Actual Sounding Length of tubing
Jul 24th, 2015
I am experimenting with making bugles from 5/8" ID lengths of old water hose and have figured out there's something I must not know about the sounding lengths of tubes.
I stuffed a TB m.p. into one end of a 9' length of hose and a large kitchen funnel on the other end and expected to get a Bb. Instead, I got an Ab. After shortening the hose by 6", making it just 8'6" long, I got an A.
Does the tubing length begin at the throat of the mouthpiece and extend to the throat of the funnel "bell," or to the end of the bell flare?
Another question: A-C#-E are well in tune, but when I try to get the A below ("fundamental?"), I get a low F (?)
Using an alto-horn m.p., btw.
Reply #1 - Jul 24th, 2015
Good questions.
My impressions are:
1) the flared end of a brass wind instrument does alter the pitch. And I would suppose that a funnel shape would impact on it differently than would one that is flared.
2) the cylindrical nature of a garden hose would impact on several things including tone, pitch, harmonics, and stability of the note produced.
3) I suspect that the mouthpiece will impact on range, as well as harmonics, but maybe less so than the remainder of the length of tubing and bell.
Reply #2 - Jul 25th, 2015
Here are the actual notes I can get on this floppy horn, starting below the bass-clef staff:
Eb (below bass staff), Ab, A, C, C#, Eb, E, Ab, middle C, F
If I blow gently, I get A-C#-E -- the Ab!
If I blow harder, I get very low Eb, Ab, C, Eb, Ab, C, F.
As for the bell -- the bells on a lot of old bugles and trombones were funnel-shaped (no flare), yet those horns worked right. The funnel on this contraption is rather cup-shaped, about 4.5" D. And the hose is about 8.5' long.
How are these notes possible? Yes, I'm using a piano! How can I tell how much hose to amputate to get it to play like a bass bugle in Bb??
Reply #3 - Jul 26th, 2015
I think the Blow harder is getting it closer to where it should be. And, you haven't gotten to the fundamental yet. If you cut off the fundamentals you get F, Bb, D, F, Bb, C, D on say a trombone. Count up one step from what you are getting and it is Eb= F, Ab = Bb, C = D, Eb = F, Ab = Bb, (skip), C = D
So, I'm thinking you still have an Ab horn.
Reply #4 - Jul 27th, 2015
Thanks -- glad somebody understands these things!
Reply #5 - Jul 27th, 2015
With the very cylindric bore, a garden hose resembles a French horn. Most French horns are not able to play their own key note, which they are actually not intended to do.
That may confuse things because you may be an octave or a quarter (or more) out of tone compared to where you think you are on the tone scale.
I have some calculus on this site:
http://musikmuseum.dk/1SVING.HTM">http://musikmuseum.dk/1SVING.HTM
The formulas given are the theoretical aspect. In practical experience, a brass wind instrument works as if the total tube length is actually a little longer than can be measured.
Measuring on the bell end is also not easy. On trombones and Sousaphones, the outer part of the bell is merely decorative. Cut it off, and the thing still plays in same tune...(but looks weird)
Reply #6 - Jul 27th, 2015
What you said about bell length agrees with my experiments, but do you know a way to predict how much/what percentage (or where the shape) of the bell "doesn't count" towards overall tubing length? (Or do you just keep slicing small increments off the tube until the horn miraculously plays the pitch you want??)
I have a 1920 Holton alto horn that's similarly "weird": the low Eb is almost a D -- yet all the other notes are in tune for key of Eb! A repair person couldn't find any internal oddities and didn't know enough about acoustics to be able to tell me why an Eb instrument is unable to play its own fundamental. Sort of like my hose "bugle" in "sort of" A/Ab!
Would appreciate some help before I waste more deceased water hose on unplayable "bugles!"
Reply #7 - Jul 27th, 2015
Bell shapes do vary, and there is (to my knowledge) no formula to calculate exactly where on the bell the borderline between "decorative" and "functional" goes, or how much extra air column needs to be added on the actual tube length.
I have made instruments/franken horns or playing replicas of historic instruments, and yes, the last adjustment of the tube length is cut and try. I know the approximate length a given tuning requires, and what shape lead pipe, bell etc. I want. But the tuning slide is usually placed on a quite cylindrical part of the bore. So instead of the tuning slide, I use some piece of garden hose, that is adjusted until it is in tune. With the now measurable length of used garden hose (minus the parts that go over the tube ends) I cannot make the tuning slide to match.
It may sound unprofessional, but there is a variety of bells, from the almost Zink-shaped to Sousaphone shaped, not to mention the special bells, like a whisper. Try to calculate that thing! I made a replacement for a lost whisper bell on a cornet with two bells and was surprised how much different in length (longer) the whisper unit had to be compared to the normal bell, measured from the switch-valve.
A tuning slide should always be pulled a little out for the instrument to be in tune.
In my view there is no use having a lot of slide movement to give off, but nothing to take.
In my experience, instruments being a little off on the lower tones often suffer of being untight somewhere. That may be cracked tubes or ferrules, worn valves, broken cork in water key, damaged mouthpiece receiver (or mouthpiece shaft) just to mention some common reasons.
Reply #8 - Jul 27th, 2015
Do you think that the larger bells after they get past the point of altering the pitch, do they still have an amplification function or are they purely decorative?
Reply #9 - Jul 27th, 2015
It is my understanding that each low note breaks free kind of, from the bell at a different point. The curvature of the flair seems very critical to the tuning of the low notes. I would propose using a French horn bell and playing full range and gradually cutting off radius between playing to see how this affects what notes?
Reply #10 - Jul 29th, 2015
This bell info. is very helpful. I suspected there was something acoustically "murky" involved with getting the bell + tubing + m.p. just right for a desired pitch. The Eb alto bugle I'm now working on changed both its pitch and its timbre when I substituted a cup-shaped funnel for a funnel-shaped funnel of the same length. Both changed again when I changed out a m.p. with a very small throat for one with a larger one. (???)
A related mystery for your "calculating" mind:
I used to have a Blessing 100 marching mellophone in F that was dreadfully flat in its second octave. Willing to try anything to get it to play in better tune, I impulsively amputated the non-flared conical bell of a cheap bugle and stuffed it into the mello's bell. (The secondary bell ended where the real bell began its extreme distal flare).
I don't understand how/why -- but the Blessing suddenly played its second octave a full octave about the low one! (Maybe I should put a bug in Blessing's ear about this!)
Thanks for everyone's help. I'm off to the chopping block!
Reply #11 - Aug 2nd, 2015
I have a Bb Alphorn made in Austria. While Conical in bore, its length should be about 9' or 108". The manufacturer says 275CM is fully assembled.
The bell piece measures 59-1/8", the other piece measures 46-3/8", the mouthpiece protrudes 2-1/2". The total is 108" The joint that allows for tuning is 2."
That gives one an idea of the variation in length that allows for tuning based on player, mpc and environmental conditions, like temperature or altitude, etc.
The scale I can achieve is similar to the open tones of a Euphonium, Bb, F, Bb, D, F, G, Ab, Bb, C, D