slotting: gap v. drill

[MikeW]

Googling about the gap, and following related topics:

Some say that widening the gap increases slotting, but causes intonation problems when overdone

Some say that drilling out the throat of a mouthpiece leaves a cylindrical "drill" between the throat and the backbore, and that increasing the length of the drill increases slotting, but causes intonation problems when overdone.

The drill is a constriction in the air-path, and the gap is a bulge, but both can be viewed as pairs of surface irregularities separated by a short distance, so it is plausible that their acoustic effects could be similar.

Does anyone know how the two effects would interact ? If you use a mouthpiece with both a drill and a gap, do the two effects add or cancel, or does one override the other ? If the drill overrides the gap, then that could explain why some people who experiment with changing the gap see no results.

Does anyone know for sure ?

[Matt Walters]

Mike,
Setting up the horn so that there is more "Slot" (The horn is harder to lip away from the pitch center.) by increasing the gap between the end of the mouthpiece and beginning of the leadpipe does not change the intonation of the tuba. It changes how a person can play the tuba and may make it harder to lip into pitch a note that was naturally out of tune due to taper ratios, turbulence, etc.
Think of it like this. Even an expensive car will drive like crap if you can't comfortably reach the pedals and steering wheel.
So, your perception may be that increasing the gap will make the horn play out of tune. What really happens is that you can no longer sub-consciously lip in-tune notes that you previously were lipping in tune. You have to find the balance between security of attack and the ability to lip in-tune.

[Dan Schultz]

I'm glad Matt responded to this question. What he describes is EXACTLY the characteristics I get from the AGR on my Miraphone 1291. I just couldn't find the words to say it.

[MikeW]

From his reply above (color added):

Setting up the horn so that there is more "Slot" (The horn is harder to lip away from the pitch center.) by increasing the gap between the end of the mouthpiece and beginning of the leadpipe does not change the intonation of the tuba. It changes how a person can play the tuba and may make it harder to lip into pitch a note that was naturally out of tune due to taper ratios, turbulence, etc.
Think of it like this. Even an expensive car will drive like crap if you can't comfortably reach the pedals and steering wheel.
So, your perception may be that increasing the gap will make the horn play out of tune. What really happens is that you can no longer sub-consciously lip in-tune notes that you previously were lipping in tune. You have to find the balance between security of attack and the ability to lip in-tune.

From a reply to a query on the Stomvi website (color added):

At some point you’re stuck with the inherent tuning of an instrument. You can only do so much with a gap adjustment. That having been said, I would definitely try decreasing the gap and see what happens.This will not make the tuning of the entire horn sharper, it will change the tuning relationships of the different modes (harmonic series) and may make things better. I’ve embedded a little video from my website below that shows how these pitch relationships change when adjusting the gap.

One of the things that makes this whole gap adjustment difficult is that how the modes move around pitch-wise varies from set-up to set-up. In this way, the change that occurs when decreasing the gap with your set-up will most likely be different when making the same change on another mouthpiece/trumpet set-up.

The pitch changes can also be different with the same set-up and a different player. This is because each player pushes his or her lips into the mouthpiece by a different amount (lip penetration) and this, obviously, affects the acoustic relationships.

http://www.youtube.com/watch?v=YqryPUViyeo

Given that the AGR is for tubas and the couplers are for trumpets, it is of course possible that these instruments are different enough for both of these authorities to be correct. Leaving that question aside, there seems to be agreement in general terms that overdoing the gap can result in the player encountering intonation problems, even though differing views are possible about the mechanism underlying those problems.

I am still curious about the effect of introducing a cylindrical section between the mouthpiece throat and the backbore: I have read that this would cause similar effects to those attributed to a wider gap, and I'm curious about what would happen if a mouthpiece had both a long cylindrical section and a wide gap: would the effects add or cancel, or would one override the other ?

[Roger Lewis]

Just about every mouthpiece has what is called a "straightaway" - a section of cylindrical pipe - before the taper begins. The length of the straightaway varies from mouthpiece to mouthpiece as it does add certain characteristics to the way the mouthpiece performs, The longer the straightaway, the better the mouthpiece will slot, but the sound will get more brittle and more harsh. The shorter the straightaway is the better the sound is but the slotting becomes more difficult. Finding the best balance is a matter of individual tastes.

The Marty Erickson line of mouthpieces (from DEG/Dynasty), in my experience, have a longer straightaway and these mouthpieces slot very well but the sound can be a little harder to control - but they are very good mouthpieces. A shorter straightaway can be found in the Bach mouthpieces, giving a good color of sound but making the slots rather wide, allowing the player to bend the pitch with greater ease.

When you drill out a mouthpiece, you increase the size of the throat which will darken the sound, but it also increases the length of the straightaway improving the slotting. There is a law of diminishing returns on this though, so work in very small increments if you try it.

Combining the length of the straightaway with the length of the bore gap in the receiver may cause these two different aspects to cancel each other out, though there is a "Venturi effect" created at the bore gap that will increase the resistance in the mouthpiece as it introduces a high pressure area at the end of the mouthpiece. The high pressure area created by the bore gap aids the embouchure in it's performance by providing a bit more back pressure. This combined with the length of the straightaway in the mouthpiece will have a significant effect on the performance of the mouthpiece. If the bore gap is right and the straightaway is long you most likely will see superior slotting, but lack the ability to bend the pitch as much. With a shorter straightaway you will get a better sound but you may also have to move the pitch around with the embouchure more. But the bore gap is going to determine how much flexibility you may have.

Finding the correct balance for each individual player is probably why everyone is not playing on a 24AW and why there is such a variety of mouthpieces available.

Just my $0.02.

Roger