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  • #46
    Re: Bagby Design Seminar Meniscus Kit

    Paul, thanks for your insight. I will try slight movement of the port tube to mitigate the glitch. While moving the port tube does not seem to have significant changes to lower frequency results, it is worth the effort to experiment for an absolutely clean frequency response. The 8 vs. 4 ohms issue will change the power results.

    If you wish to run your set of sheets these are the T/S parameters that I used (from Jeff's DATS test and his input in this thread):

    fs = 37.68 hz
    Re = 3.8 ohms
    Le = 0.157 mH at 10 kHz
    BL = 6.35 nt/amp
    Sd = 132.7 cm2
    Vas = 21 liters
    Qes = 0.469
    Qms = 5.684

    Comment


    • #47
      Re: Bagby Design Seminar Meniscus Kit

      I found that locating the port's center at 39" below the internal top (4.25" above the internal bottom) flattens out the response quite nicely. That's shown in the first graph for a 2.83-volt input (IOW an actual 2 watts into this 4-ohm driver). The second graph shows the system output with an actual 16-watt input into 4 ohms. The third graph is the driver's excursion with the 16-watt input, and the fourth graph shows the port's air velocity for this input power. I made no changes to your design other than the port's location. Since it's possible on the worksheets' versions I have, I did change the Y-axes scale factors for the two system bass response graphs for better resolution. I'm now going to break for lunch.
      Paul

      Originally posted by Jim Griffin View Post
      Paul, thanks for your insight. I will try slight movement of the port tube to mitigate the glitch. While moving the port tube does not seem to have significant changes to lower frequency results, it is worth the effort to experiment for an absolutely clean frequency response. The 8 vs. 4 ohms issue will change the power results.

      If you wish to run your set of sheets these are the T/S parameters that I used (from Jeff's DATS test and his input in this thread):

      fs = 37.68 hz
      Re = 3.8 ohms
      Le = 0.157 mH at 10 kHz
      BL = 6.35 nt/amp
      Sd = 132.7 cm2
      Vas = 21 liters
      Qes = 0.469
      Qms = 5.684
      Attached Files

      Comment


      • #48
        Re: Bagby Design Seminar Meniscus Kit

        Thanks for checking my work. The frequency response looks great with the glitch gone. Thanks for the update on the power response.

        Later today I'm going to see if a slot port at the bottom of the line will yield maintain good performance.

        Comment


        • #49
          Re: Bagby Design Seminar Meniscus Kit

          You're welcome, Jim, but there's one more thing I'll add that will improve the response even further. In my worksheet version there's the factor "Radd" appearing right before the entries for the T/S values, which allows you to add resistance in series with the driver to, for instance, account for likely or actual d.c. resistance from a crossover inductor. Added series resistance increases Qes, then Qts, of course, and can affect the response shape positively or negatively. If I don't know what this series resistance actually is, I default to 0.5 ohms. So, doing that for your design, which increases Qts from 0.43 to 0.49, and with the port's center at 39", gives this result in the system bass response:
          Click image for larger version

Name:	Docere-0.5 ohms in series.gif
Views:	1
Size:	6.8 KB
ID:	1154531

          As you can see, the overall response shape is even more smooth. Of course, the sensitivity has decreased a bit, but it's much more real world now.
          Paul

          Originally posted by Jim Griffin View Post
          Thanks for checking my work. The frequency response looks great with the glitch gone. Thanks for the update on the power response.

          Later today I'm going to see if a slot port at the bottom of the line will yield maintain good performance.

          Comment


          • #50
            Re: Bagby Design Seminar Meniscus Kit

            Originally posted by Paul K. View Post
            You're welcome, Jim, but there's one more thing I'll add that will improve the response even further. In my worksheet version there's the factor "Radd" appearing right before the entries for the T/S values, which allows you to add resistance in series with the driver to, for instance, account for likely or actual d.c. resistance from a crossover inductor. Added series resistance increases Qes, then Qts, of course, and can affect the response shape positively or negatively. If I don't know what this series resistance actually is, I default to 0.5 ohms. So, doing that for your design, which increases Qts from 0.43 to 0.49, and with the port's center at 39", gives this result in the system bass response:
            [ATTACH=CONFIG]42980[/ATTACH]

            As you can see, the overall response shape is even more smooth. Of course, the sensitivity has decreased a bit, but it's much more real world now.
            Paul
            The series inductor in the woofer's crossover has a dcr of 0.15 Ohms, then you can can a bit for speaker wire, but I don't think we'll approach .5 Ohms.

            Jeff
            Click here for Jeff Bagby's Loudspeaker Design Software

            Comment


            • #51
              Re: Bagby Design Seminar Meniscus Kit

              Okay, good to know what the actual series resistance is. I re-modeled with 0.2 ohms in series and got this system bass response:
              Click image for larger version

Name:	Docere-0.2 ohms in series.gif
Views:	1
Size:	6.6 KB
ID:	1154532
              Paul

              Originally posted by Jeff B. View Post
              The series inductor in the woofer's crossover has a dcr of 0.15 Ohms, then you can can a bit for speaker wire, but I don't think we'll approach .5 Ohms.

              Jeff

              Comment


              • #52
                Re: Bagby Design Seminar Meniscus Kit

                An f3 under 30 is impressive! I don't mean to be negative but I have read so much about speaker design being about trade-offs and compromises: what does this design give up or is it a win-win?

                Thanks, Wayne

                Comment


                • #53
                  Re: Bagby Design Seminar Meniscus Kit

                  I have not modeled anything with this driver yet, but your observation/concern of trade-offs is spot on. One thing I initially see is that this MLTL design that yields such a beautiful low F3 and flat response requires a 40+ inch tall tower vs a simple .75 cubic foot sealed enclosure which is maybe 14" tall. For some people that could be a trade off that is not acceptable. I would venture to also guess that another trade off might be power handling/max SPL. I don't have Martin's tools or Jim and Paul's extensive experience so that is just a gut feel.
                  Craig

                  I drive way too fast to worry about cholesterol.

                  Comment


                  • #54
                    Re: Bagby Design Seminar Meniscus Kit

                    Originally posted by PWR RYD View Post
                    I have not modeled anything with this driver yet, but your observation/concern of trade-offs is spot on. One thing I initially see is that this MLTL design that yields such a beautiful low F3 and flat response requires a 40+ inch tall tower vs a simple .75 cubic foot sealed enclosure which is maybe 14" tall. For some people that could be a trade off that is not acceptable. I would venture to also guess that another trade off might be power handling/max SPL. I don't have Martin's tools or Jim and Paul's extensive experience so that is just a gut feel.
                    You're always trading-off between enclosure size, F3 and efficiency. What any designer needs to take into consideration is the expected use of the speaker in its final environment. In this case, we have a speaker that isn't real large and can reach to below 30hz, but is limited by efficiency and max SPL. However, for someone who doesn't have a lot of room and doesn't listen to music very loud it may be a perfect set of trade-offs. Sure, it's a taller speaker, but probably not taller than the the smaller sealed version on a stand and with likely a similar footprint too. Now, if you like rock at loud listening levels, then this is not the right set of trade-offs for you. You might really like my Tempest speaker though, with its 98 dB sensitivity, and 12" prosound woofer, but it only reaches into the mid 40's. Still, with rock music it's something special, and a different set of trade-offs.

                    Jeff
                    Click here for Jeff Bagby's Loudspeaker Design Software

                    Comment


                    • #55
                      Re: Bagby Design Seminar Meniscus Kit

                      Let me try to put things into perspective. The accepted audio frequency band for human hearing is 20 to 20,000 Hz. Next, if you checkout a musical instrument frequency response chart and you'll see that generally 30 Hz is about the lowest they go except for special effects. The instruments that produce down to 30 Hz include harp, bass, contra-bassoon, piano, and the pipe organ. Most other instruments have spectrums that run from 40 Hz upward.

                      Now we as speaker designers wish to be able to reproduce recorded music and other sounds. So ideally we would aim for coverage down to 20 Hz if we could tolerate the size of the speaker system that enables us to re-create those sounds. But 30 Hz is an acceptable goal if we wish to accurately reproduce music down to its lowest frequency.

                      Now let us talk about the capabilities of these drivers in either a bookshelf speaker or a MLTL as covered in this design. Back in message #19 in this thread Jeff presented a vented box design in a 0.75 ft3 enclosure. His design has an F3 point of 35 Hz. Now using the P-E ready made cabinets this size enclosure is 20"H x 8"W x 13"D. These speakers would need stands to raise the tweeter to a 36" height that Jeff suggests as ideal for this design. Thus the smallest footprint on the listening room floor is the cabinet width and depth or 8 x 13 = 104 sq inches.

                      The MLTL design presented here-in is 44.75" H x 8.5" W x 9.5" D and has an F3 in the 26-27 Hz range. Its footprint is 8.5 x 9.5 = 81 sq. inches .

                      Now both proposed speakers will have about the same height in the listening room with the tweeter placed at a 36" height raised by stands for the bookshelf version and built-in the MLTL. Thus you can conclude that the MLTL will go lower in frequency (and cover the lowest output of all musical instruments) and occupy a smaller footprint in the room.

                      Jim
                      Last edited by Jim Griffin; 12-22-2013, 08:11 AM.

                      Comment


                      • #56
                        Re: Bagby Design Seminar Meniscus Kit

                        Thank you for the replies. So the trade-offs are size & efficiency but not sound quality. I can certainly live with that! My listening room is 15 X 20 and it will not be @ high volume so this design should work fine. I have wanted to try paper to reference my metal cone drivers.

                        Thanks again, Wayne

                        Comment


                        • #57
                          Re: Bagby Design Seminar Meniscus Kit

                          Well said, Jim, concise, clear and complete. Personally I always shoot for a flat response to 40 Hz or just a bit lower. Depending on the roll-off rate below the knee, f3 usually ends up in the low- to mid-30s, sometimes in the high-30s. For my musical tastes and in my room, this is always plenty low enough to reproduce music acceptably well.
                          Paul

                          Originally posted by Jim Griffin View Post
                          Let me try to put things into perspective. The accepted audio frequency band for human hearing is 20 to 20,000 Hz. Next, if you checkout a musical instrument frequency response chart and you'll see that generally 30 Hz is about the lowest they go except for special effects. The instruments that produce down to 30 Hz include harp, bass, contra-bassoon, piano, and the pipe organ. Most other instruments have spectrums that run from 40 Hz upward.

                          Now we as speaker designers wish to be able to reproduce recorded music and other sounds. So ideally we would aim for coverage down to 20 Hz if we could tolerate the size of the speaker system that enables us to re-create those sounds. But 30 Hz is an acceptable goal if we wish to accurately reproduce music down to its lowest frequency.

                          Now let us talk about the capabilities of these drivers in either a bookshelf speaker or a MLTL as covered in this design. Back in message #19 in this thread Jeff presented a vented box design in a 0.75 ft3 enclosure. His design has an F3 point of 35 Hz. Now using the P-E ready made cabinets this size enclosure is 20"H x 8"W x 13"D. These speakers would need stands to raise the tweeter to a 36" height that Jeff suggests as ideal for this design. Thus the smallest footprint on the listening room floor is the cabinet width and depth or 8 x 13 = 104 sq inches.

                          The MLTL design presented here-in is 44.75" H x 8.5" W x 9.5" D and has an F3 in the 26-27 Hz range. Its footprint is 8.5 x 9.5 = 81 sq. inches .

                          Now both proposed speakers will have about the same height in the listening room with the tweeter placed at a 36" height raised by stands for the bookshelf version and built-in the MLTL. Thus you can conclude that the MLTL will go lower in frequency (and cover the lowest output of all musical instruments) and occupy a smaller footprint in the room.

                          Jim

                          Comment


                          • #58
                            Re: Bagby Design Seminar Meniscus Kit

                            Agreed Jim, if you are able to consume any floor space with a tower or stand mount. In our living room, however, the only place I can have speakers is sitting on top of two low bookshelves that flank the entertainment center.
                            Craig

                            I drive way too fast to worry about cholesterol.

                            Comment


                            • #59
                              Re: Bagby Design Seminar Meniscus Kit

                              A TL or MLTL for the bookshelf?
                              Kenny

                              http://www.diy-ny.com/
                              DIY NY/NJ 2014 https://www.youtube.com/watch?v=FGwA...ature=youtu.be
                              Man does not live by measurements alone, a little music helps.

                              Comment


                              • #60
                                Re: Bagby Design Seminar Meniscus Kit

                                Definitely possible. For instance, you could take Jim's floor-stander design and fold the line once in a cabinet with an internal height of ~21", an internal depth of 16.5" and the same internal width. The drivers would be located on the baffle in the same positions width-wise and from the top. This a rather deep bookshelf cabinet, though, at 18" external. If one were to give up a bit in f3, the cabinet could be made less deep.
                                Paul

                                Originally posted by kenny_k View Post
                                A TL or MLTL for the bookshelf?

                                Comment

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