It is my experience that trumpet players, perhaps more so than other brass players, every so often spend time considering their mouthpiece wondering if they are using the right one. Most trumpet players I know own at least two mouthpieces and some have a drawer full of them. These mouthpiece might have smaller cup diameters, larger cup diameters, be deeper, shallower, have a different backbore, larger throat, smaller throat, etc. The variables are endless. I don't intend this article to be a discussion of the cup of the mouthpiece; far from it for me to say which mouthpiece someone should use. At the time of this writing I myself am involved in a so-called "mouthpiece safari", and am learning as I go along. That learning includes the unique challenges that my state of health incurs on me with regard to mouthpieces. In stead this article will reflect some of the, in my opinion, interesting things that have been discussed on the Trumpet Herald forum concerning mouthpiece backbore sizes. In the following I assume that the reader is familiar with the nomenclature of the mouthpiece.
During my "mouthpiece safari" I started thinking about the backbore of the trumpet mouthpiece. Since mouthpieces are available with different sizes backbore (I define size as internal volume and shape, not the length or width of the shank), what size might be appropriate? Is this strictly a question of personal taste? Is there a relation to the player's ability? Is there a relation to the instrument being played? Some searches of the Trumpet Herald forum brought up quite a lot of interesting material (you would be surprised at the wealth of information available on the Trumpet Herald forum; so many topics have been previously discussed there). What I have learned is that the internal shape of the backbore has a significant impact on the quality of the sound. "Straight" backbores apparently are "more focused" with "better projection" than internally curved backbores which give a "broader" sound. Also, internally smaller backbores are usually characterised as "commercial" while larger backbores are more often defined as "symphonic". It shouldn't surprise anyone that the smaller backbores are often described as "tight" with the larger ones being "open, free blowing". The variables of backbore shape and size make for a near infinite variety of backbores.
Several companies make two piece mouthpieces where the cup and the backbore screw appart. This allows for interchangeable backbores. Although I haven't tried these yet at the time of this writing (but hope to do so soon), these interchangeable backbores offer us the opportunity to use different backbores with the same cup. That way it becomes possible to choose the right backbore for the job at hand. As desribed above, this choice will be influenced by the type of sound that is desired. However, considering all of this the thought occured to me: Is or should the size of the backbore be affected by the design of the trumpet being played? Specifically, is a large bore trumpet better suited to one type of backbore and a small bore trumpet better suited to another? I posed this question on the Trumpet Herald forum, and the answer was a resounding YES! It is a question of balance of resistance. Most people will have a preferred level of resistance when they play the trumpet. The overall resistance when playing is a function of both the resistance of the trumpet and that of the mouthpiece. The amount of resistance added by the mouthpiece should be balanced against that of the trumpet to come out to the level preferred by the individual player. Generally this means that a larger bore trumpet will benefit from a mouthpiece with more resistance than a smaller bore trumpet. As far as I am aware the resistance of a mouthpiece is a combination of throat size and backbore size. In most two piece mouthpieces the size of the throat is a given, it can't be changed easily. That leaves the (interchangeable) backbore as the variable when it comes to resistance. Since smaller backbores offer more resistance and larger backbore less, it follows that the larger the bore of the trumpet the smaller the backbore should be and vice versa. The exact size of the backbore for a specific trumpet of course can't be determined, since this is dependant on personal preference and skill level.
How does this relate to Conn trumpets? Most modern trumpets have bore sizes ranging from 0.459" to around 0.470". Most Conn trumpets however have a bore size of 0.433". In comparison that is positively tiny! It should come as no surprise then that the average modern mouthpiece, being suited to the average modern trumpet might be somewhat on the small size for a small-ish bore trumpet such as a Conn. Even if that Conn happens to be a 38B Connstellation, generally described as being "free blowing" in spite of having a 0.433" bore. I have read more than one post on the Trumpet Herald forum stating that someone used a larger than average backbore for a 38B Connstellation and experienced improvement in the characteristics of the instrument. An example: "Last week a fellow trumpet player brought his fully restored Conn Connstellation '57 to band. Nice sound but a little stuffy for me since I was using a 0.464" bore trumpet. I switched backbores from a Warburton 7* to a 9* and as they say "to die for". What a trumpet! What a dark rich sound and easy blowing too! But I would have rejected it if I had played it with only a single mouthpiece that was set up for my larger bore trumpet."