Tunable Bell Trumpets

The Bell-Tuned Trumpet
by Dr. Colin Bloch

Editor’s note: This article was written in August 1978, initially published in The Brass Bulletin, and reprinted by the Schilke Company in connection with the promotion of the tunable bell trumpets being manufactured by the company. It was distributed at clinics and conferences.

Dr Colin Bloch is an Architect in Bristol, UK, where he plays in orchestras and as a recitalist. He has been playing Schilke since 1977 and latterly Monette. He can be emailed at cb6681@yahoo.co.uk.

The bell-tuned, or tuning-bell trumpet, is a relatively recent development in trumpet technology and design. It is the purpose of this article to demonstrate the efficiency of this innovation in improving overall intonation.

By bell-tuned trumpets, we mean those whose main intonational adjustment is made at the junction of the bell and the valve cluster, as opposed to the more conventional methods of using either a tuning slide, or a tuning shank fitted into the leadpipe.

The initial section of the trumpet tubing, from the mouthpipe to the valve cluster, is of critical importance in determining the intonational characteristics, timbre and response of the instrument. This represents a length of approximately 46 cm on the C trumpet, and it is important that it be smooth and uninterrupted along its entire length.

We normally find three interruptions along this section of tubing. Two occur at the sudden change in diameter caused by the tuning slide. The third is caused by the aperture to the waterkey.

The waterkey in itself is a relatively minor problem, and can be designed out either by using the cylindrical type ‘Amado’ waterkey; by using a studded waterkey with a nipple on the rubber which fits flush with the inside of the tubing when closed; or more simply by having no waterkey at all and emptying the instrument by inversion, as on the french horn.

It might appear that such a small change in the diameter of the inside tubing, as caused by the extension of the tuning slide, should have no noticeable effect. This is a fallacy. Intonational distortion is caused by the fact that various notes of the differing harmonic series tend to ‘focus’ at different points along the length of this critical section of tubing. The resultant effect can best be likened to the turbulence in a water pipe at any point where the diameter might change.

A series of test was carried out on a bell-tuned trumpet, which also has a tuning slide, to determine the efficiency of the bell-tuned system, as compared to the tuning-slide. The tuning slide is included on the instrument to facilitate cleaning and to allow the insertion of slides of another key. The first trumpets built with tuning-bells had no main tuning-slide.

The instrument used for the tests was C trumpet, with an XL bore, fitted with a beryllium bronze bell. (This lightweight bell has no significant effect on intonation its purpose being to improve response and projection. Tests have shown that over a given distance a drop in sound level of 5% was recorded, compared to 12% for a brass bell.)

In order to keep the tests as accurate as possible, various factors had to be kept constant for both the bell-tuned and the slide-tuned tests. These include:

  • the tuning standard (A = 442.5 Hz)
  • the test player
  • the mouthpiece (Schilke #20)

No adjustments were made to the three minor tuning slides, and they were all kept in throughout both test sequences.

It is important when examining the results of these tests to remember that it is essentially a comparative test, and that the two graphs do not necessarily indicate a tuning pattern for the instrument, as this to a large extent would depend on the player and his physical and musical characteristics. The essence of the results lies in the difference between the two graphs.

The range chosen was F-sharp to F-natural, encompassing some 36 notes. Each note was blown as a long note, then ‘bent’ up and down until the test player lost all precept of pitch. This note was then ‘centered’ until it was felt that the maximum number of overtones were being generated, and a reading was taken on an electronic tuner. This was done five times, over an extended period, for each test. The two graphs thus represent the result of some 360 readings.

Where alternate fingerings were available, those producing the most favorable results were used. The only deviations were that middle and top E-flat were fingered 2 and 3, and middle E open. (Some C trumpets require this note to be played on 1 and 2.) On the slide-tuned test, middle D was found to be better in tune on 1 and 3 than on 1.

The following facts derived from the test results, may be of interest:

  • On the slide-tuned trumpet the average deviation was 8.57 cents, compared to only 6.96 cents on the bell-tuned trumpet, representing a difference of 35.09 percent (there are 100 cents to the semi-tone).
  • On averaging out the whole range of the test with reference to the tuning standard, the slide-tuned trumpet was found to be .04 cents flat. The bell-tuned trumpet yielded the far more preferable figure of 0.03 cents sharp.
  • On the slide-tuned trumpet the usual tuning notes of A and B-flat were significantly out of tune, the A being 2.57 cents sharp, and the B-flat being 6.43 cents sharp. On the bell-tuned trumpet these notes were each less than 0.5 cents sharp.

It should in all fairness be mentioned that there are certain disadvantages attached to the bell-tuned trumpet:

  • There are of necessity no cross braces to the bell, making the instrument more susceptible to damage.
  • Quick tuning adjustments are difficult, as two screws have to be tightened and loosened.

It can thus be established that the tuning-bell system has the following range of advantages to offer over the conventional trumpet:

  • A significant decrease in intonational deviation over the whole range.
  • More accurate tuning notes ( A and B-flat) relative to the tuning standard.
  • Although not necessarily an advantage, the tuning-bell is more sensitive, requiring an extension of 17.6 mm on average, compared to 26.6 mm for the tuning slide.
  • The bell is detachable and can thus be alternated with bells of differing pitch, when using the corresponding tuning slides.
  • The bell can be used when attached only at the bell stud, so that it stands free and is not dampened by contact with either the rest of the instrument or the hands of the player.

It is hoped that this article has demonstrated some of the advantages associated with the tuning-bell system, and has also served to dispel any doubts which might exist as to its value.

The Schilke Loyalist