Node harmonics or "chimes"

General troubleshooting

Node harmonics or "chimes"

Postby Bob Lewis » Tue Oct 30, 2007 7:01 pm

Q. On two of my chromatic harps, when I play the top third of the strings in the F, Bflat, and Eflat chords and related 7ths and minors, I do not get a good tone.

Is there any way to remedy this situation short of not playing those chords?

I have harmonics on both my Orthey and Fladmark harps--more so on the Fladmark. Both are the basic models with 21 bars. Felts are 8 months old and siliconed on the Orthey, and three months on the Fladmark--but played very little. Both harps have fine tuners. The chord arrangement on both is

Cm Gm Dm Am Em Bm F#m
Eb Bb F C G D A
F7 C7 G7 D7 A7 E7 B7
(bass side)

A. There really is nothing to indicate that what you are experiencing is any more than normal for a 21 chord instrument.

The problem is caused by node harmonics. At 1/2, 1/3, 1/4, and half lengths of each of those a note can be sounded when the vibrating string is touched firmly by the felt. The 1/2 node is under the chord bars only on the top strings. The 1/3 node is the offender on both upper and lower strings. 1/4 and smaller fractions of the string length do not generally result in harmonics loud enough to be distracting. At the real problem positions, the note heard is not harmonic to the chord played so it results in a dissonant sound from the chord.

In summary, I don't think there is a complete <fix>. Compromises would be required. To give control of node harmonics complete priority while maintaining some versatility and use of a full chromatic scale, would require that the instrument be converted to 15-16 chords, leaving the worst problem area of the strings unused by chord bars.

Actually, it can be demonstrated that the autoharp can happily support no more than 10-11 chords without this harmonic problem becoming a distraction. This is only one of the reasons why diatonic 'harps are so pleasing, since that number of chords is generally sufficient for one or two keys.

Sometimes chords have to be relocated, breaking up the logical pattern of the chords, so that harmonics can be minimized. This is not a popular idea, but it gives priority to the sound. Most chord progressions are physically playable so it's just a matter of adapting and practice. I, like Alan Mager, suggest that a 7th chord can be used to mask an otherwise troublesome area on the strings. Some 21 chord chromatic configurations eliminate seldom-used keys and instead position 3 diminished seventh chords at the end of the chord bar arrangement on areas with busy harmonics.

On some designs 21 chords is too many. Some keys sound so unmusical that they never get used (nor some of the chromatic scale). Even on an 18 chord full chromatic, I have to position B7 in the center of the harp and play it with my thumb, since it is normally used when playing in keys from the other end of the chord bar set. When I first set it up, I was surprised at how easily I could play E major from one end and B7 at the other, just by using my thumb. I used that position for B7 because I didn't have anywhere else to put it and because Eb major sounded terrible there. I would rather have the key of E than Bb. Someone else might see it differently.

The second harmonic node (1/2 the vibrating length measured from the anchor end) is only under the chord bars on the higher strings. The small, angled-in run of bridge at the treble anchor end on the most sophisticated of the handmade designs serves to push the second harmonic node location further toward the tuning pin end and away from more of the chords. This works, provided that the tuning pin locations are backed away from the chords as well, effectively relocating the center of the high strings, while maintaining the overall vibrating length. Since the high strings, unlike the bass end, will mute easily near the anchor end, this works just fine without forcing the chord location to move.

Mark Fackeldey of Zephyr Hill Autoharps was essentially correct, in my opinion, when he implied that the problem is going to be there, get used to it. That may be true for chromatics with many chords, but I should note that the single key diatonic, with so few chord bars, can avoid all the second harmonics and most of the 3rd. That is the setup on most of Bryan Bowers' instruments. The two key can be a problem with some of the 3rd harmonics, but has a very clean sound as autoharps go. A little bit of maneuvering of lockbar and 7th locations usually solves the problem for a two or even three key diatonic.

One idea that has been tried by Steve Young and is fussy but works is use of a small cantilever; one per troublesome node, usually the 1/2 node. The cantilever is activated by the chord bar. The cantilever rocks and mutes the string from underneath about 1/2 inch away from the chord bar position. The chord bar has no need of felt in the position where cantilevers are employed. The cantilevers must be kept to a minimum because the most secure mounting is directly on the soundboard. That isn't necessarily as awful as it sounds. Most of them are near the edge of the frame. There are many other factors already impeding the sound anyway. There is a sound impact tradeoff for solutions to many problems.

Steve Young also employs what has been referred to as outrigger felts, most easily implemented on the last bar nearest the center of the instrument. At a position that is getting a lot of harmonic sound he attached another thickness of chord bar and felt, effectively doubling the width of the felt at that position. It works.

If you are acutely sensitized to this issue, I think you should take a look at Alan Mager's article in Autoharp Quarterly regarding 4-key, 21 chord, chromatic setups.

Another alternative is to have your harps changed to 15-18 chords instead of 21. My chromatic has 18 chords, for the very reason you mention. I am able to pretty well cover the keys of FCGDAE. Changing a few chords could make it BbFCGDA. Note however, that your Bb chord would be in exactly the same position and present the same problem in the layout that I use. The key of Eb would be dropped. The chord layout is as follows:

B7 F7 C7 G7 D7 E
Bb F C G D A
Gm Dm Am Em Bm F#m

Note that the B7 is played with the thumb for the key of E. This is easy to do and allows a 7th chord to be positioned in the worst area for node harmonics. I'm considering switching the positions of the Bb and F7 to get a cleaner sound on the Bb. This requires compromises in the neatness and uniformity of the chord layout, but that does not take priority over the sound produced, in my opinion. With a little practice I have adapted to chord layout changes on several occasions and am confident that anyone can make a switch, if they want to.
Bob Lewis
Site Admin
 
Posts: 259
Joined: Wed Jul 04, 2007 7:11 pm
Location: South Carolina

Return to My autoharp doesn't sound right

Who is online

Users browsing this forum: No registered users and 2 guests

cron