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.

  • @frank when I tried using gaffe tape I started having random dropouts - the sound would suddenly stop and I would have to stop blowing and then start again to continue. Did you have this issue?

  • @badblocks Don't block the entire hole since it creates backpressure and traps humidity! This might be why you were experiencing these issues.

  • @badblocks

    I have no such problems, i have closed less than half.. The resistence i feel while blowing is evident but soft, and the half closure gives me both good dynamic range, and endurance, i can plat ppppp FFFFF and long notes..

    The resistence is less than a sax about the pressure of a recorder piano played.



  • @Support_AODYO Thanks, yes, this was with a hole cut in the tape to get the desired level of backpressure.

  • @badblocks Are you still having this issue? Have you tried resetting or reinstalling the latest update?

  • @Support_AODYO Thank you, I have not - will try both of those things and report back, traveling today. I also have a couple of the other approaches (sponge wipes, cork) on order and will try them too.

  • I've built on the design of @meteredsection and developed another 3D-printable model, available under CC-BY at I also released the OpenSCAD source code, so folks can modify the design (especially the inside diameter of the airway) to suit their breath pressure preferences.

    It took me a series of 10 designs till it worked reliably and I was happy with the resulting breath pressure / airflow:

    (I keep getting "Something Went Wrong While Parsing Server Response" when I try to upload images ... no idea how to get around it ... oh well, check out the Thingiverse link above)

    My final design reduces the breath pressure and airflow requirements by about half.

    Some things I observed along the way:

    • Grabbing the plug with your fingers to remove it can be a challenge. I made the plug extra long and included a flared foot end with four sharp nubs is designed to make it easy to remove.

    • Wind noise is an issue! Without a bell port plug, the open bell port of a stock Sylphyo produces very little wind noise. I found that beveling the internal windway channel with numerous tapered bevels noticeably reduced wind noise, but it is still can be an issue, depending on your playing situation.

    • I wrestled with a characteristic of my early designs where, as I added breath pressure, the resistance I felt did not increase smoothly. It was weird, but there were "jumps" in the amount of resistance I felt and also corresponding changes in the wind noise. Very disconcerting while playing. I also had this issue with the @meteredsection design that I printed. I am guessing it had to do with an interaction between the tabs and the top of the air channel. When I added bevels on the internal channel, the problem went away.

    • Sanding the inside of the airway does make a bit of a difference. I did light sanding with a cylindrical needle file. It seems to reduce wind noise a bit and slightly reduces breath requirements.

    • The fit of the plug as I designed it may differ depending on what materials you use and your print settings. I printed the part in PLA at 210 degrees nozzle temperature with a 0.10mm layer height.

    I did do a small study of the amount of breath pressure needed with various designs. I measured the MIDI CC#02 Breath Pressure commands issues by the Sylphyo configured with Breath Settings: Minimum: 20, Range 600, Curve: Log, and Filters: Enabled. I measured through a Link into the Sylphyo Bench application running on a Win10x64 system. I measured pressure in milli-PSI using an intra-oral breath pressure meter that I used for a study in 2013. The meter is described in the Measurement section (pages 2-3) of Goss, 2013, "Intraoral Pressure in Ethnic Wind Instruments" available at and at

    I measured "Half Pressure" and "Max Pressure" pressure readings from the intraoral pressure meter when the Sylphyo Bench application's meter for CC#02 was showing half and full scale. All readings are in milli-PSI. The "I.D." measurements are the Internal Diameter of the air channel in that plug's design.

    • With no plug installed (bell port open) the I.D. is about 6.0mm and I got pressures of 54/96 (Half/Max pressures). For me, this is way too much pressure / airflow and I run out of breath quickly. My phrases. While playing. Became. Quite. Short. I am comparing this with Native American flutes that I typically play.

    • The @meteredsection design with an I.D. of 2.5mm (measured from my print) got pressures of 18/45. It takes very little air to reach the Half and Max MIDI CC#02 of the Sylphyo.

    • The happy medium (for me) is the final design I released. It has an ID of 4.0mm and registered pressures of 22/52 - slightly more than the @meteredsection design.

  • Here are the images I tried to post in the message above ...

    The 10 versions, with #1 being the @meteredsection design, and the #10 (in Red PLA) being the released version.


    The #2 and #3 designs used a tapered cylinder covered with heat-shrink tubing. These designs did not work so well ... the heat to shrink the tubing also melted the PLA. And, because of the taper, the tubing slipped off even after it was melted. The #5 design failed because the tabs were too slender.

    The # 9 design was a test of whether a longer internal channel changed the wind noise and/or back pressure. It hardly did at all ...

    Here is a rendering of the design file as posted on :


    And here is the plug installed in the bell port:


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