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Soon after I started tuning pianos, I started hearing about open unison tuning techniques. I was intrigued because it sounded like an advanced technique and I was interested in developing my tuning technique as much as possible. However, I could find nothing written on the subject at the time. I decided to learn how to do it on my own.

An open unison tuning technique is one where the tuner tunes all strings of the unison before moving on to the next note. The theory is that the unison must be tuned beatless for it to be used as a reference note for tuning future notes. Also, since the unison is tuned first and early in the sequence, there is more time to catch it, if it drifts.

Generally, tuning with a mute strip leaves most unisons until the end. Then if they are unstable, they will slip only after the tuner leaves, unless the tuner takes extra care to make sure they are stable.

One benefit of open unison tuning is that the tuner doesn’t have to make sure the unisons are stable, the technique demands that they must be beatless and stable, and if they slip, chances are, the tuner will catch it.

Single and Double String Open Unison Technique.

Single string open unison is when the tuner mutes two strings of a trichord, (or one string of a bichord), tunes the single string, adds a second string, and then tunes the third to make a beatless unison.

Double string open unison is when the tuner mutes only one string of a trichord, (with DSU you do not use a mute with bichords), and then tunes the double string unison (DSU) beatless, checks it to see which way it should move to be in tune, then detunes the DSU by moving one string in that direction, and follows with the second string to clean it up. The DSU is checked and moved this way until the tuner is happy with the result.

I can’t remember how I stumbled upon the DSU technique, perhaps I was intrigued by the challenge. I had heard of technicians tuning two strings at once and thought, “This is crazy. How is it possible?”. Anyway, I began to experiment with it and discovered how powerful a technique it is.

Once I started using DSU, I was amazed at how many benefits it had compared to the few benefits of single string open unison, In fact, there are so few benefits to single string unison, that it is no wonder to me why more people don’t use it.

DSU vs SSU

Double String Unison BenefitsOpen String Unison Benefits
1. You can produce better unisons; they need to be dead on, to be used to tune other SBI's.1. You can produce better unisons; they need to be dead on, to be used to tune other SBI's.
2. You do not have to open the grand lid to insert the mute strip.2. You do not have to open the grand lid to insert the mute strip.
3. Better stability. You can catch drifting unisons easier.3. Better stability. You can catch drifting unisons easier.
4. There is no need to mute the piano before starting.4. There is no need to mute the piano before starting.
5. There is no pitch drift caused by inserting and removing mute strip.5. There is no pitch drift caused by inserting and removing mute strip.
6. Less wear on dampers. No mutes in bichords means no damper wear due to mutes being put in and out.
7. More improved feedback on stability. You can hear more precisely how hammer force affects the pitch of the string by comparing with its neighbour, during the tuning stroke and after you remove the hammer. Pitch change is easier to hear in unisons than in other intervals.
8. There is no pitch change due to adding unisons. The Weinreich Effect, if there is any, has already happened.
9. Unison shimming (see explanation below) is accurate to within 0.3 cents.
10. With DSU, it is much easier to tune birdcage or overdamper pianos.
11. No mutes are needed to tune the bichords.
12. You can use mutes with handles on a grand. Handled mutes tend to fall over when inserted into the tiny space between strings of a single note on a grand, but there is much more room between the strings of adjacent notes, and the handled mutes can be inserted far under the strings and the mutes are held much more tightly by the strings and the soundboard.
13. You can use Beat Matching (see explanation below) which can be a very fast way to tune octaves and other SBI's.
14. You don't need to put the Papps mute under the hammers in the treble section. This means you can tune some spinets without removing the board over the keys, or even the lid on some.
15. You don't even need Papp's mutes. Rubber mutes with handles work in treble.
16. It is much easier, and faster, to insert a mute between two adjacent notes, than to try and insert a rubber wedge mute into the tiny space between the strings of one note.
17. Almost no mutes ever fall into the action. The grip is stronger on mutes between notes than mutes between strings of one note; It is too hard to get the rubber mute deep enough between some strings so that it doesn't fall out.

This is not an easy technique to use. Its one con is that it takes time to master, but the rewards are great. Also, you can not “see the snake in the grass” as one technician puts it, referring to hearing beat speeds while tuning intervals directly; with DSU, you do not listen directly to intervals and change their size in realtime. You have to use RBI tests to determine which way to adjust the pitch of the DSU.

Learning DSU means you will have to get good at tuning clean unisons fast, and who doesn’t mind having that skill? After learning to tune a whole piano using DSU, your tunings will be more stable, your unisons will be cleaner, and believe it or not, your tunings will be faster.

Search this site for seminars, classes, or videos that demonstrate this technique. Search for “dsu” or “double string unison”, or just leave a comment or contact me.

It has been my experience that sometimes, technicians do not understand what I am talking about when I explain DSU. I am not listening to a beating DSU with another interval note. That would be impossible! How could anyone tune an octave, for example, when one of the octave notes is a beating unison?

The DSU method requires a clean beatless DSU to be played with the other interval note (a beatless trichord for example), then a judgement is made, then the DSU is moved by changing one string a tiny bit, using beat matching or shimming (see explanations below), then the other DSU string is changed to recreate the beatless DSU.

At no time during the beat matching or shimming of the DSU, is the other interval played. The only time you will know if you moved the DSU the right amount, is after you recreate a beatless DSU, and play it with the other interval note, and use the RBI tests.

SBI tests are more challenging because the DSU and trichords must be absolutely beatless. Any roll in the unison could easily be misheard as an error in the SBI size you are playing. But, SBI are also a great way to find unisons that need to be improved. When you find a SBI that should sound beatless according to your tests, but the SBI does not sound beatless, most of the time it is because one of the unisons are not beatless.

Shimming Unisons

This is where the pitch of a unison is changed by a very small amount by moving one string of a DSU until the unison just changes color, then moving the other string to recreate the beatless unison. In this way it is possible to effect as little as a 0.3 cent change in pitch.

Beat Matching

This is where the pitch of a unison is changed by an amount that is very close to the amount needed to create a beatless SBI like an octave for example.

Consider an out of tune A3A4, and you are tuning A3, trying to make a 4:2 A3A4.

1. Play A3A4 and listen to the 4:2 partial (A5)
2. Make a mental note of the speed of the beat at A5.
3. Now, detune the A3 DSU so that the 4th partial (A5) of the DSU matches the speed you heard in step 2.
4. Move the other string of the DSU until the DSU is beatless again.

In this way, you measure how far away the 4:2 partial of A3 is from a pure 4:2 octave and move A3 exactly that much.

It is techniques like beat matching, and others, that make DSU the fastest and most accurate tuning technique I have ever used.

Listen to me tune A3A4 using DSU.

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