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  • #31
    Thanks for everyone’s input! I have narrowed down the options to the two that seem to be the front runners. The Bobinga bar and the sopranos mtm bar. It seems like the sopranos are still a possibility if the 4 ohm mids are ran in series, but may take a little bit more tweaking of the xo? I like both of these options. As a few of you have mentioned…the continuum ll’s are appealing to me for performance but I’m more drawn to the bar concept due to the confined space.

    Comment


    • Jakes_dad
      Jakes_dad commented
      Editing a comment
      There is some conflicting info on the Soprano MTMs but this is from an old post by Jeff -"The Soprano has series wired woofers for 8 ohms, which makes it nice for HT use, especially if the MT Soprano is used as rear speakers"

    • djg
      djg commented
      Editing a comment
      In that case definitely talk to the kit purveyors. They own the design (to the MTM, not the TM) and can tell you what's what. The kit page links to an 8 ohm SBA woofer which could be an error. The description states it's an 8 ohm design with series wired woofers. I apologize for my part in misleading you. Jake's Dad to the rescue.

      If you've never wired crossovers, they do an excellent job.

      Hint: call them on the voice line. They never have answered my emails very promptly.

    • djg
      djg commented
      Editing a comment
      Hopefully they'll survive the "fiery but mostly peaceful" demonstrations.

  • #32
    So if you like the look of the tv and soundbar all framed out, consider this: if the bottom of the tv is 33" high and the tv is about 37" tall, the top of a frame with 3/4" material and a touch of spacing is going to be about 70" high. Unless you are quite a tall individual (or like very high heels), that'll put your eyes below the top of the frame when standing, so I don't see any problem with putting large vents in the top piece to aid in air circulation. And actually even if those vents were visible, I'm not sure they would look bad. You could even cover the vents in some kind of perforated screening or such, like some people do with hot water radiator covers.

    For me, my decision would perhaps be based on how much SPL I think I need. The MTM's are just simply going to play louder than the single coaxials which also means that even if you don't play the MTM's to max SPL's, they are still going to play a little cleaner because they don't have to work as hard as just a single woofer. And I think the SB's are probably a better driver to start off with too.

    Good to know that the MTM's are actually 8ohm speakers, but I guess I still have a little problem with the fact that the xo is still designed for full space placement out in the room. Although Jeff does say it works well up against a wall, the design will still be 6dB less sensitive or so than if the xo is re-worked without baffle step compensation and so you are making your amp work harder than it actually has to and you only have 65W to start off with.

    And just in case this is new, the relationship between power and dB works like this: you need to double the power (W) every time you want to increase the SPL by 3dB. So just for example, if you need 16W to reach 103dB at 1m with a speaker with a 91dB sensitivity, you will need 64W with an 85dB speaker to reach the same SPL. More or less exactly what you'll be running into with a xo designed with the 6dB of bsc vs one without it.

    So if you do call about the Soprano MTM kit, besides asking about impedance, I'd also be asking about whether they can re-work the xo for no baffle step compensation. That Bobinga design actually has a bit of an advantage here because the designer offers different versions of the xo with different bsc, although the difference in values looks a little suspect to me (too small) but tbh, I haven't done any sims to check it out yet. But the Soprano MTM sims I've done use Jeff's original measured files (not the spec sheet ones which are significantly different) and swap out the original baffle diffraction responses for ones from a soundbar up against the wall without bsc. So sensitivity is increased by about 6dB over the original design. If you did want to go with a large frame around the tv and the soundbar and make both of those more or less flush, I would want to run the sims again because now basically the soundbar and the tv and frame will all be acting as 1 giant baffle and will probably need a little more tweaking to the xo again.

    Comment


    • #33
      Oops, also wanted to add that I'd go with the same driver configurations in the left and right modules as with the center one with the MTM's. You've got something a little different in your sketch above. That's for better off-axis performance. And actually sitting centered in front of the tv, you will actually be more off-axis to the L and R speakers than to the center one so good off-axis performance is probably more important with the L and R than with the center. Most of the time anyways, if the couch isn't too full.

      Comment


      • #34
        You might want to talk to the Soprano MTM kit supplier RE: cabinet size. No one has seen one

        https://duckduckgo.com/?q=soprano+mt...ages&ia=images

        Comment


        • #35
          CX120 in 1/2" material, Soprano TM in 3/4".

          Click image for larger version

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          Comment


          • eavo44
            eavo44 commented
            Editing a comment
            Those are both nice looking speakers!

        • #36
          I’m leaning towards the sopranos at the moment for the extra performance. I’ll place a call to ask a few questions as recommended by djg. I was busy with some other projects this weekend but I just sat down for a bit to look at the speaker design. I was wanting a frame around the tv, like inspiration pics, so the speaker bar and tv would read as one detail. Like you mentioned mobius…I was thinking about a frame with some ventilation but I was afraid it would introduce another pattern or material. For the moment…I like having a simple wood backdrop that ties into the finish of the speakers. Feels pretty nice and will allow the tv to breathe. As you recommended mobius…I placed the tweeters in the same position as center so the m to t relationship is the same for left, right, and center. Not sure if the left and right speaker clusters are the right distance from the edge of the box. I’m pretty happy with the look so far and I’ll get some more info on the soprano kits this week. Just out of curiosity…I noticed there is also a cx-150 coaxial. Would a slightly larger coaxial play a little louder and still fit in a bar around 6 3/4”? Thanks again for all the info you guys are sharing…really helps me out!
          Last edited by eavo44; 04-18-2022, 12:50 AM.

          Comment


          • mobius
            mobius commented
            Editing a comment
            From the front, that actually looks like a nice solution. Just maybe make sure that you'll also be happy with the side view too. Probably wouldn't matter as much if you had walls on both sides of the tv, but here it's open on the right so you'll get a good view of the back of the tv with cables and power cord every time you walk by. Maybe a good cable management strategy would help, including for the speaker wires too.

          • eavo44
            eavo44 commented
            Editing a comment
            Thanks…I do think a smart cable management layout will help keep the appearance tidy. That will def be something I’ll work into the project. The front view is better than the side, but I think it’ll be a straight forward solution that won’t cramp the tv. Seams like more of a pedestal for the tv. Tv is also fixed on a highly adjustable wall mount.

        • #37
          Originally posted by mobius View Post
          For me, my decision would perhaps be based on how much SPL I think I need. The MTM's are just simply going to play louder than the single coaxials which also means that even if you don't play the MTM's to max SPL's, they are still going to play a little cleaner because they don't have to work as hard as just a single woofer. And I think the SB's are probably a better driver to start off with too.
          I agree that your listening habits AND sensitivity to FR variations among your seating positions should be significant factors in making your choice. I have a hodge-podge HT set-up that works for our family. I switched to a KEF coax center because it did a much better job in maintaining a center image and reasonable FR from the off-axis seating positions. It doesn't match my L/R speakers, but I would not want to switch back to a horizontal MTM center.

          The CX150 would probably give you higher SPL than Bob's CX120 design, but you'll have to work out an appropriate crossover for that option to be viable. Keep in mind that you may be able to get away with a higher HP filter on the LRs if your subwoofers are relatively close. That could let the CX120's play a little louder without hitting their Xmax. You'll still hit thermal limits if you're hammering them, but I think most people over-estimate the SPL levels they need for a satisfying experience.

          Comment


          • #38
            I can't do an analysis of the CX150 because it's N/A and therefore doesn't have the spec sheet info attached. Could be a good solution but you would have to rely on a simmed xo by someone without the benefit of measurements.

            I would put the L and R drivers as close to the side edges as you can get as long as you leave enough room for back chamfer clearance. So you'll want to leave enough room for something like this:
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            Visualize the pics perhaps on their sides if necessary. Although you could probably also get by with it a little tighter if you have to. Something like this:
            Click image for larger version

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            Should apply to both the side and bottom panels btw.

            I think if you don't have people sitting more than 10-15 degrees off center most of the time, you can probably separate the woofers by about 3/4" - 1" without catastrophic off-axis differences. That will allow you maybe more back clearance for the woofers and/or perhaps just a slightly lower height requirement. But if you've got lots of people on the couch quite often, then putting the woofers right together like your last pic is the best MTM option.

            Just to re-iterate, you'll need about 8-9L net for 2 of the SB woofers in a ported alignment and about 4-5L net for the CC channel sealed. Another liter or 2 each won't hurt if you can find the room but don't look necessary to me. You could add a sand filled chamber between modules or even just double up on the separating wall panels, but with space at a premium, in all honesty I wouldn't worry about it. Separated chambers is nothing new to a 3-way speaker, and you will very rarely see anyone bothering with that kind of thing in their designs. Long and narrow panels are pretty good in terms of resonances (they'll be naturally high in frequency), but I might add a couple of small braces in the L and R modules to try to push them up even a little higher.

            Differences in off-axis response from wall reflections can also color the perceived response, but you actually have an imbalanced room in this respect - your right wall is way off to the side and it looks like those reflections might not actually make their way back to the listening position (at least very directly??). If you can, and I know how a real living room is a far from ideal environment, but I would try to actually absorb as much of those left wall reflections as I could to try to balance things out. Just a thought anyways.



            Comment


            • eavo44
              eavo44 commented
              Editing a comment
              So the cx-150 is out then…That’s ok. Great notes here…thanks! I def want keep the baffle as short as I can and the left and right speakers as far outboard as I can. The layout above will help me sort that out. Using the 1/2” mdf for top and bottom will help keep it short as a few of you guys have recommended.

          • #39
            So after hawking the CX120-8 so much here, I thought I should listen to them, as they've lost out to my Continuums for a while.

            I wish you could hear the spacious and coherent sound they put out. Truly exceptional, especially for the price. Not to mess with your mind. I'll plug in my Sopranos and try a comparison. I'm probably one of very few to have heard both.

            So, they sound similar but the CX120-8 has IMO, better imaging in a nearfield 2.1 setup. The coaxial does make a difference. Crossed to a Dayton 8" DSP sub at 80 hz, 24db slope crossover point.

            To be sure, the CX120-8 is not a KEF, but they're pretty darn good.

            Comment


            • #40
              Coaxial's well integrated with a sub-woofer can bring magic to your ears - the secret is in the cabinet size of the MT coaxial . . . and getting a flat response with EQ . . .

              Comment


              • #41
                Man, I'm just in a quandary with those Coaxial speakers.

                On the one hand, you've got at least 2 people who think they sound very good (djg and the original designer). On the other hand, I've just taken a closer look at the speaker's xo design and the tweeter and the woofer have basically been crossed right at the tweeter's resonance frequency (Fs) at 2800Hz. Never in a million years would I think of designing a xo like that. The basic rule of thumb is at least 1 octave above Fs but preferably 2, although xo slope plays a role in that too. Even the Dayton spec sheet recommends a minimum xo frequency of 4500Hz. I just don't understand how they can sound good, especially when pushed to high volumes like in a HT situation. And I don't think it's the designer's fault either. The measured on baffle response of the woofer is showing a big dip in response after that peak centered at about 1500Hz that isn't there in the spec sheet. So maybe not impossible but probably pretty darn hard to make a xo work higher up in frequency.

                And yet... we do have happy listeners.

                Like I said, I'm just in a quandary about those.

                Comment


                • djg
                  djg commented
                  Editing a comment
                  One of the PE boombox kits uses the CX120-8 and has a different XO.

                • BOBinGA
                  BOBinGA commented
                  Editing a comment
                  I really didn't like crossing the tweeter that low either, but at 2800hz the tweeter excursion is in the neighborhood of just 0.02 mm at 90db, so I didn't think it would hurt it. I simply could not find a way to mate the woofer and tweeter responses at any other point without a major increase in the XO parts count. After using it for a couple of years now, I haven't noticed any strain on the tweeter, but then I don't play it extremely loud

              • #42
                Originally posted by mobius View Post
                The measured on baffle response of the woofer is showing a big dip in response after that peak centered at about 1500Hz that isn't there in the spec sheet.
                Stuff like this and the similar differences in the ribbon tweet/s and DSA135 response (Cnote) Klippel measurements VS Dayton Specs have me feeling mixed...feelings about the Dayting listed specs VS what others are measuring.
                I understand real-world/baffle can make a difference, but not typically in these specific places in the amounts that are being shown...so what gives?
                I tend to consider Dayton/PE one of the more trustworthy sources when it comes to specs, but some of this gives me hit/miss feelings.
                My first 2way build

                Comment


                • mobius
                  mobius commented
                  Editing a comment
                  I consider Dayton spec sheets to be fairly accurate but I would still prefer to measure them myself on the baffle. Or barring that, make the comparison between the spec sheet and the results of a proven design using the drivers and make any corrections going from there. Or perhaps any changes if I want to put them on a different sized baffle for example. The diffraction programs can generally be relied upon although there are actually very small differences between the different programs, and the one thing they don't take into account is the effect of the actual cone profile of a driver on the adjacent driver being simmed. The programs assume a flat baffle surface except for the driver in question but that isn't actually the case in real life though is it? But I'm talking relatively minor differences here.

                  The CX150-8 is actually still listed at Meniscus (if I'm allowed to mention that), but I wouldn't feel confident with a xo design based just on the spec sheet, obviously for the reasons just mentioned.

              • #43
                As you recommended djg…I had a chat with the kit supplier yesterday...super nice guy. Chad and I talked about the bar concept and I shared some of the information that’s been discussed on the forum. He agreed that having the mids closer together would improve imaging but felt that keeping more true to the original plans may give me a better result. I asked if the xo could be reworked for the baffle step compensation and he seemed to like the idea of keeping the 6.5” height more…he didn’t say the xo couldn’t be reworked so I can follow up on that later. The speakers are 8 ohm. He said the link to the mid is incorrect, and the kit has two 4 ohm mids running in series. He recommended front porting all 3 speakers and maybe stuffing the ports in the center if more clarity is desired. I asked about the cabinet drawings and he texted those to me which I’ll include. He also recommended looking into a 8 ohm tm kit with 5-6” mids and placing all 3 channels horizontal if more output was desired. This would leave you with an asymmetrical design and would 100% need a grille for me…the asymmetry would drive me crazy otherwise. I took a look at the bar with these proportions and layout just out of curiosity. These proportions look better but I’m sure you could all predict that…slimmer bar with speakers centrally aligned just feels more natural and each element has a little room to breathe. Chad said that you may pick up on minimal comb filtering at 1m but at a greater distance it should be fine. Still looking into this so I haven’t forgotten about the Bobinga coaxial design…those still make a nice looking bar!

                Comment


                • djg
                  djg commented
                  Editing a comment
                  You could port all 3 out the bottom. I'd say go for it. I'd like to see how it turns out. 6.5" is not at all too big IMO. I'm sure the output would be more than the CX120-8.

                  I wouldn't mix sealed and ported. Stuffing an existing port, sure. Building without ports removes an option.
                  Last edited by djg; 04-19-2022, 08:04 PM.

              • #44
                If 3 TM's placed horizontally isn't aesthetically acceptable one way to give the bar symmetry would be to make the center TM with a mid making it look like an MTM but with one driver not connected and sealed off from the rest of the cab ... and then turn the outer TM's to have the tweeter at the ends.

                Comment


              • #45
                With a horizontal MTM, keeping the woofers closer together and the tweeter higher means there will be less of a dip in the off-axis FR centered at the xo frequency. With the Sopranos, that'll be at about 2000Hz which is pretty important for voices. I worry about that more than the imaging for HT. Running it through the sims with PCD shows that with the woofers basically side by each, you'll lose about 1dB or so at about 15 degrees off-axis at about 3m distance. With the woofers about 1" apart, you'll lose about another dB in that 2000Hz region and with the tweeter centered right in between the 2 woofers about another dB of loss again. And the losses will be greater as the off-axis angle increases. Cases 1 and 2 aren't very bad at all. Case 3 would probably be noticeable but again not too horrible.

                Of the 3 box dimensions, the least harmful to change is the depth. But going to a 72" x 7" or so front baffle is a fairly substantial change from the original design so some fine tuning of the xo is going to be necessary, so I don't see an advantage to sticking with the original 6.5" width. The plans you posted show a gross volume for 1 MTM of 9.5L. So that's 28.5L if you want to do 3 ported versions. Run the calculations to see the dimensions required and I don't think you are going to like the results. That's why I suggested about a 4L sealed CC, with an F3 of about 101Hz. Going that way, you'll need about 23L total. So for eg., 72" x 4.75" x 7" with 1/2" thick material everywhere except a 3/4" front baffle gives 24L and 72" x 4.5" x 7.25" gives 23.3L.

                Choices, choices, choices...

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