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Standing Wave in Trumpet Wind Column

October 15, 2018

I have done several blogs about how a trumpet works and I have quite a few videos about it as well. As a result of communications via these blogs and discussions I have had with other trumpeters on gigs, I decided to post this short blog about standing waves and variable acoustic length. This is essentially an addendum to last weeks blog about timbre, slotting, versus mouthpieces and horns. 

 

If you want to skip to the main theme for this week, just scroll below the review to the figure that is used in the cover page for this blog.

 

For a quick review, check out these previous posts. 

 

Timbre-and-Slots-Mouthpiece-Horn-or-Both

 

Air-Stream---Speed-or-Volume

 

How-A-Trumpet-Works
 

What-Is-Acoustic-Impedance-and-What-Does-It-Mean-To-A-Trumpeter

 

Ideas-About-Wind-in-Playing-Trumpet

 

Also, here are some videos on the basic physics of trumpet.

 

Overtone Series for my physics classes:

 

 

 

 

 

 

Overtone Series for my physics classes, but with PPT added:

 

 

 

 

 

 

 

Trumpet Physics Segment One: (more for trumpeters)

 

 

 

 

 

 

Trumpet Physics Segment Two: (again, more for trumpeters)

 

 

 

 

 

 

 

Now, to the new material. Last week, I got into quite a few discussions about slotting and where it ends on trumpet. You should notice that the slots tend to get so close together as to essentially disappear as you get up to around a G (concert F) above highC on your Bb trumpet. At that point the horn wind column is essentially moving into no more resonance. You can slide from that G on up with almost no slots any more, UNTIL YOU GET TO DOUBLE C, and then a slot suddenly appears. 

 

That slot should NOT be there, but it clearly is. In last week's blog (see the link near the top) I explain my theory as to what is happening there. All I want to do HERE is explain what is happening in general.

 

When you play a trumpet, a standing wave forms up at the resonant notes - harmonics - you are playing on a given valve combination. There is always a pressure antinode in the mouthpiece just in front of the lips. There is always a pressure node NEAR the bell.

 

That last sentence is the part that might seem odd. As you play different harmonics on the horn, the last pressure node occurs in different places. I'll now speak in "Bb trumpet speak" as opposed to concert pitch.

 

When you play a low C, there will, of course be a pressure antinode in the mouthpiece. In the figure just above (taken from Tom Rossing's book, "The Science of Sound) he shows the first four mode (harmonics) on a trumpet wind column). The first mode would be pedal C (or close to it), the next mode would be low C. Next, would be second line G. Finally, would be the C in the staff. You'll notice that the final node for each higher and higher mode gets closer to the bell. Around a G over high C, the last node is right at the bell barrier. Above that, no more nodes and antinodes. The trumpet wind column is essentially just a megaphone. 

 

This is why it is physically challenging to play those notes. There is no longer any resonance helping you out. 

 

However, as I mentioned earlier (and in last week's blog), there are a few more slots around DHC, DHB, DHD, etc. Some other part of the wind column/chamber system has begun to resonate.

 

So, that is it for this week's science-y blog. I hope it all made some sense. 

 

Now, if you are reading this, you made it through the post. Thanks! I hope you'll consider subscribing to my blog. If you found this interesting, please read the blogs in the archives. I also hope you'll consider supporting my work. As the blog evolves and as I get ready to launch my podcast later this year and as I continue to record audio and video, please remember, I am totally self funded. If you enjoy my music and have benefited in some way from reading the blogs and or watching the videos, please consider a donation to the cause. I am seeking advertisers and backers, but every individual can contribute in some way. No donation is too small, and no donation is too large! ;-) This is tantamount to digitally passing the hat on a no cover gig, but so be it. If you wish to make a contribution, just use nick@nickdrozdoff.com and send your tip/donation to me via Paypal. 

 

Finally, I am in the process of developing a series of a few concerts at jazz clubs in the Chicago and Green Bay areas as well as at school (college or high school) auditoriums. They will feature my big band version of the Variable D Postulate Ensemble. I am seeking one off sponsorships to help keep the price of admission down. If you or your company provides a small donation, I'll make sure you are amply credited both during the performance and on every promotional post leading up to the concert. If you are interested in participating, please reach out to me at nick@nickdrozdoff.com or at 847-476-1210. 

 

Respectfully submitted:

Nick Drozdoff

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