This is an edited version of a post I wrote to the Slidemeister list in 2006. Someone asked about a methodology for tuning, after having found that tuning reed by reed to a tuner produced less than ideal results.
Here is what I do for a professional tuning job for one of my customers, let's assume it's a 12 hole chromatic in C to be tuned in 12TET (standard equal temperament), although the basic process could be adapted to other harmonicas and tunings.
First of all - and this is a very important point which seems to be neglected in most of the writings on this topic - it is important to have the reedplates slightly warm. Not hot, but a little above body temperature, otherwise moisture from your breath will condense on the cold reeds and cause unpredictable pitch variation, making accurate tuning impossible
I usually do at least three passes per instrument. The first pass is to get it approximately in tune, not worrying too much about it being perfect. The second pass I aim for perfect. The third pass I check to make sure that things haven't drifted. If the instrument has to be substantially retuned, I may have to come back for additional passes, until everything is settled and holding its pitch. I like to leave at least a week in between each pass at the tuning, longer for drastic retunings. I should also add that I would be very distrustful of any technician that promises a fast turnaround (say, a couple of weeks or less). Chances are that they are not allowing any settling time for the tuning.
I usually do the first pass with the reedplate held firmly against the comb, but I don't usually bother with the covers, except with instruments where the covers have a substantial effect on pitch, such as the Hohner CX-12, the CBH, etc. The final check is done with the instrument fully assembled.
I like to tune somewhere quiet, but not silent. A radio or TV quietly in the background is nice, just providing there isn't any music. A talk show with no commercials is ideal. For some reason, I don't find birdsong to be distracting, so in nice weather I like to tune outdoors, providing the local dogs aren't barking, neighbours aren't using chainsaws, etc., etc. Electrical appliances are distracting, as they produce definite pitches that interfere with my ability to hold a pitch in my head and generally make the process more tiring than it needs to be. For that same reason (and others) I do not use rotary tools for tuning, or software-based tuners that require me to have a computer running as I work.
I take care of reed and valve adjustment as I tune, as adjusting reeds can alter their pitch and tuning reeds can alter their adjustment. As with the tuning, I get the reeds approximately adjusted (usually just by sight) on the first pass, then refine it on later passes. I don't use a provino or tuning table (a device that is used in harmonica factories, as well as by accordion technicians, which consists of a support for the reedplate, plus a blower or bellows to supply them directly with air). Although it makes the job quicker, you can never do as accurate a job as you can by tuning the harp whilst playing it normally. Tuning whilst playing it normally also offers other advantages, which I will mention later.
Of course, the usual good workshop advice applies here - make sure your chair and bench are at an appropriate height. Make sure you have good lighting and a comfortable working temperature. Do not work on a harmonica whilst tired, drunk, under the influence of antihistamines or after having imbibed too much coffee. Minimise distractions as much as you can - take the phone off the hook, banish family members from your work space, etc. Brush and floss before you start work, or at least rinse out your mouth.
The actual sequence I use for tuning may sometimes vary slightly, but usually runs something like this:
I tune the C in hole 5 to my tuner (usually set between A=442 and A=445, depending on the customer's playing style). I use an embouchure that I've developed over several years to give consistent results, by aiming for a particular overtone as I play. (This is much easier to demonstrate in person that it is to explain in text.)
I then play holes 3 and 5 together, blocking out hole 4 (being very careful to play with as open a mouth shape as possible to avoid accidentally bending either note). I then tune the G reed in hole 3 to form a pure beatless (not Beatles) interval with the C in hole 5. OK - this gives a pure fourth (Justly Intonated) rather than a tempered fourth, but it is more or less indistinguishable from the tempered version during single note play and most good players will unconsciously bend it to where it needs to be for a particular context. A pure fourth is much easier to tune and gives stronger chords. Learning to hear the beating takes a little bit of practice, but soon you will be able to hear it - and if you really work at it, eventually your ears will develop to the point that the whole world sounds out of tune and it drives you totally insane...
... however, I digress.
For more about the phenomenon of beating, plus some audio examples, please see (and hear) this page:
It is impossible to tune an interval so that it is perfectly in tune at every possible pressure level and under different attacks, so I aim for it being beat-free with medium breath pressure (my definition of "medium" varying according to the playing style of the customer for whom I am setting up the harmonica, of course). This usually results in the lower reeds being a little sharper when checked individually against a tuner with medium playing pressure.
As lower pitched reeds usually flatten more with increasing pressure than higher pitched reeds, you can tell which reed needs to be tuned by varying the playing pressure - another advantage of sounding the reeds by mouth instead of using a tuning table. If you play the G-C interval and the beating between the two tones increases as you increase the playing pressure, then either the upper note is sharp (which it shouldn't be if you tuned it properly against your tuner) or the lower reed is flat. Conversely, if the beating slows down as you increase the pressure, but speeds up again as you reduce the pressure, then either the upper note is flat or the lower note is sharp. After a while, this become instinctive. Then every now and again, particularly in the higher octave of the harp, you get the odd reed that behaves in the opposite manner, but that is thankfully not too common.
After getting holes 3 and 5 suitably tuned, I work on the C in hole 4. It should make a perfect unison with the C in hole 5 (ie, it should NOT sound like a tremolo harp!) and a perfect fourth with the G in hole 3. Playing holes 3, 4 and 5 blow all together should make a very bright sounding chord (I know, I know - it's not really a chord, strictly speaking) with no audible beating.
I then tune the C in hole 1 so that it makes a perfectly pure interval with the G in hole 3. Again, this usually means that the C in hole 1 needs to be a little sharp according to the tuner. Just how sharp depends on how hard you play and how you want it to react under different attacks. I then double check this to make sure it makes a perfectly clean octave with the C in hole 4 and the C in hole 5.
I then tune the C in hole 9 using my tuner and check that it makes a perfectly smooth octave with the C in hole 5 and the C in hole 4.
Next I tune the G in hole 7 so that it produces a perfectly pure fourth with the C in hole 9 and a pure fifth with the C in hole 5. I then check to make sure it makes a perfect octave with the G in hole 3, testing it at various pressure levels and with different attacks, etc. I then tune the C in hole 8 to make a perfect unison with the C in hole 9, checking that it makes a perfect octave with the C in hole 4, a perfect octave with the C in hole 5, a perfect fourth with the G in hole 7, then finally testing the G-C-C chord (yes - I know this is not a chord, strictly speaking).
At this point I usually tune the E in hole 6 against the tuner, then tune the E in hole 2 so that it makes a perfect octave with the E in hole 6.
I then tune the C in hole 12. This can be a tricky beast - if the reedplate has cooled by this point, it's best to make sure it is nicely warm before tuning this one. I tune it to the tuner, then check that it makes a good octave with the C in hole 9 and the C in hole 8.
I then tune the G in hole 11 so that it makes a perfect fourth with the C in hole 12 and a perfect fifth with the C in hole 9 and the C in hole 8, then a perfect octave with the G in hole 7.
Finally, I tune the E in hole 10 against the tuner, then check that it makes a perfect octave with the E in hole 6, tweaking as needed.
The harp is now 25% complete.
I use a similar process with the draw notes. First, I usually tune the D in hole 5 against the tuner.
I then tune the A in hole 3 so that it forms a perfect fourth with the D in hole 5 (again, likely to be a little sharp when played by itself against the tuner). I then tune the D in hole 1 so that it forms a perfect fifth with the A in hole 3, then check that it forms a good octave with the D in hole 5 (the low D usually needs to be quite a bit sharp to sound good like this).
Next I tune the D in hole 9 against the tuner, then check that it makes a good octave with the D in hole 5.
I then tune the A in hole 7 so that it makes a perfect fourth with the D in hole 9 and a perfect fifth with the D in hole 5. I then check that it makes a good octave with the A in hole 3.
Next, I tune the A in hole 11 so that it is about 2 cents sharp according to the tuner and check that it forms a perfect fifth with the D in hole 9.
I then go back and tune the F in hole 6 against the tuner. Next I tune the F in hole 2 so that it makes a pure octave with the F in hole 6. Then I tune the F in hole 10 so against the tuner so that it makes pure octave with the F in hole 6. Sometimes,however, I will tune the F notes by ear so that when they are played in combination with a D note, the difference tune produced is one of a low A. That gives an F that is melodically indistinguishable from an equally tempered F, but helps form stronger chord structures. However, that skill can take a while to develop. For more on difference tones, refer to this page:
I then tune the B in hole 8 against the tuner, then tune the B in hole 4 so that it makes a good octave with the B in hole 8. Finally, I tune the B in hole 12 against a tuner and check that it makes a good octave with the B in hole 8.
The instrument is now 50% tuned. As you have probably guessed, it is then simply a matter of repeating the process with the sharp notes.
The process sounds very long and involved, but it really takes longer to describe it than it does to do it. Usually the later passes are simple a matter of small corrective tunings that take a fraction of the time it takes to do the first pass. After tuning, it's not a bad idea to remove any debris from the tuning process. I like to clean the reedplates using an ultrasonic cleaner, but you could probably blow away any fine particles using one of those puffer bulbs that camera folk use.
This may seem like overkill, but the final result is (or should be, if you do it correctly) an instrument that sounds vastly superior to any factory-tuned harmonica and much better than you could ever do by simply tuning each reed individually using a tuner. Of course, I wouldn't even consider doing this work for ten dollars, unless you had some particularly good blackmail material on me...
One huge advantage of doing the tuning this way is that if often allows you to spot a fatally fatigued reed some time before it would otherwise become noticeable. As I mentioned above, reeds tend to flatten slightly under increased pressure, however tiny discontinuities in the material of the reed, such as stress fractures and the like, will tend to make this pressure/pitch response somewhat unpredictable. Most notably, reducing the pressure to the minimum amount needed to sound a reed will tend to make a flawed reed play much sharper than it would if you were to do the same thing with a healthy reed. If when tuning a pair of reeds to a perfect interval such as a fourth, fifth or octave, you hear that the beating between them is almost gone at a medium pressure, but speeds up a great deal when you back the pressure down to a whisper, then chances are that one of the reeds is already on the way out. Sometimes gently lifting the tip of the reed will reveal the physical flaw as a sudden change in an otherwise smooth curvature from root to tip. There are a few times when you will get a similar effect with a healthy reed, particularly in the upper range of a CBH, or in the upper range of short slot reedplates on a long slot comb - this is due to the frequency pulling effect of a large chamber on small high pitched reeds. This is an area where you can learn much more by experience than you can by reading a web page on the topic.
So there you go - that's what I do for a living. Amongst other things, of course. I should perhaps stress that what I describe above is simply how I approach a professional tuning job for a paying customer. I am not suggesting that this is the only way to do it, nor that it is the best way for every circumstance. However, I do consider some of the things I describe to be important - warming the reedplates gently before tuning, letting the reeds settle after tuning, etc. - and I do feel that there is considerable advantage to be gained from tuning whilst listening to how the reeds interact, rather than whilst simply watching a meter on a tuner and with practice, the method I describe does not take that much longer.
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