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Horizontal 2.5 way ?

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  • Horizontal 2.5 way ?

    What are your thoughts on a horizontal 2.5 way speaker for use as, say, a center channel? How would such an arrangement affect the horizontal dispersion and off axis characteristics compared to a traditional MTM D'appolitio arrangement? Initial thought impressions say it would help mitigate (not completely solve) the off-axis problems of using an MTM on it's side as the .5 woofer would only be playing lower frequencies (say 400 hz and below). I would also think it would require symmetrical filters on the two way portion with good phase coherence or else it could tilt the response left or right (up or down if arranged vertically like a standard TM. What do you guys think? Obviously measurements and testing would be the next step..

  • #2
    Focal does this with the Twin6 Be studio monitors, though in an MTM arrangement. Erin reviewed them a few months back.

    If you end up trying some things out and measuring be sure to post here! I’m curious too. Your logic seems sound to me at least.


    • #3
      A 2.5 is the best arrangement for using dual midbasses placed horizontally.


      • #4


        • #5
          Like anything, I guess it's possible to do, but do you wonder why it's done so rarely? Probably lots of good reasons like making the execution work out as well as the theory. Are LOW frequencies needed from a center channel speaker that you'd spend the effort on a .5 woofer system on? Most people say not really, unless you plan on very small drivers (90mm super wide range can reach 50 Hz with ease today).

          Your question is interesting, I'm not sure of a good answer, not having cut the wood and made one that works myself.


          • billfitzmaurice
            billfitzmaurice commented
            Editing a comment
            It's rarely seen in commercial offerings because it adds to the build cost, and the average consumer would have no clue as to why it's a better method of making a horizontal center. As to the low frequency content, that has nothing to do with why one should use an x.5 configuration. It's all about better midrange if you do use multiple midbasses. The reason for doing that is sensitivity and displacement. If you're making a soundbar due to space restrictions chances are it's not going to be loaded with eights.

        • #6
          This link may be of help.

          Roman does a 2.5 to compare with several MTMs


          • #7
            A 2.5 way for a center channel doesn't make sense to me. The .5 woofer typically fills in the baffle step which would not be present with most center channel mountings. You still have to address the 2- mid woofer off axis issues unless you do a single stacked mid. Then a 3-way makes sense as the mid will be small without the ability to go low (like in a 2.5 arrangement).
            John H

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


            • #8
              It makes perfect sense if you can't fit large enough midbasses so that only one fulfills the displacement requirements for the desired output capability. The off-axis issues will only exist above the .5 lowpass frequency, and assuming tight spacing of the midbasses said issues would be slight, and probably not audible. Perfect? No, but a lot better than a standard MTM.


              • #9
                Thanks bill for taking me (back) to Roman's site. Lots of great info/insight on that site.
                Hadn't gone back there in a LONG time (10-15 yrs?).


                • #10
                  Thanks for all the replies. I looked through Erin's website as well as Roman's site; Erin had a great deal of information that I was curious about, and confirmed the asymmetrical issues with putting an TM on it's side. Though, it appears that within about 15 or 20 degrees, there was virtually no difference in frequency response for seated listeners (for that speaker, anyhows), so that might be perfectly acceptable.

                  I have an existing MTM design that I really enjoy. The L/R speakers are almost perfect and so I have a matching center channel MTM turned on it's side with the tweeter above the center line of the woofers and the dome itself close to the top of the drivers as I've always done or tried to do with my MTM's. Everything moved rooms about a year ago and the room isn't ideal, the placement isn't ideal, and the seating arrangements aren't ideal (though, honestly, none of them are really that bad...) so I'm needing to reconfigure a few things. I also had to switch out my AVR as the old one was giving me fits with one channel (might have been a loose connector so it will prolly end up out in the shop) and it was little outdated and couldn't process Atmos and NeoX - which I plan to implement. I'm chasing down improvements and thought I'd investigate the benefits of a 2.5 way vs 2 way MTM as the center channel. It sounds like I might see some benefit from converting it to a 2.5 way. If not, it at least sounds like a fun experiment.

                  Dialog is a little more difficult to understand at lower volumes with this setup, which I found odd since these are by far the best set of speakers I've had in the basement and do vocals very well, IMO, with a very flat response (last set had little BBC dip that made them easier on the ears but still didn't sound muddy or muffled). The same setup in the last room in which it lived didn't suffer from the same issues; neither did any of my other center channel designs. I also like to run my receiver in Pure Direct mode, which can sometimes push content below 80hz to the front three, especially the center. So I prefer a speaker much more capable than -3db @ 80hz. As a side note, my old Yamaha sounded better all around, IMO, and it didn't make a huge difference when switched between Direct and Pure Direct; the new Pio makes much more a difference between the two. And since I like a matching soundstage, I might see about converting the mains to 2.5 ways as well.

                  Either way, the enclosures themselves are also going to be rebuild, but the baffle may stay the same. So I'm keen to experiment with them. I could also possibly do a stacked TM center channel but it would probably necessitate moving the center above the TV. This wouldn't necessarily be a horrible thing, I guess. It's all getting re-did at some point..


                  • #11
                    I still don't get it.

                    At what frequency XO is the 0.5 to be employed?

                    Shouldn't that be handled by the subwoofer or are you XO'ing much higher?


                    • #12
                      Steve, typically the .5 woofer is employed to compete with baffle step so it depends partly on baffle width and partly on how the TM woofer and tweeter are integrated. Normally, since the bass response starts to attenuate as the wavelength of the frequency becomes larger than the baffle width (around 300-600hz for most standard speaker baffles), the woofers have BSC built in by attenuating the drivers response ABOVE that baffle width frequency, with the tweeter padded accordingly.

                      In a 2.5 way, the woofer in the two way TM portion does NOT usually have baffle step compensation built in to the network making/keeping it more efficient (somebody is gonna peg me on efficiency vs whatever, but it’s early/late/whenever/IDunnoOClock so meh) than a design with BSC. The .5 woofer is then added to fill in the extra bass that was lost by not including BSC in the TM crossover. It piggybacks off of the woofer filter from the TM portion but with its own additional coil - usually fairly large - to attenuate the upper portion that the two woofer is playing and adding a 6db/octave low pass filter at the baffle step frequency. This helps mitigate comb filtering between the two mids as they would normally both be playing up to Fc when crossed to the tweeter.

                      In the case of an MTM, it’s big advantages have much to do with increased handling, bass, output, and efficiency (again, I know, prolly the wrong term but brain no werky right now) as wel as lower distortion at the same output levels compared to a TM. When used in a vertical arrangement, the lobing and comb filtering characteristics give an MTM a wide horizontal dispersion but narrow vertical dispersion (which both work well for me). But when turned on it’s side, the MTM it does the opposite - gives a tall vertical dispersion with poor horizontal dispersion compared to a TM. Some would also argue that an MTM is inherently worse sounding than a TM due to the inescapable comb filtering, but this can be argued either way as the simple counter of using anything other than a single radiating driver is going to sound inherently worse as all multi-driver loudspeakers suffer from overlapping frequencies and comb filtering. But I digress.

                      So now, in my case, I’m trying to improve my center channel and am needing a wider horizontal dispersion for watching movies than I used to, among other things. Since I already have enclosures, I looked for ways to improve the center and the inherent compromises mentioned above. I don’t quite have room to stack a TM (which I would then flank with a set of .5 woofers without changing a few other things, though it still might happen. So by changing the crossover topology of th existing speakers to a 2.5 way, I’m wondering if I can increase the dispersion, as well as gain some clarity with the speaker lying on its side in the “wrong” orientation, while retaining the same voicing, power handling, output, and distortion characteristics of the existing LR speakers. I suppose some would argue that the distortion will actually decrease in the midrange by doing this. So I might give it a whirl.


                      • Steve Lee
                        Steve Lee commented
                        Editing a comment
                        OK, thanks Blenton - you really helped with this explanation.

                        Now, have you considered a 5" coaxial in the center flanked by a pair of x" woofers?
                        Based on your descriptions/explanations - this seems the most reasonable course of action (to me . . .).

                      • Blenton
                        Blenton commented
                        Editing a comment
                        Yeah, a 5" coax in the center would prolly yield the "best" results, but it clashes with other most of the other considerations - chief among them time and voicing. I say time not because I don't it's worth investing the time but because it would be much quicker to using the existing cabinet and drivers to modify a crossover on a design that I already know I like than to build a new box for testing. Not that I'm opposed to building more boxen..

                    • #13
                      Originally posted by Blenton View Post
                      Steve, typically the .5 woofer is employed to compete with baffle step
                      Not necessarily. X.5 alignments are commonly seen in pro-sound, where baffle step is not a consideration, but low frequency output is. Multiple woofers are used to provide higher low frequency sensitivity and driver displacement. When the woofers are vertically arrayed in a 2.5 with a horn loaded high frequency driver at the top of the cab the lower woofer is low passed, so that the long CTC distance between it and the HF horn doesn't create adverse phase sourced interactions. When the woofers are horizontally arrayed in a 1.5 or 2.5 alignment one woofer, or one vertical line of woofers in a 4x10, 6x10 or 8x10 electric bass cab, is low passed for wider dispersion in the mids, and to eliminate comb filtering in the highs, the same as with a soundbar.



                      • #14
                        I like the 2.5 idea just fine. The extra cone area will likely reduce distortion and the 0.5 ways I think are crossed over low enough to not have significant dispersion issues. Or you could opt for smaller mid bass drivers which then could allow for a smaller tweeter, both of which have the potential to increase the overall dispersion.


                        • #15
                          Steve LeeBillet Those are good suggestions. In this case, there are some design considerations that I like to adhere to that limit my choices for both a coax and and a different tweeter. I very much prefer to use a matched set for the LCR or at least matched drivers that can be voiced as similarly as possible. I like voices and objects to move around the room without sounding like they are became different people.

                          The existing drivers are Seas Prestige ER18 5 ohm truncated woofers and the Peerless 1" corundum tweeter. As for finding a smaller Corundum tweeter, they don't exists in 3/4" trim as far as I know. I know Seas makes a few coax drivers but IIRC they were a different series and didn't include the reed paper cone. Also, a coax would bring a tweeter change and necessitate a complete speaker rework. In that case, I might as well just start a new project.

                          So I decided to investigate a 2.5 way center channel in order to simply modify the existing design. Hence, the focus of this thread. One other option that I mentioned above would be to build an M(TM)M. I was hoping I could rebaffle the existing enclosure to make this work but I would need to machine the faceplate on the corundum to truncate it. Even then, I'm not sure it would work. Plus, being a 5 ohm driver, it might make the impedance a little wonky to have different impedance woofers between the 2 way and .5 woofer. Maybe not, but I haven't chased that rabbit yet.

                          HOWEVER... I just checked around for a smaller 5" Seas Prestige ER15 and Madi happened to have two in stock. I haven't been able to find them in stock anywhere for a reasonable price for a while. The sensitivity rating is actually almost identical to the ER18's that I have (they are not the standard 8 ohm ER18's and have some extra excursion and little built is BSC from the slightly different motor design), so they might just work... I feel like the 5" driver could be voiced to match the 7" drive more closely so I will have to chase this route, too.