Free Plate Tuning by Alan Carruth

[John Link]

Shot and edited by Michael Collins.

Technically this is a video, but I will consider it as a multimedia book as I post it here. If Ken does not disagree it might stay.

Watchability
This DVD is 3 hours and 34 minutes long. I watched it non-stop from beginning to end, even though I had no intention of doing so when I queued it up. I have never done that with any other instructional video in my life. Alan Carruth is warm, very informative, completely open, and not in the least bit dogmatic. The subject was completely new to me as well. There are 24 clearly defined chapters that flow effortlessly from one to the next.

Audience
This DVD should be of interest to two groups of guitar makers.
1. Those who adjust tops to yield better sound.
2. Those with an interest in adjusting tops but have given up because they know of no metric that is repeatable from top to top, especially those who consider tap tuning to be either outside their abilities or simply voodoo that has little or no credibility.

Thus, many of us are potentially interested.

DVD versus printed book
This had to be done as a video. A book could supplement it, but after I watched and listened, there was no doubt the fundamental knowledge required real time for a fair presentation. The section on how to use the equipment absolutely required video.

Chlandi patterns can be helpful
I certainly had my doubts before watching. Now I am convinced they are useful. However, like everything else, they are not silver bullets. Alan focuses on one main “mode” (or pattern), the “ring and a half”. His goal is to adjust the bracing until the Chlandi result forms a closed “ring” in the top’s lower bout and an "open half" in the upper bout when it is excited at a frequency of 250-265 hertz for 6-strings and 25% higher for 12-strings (around 315-325). He has found that guitars with tops that demonstrate this characteristic are the ones most often found in guitars preferred by humans. That is the only reason he offers to support this metric, yet there is a lot of other evidence as the DVD progresses that supports his choice.

Chlandi patterns are his method for dealing with the extreme variability in the stiffness of commonly used top wood. Within a given species, he asserts there is 40% variance with the grain and 100% across the grain stiffness from sample to sample. He notes that it would be impossible to design a good automobile if steel demonstrated such variance, yet luthiers must deal with this problem as an ongoing condition of making anything. Someone viewing the video might ultimately choose different frequencies, or a different pattern, but the virtue of the Chlandi approach is that it sums up all the variables and should, if nothing else, provide a measure of consistency from instrument to instrument.

He also advocates seeking a single “ring” mode pattern that is not closed. This pattern occurs at a different frequency than the "ring and a half". This will usually take care of itself as one achieves the closed “ring and a half” but he shows how to test for both modes and what both look like as they form in real time, as opposed to a photograph that displays only the final result. Just as importantly, he demonstrates the brace carving process that moves the patterns into conformity.

Alan deliberately demonstrates on tops that present formidable challenges. I found that particularly instructive. One particularly nasty one had runout on the bark side of each piece, but not much on the heart side. It is one thing to say a lot of trial and error is involved, quite another to watch exactly how that plays out. Another top uses wood he says is too stiff across the grain for the sized guitar he was intending to use it on. Before watching that segment I might have said there was no such thing as too stiff across the grain.

Because the resolution he seeks is a symmetric form, he usually uses a double X bracing pattern, though one top uses the more common configuration of tone bars. He makes the point that there is no treble or bass side as far as where sound is formed goes. His point is to make the top as a whole work for producing pleasing sound. He asserts bass is produced by many parts moving in unison, while treble originates from anywhere it originates.

In short, the repeatability of his method is very attractive. It involves a lot of trial and error, but in the end it offers a concrete, identifiable goal for adjusting tops. It looks like a significant aid in achieving a consistent sound, if that is your desire, and for adjusting sound from one instrument to the next, if that is your wish.

One serious question
I did not understand his assertion that backs always detract from the power of the instrument’s response. My experience is that damping the back lessens response, letting it move freely augments. He did not attempt to demonstrate his assertion. I wonder if I understood it.

Five things I wish he had considered more
1. When he found a top to be too stiff cross grain I wondered why he addressed that only by removing brace material. Why not thin the top at the edges as well?
2. He explained well the negative effects of standard sound hole placement but did not consider moving it out of the way with respect to preventing the bridge from torquing towards the back.
3. He said he generally did not like the effect of scallops, yet all his tops had them to some extent. I wish he had done a top that did not have them at all. Inevitably, when he removes brace material, he hits the scallop points first.
4. He considered "Q", or the efficiency of a given piece of wood in translating input energy into motion, just indirectly. This is where he talks about preferring "low loss" tops over "high loss". He does offer a specific method that helps identify this characteristic, though.
5. Ladder bracing.

I thought about these things because he is so good at executing his method that I wanted him to extend it further, not really as a critique. When someone is good, I always want more.

Takeaway even if you never consciously “tune” tops
1. Bracing from the bridge south is the primary candidate for making lighter. This area is least critical for maintaining strength against the pull of the strings and maximally involved in pumping air. You can get very light here if you dare.
2. Never lighten bracing from the soundhole north, as this area does not move air and failure here is catastrophic. Nor is it often helpful to reduce bracing from the top of the soundhole to the front of the bridge. The soundhole introduces a significant weakness in the support system for the bridge.
3. The double X configuration is useful for making balanced tops. The bottom X should be much lighter and is not coupled to the main X.
4. The lap joints of both Xes should be topped with a long, but low strip above the joint. The length of the strip is more important for achieving stability than its height.

I also admired his wood rosettes a lot.

[dave d]

That's a very comprehensive and helpful review John, thanks for posting it.

[Dave Bagwill]

Yes, thank for the review John. I was going to write one but just don't have the patience to do it.

His set-up is certainly simple enough - I have a software-based and free, tone generator that puts out a clean sine wave (Audacity) and a small power amp, and I'm going to pick up a 6" speaker hopefully this weekend.

As you said, this method is not the be-all and end-all; but it does give more INFORMATION. Still up to us to interpret it.
I think the point is getting more consistency; but I have to rely on those who have made a lot of guitars, using this method, for databases that I don't have enough years to build up on my own.

Taking very good records of each build is a habit I need to get into.

Anyway, it will be fun, right? Can it hurt to try?? As long as someone does not make sweeping assertions about their methods - and Carruth is careful not to do that - why not experiment?

[John Link]

Yes to Dave Bagwill's statement that it all information gathered must be correlated to experience, experience that needs to be recorded to be really useful. I have no doubt when Alan says the patterns he seeks at the frequencies he wants to see them have a good track record with humans who relish the sound of a good guitar. Likewise, experience and records are the only things that will establish whether consistently achieving a certain patter results in a consistent sound. In my first look, it looks very promising.

So Dave, you seem to be saying there are databases gathered by those who use this method. Where does one access them?

[Dave Bagwill]

John, I've seen some on the 'net while cruising cyberspace, and did not mark them for a return visit as I did not think I would be using the method. I will do some digging around and see if I can find them again.
I do remember a couple of them were posted by university students doing research.

[Tim Benware]

It would be interesting to get the top where you like it and see how close it comes to the "ring and a half" before you've done anything but used you ear to tune it.