Announcement

Collapse
No announcement yet.

Need some help with an MLTL design

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Need some help with an MLTL design

    Hi guys. So I've had these Peerless woofers http://www.parts-express.com/pe/show...number=299-257 for a few years now, and I REALLY want to finally do something with them. They have a lot of great features, and they like to play low. I was hoping to do a MLTL to try something a little different, and I was wondering if anyone would like to save me a bunch of time and design an enclosure for me. :D

    Seriously though, I've done some reading on MLTLs and their variations, but I'm certainly no expert on any of it. Any takers?
    Eric L.

  • #2
    Re: Need some help with an MLTL design

    I can model an ML-TL for you but those drivers probably aren't going to give very good results. Their Fs is quite high as is their Qts, and their Xmax is really small. Probably won't play very low bass-wise and with limited SPL. The first thing I'd recommend would be to measure their actual T/S values to see what they're really like.
    Paul

    Originally posted by brkitup View Post
    Hi guys. So I've had these Peerless woofers http://www.parts-express.com/pe/show...number=299-257 for a few years now, and I REALLY want to finally do something with them. They have a lot of great features, and they like to play low. I was hoping to do a MLTL to try something a little different, and I was wondering if anyone would like to save me a bunch of time and design an enclosure for me. :D

    Seriously though, I've done some reading on MLTLs and their variations, but I'm certainly no expert on any of it. Any takers?

    Comment


    • #3
      Re: Need some help with an MLTL design

      Hmmm...some things to think about. I assumed they would play pretty low, because when I plug them into Bassbox it suggests a fairly large ported enclosure. Looks like I need to do some more research. Thanks anyway, Paul.
      Eric L.

      Comment


      • #4
        Re: Need some help with an MLTL design

        With their highish Qts, assuming the published specs are realistic, you can probably tune them low enough (per diyspeakerguy) to get a decent F3. Then the primary limitation will be SPL due to their small Xmax. I'm only making some educated guesses and can't really know how they'll perform without modeling.
        Paul

        Originally posted by brkitup View Post
        Hmmm...some things to think about. I assumed they would play pretty low, because when I plug them into Bassbox it suggests a fairly large ported enclosure. Looks like I need to do some more research. Thanks anyway, Paul.

        Comment


        • #5
          Curt's Speaker Design Works

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

          Comment


          • #6
            Re: Need some help with an MLTL design

            Curt are you sure you are looking at the same driver he is (and I am)?
            “I cried because I had no shoes until I met a man who had no feet”

            If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

            Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

            Comment


            • #7
              Click image for larger version

Name:	BC14WG79-08alignments.jpg
Views:	1
Size:	165.9 KB
ID:	1150368
              Curt's Speaker Design Works

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

              Comment


              • #8
                Re: Need some help with an MLTL design

                Curt, what is the value for Sd for this driver? I found an older thread about this driver on TT where someone measured the 4 drivers he bought. His T/S values were pretty close to those listed by PE in the OP's link, but also missing Sd. I made a guess that Sd is ~80 cm2 and did some modeling on that basis of a simple, tower ML-TL for a single driver and got decent results, albeit with limited SPL due to limited Xmax. Before posting any modeling results, however, I'd like to use the correct Sd.
                Thanks,
                Paul

                Originally posted by curt_c View Post
                I’m looking at the BC14WG79-08. I’ve double checked my T/S entries in WinISD and all looks reasonable, but I’ve been around too long to not consider I’ve made a mistake somewhere. Let me know if I’ve erred…

                I’m also remiss in not stating that there are many possible combinations of enclosure volumes, tunings, etc that will result in a usable design. The suggestions I made are only one set of points on that continuum.

                To illustrate; the plots are the BC14WG79-08 in a sealed and two vented alignments. The blue sealed, and green vented alignments are the ones I suggested in my last post. The black one is a Chebyshev alignment in 28 ltrs tuned to 45 Hz, as suggested by the software. The Chebyshev alignment does provide maximum extension and an impressive f3, but at the expense of about 0.7 dB of ripple, and its excursion below 40 Hz will be twice the published Xmax at an SPL of only 96 dB. The excursion plots shown are all with an excitation of 6.3 volts, or 8 watts.

                If your goal is near full range nearfield monitors to be used at low listening levels, the Chebyshev is a viable alignment. If you are going to be listening to them far field, I’d suggest one of the other alignments may ultimately be better, especially when augmented with a subwoofer. I incorrectly assumed only a far field scenario in my earlier post, as well as my personal preferences, but many additional alignments are viable depending on the intended application.

                C
                [ATTACH=CONFIG]37846[/ATTACH]

                Comment


                • #9
                  Re: Need some help with an MLTL design

                  Hi Paul,

                  Unfortunately I can't answer your question, as I based my models on the available data from PE.

                  I too estimated the Sd of the driver based on its cutout diameter. It looks like I may have been slightly optimistic on my Sd estimation on the earlier modeling. However, all the calculations for Bl, Mms, Cms, and Rms were based on that Sd. For modeling purposes, the actual Sd is immaterial as long as the other terms are also modifed to accommodate it.

                  Attached here is the Calculated T/S's based on a possibly more realistic Sd of 81 cm^2. Both sets of parameters will provide the identical results when modeled, but of course are predicated on the published specs being reasonably close to the actual driver parameters. Assuming that premise, Martin's mathcad worksheets should return appropriate results as well, regardless of which set of the calculated T/S parameters are used.

                  C
                  Click image for larger version

Name:	BC14WG79-08alignments1.jpg
Views:	1
Size:	56.3 KB
ID:	1150372
                  Curt's Speaker Design Works

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

                  Comment


                  • #10
                    Re: Need some help with an MLTL design

                    Did some modeling using the published specs, Curt's estimate of 81 cm2 for Sd (thanks, Curt), and an estimated Le of 0.7 mH (Martin's worksheets use Le and that was a pretty average value from the set of 4 measurements I found, although Le primarily only affects absolute sensitivity). I modeled a skinny floor-standing ML-TL with internal dimensions of 5.5"W x 4.5"D x 38"H (right at 15 liters volume). The BC14's center was 7" below the internal top and the port's center was 3" above the internal bottom. Port diameter of 1.75" and length of 3". The top half of the cabinet is stuffed with polyester fiber at a density of 1 lb/ft3. The system tuning frequency is 46-47 Hz. I modeled with 0.5 ohms assumed in series with the BC14. I've attached three graphs. The first is the system bass response for an input of 2.83 volts relative to 1 meter showing an output SPL of ~89 dB over the flat part of the response. You can see that F3 is ~48 Hz. The second graph is the system bass response for an input of 7 watts (for a nominal impedance of 6 ohms), showing an output SPL of 96-97 dB. The third graph shows the driver's excursion for the 7-watt input in mm RMS. An Xmax of 3 mm Peak converts to 2.1 mm RMS. I typically model for an excursion 15% greater (as Vance Dickason said is reasonable), which is 2.4 mm RMS. In the third graph this excursion is just reached at ~66 Hz, again at ~38 Hz, then exceeded at all lower frequencies. As has been said already, this driver's Xmax is it limiting factor, and whether this design would be useable depends on it application. Now a pair of these drivers in an MTM would be much better from this standpoint.
                    PaulClick image for larger version

Name:	BC14-1R.gif
Views:	1
Size:	6.8 KB
ID:	1150373Click image for larger version

Name:	BC14-2R.gif
Views:	1
Size:	6.8 KB
ID:	1150374Click image for larger version

Name:	BC14-2E.gif
Views:	1
Size:	7.1 KB
ID:	1150375

                    Comment


                    • #11
                      Re: Need some help with an MLTL design

                      Originally posted by curt_c View Post
                      [ATTACH=CONFIG]37846[/ATTACH]
                      As you said there are many different alignments possible. I would not use these in 21 liters, tuned that low to 20 Hz, but that is just my personal preference. I think I would use these in + 17 liters, tuned to 50 Hz. That would give an f3 of 44 Hz and xmax would be reached (in it's pass band) with 20 W in producing an SPL of + 101 dB. Perfectly adequate for a bedroom or near field monitors.
                      “I cried because I had no shoes until I met a man who had no feet”

                      If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

                      Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

                      Comment


                      • #12
                        Re: Need some help with an MLTL design

                        Originally posted by thekorvers View Post
                        As you said there are many different alignments possible. I would not use these in 21 liters, tuned that low to 20 Hz, but that is just my personal preference. I think I would use these in + 17 liters, tuned to 50 Hz. That would give an f3 of 44 Hz and xmax would be reached (in it's pass band) with 20 W in producing an SPL of + 101 dB. Perfectly adequate for a bedroom or near field monitors.
                        Curt's Speaker Design Works

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

                        Comment


                        • #13
                          Re: Need some help with an MLTL design

                          Curt, you saved me some work. I was also wondering about the driver's excursion with a 20-watt input as that seemed like it would stress the driver quite easily. I was thinking about setting up my model again and see what happens with the 20-watt input, especially since my model and thekorvers' model have very similar tuning frequencies and box volumes. I still may do that, though, just out of curiosity. As far as the form factor goes, what I modeled could easily be converted to a stand-mount simply by folding the line once, making the internal height be ~19" and the depth be ~10", ending up with the very same predicted performance.
                          Paul

                          Edit: Okay, I did set up my ML-TL model again and observed the results with an input of 20 watts (into its nominal 6-ohm impedance). The output SPL did, indeed, increase to about 101 dB, but the driver exceeded its Xmax of 3 mm Peak below ~120 Hz. At just below 70 Hz, the excursion was 5.8 mm Peak, almost twice its rated Xmax.
                          Paul


                          Originally posted by curt_c View Post
                          That would work as well. I modeled this alignment and found a peak in the upper bass of 1.5 dB centered around 95 Hz. This is similar to many smaller commercial offerings and provides impressive ‘apparent’ if not actual low bass in a small package. When I modeled the excursion at 20 watts however, I found it exceeded 5 mm around 75 Hz, and was above Xmax +15% from 55 Hz to 110 Hz. At 40 Hz the cone was unloading from the resonator and exceeded 8 mm at that point. Whether the driver can safely tolerate these excursions above its published Xmax without undue distortion or mechanical damage I can’t say, but it seems unlikely. It appears there is good correlation in power handling/Xmax limitations between Paul’s finding in his MLTL model and my simplistic vented one.

                          One observation I feel noteworthy, is the Q of the knee in the 3 suggested designs. Paul’s model has a very shallow roll off down to about 40 Hz of about 6 dB/octave. My vented suggestion emulates a sealed box roll off of approximately 12 dB/octave down to 40 Hz, albeit at a higher f3. Thekorvers alignment also starts off quite shallow, but is 24 dB/octave by 50 Hz.

                          Interestingly enough, all three alignments will have a similar f10 at about 35 Hz.

                          If I were using this driver in a design without a sub, and my application could tolerate a floorstander, I’d likely choose an alignment similar to Paul’s MLTL. However, any of the alignments suggested, and likely many more, will provide acceptable performance. The most optimum one will depend on the actual application.

                          C

                          Comment


                          • #14
                            Re: Need some help with an MLTL design

                            Originally posted by curt_c View Post
                            That would work as well. I modeled this alignment and found a peak in the upper bass of 1.5 dB centered around 95 Hz. This is similar to many smaller commercial offerings and provides impressive ‘apparent’ if not actual low bass in a small package. When I modeled the excursion at 20 watts however, I found it exceeded 5 mm around 75 Hz, and was above Xmax +15% from 55 Hz to 110 Hz. At 40 Hz the cone was unloading from the resonator and exceeded 8 mm at that point. Whether the driver can safely tolerate these excursions above its published Xmax without undue distortion or mechanical damage I can’t say, but it seems unlikely. It appears there is good correlation in power handling/Xmax limitations between Paul’s finding in his MLTL model and my simplistic vented one.

                            C
                            I re-checked my parameters for this driver, which I entered long ago, and one of them was wrong. That was the reason for my initial question in my first post (#6). It seemed like we were talking about two different drivers.

                            You were right all along Curt. Mea culpa.

                            I redid my alignment and now show a paltry 7 W max input before reaching x-max at a disappointing 96-97 dB. Probably still OK for a bedroom or as a near field monitor, but not nearly as attractive. I have 4 of these on the shelf somewhere. I like Paul's suggestion of a folded line and would probably opt for that were I to do a build with these.
                            “I cried because I had no shoes until I met a man who had no feet”

                            If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

                            Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

                            Comment


                            • #15
                              Re: Need some help with an MLTL design

                              Originally posted by Paul K. View Post
                              As far as the form factor goes, what I modeled could easily be converted to a stand-mount simply by folding the line once, making the internal height be ~19" and the depth be ~10", ending up with the very same predicted performance.
                              Paul
                              Curt's Speaker Design Works

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

                              Comment

                              Working...
                              X