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So, I am working on this LMI parlor (Sitka Spruce top and Rosewood sides and back).

When I braced the top and back I tap tuned both as I scalloped the braces. I am using an app on my Android phone called Pitch Lab (tuner) to determine the frequency the top and back ring at. I stopped when the top was at A and the back was ringing at B flat. I have done other guitars that I have rebuilt using a half note difference between the top and back and it seems to work pretty well.

A couple of weeks ago I closed up the box and have been working on putting a binding channel cutter together so I set the box aside. The other day I picked it up and started tapping on it but now both the top and back ring at C sharp. I don't have the bridge on or the neck.

I am curious if this is due to the small size of the body since the 2 other guitars I tap tuned were my Gibson J40 (same size and the J45) and my LG-0. Both of those taped a half a note difference top and back. Both of them I only had the backs removed so I was taping the top with the sides on.

Just curious if anyone has knowledge or experience with tapping and if I need to shave some more off of my braces on the top or back. I don't want to end up with Wolf notes.

Any help would be much apreciated.

Thanks
Bob

For one, any pitch referencing you do on a free plate immediately goes out the window when it becomes attached to the rest of the system, let alone that you can get different pitches by holding/tapping different spots.

For two, any tap tones that you measure only are relevant once the guitar is strung up and the guitar becomes an operating system. Glueing the neck on won't change the pitches much, but glueing the bridge on definitely will, as will adding the mass of the pins/saddle, as will adding the tension of the strings.

For three, you're way better off finding an FFT app than a tuner, or at least pay attention more to the HZ than the note name. Which C? Which A?

For four, I've personally found a half step to be a little close, and that either a major third for larger guitars, and a minor third for smaller guitars between the top and back are what I shoot for.

For five, to avoid wolf tones, you should be pitching your resonances between notes, not on them.

For six, ignore all that and buy the gore/gilet books. All the questions you don't even know you're going to ask yet are answered therein....

Thanks for the reply, In no way do I claim to know much about tap tuning but everything I have read does seem to make sense.

I am not sure what you mean by and FFT app, I will make a guess it is a frequency analyzer? Pitch Lab does show the frequency in Hz. I just checked and the frequency of both the top and back are now at 131.5Hz.

In case anyone out there has an Android Phone you should get this tuner. It is free and it seems to be a great little tuner. Here is more info about it:

https://play.google.com/store/apps/details?id=com.symbolic.pitchlab&hl=en

It has a lot of options for tuning different instruments and scales.



Actually I said I tuned the top to A but I meant A flat and B flat for the back. I am not sure if that is what you mean by between notes. I read a couple of places something to that effect so that is why I tune to a flat. Maybe I misunderstood it?



I have a birthday coming up... I will ask my wife to get it for me. Maybe I am crazy but I enjoy reading stuff like this. I know it is a bit of a black art and some people think it is just crazy talk but I do think it has some merit. I also love reading about quantum physics too so it figures I would like something as obtuse as tap tunning.

Bob

It ain't no black art no more.

A flat and b flat are still notes on the scale. You need to try to get A flat and a quarter, though not necessarily those notes specifically.

Ok, so are your back and top plates glued to the sides?

FFT= Fast Fourier Transform, so yes, freq analysis.

You are most likely observing the air resonance at 130 hz. That would be way low for a top or back

Especially for a Parlour....

I guess you are correct since there is a lot of info out there about it. I guess what I meant was there are a lot of differing ideas about what is good and bad.

OK, I guess I have been misunderstanding the idea of not tuning on a note, I guess I was thinking in terms of Whole notes.

Yes my top and back are glued to the sides. That is why I was concerned because both of the other guitars had a different tap tone for the front and backs. This one they are the same at 131.5Hz. (a few cents off of C) I don't have the bridge on yet and it is ebony so that will change things I am sure.





This is probably the complete wrong way to check it but using my Snark tuner I get the same note... C# Checking it using Pitch lab I checked it holding the tuner about 1' away from the back and got the same 131Hz and C#. Same if I check it from the front or side.

Thinking about it 130 Hz it does seem low. So how should I be checking the tone (without spending hundreds of $$$).



Bob

Use Visual Analyser (free download; works on PC)

Set up instructions for guitar tapping here.

_________________
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Try going to the android store and searching for an FFT app. Some are free, some not.

.

Thanks much Trevor, I have a laptop setup with Win7 on it so I can check it out (I run Linux as my main OS) I am sure I will be totally confused but I am always up for a challenge of learning something new.



I will do that, I am also going to check in the Linux repository. I am guessing there will be something there (Almost all Linux software is Open Source so it is free).


Cheers,
Bob

Actually that isn't really true.

By tap tuning you are sampling how the guitar responds to vibration. Yes, after it is strung up it will not be the same but knowing what a specific wood sounds like before and after gives you a reference to build by. So each time you go through the process you gain a better knowledge of how it will sound after it is built.

To some it doesn't make any sense.. and that is fine. I don't know for sure but I have an open mind and am interested in learning about it.

Cheers,
Bob

i'm puzzled by why you would be going for between notes. i've only built 3 steel strings, on all 3 once the sides and binding are attached i tuned the top and the back to specific notes. i'm a very much a novice but am happy with the results, good definition, tone and sustain for days. is there somewhere you can point me to to read more about what you are talking about?

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It isn't un-really true, either.

Having tapped hundreds of guitars I find there is barely any difference in the tap response between strings at tension and strings not at tension. But strings (and saddles, and pins - don't forget the saddle and pins) have mass, which has its usual effect.

The reason? A guitar top is not like a string or a membrane (which both have resonant frequencies related to the tension on them) but is a plate, which has a resonant frequency related to its bending stiffness. The bending stiffness is only significantly changed if the string tension significantly changes the geometry of the plate, in which case you usually have things to worry about other than the guitar's resonant frequencies.

Yes.

The "sustain for days" is a bit of a give-away. If you want sustain rather than loudness, there's nothing wrong with that. But if you want loudness rather than sustain, you need a guitar with high vibrational sensitivity, which essentially means high average admittance, which is much the same as high monopole mobility (I measure vibrational sensitivity by measuring monopole mobility). [More about monopole mobility here].

The problem is that the higher the monopole mobility, the more likely you are to see wolf tones and frequency shifts which cause certain notes to play out of tune. And this is why you rarely see high monopole mobility guitars in shops, because most manufactures haven't figured out how to economically sort out the consequential problems. Part of the solution to sorting out these problems is by placing the major guitar resonances exactly between scale tones, for example, 50 cents from a G note. The fact that you've never run into these problems almost certainly means you haven't got a high monopole mobility guitar, which is fine if you prefer high sustain over high volume and means you can avoid a lot of complexity.

_________________
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Patch,

Yes, I could point you to the gore/gilet books.

In my laymans term explanation...

If you have a resonance that is on a scale tone, that note, when sounded, will be louder but shorter than other notes, ie a wolf tone. So your best bet is to make your guitars have their major resonances be as close to halfway between scale tones as you can, so that every note on the guitar is of fairly equal volume...

Fortunately this is doable.

Trevor, FWIW, in my own guitars I've noticed a fairly consistent 1.5-2hz increase with the strings tuned up, but now your post is making me wonder if I have 'other things' to worry about...

thank you both!

i am getting close to tuning the plates on my 4th and i'm going to read more on this and give it a go. i do have the gore/gilet books but my brain only takes in so much at a time.

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Has anyone used REW for your frequency analysis? It is a free Java based FFT that does the analysis in real time. Not quite as accurate as one that averages several taps over an interval but it is pretty cool seeing the frequency curve moving around as you tap. Here is a link if anyone is interested.

http://www.hometheatershack.com/forums/downloads-area/47460-v5-01-beta-downloads-asio-support.html

Use the RTA button.

meddlingfool wrote:
" FWIW, in my own guitars I've noticed a fairly consistent 1.5-2hz increase with the strings tuned up, but now your post is making me wonder if I have 'other things' to worry about..."

That's a pretty nominal change, IMO, and should not materially affect the sound. You can get that much of a change from a shift in relative humidity!

I did some experiments a while ago (having trouble getting that written up!) on the relative effects of changes in string height off the top and break angle. I saw pitch shifts in top modes, and changes in Chladni pattern shapes, when I went from having the strings on a Classical guitar 11mm off the top to 18mm. In some cases the pitch shifts were surprisingly large when a 'top' resonant mode was shifted into, or out of, the band width of something else, such as an 'air' mode. In making violins we know that arching shape is at least as important as thickness distribution in determining the local stiffness, and affects mode shapes and relative pitches. Altering the torque on the top of a guitar does make small changes in the 'arch' shape, which could have an influence on the tone. I could detect these changes in the spectra of plucked notes, as well as in impulse spectra, but, again, they were small, and probably had little bearing on the perceived differences in the timbre. Timbre changes were probably mostly related to the relative strength of string signals that acted to torque the bridge; the 'tension' and 'longitudinal wave' signals.

That would certainly be changing the plate geometry on one of mine...


A classic example of that is when the uncoupled top and back resonances are very similar in frequency. Coupled, the high one gets repelled to a higher frequency and the lower one gets repelled to a lower frequency. However, suppose the top initially had the higher frequency resonance and then you add one gram to it to make it now the slightly lower frequency resonance. Now the repulsion is acting the other way and instead of the top being 7 or so Hz higher than the back it is now 7 or so Hz lower, looking like the addition of one gram gave a frequency shift of ~15Hz. It all adds to the fun!

_________________
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

C# eh...hmmm

Set your tuner to A@432hz and then check to see if its still C# after you get that bridge on.

Cuz if it is ... then me suggest you open tune it to C#m with A @ 432hz (there ain't no A in a C#m cord...but you'll figure it out.) Now with A at 432hz, your low C# is 136.1 hz ... Ya the Om freek~winc~E.

Of course that C# would be a wolf note...
and with any luck it will howl loud and clear.

As such me bet any of them World Beat, "Drone to OM" pickers would lay a lotta Bucks in your hand for that little parlour.


Then again ...maybe not.


Just sayin.


blessings

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Audiences and dispensations on Thursdays ~ by appointment only.


.

Man, I am having a difficult time trying to wrap my brain around this...
I know I will have to start playing around with it to grasp the idea of what I am doing. But I am excited to learn...


@ Trevor, I downloaded Visual Analyser and I thank you for the link, however my Linux box is the one set up with the Focusrite and is where I do most of my recording and midi stuff.

I found a frequency analyser called Japa that will work with JACK. (JACK is an audio server for Linux that will connect any output with any input so it is extremely versatile for Audio and Midi)

I am wondering if you could look at the specs and tell me if this will do the same as VA?

http://linux.softpedia.com/get/Multimedia/Audio/Japa-9463.shtml

Here is a section of the description of what it does But it appears to have the same type of output as VA.



I can set my Windowz laptop up for recording but would prefer to stick with Linux since I have a much better sound card than the laptop (and its Windowz...)

Thanks for any help you can give.

Cheers,
Bob

P.S. I don't mean to offend any MS fans out there... Linux geeks call it Windowz because you must run virus protection and it slows the OS down so much that at some times it seems to just DoZe off.... So. Sorry...

I personally use and prefer Audacity and it has a linux download, very easy to use and in comparing to other programs it gives the same readings. I like to record 8 to 10 taps and select them all in the wave form and it graphs the average of the taps.
http://audacity.sourceforge.net/download/linux

Fred

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I guess I must have stuttered on the Submit button, double post.

Fred

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I have used Audacity for years but never really messed around with it for anything but simple recordings....
I have always used Digital Workstations like Sonar (Windows) or Ardour (Linux) for multi-track and midi stuff.

Amazing the stuff that you miss that sits right under your nose.

Thanks Fred, I will have to check it out.

Cheers,
Bob

+1. Much to be learned with this tool. T