Forum Replies Created
- December 22, 2020 at 4:36 pm #12934
ecso, a follow-up to my previous reply.
I got curious a while back about the physics of melodicas. I did a lot of research into the topic then, and I recalled that there are a number of factors that affect how responsive a reed is.
Assuming the reeds on the 44H and 44HP are the same, then the thickness of the reed plate and the shape of the hole through which the tongue travels can affect the responsiveness. As I recall, the less thickness, the more responsive the reed is with less air, but it will fail to perform loud notes properly. More thickness and the louder notes work, but the quieter notes will not sound.
I don’t know about melodicas, but on some other reed instruments the sides of the hole have a slight taper (about 5 degrees). Supposedly, this provides the benefits of a thicker hole and still allows the quieter notes to work.
If the reeds are different, then there are some other options, although it’s the same sort of trade-off. More flexible reeds perform well quietly, but not loudly. Stiffer reeds have the opposite effect. Accordion reeds have a taper that may help with the responsiveness. Of course, accordion reeds are intended for more air than is easy to provide with lungs. People who put accordion reeds on their melodicas tend to report that they get a more solid sound but that they take a lot of air to play.
Anyway, one of these things might explain the performance difference between your hybrid 44H/44HP and the 44Hv2.December 22, 2020 at 5:16 am #12933
I have the 44Hv2 and the M37C. I do not find the 44H harder to play than the M37C; just the opposite.
It’s nice that you have three Hammonds to be able to experiment with. If indeed you put most of the 44H parts on the 44HP and obtained the tone of the 44H but the ease of the 44HP, then about the only place to left to look would be in the hidden chambers below the reeds and on to the exhaust ports. And the only way to check for differences there would be cut open the instruments! Ok, I suppose you could remove the reed plates and get a partial look.
You can hear me playing a 44Hv2 at https://youtu.be/jwUalR6XWjs. I’m not sure if that will give any insights.
Air distribution is a problem in most melodicas. It seems that the low notes are always stealing the air—the wider the spacing, the more the steal. Oscar has a way of balancing the notes on his custom designs. If you really want to hear balanced notes, though, get a Y-connector and hook up two separate melodicas. Play the low notes on one and the high notes on the other and you can hear truly balanced notes.
I have experience with only two models, though, so there may be commercial instruments that do as well as my gold standard (the two melodicas).November 9, 2020 at 5:51 pm #11828
Daren, good luck with your tuning bench!
I’m going to make some comments that are based on theory and not practice. The best advice, of course, would be from someone who has successfully built a tuning bench for a melodica (I wouldn’t assume a tuning bench for an accordion would work equally well for a melodic–it might; I just wouldn’t assume it would).
My physics site has languished as I’ve tried to come up to speed on the fluid dynamics. I’ve created a few models of reeds and run them in SimScale to check on air pressure and velocity.
When you are playing a single note, the amount of air that flows through a reed is equal the amount blown in–not more, not less. However, one can “shape” the airflow by trading velocity for pressure and vice versa. This could affect the pitch of the reed.
Using the wrong “shape” may cause reeds that are perfectly tuned on a bench to be off pitch when mounted in the melodica. While I don’t have any practical experience with this, I have run into some accounts where people noted having this problem. I wish I could give you a citation, but I’ve done a LOT of reading in the last few months and I’m not sure where I saw this.
Back to theory: it would seem that the most successful tuning bench would be one in which the airflow mimicked that of the melodica as closely as possible. The big problem with tuning with the reeds in place is that one needs to install a lot of screws in order to test the tuning. Perhaps a good melodica tuning bench would use an air chamber that could be quickly sealed and unsealed. I could imagine a system where a lever could be used to lower a cover and seal a chamber containing the reed. So: file, lower the lever, blow, check tuning, lift the lever, file, repeat.
OF course, if you build a simpler tuning bench and you find that, say, the notes are consistently sharp by a predictable amount, you could just tune them flat by the same amount.
Good luck with the tuning.October 22, 2020 at 4:49 am #11800
Congratulations and welcome to the world of melodicas!
I believe the correct nomenclature for what you bought is 44HPv2 (“HYPER”). If that’s correct, what you have is different from mine. It’s important to get the nomenclature correct as these are two different instruments and it’s sometimes hard to know which one is being talked about.
If your mouthpieces are like mine, you should have received two, one of which is short, plastic and has a gold finish on the tip. There should also be a tube with a 90 degree connector.
It would be VERY nice to know the size of the O-ring. You can buy mouthpieces made for Yamaha’s Pianica and they will fit, but it uses a slightly smaller O-ring and so the fit might not be quite as good. However, these mouthpieces are very easy to find (and cheap). If you had a set of the larger O-rings, it would be easier to adapt them to the Suzukis.
Enjoy your melodicas!October 18, 2020 at 6:20 pm #11796
Thanks for the discussion and the demo. Yes, it is very interesting that a highly pressurized bladder gives a sour note or sometimes causes the reed to block.
Here’s my new theory. The bladder can be used to control the air chamber pressure; in general, the more inflated, the higher the pressure (studies on balloons says that this is not strictly true–pressures in a balloon can rise during its final shrinkage phase and then drop again–but it’s true as a general trend).
The bass reeds don’t do well with too little or too much. This is actually true for a lot of reeds–they can be optimized for low airflows and high airflows. To make them work well for both, I’ve heard that some reed makers add a slight bevel to the reed plate hole, but that’s another story.
Now, for a comparison with rigid air chambers. Rigid air chambers can also provide a range of pressures, I would think, depending on how hard you blow. I just tried my Hammond 44H. If I pressurize the chamber as much as I can and press a key I hear…nothing.
So the difference between a bladder and rigid air chamber, is that the former resists pressure drops (and increases) longer and that this attribute is needed to get the reeds to sound. It might also be needed to keep them sounding. To really verify this would take some work.
The simplest physical model would be a tube with a balloon inserted in the middle. There is a lot of literature on flows through tubes, but I don’t know of any where the tube has expanding walls. Oddly, I asked this question on the Physics Forums site when I was exploring the physics of flexible mouthpieces. I learned a few things, but didn’t get an answer I could use in this situation.October 17, 2020 at 7:25 pm #11794
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?October 16, 2020 at 4:24 pm #11790
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.October 15, 2020 at 4:25 am #11784
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.October 15, 2020 at 12:05 am #11782
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. 🙂October 14, 2020 at 4:59 pm #11780
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.October 14, 2020 at 3:55 pm #11779
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).September 18, 2020 at 11:14 pm #11743
Good thoughts. My approach is to try to set up experiments that exaggerate whatever things I’m trying to test for—thus, the idea of using a balloon.
A lot of people were telling me that short mouthpieces (or no mouthpiece) made the melodica more responsive. So I tried a 15′ tube. There was no noticeable response difference.
I’m in the process of setting up a website to discuss melodica physics. I’ll announce it on Melodica World and you’d be welcome to show up and keep me honest. 🙂
[Why not on Melodica World? I’m adding math support, advanced formatting, the ability to edit a post without a time limit, etc.]September 18, 2020 at 3:18 pm #11741
Ok, got it! Melodica tubes seem cheap to me, so it’s surprising that people would be looking for something cheaper. For example, I bought a tube and a short, hard mouthpiece for $USD 8.88 on Amazon recently.
In any case, you identified a hole in my knowledge about an interesting topic, so thanks.
Some background: in fluid dynamics, gasses and liquids are considered fluids. Air is a fluid and so is water. If you look up “is air compressible”, you’ll find a lot of references to air being incompressible at low velocities (below Mach 0.3). The bike pump example is a counter-example, so that’s where the hole in my knowledge was. I found a detailed explanation at https://physics.stackexchange.com/questions/257851/can-air-be-considered-incompressible-as-long-flow-velocities-are-less-than-100-m. The short answer seems to be that below Mach 0.3, the error in fluid dynamics formulas that assume air is incompressible is small and air can be treated as incompressible when studying its flow.
Fluid dynamics is what you would use to analyze air flow through a melodica–at least, when one or more reeds is open.
Pressure and compression are two different things. Pressure is a force applied over an area while compression is an increase in fluid density, where fluid density is mass per volume. In a sealed container, for example, you could increase the pressure just by heating the container but it won’t change the fluid density.
When you blow into a mouthpiece, you are definitely applying a force, so you are applying pressure.
But can I compress air with just my lungs? I’m still working to find an answer. I think it’s “yes”, but you can’t compress it much. As a test, I tried to see if I could compress the air in my melodica. I put on a hard mouthpiece and blew as hard as I could without pressing any keys. No luck: this just leaked air through the mouthpiece opening. How about blowing directly into the melodica? No luck again: the air forces its way out past the reeds. How about using the hard mouthpiece and plugging it (the mouthpiece) with my finger? Ok, some luck. I couldn’t blow any air into this. For practical purposes, I suspect air compression is not a factor in melodica playing.
If you use a soft mouthpiece, then you might increase its volume–you aren’t so much increasing the fluid density of the air as just increasing the volume of air in the system. I suspect that when at least one reed is open, you would be hard pressed to inflate the mouthpiece. An interesting test for this would be to create a mouthpiece from a balloon.
Is the melodica more responsive with a hard mouthpiece? When you blow into a mouthpiece, you are creating a pressure wave. This is exactly the same as a sound wave and it travels at the speed of sound. This speed is only dependent on distance, not on the cross-sectional area of the tube. The time it takes for a reed to sound is based on the pressure wave, not the speed of the air you blow in (in fact, the air speed will increase or decrease as it travels through the system). Will the pressure wave slow down because some pressure is used to expand the tube? I don’t know; it doesn’t seem like it should. The pressure wave might be robbed of some energy which might attenuate the sound.
The balloon experiment sounds more interesting by the moment.
If you have a soft mouthpiece and continue to blow when all reeds are closed, you will increase the volume of stored air. When you press a key, what’s the effect? I don’t know.
I still don’t think there is any significant “responsiveness” difference in soft vs. hard mouthpieces, unless we get to highly stretchable mouthpieces. If I could find a balloon and a way to connect it to my melodica, it might help find the answer.September 9, 2020 at 4:38 pm #11708
This is an old thread, I know, but I’ll make some comments anyway.
I didn’t think there would be any inflation of the corrugated tube at lung pressures. But I found that if I closed off the far end and blew really hard, my tube stretched a bit.
I’m trying to think if this stretch would be a problem. When one or more reeds are open, I don’t believe you will get any stretch (you’ll increase the air flow instead), so I don’t see how it could be a problem when you are playing.
If you continue to blow when all reeds are closed off, you’ll pack a bit more air into the tube. [Since air is incompressible, you’ll only pack more air if the tube can stretch. However, this is only if you’ve got a great seal. When I tried it, I found the seal is the weak point–it releases air before the tube can stretch.] As soon as you play a note, the pressure in the tube will drop immediately. I don’t think there is enough energy in the tiny volume of air in the tube to even sound a single note. You need to continue supplying pressure (by blowing) to produce any sounds.
So why worry about this or invest time and money into work-arounds? Is there a measurable effect you’ve observed? It seems to me that if you are blowing hard enough to be concerned about the tube stretching, you are applying a lot more pressure than the reeds might like.September 9, 2020 at 4:03 pm #11707
Hey, I just looked at mine: Serial number 00052!
You know you can buy the mouthpieces, right? I’m not sure where you are, but here’s Suzuki’s European web site page for mouthpieces: http://www.suzukimusic.co.uk/products/melodion/accessories.html
The MP-161 is pricey, but then, the 44Hv2 price I paid was low enough to more than make up the difference. Plus, it’s probably for sale somewhere on eBay. Finally, if you have a 44H, can’t you just use the mouthpiece from that?