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Driver Mounting Options and Diffraction

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  • Driver Mounting Options and Diffraction

    Im just curious to others ideas and experiences on the multiple ways to mount drivers on the baffle. I personally love the look of the driver mounted on the inside of the cabinet with a nice roundover or even chamfer. To my knowledge, ideally (and I say that loosely), is to flush mount the driver so that the difference from the driver flange and baffle is minimal. When rear mounted from inside with a roundover/chamfer, would there be any horn quality to the dispersion? I would assume this would be more effective on smaller drivers where the ratio of roundover/chamfer to driver diameter is much smaller.

  • #2
    Originally posted by ameuba10 View Post
    Im just curious to others ideas and experiences on the multiple ways to mount drivers on the baffle. I personally love the look of the driver mounted on the inside of the cabinet with a nice roundover or even chamfer. To my knowledge, ideally (and I say that loosely), is to flush mount the driver so that the difference from the driver flange and baffle is minimal. When rear mounted from inside with a roundover/chamfer, would there be any horn quality to the dispersion? I would assume this would be more effective on smaller drivers where the ratio of roundover/chamfer to driver diameter is much smaller.
    Below is an extreme example of how to mount drivers on the back of the baffle. With woofers it's not as big a deal for diffraction due to the fact that the woofer area is larger and doesn't present a point source for diffraction effects like a tweeter does. Placing a tweeter on the back of the baffle will most definitely cause diffraction effects and therefore a comprehensive approach is needed. A purpose built waveguide is needed and then the crossover needs to accommodate the effects on tweeter response. Done correctly, the results can be spectacular.

    Click image for larger version

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    • #3
      Originally posted by Pete Schumacher View Post

      Below is an extreme example of how to mount drivers on the back of the baffle. With woofers it's not as big a deal for diffraction due to the fact that the woofer area is larger and doesn't present a point source for diffraction effects like a tweeter does. Placing a tweeter on the back of the baffle will most definitely cause diffraction effects and therefore a comprehensive approach is needed. A purpose built waveguide is needed and then the crossover needs to accommodate the effects on tweeter response. Done correctly, the results can be spectacular.
      It may not be the same thing but I am amazed at the improvement in imaging that my sons Apollo MTs have over the Seas Lokis I have in my bedroom. My suspicion is that it has to do with the wave guide tweeter used in the Apollo vs the coax used in the Loki but I could be wrong because I have not measured either speaker. Listening off axis to the Apollos is much more enjoyable because they have a much wider sound stage. A "wider sweet spot" for lack of a better term.
      BSME
      Kannapolis NC

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      • #4
        So it seems it affects the drivers based on wavelength more so than the diameter? Higher frequency wavelengths being much shorter?

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        • #5
          Rear mounting woofers, is not a problem as the diffraction issues are usually outside the pass band of the x-o. Rear mounting tweeter can be problematic in a simple round over as there are on axis cancellations in the 8K to 12K range. A 45-degree chamfer is better with some minor on axis cancellations. The tweeter to chamber opening size/ connection is critical and should be tested.
          John H

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

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          • #6
            Originally posted by jhollander View Post
            Rear mounting woofers, is not a problem as the diffraction issues are usually outside the pass band of the x-o. Rear mounting tweeter can be problematic in a simple round over as there are on axis cancellations in the 8K to 12K range. A 45-degree chamfer is better with some minor on axis cancellations. The tweeter to chamber opening size/ connection is critical and should be tested.
            Would fullrange designs fall victim to this if they play beyond 8k?

            And to go down this rabbit hole further, could mounting a tweeter in this way counteract a tweeter that has a rise in the 8-12k range?

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            • #7
              Originally posted by jhollander View Post
              Rear mounting woofers, is not a problem as the diffraction issues are usually outside the pass band of the x-o. Rear mounting tweeter can be problematic in a simple round over as there are on axis cancellations in the 8K to 12K range. A 45-degree chamfer is better with some minor on axis cancellations. The tweeter to chamber opening size/ connection is critical and should be tested.
              Thanks John! I'm sure I've heard this question answered before, but I always tend to forget. Hopefully this time the info will stick in my brain and I won't be so worried about trying it on a future design.
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              • #8
                Originally posted by ameuba10 View Post

                Would fullrange designs fall victim to this if they play beyond 8k?

                And to go down this rabbit hole further, could mounting a tweeter in this way counteract a tweeter that has a rise in the 8-12k range?
                The diffraction blips, waves etc. caused by the mounting are usually near the diameter wavelength. The dips cancellations on axis are due to the reflection summation from the waveguide. Move off axis they are less / go away. If you correct the on axis response without looking off axis the speaker will not sound right.

                Note that doesn't mean there are always summation cancellations, the context was with rear mounting tweeters in simple round overs and chamfers.
                Last edited by jhollander; 07-18-2018, 08:22 PM. Reason: added more info
                John H

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

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                • #9
                  Originally posted by ameuba10 View Post
                  So it seems it affects the drivers based on wavelength more so than the diameter? Higher frequency wavelengths being much shorter?
                  That's the issue for all aspects of directionality and any consequent diffraction. The off-axis is determined by the driver directionality (diaphragm properties and other driver physical characteristics) and any external influences (baffle dimensions, mounting position, nearby drivers that cause diffraction of a tweeter, etc.). All of it is based on the wavelengths involved with the specific driver.

                  dlr
                  WinPCD - Windows .NET Passive Crossover Designer

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                  • #10
                    Originally posted by ameuba10 View Post
                    Im just curious to others ideas and experiences on the multiple ways to mount drivers on the baffle...
                    On smaller cabs ( satellites, often with non-round driver frames), the drivers were front mounted - attached were front plates made from "Hobby Plywood", to come up flush to the driver flange.
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