Physics of Music 55: Brass instruments

An index to the complete Physics of Music video series can be found here:
phas.ubc.ca/~mav/POM.html

[@francissommer3653]

Great set to videos! Explains the real science behind how music is made in ways that is intuitive and easy to grasp. I learned a lot! Will share with others. Thank you Professor Van Raamsdonk for taking the time to make these!

[@skrame01]

17:05 This is a natural trumpet playing. It is twice as long as a modern valved trumpet, so it has about 2x as many resonances and they are more closely spaced than on the modern trumpet (there are more of them due to the length of the tube).

[@quistian]

So... one does not buzz to make a sound, rather one blows through one's lips and when the vibration matches the frequency of the horn, the sound is made.

[@northshorehighlanders6167]

The lips must respond (function) as membranes to the applied force (exhaling). ANY force greater than atmospheric air "pressure" (also read: molecule concentration or density), SHOULD activate the lips (make them respond). Therefore, the lips should be as relaxed as possible, while still in position to respond to minimal exhaled "force." Non response from max relaxation is a lips' positions issue, usually that they're pursing/colliding, preventing the lips from being "membranes." In other words, there's a very specific position for the lips to respond. (This can best be felt from the INSIDE of the lips.) "Buzzing" resists and actually prevents the lips from responding to minimal force, all that's necessary for making a brass instrument speak. The mouthpiece restricts the lips' response area. Smaller mouthpieces make lip response FEEL like buzzing, but this isn't what's happening. The action is MUCH closer to flapping the lips, adjusting for what the mouthpiece rim allows inside, sometimes quite small. Also, the wave patterns inside the instrument require the lips to be in sync with the wave-completion (from the bell), something that's both physically and acoustically impossible with buzzing. Maybe you can buzz (free or with the mouthpiece), but that's not what's going on in the instrument.

[@TehMuNjA]

I find it fascinating that they manage to turn the roughly closed-open pipe spectrum into a harmonic spectrum using the bell and mouthpiece effects (and maybe some other effects?) Practically speaking, I am wondering how many degrees of freedom the builders of brass instruments are effectively working with in order to ensure the all of the low resonance are properly in tune with the harmonic series

[@svenlarsson]

A pretty good explanation of the trumpet. How about the pedaltones of the trombone, horn and tuba? Those tones are very important part of the basstrombone and tuba music.

[@eyesonly4451]

The cylinder, cone, and bell seem to me to be a lot like a radio transmission line, impedance matching network, and antenna.

[@olympicfan2]

Good in depth but I missed the tongue here. The correlation between air pressure, resistance and range.

[@darryljones9208]

The tongue has nothing to do with it. The lip posture chooses the resonance frequency played. The air pressure then controls dynamic level.

[@darryljones9208]

The lips are not sheets of paper and the Bernoulli effect is negligible. It is the RISE in pressure in the mp cup that allows the lips to close by lip elasticity. The pressure in the oral space is constant. The pressure in the mp cup when playing a tone on the instrument varies drastically in the cycle. You are in error at 15.00 it is when rhe pressure is LOW in the cup that the lips open and air begins flowing through the aperture. You are correct that lip tension controls the pitch played. Regarding your drawing, the lips do not protrude inro the mouthpiece like that. Pedal tone: there IS a resonance there and it is flater than C. About a minor third plus one octave below low C you did get close but its still a bit lower. A played pedal C is simply by raising this tone. It has nothing to do with upper harmonics.

[@northshorehighlanders6167]

Watch a strobe video of the lips while playing a brass instrument. The lips are constantly in motion and DO protrude into the mouthpiece cup during each frequency cycle, different amounts for different players and registers, often not starting in the position depicted in this video. "Aperture" is an optical illusion and does not exist, as a strobe easily demonstrates. The lips close through a combination of elasticity and force over the lips' surfaces which reduces air density between them. A clarinet reed is "sucked" closed by this same reduction of air density between the reed and mouthpiece.

[@darryljones9208]

​@northshorehighlanders6167 but a clarinet reed has more surface area for air pressure to act on. The trumpet lip aperture responds to pressure difference and elasticity primarily. And no, the lips DO NOT protrude into the cup to the degree you have shown in this drawing. And any Bernoulli effect is dwarfed by static pressure. Simply equalization of pressure allows the elasticity to close the lips. Also, The pedal tone is fundamental. The low C is the 2nd harmonic.

[@northshorehighlanders6167]

Yes, the lips, acting as membranes, (should) respond to even minor variations (from atmospheric air pressure) of exhaled force, if they're precisely positioned positions relative to each other - and with as little muscular resistance as possible. (The illusion of lips' muscle tension is created by mouthpiece inner-rim size, lower jaw position and mouthpiece position.) This protrusion of the lips (created from their response to exhaling) establishes their position for the "Bernoulli, effect," which also plays a role in the lips closing, yes, not as much as a clarinet but still quite in the mix.

[@darryljones9208]

@northshorehighlanders6167 "illusion" of lip tension? Uhm, no, it's an actual increase in the firmness of the lips by the muscles of the lips. Increased to ascend to higher tones and decreased to decend to lower tones.

[@northshorehighlanders6167]

The vast majority of how notes are produced on a brass instrument has always been based on how it feels, rather than a thorough analysis of what's really taking place. There is no proof of any additional muscle contraction beyond what I described in my past previous reply, regardless, how the "sensation" feels.

[@twbarf]

The lips don’t close. There is ample proof of this when we review endoscopic video.

[@northshorehighlanders6167]

THEY DO CLOSE. An endoscope does not show what the lips do. A strobe does. The lips are constantly in motion, flapping open and closed. They close only for an instant, but a strobe conclusively shows they close.

[@T-Slider]

How about new graphics that depict the lip mouthpiece interface accurately. Your slides are completely wrong. Actually, they are absurd.

[@caascade]

would you have other examples with accurate depiction please ? I'm interested. thanks

[@darryljones9208]

Oh yes that is one strange rendering of what the lips look like when playing. Otherwise his explanation is fairly accurate. I don't buy his Bernoulli interpretation. The pressure variance in the mouthpiece cup are sufficient to close the lips. Bernoulli effects would be negligible comparatively.

[@albertbeer4809]

Geistiger Dünnschiss eines Gehirnakrobaten