So what’s the solution to our tuning problem introduced in my last blog post? On the one hand, if we tune the five lowest partials in all the bells to perfect equal temperament tuning, we will avoid beats (an unpleasant effect resulting from tones very close together in frequency sounding simultaneously) when different bells ring together, but the upper bells will still sound flat compared to the other bells. On the other hand, we can tune the partials so that the strike notes of all the bells will sound in tune with one another. This is what John Taylor & Co. Bell Foundry did with St. Paul’s peal. It’s called stretch tuning, and it was commonly used by English bell founders until the early 20th century, and the Taylor Bell Foundry even brought back the tuning system in the 1950s and 60s.
Stretch tuning means that the bell founder sharpens, or raises, the nominal partial, or the fifth partial, in the upper bells. By doing this, the strike note is also raised, which then aligns it to be in tune with the strike notes of the other larger bells. The strike notes of the peal are now in tune. So what’s the downside? The drawback is that the sharpened nominals in the upper bells will clash with the tuned partials and strike notes in the other bells. One can detect a little bit of dissonance when hearing the bells ring together. To the ears of the bell founders, this scenario was preferable to peals that could sound flat and dull.
In St. Paul’s peal the strike tones of the bells form a nice scalar series and they sound bright. Compare St. Paul’s peal with stretch tuning to the Llandaff peal precisely tuned to equal temperament, no stretching. The Llandaff peal sounds more mellow, gentle. This is a good lesson that technically perfectly tuned bells are not necessarily better.