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Mounting Drivers front vs back side of baffle?

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  • Mounting Drivers front vs back side of baffle?

    I'm wondering in there are any acoustic advantages mounting a driver on the back side of the baffle vs the front side; I can only think of one. I have seen drivers mounted on the back side on production and DIY speakers.

    Acoustic Advantages
    1. Thickness of the baffle doesn't restrict the air flow on the inside.

    Acoustic Disadvantage
    1. Places the acoustic center point of the driver farther behind the front baffle surface. This can make the time alignment with the tweeter worse.

    Non-Acoustic Advantages
    1. Hide an ugly driver frame behind the baffle.
    2. Lower cost stamped steel frames are hidden.
    3. Aluminum frames don't need to be painted; probably more common on production speakers.
    4. Lower cost clear zinc plated screw can be used to mount the driver since they will be out of sight.
    5. Looser tolerances for the mounting hole locations are possible with slightly oversized holes in the driver and the use of washer head type screws.

    Non-Acoustic Disadvantages
    1. Baffle or Back panel of enclosure needs to be a separate piece so that the driver can be mounted on the inside.

    Shawn

  • #2
    Generally speaking, drivers are back-mounted these days to get the acoustic center back so that the crossover is more optimum. That's mainly an advantage when you're using a waveguided tweeter. I suppose some people like the old-timey "vintage" look, too.
    Francis

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    • #3
      Originally posted by Shawn_K View Post
      Baffle or Back panel of enclosure needs to be a separate piece so that the driver can be mounted on the inside.
      Not needing a removable back is the main advantage, especially in mass production.

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

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      • #4
        Baffle thickness affects open frame drivers regardless whether the driver is front (from the outside) or rear (from the inside) mounted, that is why we chamfer or round over the offending edge, be it the inside or the outside.

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        • #5
          This used to be quite common on older vintage speakers. Most I have seen were installed from the rear with screws, washers and nuts, and back was subsequently screwed on around its perimeter.

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          • #6
            Originally posted by View Post
            Baffle thickness affects open frame drivers regardless whether the driver is front (from the outside) or rear (from the inside) mounted, that is why we chamfer or round over the offending edge, be it the inside or the outside.
            That only matters for very small drivers. An 8" woofer, mounted on the back of a 1" baffle wouldn't see any appreciable diffraction anomalies over its typical operating band.
            R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio

            Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51


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            • #7
              Originally posted by Pete Schumacher View Post

              That only matters for very small drivers. An 8" woofer, mounted on the back of a 1" baffle wouldn't see any appreciable diffraction anomalies over its typical operating band.
              Well, I don't give a darn whether you mount your drivers from the front or back of the baffle.

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              • #8
                Originally posted by View Post

                Well, I don't give a darn whether you mount your drivers from the front or back of the baffle.
                That's nice to know.

                The reason you chamfer the baffle when mounting on the front is because the basket and motor structure can completely block the rear air flow. When mounting to the back of the baffle, air flow out the front isn't a problem since there's no motor structure in the way.

                Apparently, that's not obvious to everyone.
                R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio

                Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51


                95% of Climate Models Agree: The Observations Must be Wrong
                Gravity is an overrated force on the cosmic scale. Physicists are missing the bigger picture. They fell into a black hole and were never seen advancing the understanding of the cosmos again.

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                • #9
                  Originally posted by Pete Schumacher View Post

                  That's nice to know.

                  The reason you chamfer the baffle when mounting on the front is because the basket and motor structure can completely block the rear air flow. When mounting to the back of the baffle, air flow out the front isn't a problem since there's no motor structure in the way.

                  Apparently, that's not obvious to everyone.
                  Blah, blah, blah.

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                  • #10
                    Thanks for all the input! I don't see much advantage to mounting the woofer on the back side of the baffle and will stick with front mounting. I was reading a review for the Sonus Faber Venere 1.5 speaker which has the woofer mounted on the back side of the baffle; technically the driver is mounted on the front side, but the frame is covered with a facade that sets the woofer back from the front surface, This speaker has a waveguide on the tweeter and effectively sets the tweeter back behind the baffle front surface. Sonus Faber sells stands for these speakers that tilt the speakers back about 5 degrees. The test reviewer determined that at the crossover point 2kHz they summed better when the speaker was tilted back 5 degrees. So I guess if you don't use the optional stand you have to put spikes on the front or block underneath or put them on a higher bookshelf to get the 5 degree tilt back. If they would have surface mounted the woofer they wouldn't have need to be tilted back 5 degrees. I think this is a case where someone thought aesthetics were more important. I'm not saying that I dislike the look of speakers that are tilted backwards slightly but it doesn't make sense with a bookshelf speaker like this. My $.02.

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                    • #11
                      Originally posted by Shawn_K View Post
                      Thanks for all the input! I don't see much advantage to mounting the woofer on the back side of the baffle and will stick with front mounting. I was reading a review for the Sonus Faber Venere 1.5 speaker which has the woofer mounted on the back side of the baffle; technically the driver is mounted on the front side, but the frame is covered with a facade that sets the woofer back from the front surface, This speaker has a waveguide on the tweeter and effectively sets the tweeter back behind the baffle front surface. Sonus Faber sells stands for these speakers that tilt the speakers back about 5 degrees. The test reviewer determined that at the crossover point 2kHz they summed better when the speaker was tilted back 5 degrees. So I guess if you don't use the optional stand you have to put spikes on the front or block underneath or put them on a higher bookshelf to get the 5 degree tilt back. If they would have surface mounted the woofer they wouldn't have need to be tilted back 5 degrees. I think this is a case where someone thought aesthetics were more important. I'm not saying that I dislike the look of speakers that are tilted backwards slightly but it doesn't make sense with a bookshelf speaker like this. My $.02.
                      ​Tilting also helps a bit with tweeters that are too bright directly on axis. At least so in my experience.

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                      • #12
                        behind baffle also makes decoupled mounting easier.

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                        • #13
                          Originally posted by badman View Post
                          behind baffle also makes decoupled mounting easier.
                          ​Many years ago in an issue of Speaker Builder Magazine, they described a flush mounted decoupled driver mounting technique using RTV Silicone. Basically you cut an oversized hole in the baffle maybe an eighth of an inch in diameter larger than the driver. Then you mask the hole (masking tape or whatever) and place the front baffle flat on its face. Then you set the driver inside the opening also flush with the front of the baffle and then fill in the gap with RTV Silicone. If you do it carefully, you have a very neat flush and decoupled driver. The driver doesn't make direct contact with the baffle, but is held in place by the Silicone.

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                          • #14
                            Originally posted by View Post

                            ​Many years ago in an issue of Speaker Builder Magazine, they described a flush mounted decoupled driver mounting technique using RTV Silicone. Basically you cut an oversized hole in the baffle maybe an eighth of an inch in diameter larger than the driver. Then you mask the hole (masking tape or whatever) and place the front baffle flat on its face. Then you set the driver inside the opening also flush with the front of the baffle and then fill in the gap with RTV Silicone. If you do it carefully, you have a very neat flush and decoupled driver. The driver doesn't make direct contact with the baffle, but is held in place by the Silicone.
                            Why do YOU give a darn?
                            Craig

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                            • #15
                              The way I see it, IF you COULD mount a driver (a woofer, let's say) that was completely decoupled from the box (baffle), then when the V.C. got energized, there'd have to be SOME kind of distortion introduced - 'cause the V.C./cone would be moving somewhat, but the driver frame would also end up moving SOME (one of Newton's Laws of Motion - no?). The cone would not be moving the "designed" amount of air molecules, would it? Now, I DO believe that decoupling a tweeter could be beneficial, provided that the woofer was making the tweeter's mounting vibrate (which SEEMs like it could introduce some kind of H.D. or I.M. distortion).

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