Picking out a used acoustic guitar.

There is a lot of good information available online about picking out an acoustic guitar so I won't go into how to find the right guitar for you -- but how do you know if the guitar you're looking at is a good one. I found very little information on the web about checking out a used instrument. So I've decided to rectify the problem.

 

After you have found something that looks and feels right, the first thing to do is listen to the instrument. Does it sound good? Listen carefully to each string as it rings out. Don't worry if it's not in tune -- they seldom are in a used music store. If you are unsure of what you're listening for due to lack of experience, get some. Play several other instruments in the store and compare. By "play" I mean use a pick to sound each string individually -- often, it isn't necessary to remove the other instruments from the rack.

If you're satisfied with the sound of the open strings, it's time to start testing. The first takes the longest but it's probably the most important. Carefully play every string on every fret. This may seem obvious but I have known several fellow musicians who regretted skipping this step. If you hear buzzing, especially if it happens to several strings on the same fret, there is a problem. Probably a raised fret. If it only occurs on one fret it might be easily repairable. If you hear buzzing on several frets it's probably a different problem. That is what to check for next.

Set the instrument on its strap peg on the floor holding it by the head so you can look straight down the neck. Check the ends of the frets on both sides of the fingerboard. They should be in line. This will tell you if the neck is straight. If you see a small amount of curvature and the instrument has an adjustable truss rod (more about that later) it can be straightened. If you see a bend in the alignment where the neck and body meet, the neck has probably shifted. This too can be repaired, but it's not cheap. Next compare the top edges of the nut and saddle. Their curves should match. Note: both will be slightly taller on the low string side. This is normal. If they don't line up, either the saddle needs to be reset or the neck is twisted. The former is fairly easily fixed but not the latter.

 

To verify it is a twisted neck, align the bottom edge of the nut with the top edge of the body. They should form a straight line. Note the red line in the image bellow. This neck is not twisted.

 

Now look at the back of the instrument. Check the joint between the heel and body. It should be tight with no cracks in the finish. If you see a gap the neck has shifted. As mentioned before, bad news.

 

Look across the top between the sound hole and bridge. It should be perfectly flat or slightly convex. If you see a slight, or worse, depression in this area there is an issue with the reinforcing strips underneath. Not easily repairable.

 

Next is what I call the thump test. Muffle the strings with one hand and thump with the thumb of your other hand all around the top and back of the instrument. You should hear a nice percussive ring like a drum head. The sound will change as you move around. You're listening for a dull thud or short buzzing sound. Either indicates some structural damage or delamination of the reinforcing strips inside.

Finally, look very closely at the details. Scratches in the finish and such are only aesthetic. But cracks and splits in the joints, especially at the bridge, can be signs of trouble. If the decorative binding around the edges of the body has pulled away, it will usually continue to get worse. Check the tuning pegs. Do they operate smoothly.

All of this assumes that you really don't want to have to perform repairs on an instrument that you just bought. But it's up to you. You have to weigh the cost of repairs -- and the price of the instrument itself -- against how much you like it. If it's a really nice piece with a low price tag and repairs are minimal, it might be worth it!

 

Here are some further clues as to the quality and workmanship of an instrument. You will need a small flashlight, a dental mirror and, if you're like me, your glasses.

The ideal joint has full coverage of glue with no gaps. It is very difficult to apply precisely the right amount of glue. But better to have too much than not enough. This means "squeezed out." Inside the body of a quality instrument you will see wipe marks were excess glue was carefully removed during construction. If you see globs of glue clinging to the joints -- and usually some rattling around inside -- no one bothered to clean up.

Look at the edges of all the parts inside. The cuts should be clean and smooth. If you see frayed edges, no one took the time to do any sanding.

The reinforcing ribs across the back are another clue. There are usually four -- two down inside the wide part of the body and another two below the sound hole. In a high quality instrument the two pairs will have a different profile. Usually the longer ones down inside will have a bar shape while the others will be taller and thin. In a less expensive instrument all four will be the same -- because it's cheaper to manufacture that way.

If there are no reinforcing ribs across the back then it is probably made of plywood. Plywood is made by gluing several thin sheets of wood together with the grain 90° to the previous one. It is strong and resists the effects of temperature and humidity better than a traditional plank. The drawback is that it doesn't transmit sound very well. It tends to dull the resonance a bit. However, this might not be a problem if you are looking for a tough beach guitar.

The top of the guitar -- and usually the sides and back -- will be "book matched." This means that a plank is cut edgewise and opened like a book. The resulting grain on either side of the center line will be identical. In a really high quality instrument the joint will be so precisely cut that it will be nearly impossible to see.

Are the decorative elements decals or real inlays? If the latter they should be smooth and neat with no raised edges or gaps.

Look at the hardware. Are the screws that hold the tuning pegs in place chrome plated or galvanized?

The saddle should be made of genuine bone. Don't worry, it's not ivory. It comes from cows. Bone is an excellent material for this application because it is durable and transmits sound very well. If the saddle is the adjustable kind with screws on either end, avoid it. The extra mass of the mechanism and it's inherently sloppy fit will dull the sound of the instrument. Even on an inexpensive guitar the saddle should be set properly and never need to be adjusted.

Finally there is of course the name on the head. If it says "Martin" then you are in business. However you are not likely to find an inexpensive example in a used music store. Other names require some research and knowledge of the year the instrument was manufactured. Often the serial number can tell you this. It's usually visible through the sound hole on the big block that anchors the neck to the body.

Good luck and happy hunting.

I will periodically update this information as I discover new things and receive suggestions from readers.

 

Some repairs are easier than others. If you are confident in your abilities there are those you might attempt yourself. Adjusting the truss rod is one (if the guitar has a truss rod, it can be accessed under the cover on the face of the head or just inside the sound hole). It only requires a good eye, an Allen wrench, and maybe a screwdriver. Again, there are plenty of good sources of information about how to do this and other repairs online.

Some anatomy -- in case you are unsure of what I'm talking about.