Suzuki B24 Bass Melodion – Gapping

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  • #10149
    AvatarDavid I Am
    Participant

    I think it might be worthwhile to consider in a fluid dynamics sense that the bladder is what provides the proximate gust of air that permits the attack it DOES have to actually happen.

    When that big valve/reed clearance opens, the air must rush through – if there’s no spring-loaded proximate air reservoir to dump, it would start swinging much more slowly.

    This is synchronous with how the attack is so gentle if you don’t build pressure before you hit the key. Effectively you could say that is the effect you get without the bladder under tension.

    A not dissimilar effect as the air tank on the trailer of a big rig, that provides a gust of air in close proximity to the brake actuators when needed, so that the truck can maintain control better. Or any pneumatic system with storage bladders/tanks close to the point of use, so that the working fluid can fill the gap without needing to chain-release all the way back to the main source with the accompanying velocity-related drag and pressure drop.

    #10151
    AvatarMelodica-Me
    Participant

    The bladder is absolutely necessary. The reason I replaced the bladder on the Hohner Basso was that it had a small tear that let all the air pressure escape and there was not enough pressure to sound a note once the tear got a little too big.

    #10185
    AvatarKevin
    Participant

    I don’t have a B24 (refuse to pay that much for an instrument of less than 2 octaves).
    I did look at my M37C and it also has the bladder.
    Looking at the inside of the reed cover the bladder only covers a small straight drilled hole (about the size of the screw holes.)
    I covered this hole with a piece of duct tape and reassembled.
    It seems to play fine to me?
    I Don’t know if the B24 has the same one hole construction but it’s a simple non-destructive, easily reversible experiment to try.

    #11018
    AvatarKevin
    Participant

    I’m going to resurrect this over a year old thread since this is where the Suzuki bladder was being discussed.
    I indeed took a piece of thick duct tape and placed it over the pencil sized hole on the inside of the reed cover of my Suzuki M-37C.
    That way air-flow bypassed the bladder but also kept it intact.
    I put it away shortly after that(just don’t enjoy the sound). After some time I recently got it out and played it.
    I noticed the low D next to middle C had a sour bleating quality.
    That put me to wondering about my duct tape job. I removed the tape re-assembled and immediately the low D note was back to normal!
    I found that just taking my finger and pressing in on the bladder from the outside as I played caused the D to sour.
    It’s interesting the D isn’t the note directly below the hole. I sure can’t explain the physics of what is going on.
    I would greatly appreciate someone else removing the shell of their Suzuki and pressing in on the bladder and finding out if they get the same effect.

    #11779
    AvatarAntonio Freixas
    Participant

    I, too, will resurrect this thread by replying to a post from almost a year ago.

    The physics behind the little bladder hole in my Suzuki M37C is something I would definitely like to understand. I didn’t know the bass melodicas had bladders covering the entire air chamber!

    Let’s look at the physics of balloons. Blow up a balloon and tie it off. The balloon, at this point, is neither growing nor shrinking. This tells us that the forces trying to make the balloon larger are equal to the forces trying to make it smaller.

    The air pressure in the balloon is trying to make it bigger. The air pressure outside the balloon and the elastic potential of the balloon’s skin are trying to make it smaller. Therefore, the air pressure inside the balloon must be greater than the air pressure outside and it is greater by just enough to counteract the elastic.

    So, in a closed system, anything stretchy increases air pressure. The stiffer the elastic, the higher the pressure.

    Ok, that’s interesting but doesn’t seem to get us anywhere. If the stiffer the material, the higher the pressure, the highest pressures would be achieved with a material that was not elastic. At that point, the pressure would be whatever you could achieve with lung power.

    If you have an open system, air becomes essentially incompressible, so it’s difficult to raise its static pressure (the pressure on the walls of the system). Think about what happens if you cut off the end of a balloon and try to inflate it. You can’t.

    If you transition from a closed system to an open one, the elastic potential of the bladder will convert the static pressure in the air chamber into dynamic pressure (moving air–think about what happens when you release a filled balloon).

    So here’s my guess: if you blow into the melodica when no keys are pressed, the pressure in the chamber goes up. When you press a key there is a large pressure difference between the top and bottom of the reed tongue. This should help get the reed moving. As you continue to sound the note, the extra pressure disappears and the reed now operates in the “normal” way (I’d have to explain the “normal” reed physics, which is complicated). The pressure in the chamber is probably about the same as the outside air. Lift the key and the pressure begins to build up again.

    If my theory is correct, then if you play a note on the bass melodica, hold it for 1/2 second or so and then do a quick switch to another note, the second note may have a bit of problem getting started.

    When I get a chance, I can try pressing on the bladder of my M37C to see if I can reproduce the “sour” note. Also, I’ll try to see if the bladder completely deflates when I hold a note. It may be that even in an open system, we can maintain a slightly higher pressure in the air chamber than outside. This would be surprising, but that’s how I learn things.

    Anyone with a bass melodica can try the test I suggested. I’d be curious about the results. It would also be useful to check if the bladder deflates completely when playing a long note (I understand long notes are difficult on a bass melodica as the notes need a lot of air).

    #11780
    AvatarAntonio Freixas
    Participant

    Ok, I reassembled my M37C (but just the air chamber, not the case) and got some interesting results.

    If I blow hard without pressing any keys, the bladder inflates, as expected.

    If I blow hard and then press a key, the key fails to sound. Too much pressure? As long as I continue to blow hard, I get no sound. And it’s not just the low notes.

    If I ease up a bit, I get sound. And while I blow, the bladder remains somewhat inflated, which is a bit of a surprise, but it just means that I have more to learn.

    I’m not sure if the bladder inflation does anything useful at this point. I suspect if may just be acting as a pressure gauge: it tells me the pressure in the air chamber is slightly higher than the atmospheric pressure, but that would probably also be true without the bladder. As long as the bladder remains inflated, it can’t contribute to the airflow.

    Actually, it’s hard to tell that it does anything at any point. I can’t hear much difference when I block the bladder than when I don’t. I did try pressing on the bladder as I played low notes. Oddly, the low D was the only one that produced any sort of bend-y effect.

    One other thought: when one stops blowing, the bladder should keep the air pressure up for a bit. If you keep a key depressed, the decay should be slower.

    Could the bladder be used to balance the notes? (My current definition of “balanced” is that two notes played simultaneously have the same volume.) Nope. If I play a low note and a high note together and release the low note, the high note gets a lot louder. If I release the high note, the volume of the low note doesn’t change significantly. If the notes were balanced, both would get equally louder when the other note was released. Of course, it could be worse without the bladder.

    Bottom line: I don’t know why there’s a bladder on the M37C. It does seem to affect the low D, but that could be re-tuned to work without the bladder.

    #11781
    AvatarDavid I Am
    Participant

    As I have one of these B24’s, I thought I’d weigh in.

    The thing I think the bladder does is a sort of capacitor for air – a capacitor or ‘tank’ in a circuit can be used to supply surges of current that otherwise would incur losses (proportional to its current) as it travels through wires and connections.

    So what the bladders does is like a capacitor increases the supply of charge to rush into an inductor, increases the supply of air immediately available to rush into the opening, sounding the reed.

    I have a tendency to stop blowing between notes on my alto/soprano melodicas as a form of expression while playing them – it alters the attack form in some way that my brain likes to play with. Or maybe its left over from trumpet playing. Anyway. When I play the B24 with that pressure dropping technique the bladder isn’t charged and the notes (especially the low ones) on the B24 won’t sound! Every time I pick the thing up I have to remind myself to maintain a steady pressure rather than relaxing it. And even then its a touch tricky.

    #11782
    AvatarAntonio Freixas
    Participant

    I thought about this and I can’t say right now whether I agree or disagree.

    “More air” only occurs if an expanded bladder shrinks. If the bladder is inflating or staying the same size, there is no additional air flowing through the reeds. I don’t know about the B24; on my M37C, the bladder can stay inflated or even increase in size while playing.

    Originally, I thought the bladder might provide more pressure, but I think I convinced myself you can actually get higher pressures with a rigid case than with a bladder. Or, at least, the same pressure (at some point, the lungs become the limiting factor).

    The bladder expands the available air. But then, why not just start with a larger rigid air chamber?

    I think the complete explanation might prove a bit more complicated than one might think. The main characteristics of the bladder are that, if your blowing pressure drops, it delays a pressure drop and that, if your blowing pressure increases, it delays the increase. In other words, it smooths out pressure changes.

    This may not be how it works, it’s just the only explanation that fits in with the rules of physics that I know. And, if I understand the rules properly, I’m not sure why smoothing the pressure changes would be useful for a bass melodica.

    If I had a B24, I could test this by using my airbrush. I’d feed it a constant flow while holding a key down. If my theory is correct, the note would sound quiet and then get louder as the bladder filled. Then I would reduce the flow. Again, my theory would say that the volume would stay steady for a bit, then drop.

    If it behaved some other way, I’d need a new theory, of course. 🙂

    #11783
    AvatarDavid I Am
    Participant

    I don’t think you’re considering Viscosity Antonio! In the milliseconds of note valve open/attack, if the air has to move from further away than it would were it pushed by the bladder, it wouldn’t get there in time.

    I suspect this is a really dynamic effect – its not visually visible to human eye, you probably could get more of an idea what’s going on if you took high speed footage of how the part of the bladder closest to the opening momentarily dips as the note opens – supplying more air volume to the opening than the pressure front alone would permit…

    #11784
    AvatarAntonio Freixas
    Participant

    I don’t think you’re considering Viscosity Antonio! In the milliseconds of note valve open/attack, if the air has to move from further away than it would were it pushed by the bladder, it wouldn’t get there in time.

    Nothing above makes any sense, sorry. You’ll need to try to explain more clearly before I can really comment.

    In trying to decipher your meaning, it sounds like you might be comparing a rigid air chamber to an air chamber with a bladder. And perhaps you are trying to describe what happens right after a key is pressed? If so, are we looking at a case where someone is also blowing into the air chamber or a case where we are just relying on just what is in the air chamber?

    supplying more air volume to the opening than the pressure front alone would permit…

    As I said, “more air” is only possible if the bladder shrinks.

    I’m not sure what “pressure front” you’re thinking of—I’m not saying there is or isn’t a pressure front, just that I don’t know what specific situation you’re picturing.

    #11789
    AvatarDavid I Am
    Participant

    Okay, here’s the sequence of events.

    1. the aperture is closed. There is a pressure differential between the air distribution chest and the reed, but no air is moving. There is a static air pressure across the chest.

    2. the aperture opens. No air has moved, but there is now a path for it to flow.

    3. A front forms as the air immediately adjacent starts moving into the opening rushing towards the lower pressure.

    4. the air next to the initial air moves to follow the previous air, advancing the front and diminishing it somewhat, expanding radially from the opening.

    5. the air next to the next air moves to follow the previous air, advancing the front and diminishing it somewhat, expanding radially from the opening.

    6. within milliseconds the front has moved across the entire chest, impacting first the diaphram, then the long walls, and finally the short walls and right up the mouthpiece to the source of the air pressure.

    At this point consider, you have a pressure gradient – on the outside of the reed is atmospheric – there’s a differential across the reed block – then a somewhat smooth gradient of increasing pressure that could be measured all the way from the reed block to the pressure source. This pressure gradient will exist so long as there is flow, based on the viscosity of the air.

    In a rigid chest, the large opening of the bass reed will allow a drop in the pressure – too much air rushing out too fast per the size of the chest, with the viscosity of the air involved the pressure will drop too low in the chest to continue to deliver enough impact air to the reed to make it start sounding. You’ll get a puff, a momentary pause, and then the fronts will have propagated up and dynamic flow conditions will set up the volume.

    In an elastic diaphram chest, when that front impacts the diaphram it allows the diaphram to tighten – to maintain the pressure in front of near at near that of the elastic tension of the diaphram provides – proving a a much shorter path – from across the shortest way of the chest – to provide fill air in the critical initial milliseconds of a valve opening, while the worst of the pressure gradient is in place.

    This may be somewhat unintuitive because of the high speeds involved – I just typed all these paragraphs literally describing what takes places in the time it takes me to strike a single letter. 🙂

    It may help to think of it like with water which is more obviously viscous – water buffer chests/tanks are used for exactly this purpose in applications where they need a surge-blast of water all at once – such as a commercial dishwashing machine. A pressure tank is colocated with the washing machine and connected with thick pipes to its outlet. the smaller inlet and outlet are both at the bottom – it may or may not have a diaphragm, but it will have pressurized air – a bubble at the top of the tank. When the valves snap open on the dishwasher, rather than depending on the pressure gradient driving all the way back to the main water heater, instead the water rushes down the pipe from the pressure tank. It can’t provide more than 20 or so gallons of water at any one surge – but it doesn’t need to. While the machine uses the surge of water it slurped in, the smaller inlet is busily recharging the tank – just like the mouth of the player is recharging the chest diaphragm of the melodica far slower than the rush of air when a valve opens.

    #11790
    AvatarAntonio Freixas
    Participant

    OK, good. Your original “air wouldn’t get there in time” had me worried. Pressure waves (regions where pressures differ) travel at the speed of sound (sound is a pressure wave). This is 343 m/s, but I prefer to think of it as 2.92 ms/m. The distance from the bladder to a reed is what, 20 mm? So a pressure wave could move across that distance in 58.4 microseconds. A pressure wave could cross the entire air chamber in about 1.168 ms.

    I’m also not sure why you mentioned viscosity. Everything I am going to describe will work with a perfect gas, which is considered an inviscid fluid.

    The physics at the reed is a bit more complicated than what you described, because when the reed enters the hole in the reed plate, the flow is almost entirely cut off. You described the physics as if the tongue were removed, but that’s fine for our purposes.

    Even then, the pressure gradients are much more complex. The continuity equation tells us the speed of the flow changes depending on the cross-section of the system. Bernoulli’s equation tells us that as speed increases, pressure drops and vice versa. So the (static) pressure would be lowest through the reed plate and highest in the air chamber.

    Let’s analyze some specific situations. We’ll start with a pressurized chamber. You place your tongue over the mouthpiece to block any loss of pressure and to keep you from adding to the flow. You open a key. With a rigid air chamber, you get your quick “puff”–just enough air to equalize the density of the inside air to that of the outside. And the air speed through the reed probably drops the closer you get to equal density. We’re in agreement here.

    If you have a bladder, it has the ability to maintain the pressure longer. The elastic tension from the bladder powers the air. In this case, the air chamber is shrinking, so you can maintain the higher air density–and pressure–longer. Again, I think we’ve reached the same conclusion even if we might quibble on a few of the fine points.

    Now, for the big question: why is this desirable? When you blow harder, I would think the bladder would keep the pressure from rising as fast as without (since some air goes into an expanding bladder) and when you blow less hard, it would keep the pressure from dropping (since the bladder would shrink and contribute some air).

    This should play hell with vibratos. Vibratos might be off-phase a bit and might never get very loud. Of course, that’s from my back-of-envelope estimate. I’d rather hear whether a bass melodica player notices any vibrato weirdness.

    We looked at the situation where the mouthpiece was blocked and a note was played. What if someone is blowing and then plays? As I noted, a rigid air chamber could start out with higher pressures than one made from a bladder. If you start blowing quietly, though, the bladder will maintain the higher pressure longer than the rigid case. Perhaps this is needed to get the heavier reeds moving?

    When you want a note to stop, you have two choices: lift the key or stop blowing. If you lift the key, rigid and bladder chambers should work identically. If you stop blowing but keep the key down, the note will have a longer decay with a bladder. Since most of us probably lift the key most of the time, the long decay is an effect we could avoid–unless we wanted it.

    So my best guess now is that the bladder keeps more pressure on a reed for a longer period when it’s starting to sound. The degradation of the vibrato would just be an unfortunate side effect. It would also smooth out any transitions from quiet to loud (or vice versa), but if the smoothing function is not too long, it might not be noticeable (except on vibratos, of course).

    The elasticity of the bladder control the smoothing. Making it stiffer or less stiff would probably change the behavior of the instrument. To pick the perfect material would require knowing a lot about the bass reeds and doing a lot of calculations–or using trial-and-error.

    Again, this is just a hypothesis based on the little physics I know. Before I would accept my explanation as being accurate, I would want to run some real-world experiments. Things often prove to be more complicated than one expects.

    #11793
    AvatarDavid I Am
    Participant

    I think the why its desirable is that without the bladder, the big bass reeds have trouble reliably sounding – if I open the valve THEN blow, its difficult to get the reed to sound with good attack. If I pressurize the chest THEN open the valve, the reed sounds reliably.

    I think that is indicative of one of two things.

    – a charged bladder is necessary for reliable sounding because of initial puff volume
    – a discharged bladder will stop reliable sounding because it lowers the speed of pressure rise

    But if we combine that with the other data point that I’ve heard (though not personally experimented with)

    – these bass melodicas don’t work well without bladders

    it would tend to cancel out the second option leaving only the first.

    Seem logical?

    #11794
    AvatarAntonio Freixas
    Participant

    I think the why its desirable is that without the bladder, the big bass reeds have trouble reliably sounding – if I open the valve THEN blow, its difficult to get the reed to sound with good attack. If I pressurize the chest THEN open the valve, the reed sounds reliably.

    Very useful, thanks!

    – a charged bladder is necessary for reliable sounding because of initial puff volume

    I think air chambers that are either rigid or incorporate a bladder would be equally capable of providing an initial “puff” of high pressure. From my analysis, I suspect the bladder just maintains the higher pressure longer.

    A reed’s first swing is small and it builds up with time. The more massive bass reeds may just need a bit more time to get going. The pressure in a rigid case may drop too quickly once the exhaust is opened for them to get going.

    In case it’s not clear: I’m agreeing with you, but trying to be a bit more precise about the “puff”.

    – a discharged bladder will stop reliable sounding because it lowers the speed of pressure rise

    I think you are saying that your test could also be interpreted to imply this, but I’m not sure what “this” is.

    If you are saying that when the bladder is discharged you can’t get notes to sound, your test already shows this.

    If you are saying something about what happens when a bladder discharges while blowing, I would say that I suspect the bladder never fully discharges while blowing. I believe the only way for it to fully discharge is to hold a key pressed without blowing or take your mouth off the mouthpiece for a while. If you leave it discharged before pressing the next key, we’re back to the first statement.

    So I’d say the bladder is there to get the notes going, period.

    Could you test this? Sort of. You have to blow hard enough to expand the bladder to its maximum. At this point, the bladder acts just like a rigid air chamber both in volume and pressure. You would want to hold a single note open while you do this. This would make the statement “bass melodicas don’t work well without bladders” false except when you are starting to sound a reed.

    The real test would require replacing the bladder with a rigid air chamber and seeing if you could maintain a note once you got it going (even if it was hard to get it going). This would be a difficult test. 🙂

    You could also check to see what the bladder does while playing. Just remove the cover and watch the bladder as you play. On my M37C, the bladder never fully deflates as long as I’m blowing. In fact, if I blow harder, it inflates more.

    Have you tried a vibrato?

    #11795
    AvatarDavid I Am
    Participant

    I think you are saying that your test could also be interpreted to imply this, but I’m not sure what “this” is.

    The hypothesis would be that the presence of the bladder itself decreases the ability of the sharp sounding of the reed, that wouldn’t be true with the hard chest.

    I include this as a measure of ‘I’m not ignoring a possibility’ but I really don’t think it is the case. If the lack of a bladder also avoided the symptom I don’t think they’d have put the bladder in there.

    This little youtube video demonstrates some of the effects of sequences of pressure on the suzuki B24.

    I think its telling how too much pressure (or too little) makes the sounding unreliable. I didn’t get it to happen in the video but not-sounding while starting to blow with the valve open is another thing that will happen.

    The bladder no doubt makes the playing easier – by enabling more air with less pressure – widening the range-of-what-works. Even with that said, its a good bit trickier to play than my other M-37 melodion.

    And uses a LOT of air.

    David

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