Announcement

Collapse
No announcement yet.

MTM driver spacing using XDIR

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

  • #16
    cone break up and cone resonance are two very different things.
    craigk

    " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

    Comment


    • #17
      Originally posted by billfitzmaurice View Post
      If you can get the midbasses close enough together to fully couple within three feet or less from the baffle you're good as far as combing goes, but that means placing the tweeter to one side. Not that there's anything wrong with that, but then it has to be very tight to the midbasses to prevent combing on the horizontal plane, which is worse than on the vertical.
      Ran the test with two 3 inch full range drivers 318mm apart, and it works as I had hoped!

      As close as 8 inches away from the center of the array the speakers operate as omni below 800Hz and flat out to the range of the drivers. The polar control works as I move off axis vertically to reduce higher frequencies from 800 Hz to 2000. Above 2000 is susceptible to combing, as expected, without the tweeter in place. The combing peaks are what I wanted to avoid, and I really need to be way off axis vertically (60+degrees) for the comb peak to reach down to 2000Hz, but it never gets any lower than that.

      All of this should work better with a tweeter in place, this is a sort of worst case mock up, and it works very well. Also, the response and vertical polar behavior appears to be linear as much as 80 degrees off axis horizontally, so it should work well with the wide dispersion of the ribbon driver.

      Comment


      • #18
        Originally posted by craigk View Post
        cone break up and cone resonance are two very different things.
        If I am misusing the term, which is very possible, it seems to be a common misuse:
        http://redspade-audio.blogspot.com/2...e-breakup.html
        http://www.linkwitzlab.com/mid_dist.htm

        Comment


        • #19
          Originally posted by noaudiophile View Post

          If I am misusing the term, which is very possible, it seems to be a common misuse:
          http://redspade-audio.blogspot.com/2...e-breakup.html
          http://www.linkwitzlab.com/mid_dist.htm
          you are correct, it is misused.
          craigk

          " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

          Comment


          • #20
            Originally posted by craigk View Post

            you are correct, it is misused.
            I always though cone resonance was the FS of the driver, and cone breakup was the point at which the signal from the cone breaks up. I'll keep saying it the way everyone else in the world does. I'm sure if you can work around linkwitz and others, I should be almost no bother at all.

            Comment


            • #21
              Past related post:

              * Note: Infinity CMMD.pdf can be found here:
              "Not a Speaker Designer - Not even on the Internet"
              “Pride is your greatest enemy, humility is your greatest friend.”
              "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

              Comment


              • #22
                In a true D'Appolito the crossover frequency will be determined by the distance between the midbass drivers. With 6db/octave crossovers the tweeter is in the passband for a long long time. If you look at the phase response most tweeters will go through a 180 degree phase reversal at lower frequencies. So no matter how you adjust tweeter polarity you will always have a suckout. The Dynaudio Gemini speaker crossover deals directly with this phase issue. It was a kit offered by Madisound . The crossover is a brilliant design by Dynadio. It keeps the tweeter in phase with the mids for the entire passband. This desigh came out when Dynaudio still offered raw drivers. If you can download a schematic of this Gemini speaker crossover you'll be amazed at the complexity of a 6db/octave crossover. If you want to give it a try you'll need to wind some of the inductors yourself'

                Tweeter Dynadio D28 horn loaded

                Midrange Focal 5n313 matched pair

                Crossover 6db/octave

                Crossover sums 6db down at 1800 hz.

                Comment


                • #23
                  Originally posted by Roger Beltmann View Post
                  In a true D'Appolito the crossover frequency will be determined by the distance between the midbass drivers.
                  Joe hasn't employed that formula since at least 2002, so I guess he's not making true D'Appolitos any more.

                  www.billfitzmaurice.com
                  www.billfitzmaurice.info/forum

                  Comment


                  • #24
                    Originally posted by noaudiophile View Post

                    I don't think we are talking about the same thing. I'm referring to the resonance peak in the response of any driver, dependant upon material choice and cone size. Above this point the speaker can not produce a linear sound as the sound waves tend to bounce around and cancel each other before leaving the cone.

                    While you could try and use a 2.5 inch full range driver made of aluminum - both small size and stiffer material push the break up higher in frequency - you would end up with ear bleeding breakup in the 10-15kHz range.

                    I'm looking for the opposite of that sound in this design.
                    I'm trying to design a similar speaker. I can't decide to proceed with a 6.5" with a waveguide or an MTM.

                    For simulation and design I'd highly recommend you use VituixCAD, which can simulate drivers off axis response on a given baffle. This should give you an idea of the lobing.

                    However, I would personally avoid using a tall ribbon here - it unnecessarily spaces your mids out, and matching the directivity of the mid array and the tweeter is not really important since the direct sound dominates in this use.

                    I have another question - which I asked on reddit - on your website for the TRUTH and LSR305/8 measurements, are you gating the measurements or do they include room effects? I'm trying to find accurate FR data for these speakers and can't find any besides your measurements.

                    Comment


                    • #25
                      Originally posted by billfitzmaurice View Post
                      Joe hasn't employed that formula since at least 2002, so I guess he's not making true D'Appolitos any more.
                      I designed mine based on the principles discussed in Speaker Builder magazine back in 1984. I also studied the Dynaudio Gemini speaker design which used 6db/octave slopes versus Joe's 18db/octave. I have built both but prefer 6db slopes because horns sound smoother and less edgy with lower order crossovers.I was unaware that there was a new "Formula" to achieve the proper polar response. Joe designed many different versions to achieve the same end result. Mid bass drivers in series, parallel and even one using dual voice coil mids. The second voice coil was crossed out at a much lower frequency to improve bass response. I would guess you could try any type of alignment or "formula" as long as it fulfills the basic principles of the design. I integrated my D'Appolito into a larger cabinet using 12" drivers above and below the MTM. The sound is excellent and minimizes reflected waves. At distances greater than two feet the wave front is fully integrated. I don't hear the mids or the tweeter. It just sounds like one large full range driver up close.. The port tuning on the 12's is 24 hz. so subs are not required. All of the drivers I used are now out of production . All of the drivers used in the original Swan 4 system are also out of production Back issues of Speaker Builder magazine and Vance Dickasons.Loud Speaker Design cookbook are invaluable to achieving success.

                      Update... The mid and high frequency chapter in the loudspeaker design cookbook has a nice chart showing driver spacing versus crossover frequency.

                      Comment


                      • #26
                        I'm hip to 'Speaker Builder', I was a contributing editor. One of the last pieces Joe published in 'AudioXpress', the successor to 'Speaker Builder', was the Thor MTM-TL.

                        https://www.audioxpress.com/article/...nsmission-line

                        His methodology used to create the Thor crossover was markedly different than in his earliest MTM designs. The 2.5kHz target crossover frequency was chosen with little to no regard to the driver spacing. For that matter he doesn't mention it at all. If my memory serves a letter to the editors asked Joe why this was the case, and he replied that he'd learned over the years that driver spacing wasn't as important as he once thought. Put them as close together as is practical, but don't let a formula get in the way of the final result.
                        www.billfitzmaurice.com
                        www.billfitzmaurice.info/forum

                        Comment


                        • #27
                          I've been out of the loop since i first built my d'appolito back in the 90's. I had no idea he changed his design philosophy. Back then he said odd order crossovers were mandatory to get the correct polar response. Now it appears he's recommending 4th order LR crossovers and driver spacing isn't that critical. Live and learn. Thanks for setting me straight.

                          Comment


                          • #28
                            Originally posted by billfitzmaurice View Post
                            Can't say I'd trust that calculator, since it doesn't consider the size, and therefore the polar pattern, of the midbasses. The original midbass CTC postulated by Joe D'Appolito was 1 wavelength at the crossover frequency, but he stopped doing that long ago, because of another factor, wavefront integration. Depending on the polar patterns of the midbasses at some point the two wave fronts will become one, as shown by this applet:
                            http://www.acoustics.salford.ac.uk/f.../diffract4.php
                            This means the further the listening distance the wider the CTC can be, So unless you're using the speakers as near field monitors you can get away with a lot more than 1 wavelength CTC on the midbasses. But if you have doubts put the midbasses adjacent and the ribbon to one side.
                            Hello. First post here!

                            I'm looking into building an MTM (plus separate midbass and subs) for music at home using a Beyma TPL-150H and two 8" (B&C 8PE21). The drive to use two midranges is to gain sensitivity to go with 2A3 SET, however the large size of the tweeter and midranges make me wonder about lobbing. My listening position is 6 feet from each speaker - could stretch to 7 feet. Would that be enough for the wave fronts to become one?

                            I'm aware of people crossing over the TPL from 1.2kHz all the way up to 2kHz although the latter not in MTM. I would probably end up xo somewhere between 1.2 and 1.7kHz and will have flexibility as I use an active system. But my key concern is whether distance would be enough.

                            Thank you!

                            Comment


                            • #29
                              I wouldn't use a horn loaded tweeter with 80 degree horizontal dispersion at listening distances less than 15 feet. I also wouldn't use an MTM along with a separate midbass. There's no reason why you can't have an MTM fully capable of going to 80Hz to cross over to a sub, especially if you're using 8" midbasses.
                              www.billfitzmaurice.com
                              www.billfitzmaurice.info/forum

                              Comment


                              • #30
                                Originally posted by billfitzmaurice View Post
                                I wouldn't use a horn loaded tweeter with 80 degree horizontal dispersion at listening distances less than 15 feet. I also wouldn't use an MTM along with a separate midbass. There's no reason why you can't have an MTM fully capable of going to 80Hz to cross over to a sub, especially if you're using 8" midbasses.
                                Thanks for the quick reply!
                                Could you please elaborate on why not use the tweeter with 80 degree waveguide at a listening distance of less than 15 feet? Would it make a significant difference if I rotated the tweeter so the 80 degree dispersion would be vertical and use 30 degree dispersion as horizontal?

                                If the tweeter had narrower dispersion and the woofers were used from midbass up to the tweeter xo, would it be a plausible solution? Or still too close a listening position for wave front integration?

                                Comment

                                Working...
                                X