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Should this cabinet be modeled as an ML-TL?

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  • Should this cabinet be modeled as an ML-TL?

    Hi,

    Should a MTM cabinet 40" tall x 9" wide x 12" deep be modeled as an ML-TL? If so, can somebody help me out please.

    Thanks,

    John.

  • #2
    Re: Should this cabinet be modeled as an ML-TL?

    There's certainly enough length. What are the drivers?
    John H

    Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

    Comment


    • #3
      Re: Should this cabinet be modeled as an ML-TL?

      Thanks for the repy John, 2x RS180-8 and RS28A-4.

      Comment


      • #4
        Re: Should this cabinet be modeled as an ML-TL?

        There won't be a lot of contribution to the system tuning from the 1/4-wavelength resonant frequency created by the internal height of the cabinet, which will be around 85-90 Hz, but it will have an effect and contribute to the tuning, and optimum results will be obtained taking that into account. More important, the location of the mass-loading port can be optimized relative to the woofers' locations to result in the flattest possible response. You didn't say, but I assume this will be an MTM? If so, the TL design center will be the tweeter's center. If it's a TMM (MMT?), the TL design center is the midpoint between the two woofers.
        Paul

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        • #5
          Re: Should this cabinet be modeled as an ML-TL?

          I'm not seeing much if any gain over a vented speaker. I had played around with this before and needed another 10 liters and to mount the drivers in the middle of the line to reduce the 200 to 400 Hz noise and still not much lower FR extension. Your box comes out to F3 of 34 with a 3 inch PVC port 17 cm long, which looks like a decent design to me.
          John H

          Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

          Comment


          • #6
            Re: Should this cabinet be modeled as an ML-TL?

            Thanks Paul & John,

            I did mention that it was a MTM cabinet in my first post, it is based on a mash up of Jeff Bagy's RS180 MTM & Dr K's MTM but in a larger tower cabinet. In fact I hadn't considered the ML-TL modeling until I read Paul's comments in this thread http://techtalk.parts-express.com/sh...n-Tower-Design. Prior to reading this thread I was just going to model it as a vented speaker. I am mostly interested in the optimum size and location of the port due to the length of the cabinet. The tweeter's center will be 10.75" down from the external top of the cabinet (3/4" offset), cabinet will be 3/4" MDF.

            I had checked the cabinet tune to be ~35Hz with a 3" x 6.75" port in WBCD, but after reading this thread realized there is more to it. As I don't have access to MJK's software (and probably wouldn't know how to use it if I did) I thought I would ask for some help.

            Thanks again,

            John.
            Last edited by 01-0077; 09-05-2015, 12:54 PM. Reason: added extra detail

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            • #7
              Re: Should this cabinet be modeled as an ML-TL?

              Darn, it sure is the pits to get old and make mistakes like not remembering (or double checking) you did say MTM in your opening sentence! :o I don't know if John has Martin's software but have to assume he does, or something similar, based on his modeling comments. I'm not about to suggest I'd be "checking" John's work, but I'd be happy to model your proposed design with Martin's software. I assume that all of the cabinet dimensions you've listed are external, making the internal dimensions be 38.5"H x 7.5"W x 10.5"D? What T/S values would you want me to use for the RS180s?
              Paul

              Originally posted by 01-0077 View Post
              Thanks Paul & John,

              I did mention that it was a MTM cabinet in my first post, it is based on a mash up of Jeff Bagy's RS180 MTM & Dr K's MTM but in a larger tower cabinet. In fact I hadn't considered the ML-TL modeling until I read Paul's comments in this thread http://techtalk.parts-express.com/sh...n-Tower-Design. Prior to reading this thread I was just going to model it as a vented speaker. I am mostly interested in the optimum size and location of the port due to the length of the cabinet. The tweeter's center will be 10.75" down from the external top of the cabinet (3/4" offset), cabinet will be 3/4" MDF.

              I had checked the cabinet tune to be ~35Hz with a 3" x 6.75" port in WBCD, but after reading this thread realized there is more to it. As I don't have access to MJK's software (and probably wouldn't know how to use it if I did) I thought I would ask for some help.

              Thanks again,

              John.

              Comment


              • #8

                Comment


                • #9
                  Re: Should this cabinet be modeled as an ML-TL?

                  Using PE's published T/S values, I modeled with your stated internal dimensions, except I used a depth of 10" so that when building it with a 10.5" depth, you'll have ~145 "extra" cubic inches to help compensate for consumed volumes, like braces, etc. I've attached the predicted system bass response (red line) for an input of 2.83v/1m. You'll see that F3 is 37-38 Hz. The system is tuned to 40 Hz with a 3" diameter port that's 3.5" long. The top 20" of the cabinet are filled with polyester fiber at a density of 0.75 lb/ft3, requiring a total of ~10 ounces of fiber. The response can be smoothed out a bit more by either increasing the stuffing density to 1 lb/ft3, or by increasing the stuffing length another 5", either method will increase F3 a bit more. The port's center is located 3.25" above the internal cabinet bottom. The attached graph assumes an ideal acoustic environment and doesn't take into account baffle step losses or room effects.
                  Paul
                  Click image for larger version

Name:	RS180 MTM ML-TL.gif
Views:	1
Size:	6.6 KB
ID:	1169180

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                  • #10
                    Re: Should this cabinet be modeled as an ML-TL?

                    John 01 are you using the S version of the RS180s?

                    Paul you are always welcome to check my work. I did not optimize the design or box, I just took what John 01 had for a box size and used Horn Response to see if there was any gain. I also doubled the line length in the same cabinet to see if the was any improvement. I've got a better design but it's a squat cabinet of about 59 liters.
                    John H

                    Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

                    Comment


                    • #11
                      Re: Should this cabinet be modeled as an ML-TL?

                      The specs John 01 linked are for the non-S RS180, but whatever, I would feel more comfortable having someone's actual and reasonably current measurements. The only thing I played with, besides shortening the depth for the reason stated, was port length and location, to optimize the response shape.

                      I, for sure, didn't want to insult you in any way since you were able to give some design feedback before I even saw this thread.
                      Paul

                      Originally posted by jhollander View Post
                      John 01 are you using the S version of the RS180s?

                      Paul you are always welcome to check my work. I did not optimize the design or box, I just took what John 01 had for a box size and used Horn Response to see if there was any gain. I also doubled the line length in the same cabinet to see if the was any improvement. I've got a better design but it's a squat cabinet of about 59 liters.

                      Comment


                      • #12
                        Re: Should this cabinet be modeled as an ML-TL?

                        Originally posted by Paul K. View Post
                        I, for sure, didn't want to insult you in any way...
                        Paul
                        John H

                        Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

                        Comment


                        • #13
                          Re: Should this cabinet be modeled as an ML-TL?

                          Thank you gentlemen, I really do appreciate your help.

                          John it is the unshielded version of the RS180. Paul Carmody did a comparison of the RS180 and RS180S http://techtalk.parts-express.com/sh...26#post1683626 and they seem pretty close.

                          Paul posted the measured T/S parameters for both drivers, the RS180 unshielded are reproduced below.

                          Click image for larger version

Name:	Dayton RS180 TS.jpg
Views:	2
Size:	67.5 KB
ID:	1169184

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                          • #14
                            Re: Should this cabinet be modeled as an ML-TL?

                            In Post #5 there's a port length with your box (49 liters with 3/4 inch wood) for a F3 of about 34.
                            John H

                            Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

                            Comment


                            • #15
                              Re: Should this cabinet be modeled as an ML-TL?

                              Obviously I can tune the box lower if desired with a longer port, and while that will lower F3, it also gradually lowers the SPL output a bit starting around 200 Hz on down. The tuning frequency of 40 Hz was simply the one that gave the flattest overall response from just above the knee in the curve on up (my default response shape) based on the drivers' T/S values and the box dimensions. I can also redo the modeling using the T/S measurements you posted. Those show a higher Fs, which will require a higher tuning frequency, but the Qts is also higher, which will require a lower tuning frequency, so they're likely completely compensating. Vas is lower with Paul's measurements and that should have the same effect as making the box larger, which would lower F3.


                              Darren Kuzma's larger box did not include the 1/4-wave resonance as far as I know.
                              Paul

                              Originally posted by 01-0077 View Post
                              Thank you gentlemen, I really do appreciate your help.

                              John it is the unshielded version of the RS180. Paul Carmody did a comparison of the RS180 and RS180S http://techtalk.parts-express.com/sh...26#post1683626 and they seem pretty close.

                              Paul posted the measured T/S parameters for both drivers, the RS180 unshielded are reproduced below.

                              [ATTACH=CONFIG]60038[/ATTACH]

                              These measurements were taken back in 2010 but I guess are probably more accurate than those published by the manufacturer.

                              Paul, in your modeling you had the system tuned to 40 Hz, is it just a simple matter of making the port longer to get a lower tune or does the enclosure have to be bigger? I would like it to be around 35 Hz.

                              I just reread the Dr K's MTM writeup where he used the 1.0 cu ft PE cabinet and stated "A larger “extended bass” version of the tower would be approximately 1.7 cu. ft., tuned to 35 Hz via a 3″ x 6-1/2″ port." I am guessing this box tune wasn't simulating the enclosure as a 1/4 wave resonator.

                              John.

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