Blocking the Bell Port

  • Is is OK to completely block the Bell Port?

    ("bell port" is my name for the breath exit hole at the foot of the instrument inside the bell.)

    I really need a lot more back-pressure that is provided when the bell port is completely open. If I completely block the port with my finger, there does seem to be another exit path for the air ...

    There are mentions on this forum of partially blocking the bell port, but no mention of fully covering it up.

  • Hi Clint! Happy to hear you've received your Sylphyo. You shouldn't block the exit port completely as that can create too much pressure for the internal tubing. You can however block it almost fully as long as you leave a bit of space. We are in the process of making small plugs to block the exit hole which will have different pressure levels.

    Let me know if you have any more questions.

    Aodyo Instruments

  • Yesterday I prototyped and 3d printed a small plug that effectively reduces the output port diameter to about 2.75mm (vs 6mm out-of-the-box), which feels pretty good to me. It does increase the breath noise of the instrument a bit as the air is forced through the smaller opening, but with headphones I don't notice, and overall it seems much more consistent than the piece of tape I started with.

    @Support_AODYO is there guidance on how much constriction is too much constriction?

  • @meteredsection would you be open to sharing your design? Maybe a photo? Possibly an STL file??

    I will be away from my 3D printer for a while, but would be interested in a range of options for controlling flow and back pressure.

    Was thinking of maybe a series of different plugs with different port diameters, possibly in different colors to keep them from getting mixed up. Alternately, a single, adjustable device, maybe with a screw-type arrangement that could be turned to change the port size.

    Would be interested in how your plug sits in the hole. Hard plastic (PLA, I am assuming) my not be easy to wedge into the existing Bell Port hole.

  • @Clint

    I blocked the port with a piece of gaffa tape, than made a hole with a pencil, till i found i had the right adjustment.

    I tried several valves from aquarium shops, found that those intrinsically have to much resistance.

    With each adjustment one has to learn how to play with that: so i concluded that a valve is overkill. I used black gaffa tape.

    Kind regards


  • @Clint though it's hard to see the exact shape at the bell end, I believe there is a continuous taper from the mouthpiece diameter to the output port diameter. So the idea was to create a ring of tabs that bow slightly outward. This gives just enough flex to get it in without much force, but keep it snugly in presumably without putting much deformation pressure on the tube inside due to the taper of the tube.

    Fundamentally it's just three stacked rings: an outer 8.5mm diameter ring to keep it from migrating up the tube, the "plug" itself at 6mm, and a smaller ring on top of that to support the tabs and reduce the risk that they snap from too much flex. The tabs bow out 0.25mm, which is plenty to provide a snug fit. I can easily push it in by hand, but need pliers to pull it out because it's too small to grab with my fingers.


    One hopefully minor issue is that water can and does pool in between the tabs; going to have to keep an eye on that. I might try a version without the middle tier, though I suspect it will pass more air. Would like to refine a bit more but happy to share the STL.

  • An outstanding design @meteredsection ! I work in OpenSCAD (a solid geometry design language), but an STL file would be very helpful as a reference.

    Would you consider releasing it (maybe Thingiverse) or sharing it here? Alternately by direct email (I am at would be great ...

    Thanks for this design!!

  • This post is deleted!

  • @Clint apologies for the delay, the STL is here.

    This version is a little easier to remove and is probably slightly better about pooling moisture. At some point I'll probably do a V3 that's a little taller--this one is still hard to grab with my fingers, and I think it is probably best to be able to take it out to let it dry out.

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