On trumpet forums I often see discussions about one piece bells vs two piece bells. Manufacturers often make a big thing out the fact that their bells are one-piece, and players get excited by the term "hand-hammered".

Maybe in previous years there was a big difference because of the method of stiching and brazing the seam, but currently the two piece bells have a circular join that is fused together (and almost invisible).

But nobody seems to question the cruder joins that exist in multi part mouthpieces. By these I mean cups and back bores which are interchangeable and screw together.

Well, they are convenient, and much emphasis is often given to the convenience of new products like CDs, YouTube, Fast Food, Microwave Cookers and Remote Controls. But little consideration is actually given to whether or not these convenient new products are actually better than what they replace, or even if they are a good as what they replace. Only that they are convenient.

In trumpet mouthpiece choices we have convenience presented to us. Instead of having to make a decision on the mouthpiece as an entirety, we are able to choose cups and rims separately from back bores.

Wow, you say. This makes it so much easier. Trouble is that easier does not necessarily equal better. We end up with either an unwanted 7” long sealed, resonant chamber or a 7” tube to nowhere inside the mouthpiece right at the venturi throat, one of the most critical places in the whole trumpet system.

A screw thread must have clearance between the male and female, otherwise they will bind and not turn. This means that there will always be a gap between the male and the female. You can see this for yourself by screwing any thread together just 1 or 2 turns and noticing that you can wobble the parts. They are not rigid until one part gets screwed hard up to another.

On the illustration above of a typical modular trumpet mouthpiece back bore I have labelled 2 faces A and C and the spiral thread B. This thread is typically 3/8” diameter with 6 or 7 turns giving a spiral length of 7 inches (pi x dia x no. of turns). In a perfect world, the face A will seal against a matching face machined at the end of the female thread on the bottom of the mouthpiece cup. This pushes one face of the male’s  “V” against one face of the female’s “V” leaving a gap between the other faces and creating a spiral cavity. This spiral cavity is a sealed chamber, inviting resonance. However if the face C contacts the mouthpiece cup before the face A, then there is effectively a spiral diverticulum out of the mouthpiece throat and along the thread.

This seven inch spiral is close to the length of a trumpet lead pipe and also close to the wavelength of a double high C! 

Like so many other heavily marketed features, this one greatly benefits the manufacturer:

Less raw material wasted - they can use smaller rod to machine the back bore.

Less Inventory because only one set of back bores is required which can fit all of the cups.

If they have 7 basic size cups and 5 different back bores, instead of 35 inventory pieces, they only have 12.

Once again, like reverse lead pipes and silver plating, a cost reduction by the manufacturer gets passed on as a price increase for the customer's convenience. Yes, it can be handy for the player when assessing different options, but from our experience with interchangeable lead pipes and bells, a one piece version will not necessarily behave the same as the multi part item upon which it is based.