Learn about the annulus gap

Learn about the mouthpiece/trumpet annulus (gap)

The Gap is important. It is the best way to optimize the performance of your set-up.
The optimum gap is specific to the individual player, their mouthpiece, and their trumpet.
The optimum gap for each situation must be discovered through experimentation.

The information below will explain the what, how, and why of the gap based on our studies, experimentation, and experience.

ADJUSTING THE ANNULUS (GAP) IS PRIMARILY AN ACOUSTIC PHENOMENON.
IT HELPS DETERMINE THE LOCATION (RELATIVE PITCH) OF THE SLOTS.

Definition of The Annulus, or Gap

Receiver cut-away showing the “gap”

The “gap” affects the pitch center, or slot of every note on the trumpet. It does this by affecting the intonation of every note.

When the gap is not correct, you must compensate using your chops and air in an effort to make all the notes be in tune and sound as even in possible. This means you are working harder than you need to to play the instrument.

Signs of an incorrect gap:

Some notes are sharp and some notes are flat.
The upper register speaks well, while the low register speaks badly.
The low register speaks well, while the upper register is difficult.
All or some registers feel stuffy.
All or some registers feel too open.

The Annulus, or “Gap” as it is commonly referred to, is the space (chamber) between the end of a trumpet mouthpiece and the beginning of the leadpipe.

THE GAP IS THE MOST IMPORTANT DIMENSION THAT CAN EASILY BE ADJUSTED TO:

Make the upper register as easy as possible.
Improve your endurance.
Give you a full, resonant sound full of harmonics, or tonal colors.
Improve the low register.
Ensure the best intonation possible with your mouthpiece, your trumpet, and the way you play.
Give you more sound for less work.

The video below explains what the gap between the mouthpiece and leadpipe is.

The goal in adjusting the gap is to get the highest percentage of notes in tune with themselves.

The Function of The Gap

Different gaps using different Flex Couplers

When the gap is adjusted correctly, it allows you to use your air
in the most efficient manner possible.

Determining the Correct Gap

Using a Mouthpiece that is Converted for Couplers:

Start with the smallest number Coupler you have and play an F major scale from F in the staff to the octave above (just on top of the staff).

When you get to the top F listen and see if you have to:

Push up to be in tune.
Come down to be in tune.
Do nothing to be in tune (in other words, the pitch, or slot, is right where you want it to be).

Then try the next numbered Coupler you have and do the same thing. After you experiment a bit, you’ll start to hear and feel the gap adjustment.

The goal is to find the gap that gives you the best intonation.

Then use the one you find best in your routine. Don’t be afraid to change Couplers as you become more experienced with the gap effect.

The video below explains an easy way to determine the best gap for your mouthpiece, your trumpet, and the way you play using only an F Major Scale.

Using a solid shank mouthpiece – Follow the directions to the right:

Start by playing an F major scale from F in the staff to the octave above (just on top of the staff).
When you get to the top F listen and see if you have to:

Push up to be in tune.
Come down to be in tune.
Do nothing to be in tune (in other words, the pitch, or slot, is right where you want it to be).

Then add a small piece of paper on the side of the shank as shown in the picture and play the scale again. If it improves you know you can benefit from a different gap.
If it gets worse or stays the same you know you are either:

At optimum Gap
Or you need to decrease the gap which can be done easily by having your mouthpiece converted for Flex Couplers.

The correct gap for each mouthpiece/trumpet system and player cannot be calculated.
It must be discovered through experimentation.

Gap Calculation?

Unfortunately, it is not possible to calculate the correct gap for a system or individual. Remember that adjusting the gap is primarily an acoustic phenomenon. It affects the relative intonation of the notes (pitch center).

Because each player pushes their lips into the mouthpiece by a different amount, this alone affects the relative intonation of the mouthpiece/trumpet system. The video to the right shows this in graphical terms.

The video below explains why gap calculations don’t work.

Annulus (gap) Frequently Asked Questions

Flex Mouthpiece with Couplers for Gap Adjustment

What is the Annulus, or Gap?

The gap is the space that can exist between the end of a trumpet mouthpiece and the start of the receiver.

Why is the gap important?

Adjusting the gap is the best way to ensure your set-up is in tune with Mother Nature’s harmonic series. When your set-up is in tune with the harmonic series, you get the maximum amount of sound along with ease of play.

What does the gap do?

The gap affects the location of the slots, or modes, and this affects the back pressure the player feels.

How do I know if I have the right (or wrong) gap?

If you experience:

Stuffiness in any or all registers
Too open in any or all registers
Bad pitch in any or all registers

Odds are high that adjusting the gap will improve things.

Is it possible to calculate the gap?

Unfortunately, no. This is because the gap is primarily an acoustic phenomena. Each player pushes their lips into the mouthpiece a different amount. This changes the effective resonance frequency of the mouthpiece and thus the relative intonation of the mouthpiece/trumpet system.

Can I expect to use the same gap with different trumpets?

Generally no, it can’t be predicted. You must discover the correct gap for your mouthpiece and trumpet and the way you play.

I bought a Flex Mouthpiece with three Couplers: How do I know which one is best for me?

Start with the smallest number Coupler you have and play an F major scale from F in the staff to the octave above (just on top of the staff). When you get to the top F listen and see if you have to:

Push Up To be in tune.
Come down to be in tune.
Do nothing to be in tune (in other words, the pitch, or slot, is right where you want it to be).

Then try the next numbered Coupler you have and do the same thing. After you experiment a bit, you’ll start to hear and feel the gap adjustment.

The goal is to find the gap that gives you the best intonation.

Then use the one you find best in your routine. Don’t be afraid to change Couplers as you become more experienced with the gap effect.

Can I expect to use the same gap with different mouthpieces?

Generally no, it can’t be predicted. You must discover the correct gap for your mouthpiece and trumpet and the way you play.

How can I adjust the gap?

The most effective and portable (meaning you can use it from horn to horn) method is to use our Flex Coupler system.

What is better; a smaller or larger gap?

Any gap can be correct. Empirical evidence shows that most players do better with more, versus less gap.

My friend and I use the same mouthpiece and trumpet. Should we use the same gap?

Most likely not as each player pushes their lips into the mouthpiece a different amount. This changes the effective resonance frequency of the mouthpiece and thus the relative intonation of the mouthpiece/trumpet system.

Does a mouthpiece converted for Flex couplers play as well as a solid shank version?

Yes. Due to the Flex Alloy, increased coupler mass, and our synthetic o-ring, our Acoustic coupling system gives you all the benefits of adjusting the gap without any of the deficiencies of other systems.

Do the cornet, flugelhorn, and piccolo have a gap?

Generally no. For any horn where the receiver to leadpipe junction is smooth (without a step), the amount the shank penetrates into the receiver has a similar affect as adjusting the gap. This is because it is a change to the shape of the air column, which changes the intonation pattern of the horn.

Does the gap affect the airflow?

It does to a degree: When you have the correct gap acoustically for your mouthpiece, your horn, and the way you play, you are able to use your air in the most efficient manner. This is true whether you are someone who pushes a lot of air through the horn or for someone who does not.

When the gap is not correct acoustically, it will “feel” as though you have too much or too little back pressure, depending on a number of other factors.

Does Stomvi make quarter size Flex Couplers?

No, for the following reasons:

Remember that the gap affects the relative intonation of all the notes.
The intonation change caused by a quarter size is, on average, only 2 musical cents.
The best human ears can hear about 5 musical cents.

—Therefore a quarter size gap change
is not discernible by human ears.—

In addition:

The penetration change of a quarter size is only .015″
It is easy to change the gap by virtually a quarter size by using excess pressure when you insert the mouthpiece into the trumpet.

—Therefore a quarter size gap change is impractical
from a mechanical standpoint.—

Furthermore:

Keep in mind that the gap is affecting the alignment of the pitches, or frequencies, of the notes. Another factor affecting this is lip penetration. How far you push your lips further into the cup of a mouthpiece affects the resonance frequency of the mouthpiece. The amount of lip penetration can vary the pitch by as much, if not more, than the pitch change caused by a quarter size gap change. Therefore you can easily end up chasing something that you’ll never catch.

—The bottom line is a half size gap change (.032″)
is more than enough to “dial things in” for your
mouthpiece, trumpet, and the way you play.
Any gap change finer than that is
impractical and therefore unnecessary.—

When your gap is optimized, you are getting the most sound for the least amount of effort.
Think of it as though Mother Nature is giving you “free gas!”

Average gap per manufacturer

Gathered through empirical measurement. Your gap may vary depending on age and model. For reference use only. All measurements in thousandths of an inch (.001).

Download Gap Chart As PDF