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  • How to design TL mids

    Thanks'

  • #2
    Re: Well......

    I see references to TL enclosures for midrange drivers that, to me, are just open backed tubes or tunnels with stuffing without the actual length of the tube/tunnel and its 1/4-wavelength resonant frequency being used to provide response support. The primary benefit of such is the elimination of backwave reflections, IMO. I've used these types of midrange "enclosures" several times and liked their effects (or lack thereof) very much. Nevertheless, there could easily be instances, depending on crossover corner to a woofer and other factors, where a midrange driver could use some "low" frequency support.
    Paul

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    • #3
      Re: Well......

      Originally posted by Paul K. View Post
      I see references to TL enclosures for midrange drivers that, to me, are just open backed tubes or tunnels with stuffing without the actual length of the tube/tunnel and its 1/4-wavelength resonant frequency being used to provide response support. The primary benefit of such is the elimination of backwave reflections, IMO. I've used these types of midrange "enclosures" several times and liked their effects (or lack thereof) very much. Nevertheless, there could easily be instances, depending on crossover corner to a woofer and other factors, where a midrange driver could use some "low" frequency support.
      Paul
      Thanks'

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      • #4
        Re: How to design TL mids

        Hi Texan,

        Curt is the man to answer questions about the implementation of the open back transmission line design on all of the Statements. It is in fact an open path to the back of the cabinet which exits in the rear. It is not stuffed in the sense that a transmission line cabinet usually is to tune the bass but it is lined with 1" foam to absorb part of the back wave and blend it with the front wave much as a di-pole does. However it's not a true di-pole and we don't refer to it as one. You do get much of the di-pole effect with out the placement problems di-poles usually present though.

        I hope Curt reads this thread and offers his thoughts.

        Jim

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        • #5
          Re: How to design TL mids

          In most instances I would consider it detrimental to choose the passband of a midrange to encompass the compliance controlled region of the driver. Distortion increases with excursion, so it just makes sense to keep the mid passband from those frequencies where a TL (or vented enclosure) would be actually utilized to extend the passband.

          Consequently, I suggest that the typical purpose of what appears to be a TL mid enclosure, is not a TL at all, but a method to ameliorate the rear pressure wave from the driver, and any standing waves generated due to the enclosure geometry.

          The Statement series, I chose a line length such that the pass band of the mids was above the frequencies where the dipole roll off would occur. The line was lined, but not stuffed, using the TLAR method and auditioning the results.

          C
          Curt's Speaker Design Works

          "It is the mark of an educated mind to be able to entertain a thought without accepting it."
          - Aristotle

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          • #6
            Re: How to design TL mids

            Originally posted by curt_c View Post
            In most instances I would consider it detrimental to choose the passband of a midrange to encompass the compliance controlled region of the driver. Distortion increases with excursion, so it just makes sense to keep the mid passband from those frequencies where a TL (or vented enclosure) would be actually utilized to extend the passband.

            Consequently, I suggest that the typical purpose of what appears to be a TL mid enclosure, is not a TL at all, but a method to ameliorate the rear pressure wave from the driver, and any standing waves generated due to the enclosure geometry.

            The Statement series, I chose a line length such that the pass band of the mids was above the frequencies where the dipole roll off would occur. The line was lined, but not stuffed, using the TLAR method and auditioning the results.

            C
            And for anyone that doesn't know "TLAR" stands for That Looks About Right.
            Doug
            http://dpeterson.home.mchsi.com/

            I just checked and my "give a damn" is broke :D

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            • #7
              Thanks'

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              • #8
                Re: How to design TL mids

                I used a transmission line in my three-ways:



                The final version will be lined rather than stuffed, I was just out of foam for this initial test. It sounds very good! The front-to-rear length is just about exactly at the Fc of the woofer/mid at 350hz, meaning the OB cancellation basically makes it a steeper filter when combined with the highpass midrange crossover.

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                • #9
                  Re: How to design TL mids

                  Originally posted by Max_Andrews View Post
                  I used a transmission line in my three-ways:

                  The final version will be lined rather than stuffed, I was just out of foam for this initial test. It sounds very good! The front-to-rear length is just about exactly at the Fc of the woofer/mid at 350hz, meaning the OB cancellation basically makes it a steeper filter when combined with the highpass midrange crossover.
                  Thanks'

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                  • #10
                    Re: How to design TL mids

                    Originally posted by Texan View Post
                    What frequency will determine the length of a TL mid?
                    There seems to be some variance in approach, so I'll throw in my $0.02.

                    The speakers that I build for myself have been midrange (TLs, stuffed open pipes, atmosphere loaded, tunnel, tube-ish... whatever, pick one) for many years. The method that I use is to make the line length correspond to the crossover point (Fcr/4) and then use a combination of 1/2" wool automotive carpet pad (or the felt from McMaster/Carr) to line the walls and then use raw cotton or teased wool very lightly stuffed, as determined by measurements and listening tests. I use Schedule 40 PVC pipe for the (TLs, stuffed open pipes, atmosphere loaded, tunnel, tube-ish... whatever, pick one) with a large coupler used to make a chamber for the driver and then reduced down with PVC transitions to the Sd of the driver. The measurement and ear tuning part of the equation is to use only enough stuffing to kill any resonance created by the pipe.

                    The sound is without enclosure artifacts so care should be taken to select drivers that have very low coloration in the passband. The result is fast, open and very detailed without any shout, honk or boxiness.

                    I like 'em.

                    Dave
                    "A man with an experience is never at the mercy of a man with an argument." - Hilmar von Campe

                    www.piaudiogroup.com

                    http://www.avguide.com/blog/tas-rmaf...w-technologies
                    http://positive-feedback.com/Issue47/ramblings.htm
                    http://positive-feedback.com/Issue47/uber_buss.htm

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                    • #11
                      Re: How to design TL mids

                      Another consideration that Jeff B alerted me to is that with an open backed midrange, the apparent sensitivity will be 2-3dB higher than a mid in a closed box, because the rear wave energy adds ambient midrange energy to the room. I can vouch for this as I needed to pad my midrange down more than I had originally modeled for.

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                      • #12
                        Re: How to design TL mids

                        Originally posted by dbe View Post
                        The sound is without enclosure artifacts so care should be taken to select drivers that have very low coloration in the passband. The result is fast, open and very detailed without any shout, honk or boxiness.

                        Dave
                        This has been my experience as well, and certainly is much easier to control the box resonances than with a sealed design, which generally requires a larger enclosure to accomplish a similar effect.
                        Originally posted by Max_Andrews View Post
                        Another consideration that Jeff B alerted me to is that with an open backed midrange, the apparent sensitivity will be 2-3dB higher than a mid in a closed box, because the rear wave energy adds ambient midrange energy to the room. I can vouch for this as I needed to pad my midrange down more than I had originally modeled for.
                        True enough!
                        Due to the open back mid tunnels, the Statement series all have a measured 'Smiley Face' response curve, even with far field ungated measurements, yet sound flat in room.

                        C
                        Curt's Speaker Design Works

                        "It is the mark of an educated mind to be able to entertain a thought without accepting it."
                        - Aristotle

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                        • #13
                          Can this be a TL??

                          The sales brochure for these 1970's era Celestion Ditton 33 specified a 5" diameter transmission line loaded midrange loudspeaker operating between 500 Hz and 2.5 kHz." These pics show a sealed sub enclosure for the mid, yet they called it a TL loaded mid!? Can it still be TL if it is sealed?

                          I am still impressed with the build quality of these old speakers. They used t-nuts for all drivers, the entire enclosure (mid & main) is completely stuffed with foam. The foam is still very soft, not dried or crumbly. The surrounds are still like new. Not bad for 30 years old!! They still sound pretty good too

                          Marvin
                          Attached Files

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                          • #14
                            Re: Can this be a TL??

                            Originally posted by marvin View Post
                            The sales brochure for these 1970's era Celestion Ditton 33 specified a 5" diameter transmission line loaded midrange loudspeaker operating between 500 Hz and 2.5 kHz." These pics show a sealed sub enclosure for the mid, yet they called it a TL loaded mid!? Can it still be TL if it is sealed?
                            It CAN be referred to as a TL if it is ~ 6.8" deep. This would be a terminated length for a 500Hz XO. Normally a terminated TL reduces in cross section as it progresses away from the driver. Dave Seymour was very big on terminated TL's back in the late 70's to early 80's. He produced (Great American Industries) an 8" driver that was -3dB @ 30Hz in a terminated TL. It was very popular back in the old Transcendental Audio days. It was usually used in conjunction with 4 Jordan 50mm modules and a Panasonic H400 leaf tweeter or a JVC leaf. I wish I still had mine. As I remember they sounded very good.

                            Dave
                            "A man with an experience is never at the mercy of a man with an argument." - Hilmar von Campe

                            www.piaudiogroup.com

                            http://www.avguide.com/blog/tas-rmaf...w-technologies
                            http://positive-feedback.com/Issue47/ramblings.htm
                            http://positive-feedback.com/Issue47/uber_buss.htm

                            Comment


                            • #15
                              Re: Can this be a TL??

                              Originally posted by dbe View Post
                              It CAN be referred to as a TL if it is ~ 6.8" deep. This would be a terminated length for a 500Hz XO. Normally a terminated TL reduces in cross section as it progresses away from the driver. Dave Seymour was very big on terminated TL's back in the late 70's to early 80's. He produced (Great American Industries) an 8" driver that was -3dB @ 30Hz in a terminated TL. It was very popular back in the old Transcendental Audio days. It was usually used in conjunction with 4 Jordan 50mm modules and a Panasonic H400 leaf tweeter or a JVC leaf. I wish I still had mine. As I remember they sounded very good.

                              Dave
                              I reassembled it since taking the pics, but estimated internal depth of the mid enclosure is roughly 8 inches.

                              Thanks Dave.

                              Marv

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