ampeq

    ampeq Active Member

    Joined:
    Sep 14, 2017
    Messages:
    206
    Likes Received:
    83
    OK, I tried mine out and it worked fine. Make sure you set the little switch on the cab to stereo and make sure you set the ohms to whatever is on each speaker. I used a V3 and a JVM 410 The speakers are a Vin. 30 and a G12h-75 together they sound ok, but separate the h-75 sounds much better than the V30 (esp. with the Marshall, it sounds thin and raspy) Anyway with the switch’s set right yours should work, good luck.
     
  8. RLW59

    RLW59 Active Member

    Joined:
    Nov 30, 2017
    Messages:
    364
    Likes Received:
    170
    I adked if there was less bass when running both speakers together than when running either speaker by itself.

    And you answered "No. There is less bass when both run together."

    Less punch and bass when using both speakers together?

    All of that is classic textbook "out of phase".

    But you then said the 9 volt battery test shows the speakers are in phase.
    ------------------------
    As Amp Mad Scientist requested, pictures of the wiring might help.

    I have no idea how it can sound out of phase when the speakers are in phase, but from what you've described something odd is going on.
     
  9. mickeydg5

    mickeydg5 Well-Known Member VIP Member

    Joined:
    Sep 30, 2011
    Messages:
    17,795
    Likes Received:
    6,317
    Location:
    US of A
    Models 1987 and 2203 output different phase to begin with so you should not use them close to each other and especially not through the same cabinet.

    What make and model cabinet is this? It most likely is one box and two speakers, no isolation.
     
  10. Rockcity

    Rockcity Member

    Joined:
    May 24, 2012
    Messages:
    130
    Likes Received:
    23
    Sorry! Read it last night, a bit tired and didn't read it well. Yes, the sound is "thin" running both speakers together. I didn't have enough time on last rehearsal to open cab and switch contacts on one speaker, but I will do it soon. Only loud test can show "in" or "out of phase". I am confused because I also thought they were "out of phase" but 9v battery test should be a proof. On the other side, the best test is listening to it. So next time I will take some more time with it.
     
  11. Rockcity

    Rockcity Member

    Joined:
    May 24, 2012
    Messages:
    130
    Likes Received:
    23
    Cab is Harley Benton G212

    https://www.thomann.de/gb/harley_benton_g212_vintage.htm

    No isolation, that's right. But what cab actually has an isolation? They are made to support one amp, not two. Theory says one thing and it looks like practically isn't that smooth and easy.
    I don't see how 1987x and 2003 differ in output freq range if input freq, which follows the electric current, is constant. In a place of the world where I live it is 50 Hz. And every Marshall's tag says "40 - 60 Hz". And I plugged the both power cables into the same power plug making the same current phase supplies both amps. No oscillation causing different alternative current amplitude. But if amp can supply both speakers with two cables which makes both speakers run separately thru the same amp, and if there is no feed back (the sound is "piiiiiiiiii"), I will take this "different phase" as a possibility for causing the problem. Next weekend I will test it in different ways and report the results.
     
  12. Rockcity

    Rockcity Member

    Joined:
    May 24, 2012
    Messages:
    130
    Likes Received:
    23
  13. mickeydg5

    mickeydg5 Well-Known Member VIP Member

    Joined:
    Sep 30, 2011
    Messages:
    17,795
    Likes Received:
    6,317
    Location:
    US of A
    No not the 50 or 60 Hz supply frequency of your area. We are talking about the audio signal phase at the output of the amplifier. If they are out of phase then frequencies will be cancelled out giving a lacking/weaker sound.
     
  14. mickeydg5

    mickeydg5 Well-Known Member VIP Member

    Joined:
    Sep 30, 2011
    Messages:
    17,795
    Likes Received:
    6,317
    Location:
    US of A
    Your issue is playing two different amplifiers which are out of phase into one cabinet. That device will not help you in that case.
     
  15. Rock city

    Rock city New Member

    Joined:
    Feb 7, 2018
    Messages:
    6
    Likes Received:
    0
    I didn't mean getting that device, I mentioned it in a way it looked it was not so simple connecting two amps with one cab as I thought
     
  16. Rock city

    Rock city New Member

    Joined:
    Feb 7, 2018
    Messages:
    6
    Likes Received:
    0
    We'll see next time. I will switch contacts at one speaker and make it "out of phase". Also, I plan to connect two cabs to one amp and see what happens
     

Share This Page