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100 Ohms of Resistance?



 
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Steve A
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PostPosted: Tue Jan 12, 2021 3:48 pm    Post subject: 100 Ohms of Resistance? Reply with quote

DISCLAIMER: I realize that this understanding isn't required for playing the trumpet well. If you think this is a waste of time, please feel free to ignore it, rather than arguing against trying to learn or understand. Thanks!

Possibly opening a can of worms, but in hopes of learning something, here it is:

In this video, KO Skinsnes of Stomvi says there's debate about whether or not lips start closed, or open and act in response to 100 ohms of acoustic resistance to start the buzz cycle:

https://www.youtube.com/watch?v=bdDTVdYOXNQ

I understand the cycle when starting from closed lips. Can anyone explain in layman's terms what the 100 ohms model would entail?

Thanks!
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Tpt_Guy
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PostPosted: Tue Jan 12, 2021 4:40 pm    Post subject: Reply with quote

100 ohms?

If acoustical resistance is measured in ohms then I would think playing trumpet would be rather shocking!

Sorry to be a bit of a joker. The ohm is the SI unit of measurement of electrical resistance; I couldn't find any use of ohms to measure any other resistance.

He may be trying to use it as an analogy, but using ohms to measure something nonelectrical seems a bit discrediting.
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cheiden
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PostPosted: Tue Jan 12, 2021 4:46 pm    Post subject: Reply with quote

Not exactly laymen's terms but might help some...
https://www.animations.physics.unsw.edu.au/jw/sound-impedance-intensity.htm
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kalijah
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PostPosted: Tue Jan 12, 2021 5:41 pm    Post subject: Reply with quote

Quote:

He may be trying to use it as an analogy, but using ohms to measure something nonelectrical seems a bit discrediting.


Acoustic ohm is defined as:

Pascal x second/cubic meter
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kalijah
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PostPosted: Tue Jan 12, 2021 6:06 pm    Post subject: Reply with quote

In the video, when he referred to 100 ohms he was describing the resistance of closed lips.

However, the resistance of closed lips is infinite as there is zero flow.
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Tpt_Guy
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PostPosted: Tue Jan 12, 2021 9:26 pm    Post subject: Reply with quote

kalijah wrote:
Quote:

He may be trying to use it as an analogy, but using ohms to measure something nonelectrical seems a bit discrediting.


Acoustic ohm is defined as:

Pascal x second/cubic meter


Learn something new every day, sort of.

I see on the link from cheiden Z [impedance] = p [pressure]/U [flow] - brackets are for clarification and not part of the forumla. Math isn't my strong suit. How does that relate to the formula you posted?
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kalijah
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PostPosted: Wed Jan 13, 2021 3:52 am    Post subject: Reply with quote

Pascal = pressure

Flow=cubic meters/ second

Impedance = pressure/flow = Pascal/(cubic meter/sec)

= (sec/cubic meter)x Pascal = Pascal × sec/cubic meter
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Steve A
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PostPosted: Wed Jan 13, 2021 11:37 am    Post subject: Reply with quote

All right, I'll be honest, I'm not sure I'm understanding this any more than I was to start with, but that's probably a reflection of me more than anything else. Thanks, all.
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Crazy Finn
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PostPosted: Wed Jan 13, 2021 12:32 pm    Post subject: Reply with quote

There seems to a discrepancy in understanding what “layman’s terms” actually constitutes.

Lol.
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hibidogrulez
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PostPosted: Wed Jan 13, 2021 1:05 pm    Post subject: Reply with quote

kalijah wrote:
In the video, when he referred to 100 ohms he was describing the resistance of closed lips.

However, the resistance of closed lips is infinite as there is zero flow.

I suppose that's mathematically true, but the moment you start exhaling there will be an airflow (unless you manage to squeeze your lips really tight, but even then the airflow usually wins out eventually). I guess their description isn't 100% accurate in this case, as the flow automatically means there'll be a gap between the lips, but for a non-phycisist it'll be easier to understand that the lips start 'closed', even if they technically open as soon as the flow starts.
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kalijah
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PostPosted: Wed Jan 13, 2021 1:27 pm    Post subject: Reply with quote

If the pressure is sufficient to push the lips open, that will occur and flow will begin. And there will then be a finite resistance.

When playing a tone, both the lip aperture AND the instrument resistance contribute to the total resistance. The total (average) resistance is then the air lung pressure divided by the average flow.
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BraeGrimes
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PostPosted: Wed Jan 13, 2021 4:41 pm    Post subject: Reply with quote

This is super interesting. Thanks for sharing. You're right in that there would be a little paralysis by analysis here, but still very interesting to see trumpet physics. I'm guessing they get this Ohm resistance figure by calculating the time it would take to reflect back in conjunction with the cubic area (maybe including the cavity of the mouth?). I'm no scientist! Super cool
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Lionel
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PostPosted: Wed Jan 13, 2021 4:43 pm    Post subject: Reply with quote

kalijah wrote:
In the video, when he referred to 100 ohms he was describing the resistance of closed lips.

However, the resistance of closed lips is infinite as there is zero flow.


You forgot one thing Darryl (lol)! it isn't necessary but it is interesting. Here goes:

While playing your trumpet or any brass instrument for that matter the horn doesn't care which direction through the pipes that the air flows. Although this can create a difficult and kinda yucky condition. That is when you consider all the scum that eventually resides within the brass tubing of an instrument. Then follow that up concept up by just thinking of all that gunk meanwhile drawing IN the air towards the mouthpiece. Also, you'll need a set of chops that works backwards as well as forward too. So this will eliminate a number of players who roll in the lower lip and point the horn angle downwards. The air just doesn't like taking that path through your lips while trying to maintain a playable tone. This channel creates way too much resistance to REVERSE the airflow when using the breathing and mouth apparatus that never was designed to allow a backwards flow of air.

In fact you can prove this to yourself another way too. Perhaps all of us have seen that clever Youtube trumpet player who promises "everyone a solid G above high C within just a couple of minutes". This is the guy who removes the squeaker reed assembly from a little kid's bathroom toy. He carefully attaches it inside his third valve slide. Because the third valve is much less used than the other two he can now make it SEEM like he's actually playing an ascending run-up to G/High C. Only when he reaches the point where he needs to play the High G?

He merely presses down the third valve and blows like Hell into the horn without buzzing his lips. It's funny as can be. However the exact same high note can be sustained easily by drawing IN the air while pressing down the third valve.

Another thing I've noticed is that despite the mechanical advantage the toy squeaker element provides, the quality of the G/High C can sometimes run a little thin. Just as some trumpet players who can blow G/High C and yet not get a truly big sound.
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