Rerurn to Romy the Cat's Site
In the Forum: Horn-Loaded Speakers
In the Thread: The Ridiculous Japa-Brazilian horn.
Post Subject: Ringability, chewing gum, & Japanese swordsPosted by jessie.dazzle on: 3/3/2007
I see some posts predicting that the use of bronze for the Mid-Range horns (see photos above) would result in ringing... Well, I respectfully beg to differ; I think this is one area where the designer may have done well... Too bad he polished them.
While not a horn expert, I do have a lot of experience working with metals.
It is not correct to assume that because bells are made of bronze, anything made of bronze will ring.
All materials have a sonic character, which reveals itself differently according to the form the material is given (yes I know the form of these horns approximate that of a bell, but read on), and of course the nature of the forces to which it is subjected.
"Ringability" resulting from a sharp blow (as is the case with bells) is one thing... The ultimate in that sort of "ringability" can be found by lightly tapping a wrench on a high-quality forged steel anvil sitting on concrete; a good one will rival a musician's triangle. The grain imparted to steel by the forging process reinforces propagation of the resonance. (Remember this next time you shop for a vice... or a Katana).
To get good ringing, you need stiffness. Steel, glass, the wood used in xylophones ; it will all ring if the conditions are correct when the material is struck.
Does this mean we should make our horns from chewing gum?
No. The kind of ringing we might encounter with horns is not the result of sharp impact ; It is a resonance born of sound pressure.
You can yell at the anvil or the triangle all day long, and neither will resonate with your voice. However, yell loudly enough at a big gong and it will resonate audibly.
Resonance is directly related to mass for a given area, or in the case of a horn or bell, a "Radius-to-Wall Thickness Ratio". This resonance is driven upwards (in frequency) by the addition of mass to a given surface area... (this is why you don't see anvils hanging in bell towers). Resonances in a horn can be effectively negated by mass (in theory, driven up out of the audible range).
More area with less mass = More resonance, so the material is allowed to express itself in combination with the form, and deliver whatever accent the combination might yield. (A brass trumpet or a bronze French horn are good examples...BTW, the only place they are called "French" horns is in the US and some times in the UK... The remainder of the world simply calls them... "horns").
Less area with more mass = Less resonance (higher frequency really), so the material is not "allowed to express itself", and the form is nothing more than a series of reference points which conspire to shape the results. (A lead, gold, or bronze ingot is a good example).
The MF horns in the photo appear massive for their internal area, and therefore have a ratio more akin to an anvil than a bell. And like the anvil, you could yell at them all day, and they would not resonate with your voice. But unlike the anvil, due to the structure of bronze and the mass involved here, tapping them with a wrench would likely result in... a tapping sound. Make them from forged steel, tap them, and they would ring nicely. For audio, at this sort area to mass ratio, they could be made of just about anything... Surface finish would probably have more influence. I have been conducting some experiments (excrements I mean) with Upper MF horns which confirm this.
The mass to area ratio of the anvil means the pitch is high. I would like to hear a church bell that would still have the form of the bell (to achieve a lower, directional pitch), but be made from forged steel!
By the way : Bronze became the preferred material for construction of bells because it can be cast thinly and still resist shock (as compared to iron for example, which is brittle and involves more difficult-to-maintain casting conditions; mainly temperature), and of course bronze does not oxidize.
jd*Rerurn to Romy the Cat's Site