Air Pressure / Air Flow

Many students came to Mr. Jacobs with problems differentiating between Air Pressure and Air Flow. Because of this Mr. Jacobs studied this including bringing colleagues from the CSO for testing. The results were amazing! Here is Mr. Jacobs talking about Air Pressure and Air Flow.

From Arnold Jacobs: Song and Wind*

The relationship between air flow and air pressure has been puzzling to wind instrument players. Air as pressure uses the same musculature as air as wind. However, the musculature is used in different ways. “With wind there is always air pressure. With air pressure, there is not always wind.” He often tells students to play with Song and Wind, not song and air pressure. Pressure can only be experienced as it enters and leaves the body through the lips. Within the body, it can only be detected as air pressure. To move air outside the body, air pressure is required as moving air requires pressure. Jacobs calls this, “the phenomenon of wind.”

“The psychology of wind is very different than the psychology of pressure. If you go by the psychology of pressure, you can have pressure with practically empty lungs. “In 1995 at the International Brassfest in Bloomington, Indiana, Jacobs commented: “You learn to differentiate between air pressure and wind. With wind, there is always air pressure. If you think about it, there can never be wind unless there is air pressure. If you have a piece of tubing and put your hand near one end, you feel a little air coming out—the air pressure can be measured. Where it enters the tubing you will find it higher than where it comes out. When you use an anemometer, you can measure the differences in the air pressure, and you will always find that where there is wind, there are differences in pressures. When you order wind, a gentle wind [he blows softly], or a powerful wind [he blows hard], there is a great difference in pressure in those two that you actually measure flow and pressure.

Jacobs draws two lines to demonstrate the air pressure in the oral cavity and air volume (flow) in the instrument. There is nearly four times the air volume. For air flow, Jacobs differentiates this as thin air and thick air. To show thin air, he has a student hold his hand in front of his mouth and say “sssssss.” The air is under high pressure, but there is little quantity. Blow “whoooooo” (as in who) for thick air. The feeling is a considerable volume of air under low pressure.

All wind instruments have their flow rate—the quantity of air required to play a note on an instrument for one minute. Variables include the instrument, range and dynamic. Just as there are variables for air flow, air pressure has the same variables.

In the brass family, the trumpet uses the least amount of air flow but under the greatest amount of pressure, around one-half to one pound of pressure [of mercury]. In extreme circumstances, the pressure can be as high as three pounds. The tuba uses the greatest air flow, but under the least pressure—one to ten ounces.

In 1959 or 1960, four members of the Chicago Symphony, with instruments, traveled to the University of Chicago for tests. They were Adolph Herseth, trumpet; Philip Farkas, horn; Robert Lambert, trombone; and Jacobs, tuba. In the 1950s, Dr. Bruce Douglass, a tubist and physician from the Mayo Clinic, traveled to Chicago for lessons with Jacobs. Douglass put him in contact with Dr. Benjamin Burrows then at the University of Chicago’s Billings Hospital. It was here that Jacobs did research with full laboratory equipment.

Jacobs spoke to Bill Russo on Chicago radio station WFMT-FM about these tests:

Russo, (BR) – What’s the difference between [brass] instruments?

Jacobs, (AJ) – “The trumpet would use the least amount of breath, but under the greatest amount of pressure of any of the brass instruments. The tuba would be just the reverse. It would use the most in terms of volume of air and flow, but under the least pressure. We found that the flow rates in very high range playing would be very low—say maybe ten-liter-per-minute flow rate under a pressure of sometimes in excess of a pound-and-a-half to two pounds. In his lower range, he might be playing with a flow rate of maybe twenty-five to thirty-liters-per-minute under a pressure of maybe eight or ten ounces.

“On the tuba, my intra oral pressure—the pressure as measured in the mouth cavity while playing—we inserted a little tube into the mouth while playing, and the pressure was read—goes as low as two ounces in general playing, but at the same time, my flow rates may go anywhere from seven-liters-per-minute playing as softly as I can, to well in excess of 120 liters-per-minute playing in full volume.

“Dr. Benjamin Burrows who helped me with these experiments was rather intrigued with the fact that you could draw one curve for the entire brass family in terms of how much air is used, and how much pressure is used in producing this flow rate on the instruments.

“Wherever we played notes that were enharmonic, even though they were on different instruments—our work efforts and flow rates were practically identical. As an example, when I played a high C at a given dynamic that we were working to, I was using about six ounces of intra oral pressure and about ten liters flow rate per minute, and in graphing this we found that Mr. Herseth, on exactly the same note, was using practically identical pressure and flow.

“On a different note, with Mr. Farkas, again we found that my pressure and his were about the same. Flow was about the same—even though we were using different instruments. Our embouchures in coming to a given size and shape had a certain requirement for the breath in terms of pressure and movement.”

BR – “The flow rate increases for lower notes on a given instrument?”

AJ – “In the brass family, yes. At a given dynamic level, the flow rate is almost invariably greater in the low range compared to the high range.”

BR – “And the pressure decreases for the lower notes?”

AJ – “Exactly.”

BR – “But now, when you say that different instruments have the same flow rate and same pressure for a given same note . . .”

AJ – “Enharmonic, yes.”

BR – “Say for middle C, does that mean then that as the tuba increases its flow rate to ten, the trumpet decreases its flow rate down to ten?”

AJ – “Exactly. As the trumpet goes into his low range, the pressure eases off and his flow increases—as I go into my high range on the tuba, my pressure increases and the flow decreases.”

BR – “Terrific. What are the implications of this? There must be millions.”

AJ – “Well, there are many implications, as you say, one is psychological to those of us who play the tuba. We must realize that we do not have to work very hard when we play in the high range. I have many students who will go into severe isometric contraction simulating the work effort of the trumpet when he is working in his high range, when actually it is not needed.”

 

“Tuba players use their breath up about three times as fast as the horns and trumpets do, and as a result, should be permitted to breathe more frequently. [This comment is based on playing at the same proportionate volume levels as the higher pitched instruments].”

The embouchure for the tuba requires low pressure air but in large quantities. For soft playing, the flow rate can be as low as seven liters per minute. In a work involving low, loud playing, for example the Wagner Ring operas, the flow rate can be as high as 140 liters a minute. At the other end of the scale, an oboe may require seven liters at a loud dynamic. Because of the high flow rate required by the tuba, its players commonly suffer from hyperventilation.

Going up an octave almost doubles the amount of intra thoracic pressure. Jacobs states, “On the trumpet, if you use ten ounces of pressure while you are playing, for the next octave you may go to approximately twenty ounces of pressure. That again is simply tied into the mass of air so that you blow with greater volumes of air—thick air. It will be that thick volume of air based on the resistance of your embouchure in that particular register. You cannot use this as a blanket rule for the entire spectrum of notes on your instrument. It will be different in the bottom as well as the top register.” The trumpet, conversely, is a low flow rate instrument compared to trombone and tuba, and therefore uses less air but under higher pressure.

The oboe requires the least amount of air of all wind instruments. In pianissimo playing, the flow rate is about two and one-half liters per minute and in fortissimo, would go up to about five liters per minute.

Jacobs elaborates on this. “The oboe is almost like a static breath pressure. Ray Still [former CSO principal oboe] has the lung capacity of slightly more than five liters. He has a flow rate of about five liters per minute (in loud playing). So, if he were to take a full breath at that particular flow rate, he could obviously hold a note for a full minute. Now, if he is playing softly, he will have a flow rate of maybe three liters per minute. So he can go considerably more than a minute.”

The musculature of the body is capable of extremes with the use of air pressure. For example, to equate pressure to speed, a cough can generate a release of air up to one hundred miles an hour.

*Arnold Jacobs: Song and Wind, Copyright 1996 Windsong Press, Ltd., All rights reserved.