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  • 2X12 Cab problem.

    I built my self a 2X12 guitar cab, modelled pretty much on the Marshall 1936 cab.

    When I play through my Marshall JMP, it sounds like theres a continental quilt covering the speakers, its so dull !!

    Any ideas please?

    Thanks

  • #2
    Double-check the speaker impedences (ohms) and that the wiring is doing what it is supposed to (i.e. series or parallel).
    Guitars:
    -Fender Wayne's World 2 Stratocaster w/Fat '50s pickups
    -Fender Blacktop Jaguar HH
    Amps:
    -Fender Champion 110 w/Lil' Buddy
    -Fender Princeton 112 Plus w/Red White and Blues
    -Crate Palomino V8
    Effects:
    -Way Huge Swollen Pickle Jumbo Fuzz
    -Pro Co You Dirty Rat Distortion
    -MXR Carbon Copy Delay

    Comment


    • #3
      Double-check the speaker impedences (ohms) and that the wiring is doing what it is supposed to (i.e. series or parallel).
      Guitars:
      -Fender Wayne's World 2 Stratocaster w/Fat '50s pickups
      -Fender Blacktop Jaguar HH
      Amps:
      -Fender Champion 110 w/Lil' Buddy
      -Fender Princeton 112 Plus w/Red White and Blues
      -Crate Palomino V8
      Effects:
      -Way Huge Swollen Pickle Jumbo Fuzz
      -Pro Co You Dirty Rat Distortion
      -MXR Carbon Copy Delay

      Comment


      • #4
        Question is, what kind of speakers are you using.

        If the tone is bad, it might be the speakers frequency responce.

        If the levels are low (and the impedance is matched as Wyane mentioned)

        Then the speakers may have a low SPL.



        The only other item I can think of besides faulty wiring where contacts are shorting is

        the speaker baskets are not mounted on a flat surface and the baskets are twisted.

        This can cause the speaker coil to rub and not move freely.



        My First guess is you're using non guitar speakers and you have a big frequency/volume loss

        Bass guitar or HiF speakers will do this. They are designed to push lows in an acousticaly designed cab.

        Guitar speakers push midrange and will sould good in just about any cab, open backed or enclosed.

        Comment


        • #5
          Question is, what kind of speakers are you using.

          If the tone is bad, it might be the speakers frequency responce.

          If the levels are low (and the impedance is matched as Wyane mentioned)

          Then the speakers may have a low SPL.



          The only other item I can think of besides faulty wiring where contacts are shorting is

          the speaker baskets are not mounted on a flat surface and the baskets are twisted.

          This can cause the speaker coil to rub and not move freely.



          My First guess is you're using non guitar speakers and you have a big frequency/volume loss

          Bass guitar or HiF speakers will do this. They are designed to push lows in an acousticaly designed cab.

          Guitar speakers push midrange and will sould good in just about any cab, open backed or enclosed.

          Comment


          • #6
            I wired the cab to be 16 Ohms, in series. The drivers are Celestion G12T-75. Its a closed back cabinet and trying to rectify the dullness I cut a two and a half inch port near the bottom of the cab. The drivers are flat against the front as theyre supposed to be. I have made several guitar cabinets over the years and would like to think I construct a well made cab.

            Comment


            • #7
              I wired the cab to be 16 Ohms, in series. The drivers are Celestion G12T-75. Its a closed back cabinet and trying to rectify the dullness I cut a two and a half inch port near the bottom of the cab. The drivers are flat against the front as theyre supposed to be. I have made several guitar cabinets over the years and would like to think I construct a well made cab.

              Comment


              • #8
                What kind of grill/grill cloth are you using?
                "The Web puts all of the world's knowledge at our fingertips; unfortunately it's mixed with all of the world's bull****************."
                -- Bob Parks

                "A thing is not necessarily true because a man dies for it."
                -- Oscar Wilde

                "No man dies for what he knows to be true. Men die for what they want to be true, for what some terror in their hearts tells them is not true."
                -- Oscar Wilde

                "It is a trap of history to believe that eyewitnesses remember accurately what they have lived through."
                -- Theodore White

                Comment


                • #9
                  What kind of grill/grill cloth are you using?
                  "The Web puts all of the world's knowledge at our fingertips; unfortunately it's mixed with all of the world's bull****************."
                  -- Bob Parks

                  "A thing is not necessarily true because a man dies for it."
                  -- Oscar Wilde

                  "No man dies for what he knows to be true. Men die for what they want to be true, for what some terror in their hearts tells them is not true."
                  -- Oscar Wilde

                  "It is a trap of history to believe that eyewitnesses remember accurately what they have lived through."
                  -- Theodore White

                  Comment


                  • #10
                    The 75's should be plenty loud.

                    Unless you're playing bass, the cab should not be ported and when it is ported,

                    the port needs to be tuned so the back wave is in tune with the front wave.



                    You likely have phase cancellation occuring due of the port. Try closing it up

                    or you have to tune the port with the proper tube length so the resonant frequency

                    of the bass signal is in phase with the front of the speaker. There are several ways of doing this.



                    You can google up the details if you dont know how already. One is to use a multimeter, punp

                    the resonant frequency into the cab while monitoring the signal, and adjust the tube length

                    till the meter gives you maximum voltage. The other would method which is better is to use

                    two mics, one on the port and one on the speaker. Run both mics into either a dual scope or dual

                    channel audio analyzer and visually match the two waveforms as you pan through the audio frequencies.

                    You would then tune the tube length so the two waves go positive and negative at the same time.

                    If the port length is too long of short, the waves will be shifted and cancel eachother out.



                    How well this will work depends on whether the cab has the right air volume to begin with for the speakers resonant frequency.

                    Since this is a critical factor in ported cabinet building/tuning, you may or may not be able to tune the cab for optimal frequency response.

                    If the cab is too small, even with the port in phase, you can wind up having too much upper lows making the speakers sound muddy for guitar.

                    If the cab is too big the speakers wind up sounding farty and lifeless.



                    This is why I suggest closing the port first. Sealed cabs do have to have the right air volume too but you wont have to deal

                    with te phase cancellation issue. The air inside a sealed cab does act as a shock absorber for the speaker piston and it will

                    bounce back quickly if the air is right. This gives the guitar strings a snappy responce. You can however pack the cab with

                    additional insulation to reduce the air volume if the cab is larger and sounds too bassy.

                    A cab size of 15"H x 28"W X 14"D is just about perfect for a 2X12" cab and should get you the proper bass response.



                    If its smaller/shallower than 14" then your lower guitar strings wont have as much thump on the low notes.

                    You'll have to use the amps EQ to boost the frequencies it lacks. If its bigger simply pack the cab tightly with

                    additional fiberglass insulation against the sides to reduce the air volume which reduces the bass response.

                    The ideal amount of insulation lets you run the amps bass EQ setting at 120



                    If you have the cabs interior dimensions I can calculate what you're getting now by plugging the dimensions

                    and speaker specs into an online calculator that calculates the proper cab resonance. For guitar its isnt a hyper

                    critical calculation. Guitar is a midrange instrument and unless you are into playing Jazz Guitar you want most

                    fundamental frequencies of the guitar strings that go as low as 80hz to be tapered off at below 150hz.

                    to be Its mainly when you port a cab and want to achieve maximum bass volume in HiFi, Bass guitar

                    A normal electric guitar range is between 150~6Khz. Everything below is rolled off by both the amp head

                    and speakers.



                    What you hear as a nice thump from the strings is actually the strings first harmonic which is an octave

                    above the strings fundamental tone which begins at about 165Hz. Having a port, even when its tuned, produces

                    too much fundamental frequencies, which overpowers the speakers abilities to produce the secondary harmonics.

                    This makes the strings sound like muffeled crap. Reduce the fundamental bass responce and more direct midrange

                    from the speakers will be heard and those speakers will clean right up and come alive.

                    Comment


                    • #11
                      The 75's should be plenty loud.

                      Unless you're playing bass, the cab should not be ported and when it is ported,

                      the port needs to be tuned so the back wave is in tune with the front wave.



                      You likely have phase cancellation occuring due of the port. Try closing it up

                      or you have to tune the port with the proper tube length so the resonant frequency

                      of the bass signal is in phase with the front of the speaker. There are several ways of doing this.



                      You can google up the details if you dont know how already. One is to use a multimeter, punp

                      the resonant frequency into the cab while monitoring the signal, and adjust the tube length

                      till the meter gives you maximum voltage. The other would method which is better is to use

                      two mics, one on the port and one on the speaker. Run both mics into either a dual scope or dual

                      channel audio analyzer and visually match the two waveforms as you pan through the audio frequencies.

                      You would then tune the tube length so the two waves go positive and negative at the same time.

                      If the port length is too long of short, the waves will be shifted and cancel eachother out.



                      How well this will work depends on whether the cab has the right air volume to begin with for the speakers resonant frequency.

                      Since this is a critical factor in ported cabinet building/tuning, you may or may not be able to tune the cab for optimal frequency response.

                      If the cab is too small, even with the port in phase, you can wind up having too much upper lows making the speakers sound muddy for guitar.

                      If the cab is too big the speakers wind up sounding farty and lifeless.



                      This is why I suggest closing the port first. Sealed cabs do have to have the right air volume too but you wont have to deal

                      with te phase cancellation issue. The air inside a sealed cab does act as a shock absorber for the speaker piston and it will

                      bounce back quickly if the air is right. This gives the guitar strings a snappy responce. You can however pack the cab with

                      additional insulation to reduce the air volume if the cab is larger and sounds too bassy.

                      A cab size of 15"H x 28"W X 14"D is just about perfect for a 2X12" cab and should get you the proper bass response.



                      If its smaller/shallower than 14" then your lower guitar strings wont have as much thump on the low notes.

                      You'll have to use the amps EQ to boost the frequencies it lacks. If its bigger simply pack the cab tightly with

                      additional fiberglass insulation against the sides to reduce the air volume which reduces the bass response.

                      The ideal amount of insulation lets you run the amps bass EQ setting at 120



                      If you have the cabs interior dimensions I can calculate what you're getting now by plugging the dimensions

                      and speaker specs into an online calculator that calculates the proper cab resonance. For guitar its isnt a hyper

                      critical calculation. Guitar is a midrange instrument and unless you are into playing Jazz Guitar you want most

                      fundamental frequencies of the guitar strings that go as low as 80hz to be tapered off at below 150hz.

                      to be Its mainly when you port a cab and want to achieve maximum bass volume in HiFi, Bass guitar

                      A normal electric guitar range is between 150~6Khz. Everything below is rolled off by both the amp head

                      and speakers.



                      What you hear as a nice thump from the strings is actually the strings first harmonic which is an octave

                      above the strings fundamental tone which begins at about 165Hz. Having a port, even when its tuned, produces

                      too much fundamental frequencies, which overpowers the speakers abilities to produce the secondary harmonics.

                      This makes the strings sound like muffeled crap. Reduce the fundamental bass responce and more direct midrange

                      from the speakers will be heard and those speakers will clean right up and come alive.

                      Comment


                      • #12
                        The info that is missing in this thread is: sounds blanketed compared to what. What speakers have you been playing through (and hence adjusted your hearing toward)?



                        Did the same speakers sound bright in another cab, or are you comparing to different speakers?



                        There can be a big difference between how much high end different guitar speakers deliver, when all else is equal (similar cabinet, same amp, etc). This is one reason for the presence control on the amp. You need to dial in more for some cabinets, less for others.



                        But the bottom line is that it is perfectly possible to plug into a different cab with different speakers and feel like it is covered in wool, without there being anything wrong with the speakers or cab.



                        Are the speaker cones doped? Are they smooth, or do they have concentric ribbing? All else being the same, a ribbed speaker cone will more easily show higher modes of vibration (2D version of string harmonics) than a flat one. Likewise, an undoped speaker cone will also break up more easily than a doped one, which is stiffer and forced to move as a unit, emphasizing its fundamental resonant frequency.
                        Music DIY mailing list: http://www.kylheku.com/diy
                        ADA MP-1 mailing list: http://www.kylheku.com/mp1

                        Comment


                        • #13
                          The info that is missing in this thread is: sounds blanketed compared to what. What speakers have you been playing through (and hence adjusted your hearing toward)?



                          Did the same speakers sound bright in another cab, or are you comparing to different speakers?



                          There can be a big difference between how much high end different guitar speakers deliver, when all else is equal (similar cabinet, same amp, etc). This is one reason for the presence control on the amp. You need to dial in more for some cabinets, less for others.



                          But the bottom line is that it is perfectly possible to plug into a different cab with different speakers and feel like it is covered in wool, without there being anything wrong with the speakers or cab.



                          Are the speaker cones doped? Are they smooth, or do they have concentric ribbing? All else being the same, a ribbed speaker cone will more easily show higher modes of vibration (2D version of string harmonics) than a flat one. Likewise, an undoped speaker cone will also break up more easily than a doped one, which is stiffer and forced to move as a unit, emphasizing its fundamental resonant frequency.
                          Music DIY mailing list: http://www.kylheku.com/diy
                          ADA MP-1 mailing list: http://www.kylheku.com/mp1

                          Comment


                          • #14






                            Quote Originally Posted by Kazinator
                            View Post

                            Are the speaker cones doped? Are they smooth, or do they have concentric ribbing? All else being the same, a ribbed speaker cone will more easily show higher modes of vibration (2D version of string harmonics) than a flat one. Likewise, an undoped speaker cone will also break up more easily than a doped one, which is stiffer and forced to move as a unit, emphasizing its fundamental resonant frequency.






                            He says they are Celestion G12T-75 speakers that should sound pretty good with a Marshall head.

                            I use 4 of them in my Marshall 1960 cab with my Marshall head and they kick butt. Surely dont lack for highs.

                            He'd have to re-EQ his head for the different cab size of course. My bet is on the back wave being out of phase

                            with the front wave because of the port.

                            Comment


                            • #15






                              Quote Originally Posted by Kazinator
                              View Post

                              Are the speaker cones doped? Are they smooth, or do they have concentric ribbing? All else being the same, a ribbed speaker cone will more easily show higher modes of vibration (2D version of string harmonics) than a flat one. Likewise, an undoped speaker cone will also break up more easily than a doped one, which is stiffer and forced to move as a unit, emphasizing its fundamental resonant frequency.






                              He says they are Celestion G12T-75 speakers that should sound pretty good with a Marshall head.

                              I use 4 of them in my Marshall 1960 cab with my Marshall head and they kick butt. Surely dont lack for highs.

                              He'd have to re-EQ his head for the different cab size of course. My bet is on the back wave being out of phase

                              with the front wave because of the port.

                              Comment



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