Zoom discussion on physics of instruments

[AndrewMeronek]

The discussion starts at 4:44

[Basbasun]

Tank you for posting this, I know that you know this, I do to but for many on this forum its news!

[AndrewMeronek]

Tank you for posting this, I know that you know this, I do to but for many on this forum its news!

And also a nice reference for someone looking to provide students with materials.

[robcat2075]

I like that video. The explanation of the bell working to make the sound louder by making more "room-sized" is one I hadn't heard before but i guess that's like "impedance matching" that i often hear of?

But I'm wondering... if the bell just acts to make the horn louder, could we fashion substitute for the bell section that retains the desired pitch of the horn but doesn't make it louder, for practice purposes instead of a practice mute that obstructs the air flow?

Of course, it is not that simple. Even with a proper mouthpiece and a proper lead pipe, a tube with no bell will not produce partials with the same interval relationships as a tube with a bell. The bell does have some role in tuning the pitches beyond the mere length it adds to the overall horn.

But maybe there is some "practice bell" possible?

[andym]

A practice bell is an interesting idea. Here’s an intuitive guess: anything you do to make the horn quieter will change the feel and intonation. A reason: if you change the impedance between the bell and the rest of the horn and the room, that should be felt by the player. A practice bell may not change it as much as a mute but probably won’t be as quiet either and will cost more.

Example: when living in an apartment for a year, I bought a sackbut. It is quieter than a trombone but feels a lot different.

[robcat2075]

I'm also reminded of an explanation of why clarinets have bells. What good does the bell do when most of the pitches are coming out of open holes above it?

It seems that the true function is not to make the clarinet louder but to approximate for the two closed-hole notes the effect that other notes get from having several open holes below them. The alternative would be to add a longer cylindrical tube with open holes to the end.

Indeed, there are accessory attachments sold for clarinets that do this very thing.

Similarly... why do serious flutists almost always have flutes with a "B foot" when there is almost no need for the note? They say that having that extra hole makes the low C respond better.

So, I'm imagining some sort of practice "bell" that may or may not have some bell shape but has holes along the length that create some of the "feel" of the bell without all the amplification.

[paulyg]

How did I miss this, that is my youth orchestra director!

[Basbasun]

A practice bell is an interesting idea. Here’s an intuitive guess: anything you do to make the horn quieter will change the feel and intonation. A reason: if you change the impedance between the bell and the rest of the horn and the room, that should be felt by the player. A practice bell may not change it as much as a mute but probably won’t be as quiet either and will cost more.

Example: when living in an apartment for a year, I bought a sackbut. It is quieter than a trombone but feels a lot different.

Yes that is right. I do play sackbuts and have done that for many years, it is a totaly different instrument from modern trombone. The bell (as it is said in the video) is not only for the loudnes, but for bringing the partials to line up (closer to the overtone series). In some other cultures the partial dont line up like that.



Intersting?

The question about clarinett and sopranosax is intersting since the difference in range and that the partials line up differently.

Another cultur instrument with partials that line up different from trombones.

[robcat2075]

The bell (as it is said in the video) is not only for the loudnes, but for bringing the partials to line up (closer to the overtone series).

Does he say that the bell changed the intervals? I watched the video waiting for him to say that but all he asserts is that the bell "raised" the pitches. When he plays it, it is clear that that intervals have changed but he doesn't make that point.

Example: when living in an apartment for a year, I bought a sackbut. It is quieter than a trombone but feels a lot different.

Yes that is right. I do play sackbuts and have done that for many years, it is a totaly different instrument from modern trombone.

Is it really more totally different than a practice mute?

The argument I'm hearing here is that the practice bell would unsuitable because it wouldn't be the exactly the same as a regular trombone... so lets keep putting a cork in the end of the horn, which is not at all like a regular trombone.

I suspect there is more successful investigation that could be made into this than picking up a sackbut, which was never designed to be quiet anyway, and presuming that is the end of the road..

[andym]

My apologies if the sackbut wasn’t a satisfactory example for you. My goal with playing the sackbut wasn’t just to have a quieter instrument but to take living in an apartment as an opportunity to explore that instrument.

My point was that if you change the impedance variations along the wave path then that will feed back in various ways to the sound and back to the mouthpiece.

Besides intonation and volume, we probably also need to consider tone quality. You want something where the tone quality is optimized in a similar way to the open horn so we don’t learn to compensate. Of course, that is true for a practice mute.

You may be able to get something closer to an open horn that is somewhat quieter by changing the bell. I suggest experiments with a pbone and 3D printer or some pvc pipe might be useful.

[boneagain]

Does he say that the bell changed the intervals? I watched the video waiting for him to say that but all he asserts is that the bell "raised" the pitches. When he plays it, it is clear that that intervals have changed but he doesn't make that point.

You might find Chapter 20 of "Fundamentals of Musical Acoustics" by Arthur H. Benade interesting.

Also, with your cello readily available, and a piece of garden hose, and tuner, you might enjoy some empirical experiments.

First, plot out some "harmonics" on a cello string. Make note of the nodal points. Factors of interest are: distance to nodal point vs length of string; fundamental measured tone of string; measured tone at nodal point; ratios of these things. I believe you will get a pretty darned close adherence to the "overtone series" we get on trombone.

Next, plot out the "overtone series" in one position on your trombone. For this I recommend just measuring the tones themselves because measuring lengths is fraught with acoustical complications. Calculate ratios of "fundamental" and "overtones." Again, you should get a pretty darned close adherence to the "overtone series" we expected.

Now take your garden hose. For fun, cut it to the same length as measured from mouthpiece receiver to bell end on your horn. Smooth one end a little so it won't cut your lips. leaving EITHER of the threaded fittings on the hose will reduce the effectiveness of the test.

Using the hose WITHOUT ANY MOUTHPIECE play and plot out the "overtone series" for this and calculate the ratios. Let your lips find the places where notes are stable and not "wobbly." Do not try to force the notes into what you expect.

If theory and past empirical studies hold, you should find that this departs GREATLY from the expected "overtone series." Yet this IS the "overtone series" for a pipe excited at one end.

Benade's Chapter 20 explains how the combination of bell AND mouthpiece work together to shift the actual, versus expected, overtone series of the straight pipe such that the result is the expected overtone series. Or, as stated simply in the video "raises pitches."

If you still have your garden hose handy you can do more to check this out. Stick a mouthpiece in and and remeasure pitches and ratios. Stick a big funnel on the end and do the same. Last time I tried this (probably 30 years ago) I was surprised at how big the difference was. I could NOT play a non-wobbly bugle-call on the straight hose. Bugling got easier and easier as I first added mouthpiece then added funnel.

On top of this we have the acoustical impedance matching transformer function of the bell. Benade also covers this.

The Benade book is available on Kindle, which makes it quite easy to find specific things like this. I have that, but find myself enjoying having the Dover reprint right in my grubby hands. It's an unusual book in that it has the details to support actual calculations, but does not require the reader to fully understand the mathematics to be able to "get" the meaning of the sections with that math.

[Basbasun]

https://acousticstoday.org/wp-content/u ... /Brass.pdf
This above is a simple explantion of brass insrtuments evolution.

The garden hose thing you describe boneagain is close to one thing I did in many acoustic lessons to demonstrate the acoustic behavior in brass instruments. The lengt of the hose I used was half the length of the trombone, 142 cm, (actually just a bit longer the half the trombone length) to make a very long story short, the tones, the partials you could get with stability was as follows BBb F d ab , the same tones as the trombone partials exept only the odd numbers of the partial series. First third fifth and seventh. I made tubes with different shapes to show that a trumpet with odd series of partials was possible, like FF BBb Eb Ab. This was in the 80th.

[Basbasun]

A good practise mute is good.
A good sackbut is expencive.

[boneagain]

https://acousticstoday.org/wp-content/u ... /Brass.pdf
This above is a simple explantion of brass insrtuments evolution.

The garden hose thing you describe boneagain is close to one thing I did in many acoustic lessons to demonstrate the acoustic behavior in brass instruments. The lengt of the hose I used was half the length of the trombone, 142 cm, (actually just a bit longer the half the trombone length) to make a very long story short, the tones, the partials you could get with stability was as follows BBb F d ab , the same tones as the trombone partials exept only the odd numbers of the partial series. First third fifth and seventh. I made tubes with different shapes to show that a trumpet with odd series of partials was possible, like FF BBb Eb Ab. This was in the 80th.

... and there it is empirical validation of both prior empirical evidence and theory. Odd partials without bell.... ALL partials with bell...

If you ever look at the Benade book you'll see good pictures showing the odd partials essentially squeezing together until the LOOK like the full partial set. (full partial... if English were not my 1st language I would hate it even more...)

Put another way: what we think of as the SECOND partial on trombone is the THIRD partial of the odd-partials-only tube squashed into that particular tuning spot.

And different points on the bell flare accomplish this for the different partials. And the place in the bell they do this (high note vs low note, large end of bell vs small end) is counter intuitive.

This DOES help explain why some horns have their "partials" more in tune than others.

But as so often pointed out on the old Forum and here, bell shape is only a part of the whole thing. SO many places for things to go awry!