sum tones and piano wire

>>The stuff I hear is much higher in pitch than the notes sounding, so it
>>couldn't be difference tones. Maybe I'm listening to partials.
>
>Well, two piano strings that are supposed to be in unison should have the
>same inharmonic partials.

Oh yeah?

>Is the phenomenon different with two strings than with one string?

Only happens with two strings.

>If so, you probably have a defective string and/or piano that's causing
>different degrees of inharmonicity on the two strings.

I've tuned a Baldwin acrosonic, a Lester baby grand, a Chase half-plate
upright (restored), and a Wurlitzer console piano with the help of these
mysterious tones. Not exactly a collection of fine instruments, I'll grant
you...

Remember I said sometimes they don't stop beating together. About half of
the time, and most of the time they are _very_ close. Just not close
enough, for someone as picky about unisons as I; the best tuning always
comes from zero-beating the fundamental. It's just harder to listen to,
for me at least.

>Then of course the partials will beat when the fundamentals don't, and vice
>versa. The people on the pianotech list can probably tell you more about
>what kind of pianos are particularly prone to unpredictable inharmonicity,
>but this is a well-known phenomenon (even in a few Steinways) and is quite
>mysterious theoretically.

Why should all strings have the same inhamonicity? The structure of the
metal changes with age and tension. The manufacturing process can't be
perfect- make them all of the same uniform thickness...

-C.

As I recall, Scientific American had quite a good article on this some years ago. Check it out through the Readers' Guide to Periodical Literature. Again, from recollection, the problem with piano wire is that it doesn't vibrate according to the theoretical physics ideal because of its stiffness. The lower tones use wrapped wire which is even further from ideal. And the lowest tones have very weak fundamentals, so what one hears as a fundamental is mainly psychoacoustic; the brain generates some of the fundamental through the harmonics. Besides that, if the piano is tuned in equal temperament, the harmonics are neither that nor quite just intonation either. Also note that pianos of about a century or more old were originally strung with a softer wire at lower tension which gives a softer sound (less harmonics) than the modern high tension stronger wire which gives a more brilliant tone. If one of these old pianos is restrung with modern wire, it's likely to cause structural damage.

>>> Carl Lumma <clumma@nni.com> 09/22 9:52 PM >>>
From: Carl Lumma <clumma@nni.com>

>>The stuff I hear is much higher in pitch than the notes sounding, so it
>>couldn't be difference tones. Maybe I'm listening to partials.
>
>Well, two piano strings that are supposed to be in unison should have the
>same inharmonic partials.

Oh yeah?

>Is the phenomenon different with two strings than with one string?

Only happens with two strings.

>If so, you probably have a defective string and/or piano that's causing
>different degrees of inharmonicity on the two strings.

I've tuned a Baldwin acrosonic, a Lester baby grand, a Chase half-plate
upright (restored), and a Wurlitzer console piano with the help of these
mysterious tones. Not exactly a collection of fine instruments, I'll grant
you...

Remember I said sometimes they don't stop beating together. About half of
the time, and most of the time they are _very_ close. Just not close
enough, for someone as picky about unisons as I; the best tuning always
comes from zero-beating the fundamental. It's just harder to listen to,
for me at least.

>Then of course the partials will beat when the fundamentals don't, and vice
>versa. The people on the pianotech list can probably tell you more about
>what kind of pianos are particularly prone to unpredictable inharmonicity,
>but this is a well-known phenomenon (even in a few Steinways) and is quite
>mysterious theoretically.

Why should all strings have the same inhamonicity? The structure of the
metal changes with age and tension. The manufacturing process can't be
perfect- make them all of the same uniform thickness...

-C.

You do not need web access to participate. You may subscribe through
email. Send an empty email to one of these addresses:
tuning-subscribe@onelist.com - subscribe to the tuning list.
tuning-unsubscribe@onelist.com - unsubscribe from the tuning list.
tuning-digest@onelist.com - switch your subscription to digest mode.
tuning-normal@onelist.com - switch your subscription to normal mode.

John Sprague:

The inharmonicity you mention is well known and understood scientifically.
What I was talking about was instances where the inharmonicity is not what
is theoretically predicted -- in fact, it is sometimes negative!
You can also feel quite secure that Carl is familiar with the additional
problems of tuning equal temperament.

-Paul

A few words on this subject. As Paul Erlich writes, the idea of inharmonicity is well documented, and it is integral to the Electronic Tuning Devices now used by many piano technicians.

The design and manufacture of bass strings has improved greatly with computer scale design programs, and in my opinion contradicts the notion that they have very little fundamental (stand near a concert grand...); yes, they are not necessarily perfectly executed, and the core wires probably aren't uniform, but these are not enough to make them unmusical.

When rescaling pianos, it is often useful to enter data from the original stringing. many of these (now) 100 year old pianos have higher tension than modern practice prefers. My own research has shown that the issues of scale design were known at least empirically by 1850. The lower tension is not an issue of hard or soft wire, but one of string lengths, and changing to the same size of modern wire does not damage the piano structurally.

Returning to the subject of beating fundamentals, Acrosonics in particular often do not have uniform trichord unison speaking lengths. This is a cost saving measure, and the unisons suffer tremendously. The same effect has been seen as desirable. The two 9' pianos we have (1960's Baldwin, 1890's Kimball) both have bridges notched at slight angles in the middle tenor range. Steinway did this for a short period as well.

_Beating_ can be heard on single strings as well. Many pianos intentionally have unmuted end lengths - so-called "aliquots" - which often are untuned and uncontrolled. Another reason for beating single strings is improper termination at the string ends, either from damage or from poor work. Additionally, changes in bridge impedance, bass strings with loud longitudinal mode vibrations all can lessen the overall sound of a piano.

Clark

Very interesting, thank you. When I toured the Kimball factory in southern Indiana about ten years ago they had on display an old piano. I don't recall if it was 150 or 200 years old. But we had quite a discussion about the lower tensile strength steel they had to use to restring it to avoid damage. Apparently higher tensile strength steel had been developed later. It was easy to hear that it had a softer, less brilliant tone quality. The difference was ascribed mainly if not entirely to the strings. They also had a Bosendorfer, as the U. S. distributors, on which it was fun try those extra low tones. I'll look this up again if not too difficult to find, but clearly (perhaps mistakenly) recall that the low harmonics are stronger than the fundamental on the lowest piano tones. A twelve foot concert grand should have stronger bass fundamentals than a spinet.

>>> Clark <caccola@net1plus.com> 09/24 8:23 AM >>>
A few words on this subject. As Paul Erlich writes, the idea of inharmonicity is well documented, and it is integral to the Electronic Tuning Devices now used by many piano technicians.

The design and manufacture of bass strings has improved greatly with computer scale design programs, and in my opinion contradicts the notion that they have very little fundamental (stand near a concert grand...); yes, they are not necessarily perfectly executed, and the core wires probably aren't uniform, but these are not enough to make them unmusical.

When rescaling pianos, it is often useful to enter data from the original stringing. many of these (now) 100 year old pianos have higher tension than modern practice prefers. My own research has shown that the issues of scale design were known at least empirically by 1850. The lower tension is not an issue of hard or soft wire, but one of string lengths, and changing to the same size of modern wire does not damage the piano structurally.

Returning to the subject of beating fundamentals, Acrosonics in particular often do not have uniform trichord unison speaking lengths. This is a cost saving measure, and the unisons suffer tremendously. The same effect has been seen as desirable. The two 9' pianos we have (1960's Baldwin, 1890's Kimball) both have bridges notched at slight angles in the middle tenor range. Steinway did this for a short period as well.

_Beating_ can be heard on single strings as well. Many pianos intentionally have unmuted end lengths - so-called "aliquots" - which often are untuned and uncontrolled. Another reason for beating single strings is improper termination at the string ends, either from damage or from poor work. Additionally, changes in bridge impedance, bass strings with loud longitudinal mode vibrations all can lessen the overall sound of a piano.

Clark

John,

We have a local _authority_ on antique pianos who maintains quite a collection. He is very fond of telling us all about the practice of stringing with hard-drawn wire vs. soft-drawn wire, embellished mostly with mythological piano pseudoscience (and now he _restrings_ with quite as unauthentic stainless steel...).

You are right, the difference in sound between hard and soft wire, yellow and red brass wire, etc. is quite audible, but these pairs have approximately the same density, so I don't understand (no, I do) why they at Kimball would think they were avoiding damage by stringing with one instead of the other. The soft wire is still harder than the bearing pins, and I've seen where it has sheared the bridge pins right off.

I recall an article, perhaps in Scientific American, which featured microscopic photos of music wire, comparing antique and modern drawing technology in terms of sound and strength. Fractures in old wire were along the diameter of the wire where modern wire had them along its length.

Rosamond Harding's "The Piano-Forte" has a substantial appendix on the subject of historical piano strings. Malcolm Rose, who draws several types of low tensile wire, has compiled stringing data in "Historical Stringing Practices."

Perhaps what further confuses the issue of bass string fundamentals is their inharmonicity. The vogue of imparting high inharmonicity to their partials continues with scaling software, but within the boundaries of length to an extent this can be countered. The 12' piano simply has longer strings, and the harmonics are better related to the fundamental. Still there are a lot of bad bass strings.

Clark

They had tried modern wire and damaged the wooden pin block, which they then had to replace. I think that the old piano was something of a restoration job in any case. It looked as good as new, unless the guide carefully pointed out what had been done.
Ah, stainless steel. Reminds me of the early tape recorders used by the BBC, with thirty inch reels. I wasn't there, but have seen pictures. After the war, wire recorders had a brief popularity. I saw an old one sometime in the last ten years, but didn't buy it. As I recall, there was no rust on the wire, indicating that it might also have been stainless.

>>> Clark <caccola@net1plus.com> 09/24 10:13 AM >>>
John,

We have a local _authority_ on antique pianos who maintains quite a collection. He is very fond of telling us all about the practice of stringing with hard-drawn wire vs. soft-drawn wire, embellished mostly with mythological piano pseudoscience (and now he _restrings_ with quite as unauthentic stainless steel...).

You are right, the difference in sound between hard and soft wire, yellow and red brass wire, etc. is quite audible, but these pairs have approximately the same density, so I don't understand (no, I do) why they at Kimball would think they were avoiding damage by stringing with one instead of the other. The soft wire is still harder than the bearing pins, and I've seen where it has sheared the bridge pins right off.

I recall an article, perhaps in Scientific American, which featured microscopic photos of music wire, comparing antique and modern drawing technology in terms of sound and strength. Fractures in old wire were along the diameter of the wire where modern wire had them along its length.

Rosamond Harding's "The Piano-Forte" has a substantial appendix on the subject of historical piano strings. Malcolm Rose, who draws several types of low tensile wire, has compiled stringing data in "Historical Stringing Practices."

Perhaps what further confuses the issue of bass string fundamentals is their inharmonicity. The vogue of imparting high inharmonicity to their partials continues with scaling software, but within the boundaries of length to an extent this can be countered. The 12' piano simply has longer strings, and the harmonics are better related to the fundamental. Still there are a lot of bad bass strings.

Clark

>The inharmonicity you mention is well known and understood scientifically.
>What I was talking about was instances where the inharmonicity is not what
>is theoretically predicted -- in fact, it is sometimes negative!

Negative? I wrote...

>The structure of the metal changes with age and tension. The
manufacturing >process can't be perfect- make them all of the same uniform
thickness...

I don't know about the second suggestion, but surely the former one can
explain inharmonicity differences between strings. Strings get stiffer
with age, and can develope a condition known as "false beats", where a
single string beats against itself.

-C.