Tuning and Strings
The most common dobro tuning is open G, and that's the tuning we'll use in all of the instructional videos (for 6 string dobro). The strings are, low to high, GBDGBD. For strings, most people use phosphor bronze strings, gauges 56-16 or 56-17. Here are my two favorite string sets...
One issue with dobro strings is that the 3rd string (G) tends to die very fast. When it starts to die, it will not only sound dead, it can create a buzzing sound in the instrument. I've had quite a few people think that their dobro had a buzz, when it just needed a new G string. Sometimes I buy extra G strings (PB26 or PB28) so I can just change one string instead of the whole set. The GHS CR1600 strings are cryogenic, and the G string lasts much longer. I still really like the tone of the D'Addario EJ42 set, but they don't last very long. The GHS "Tim Scheerhorn" set is also great, but as far as I can tell, it's identical to the CR1600 set, and the CR1600 set is cheaper!
There are lots of other good sets available, and I encourage you to try as many as you want, and see what works best for you, just make sure the gauges are close to what you see here...
Tuning the B strings flat
Another thing to consider is tuning the B strings a little flat. Most dobro players do this in varying degrees, here is my take on it. For most of my career, I've tuned my dobro to standard (equal tempered) tuning. Right now, I'm starting to tune my B strings flat, and here's why...
First of all, I will talk a lot about 3rds, I should explain what they are. A major chord is made up of 3 notes, the root, the 3rd, and the 5th. In the key of G (our tuning is in G), G is the root, B is the 3rd, and D is the 5th. So, our tuning (GBDGBD) can be viewed as Root 3rd 5th Root 3rd 5th. When we lay the bar across the strings, for example on the 5th fret, we get a C chord (CEGCEG). It's a new chord, but it's still Root 3rd 5th Root 3rd 5th. Make sense?
A major chord sounds good because the harmonics of the notes line up in a pleasing way. With standard tuning, the 3rds (in our case the B strings) aren't quite right. The chord is more "in tune" if the 3rds are a little flat. When using an open tuning like open G, our 2nd and 5th strings are almost always used for the 3rd in a major chord. So, if we tune them flat by about 10 cents, our major chords sound better. Where we can run into trouble is when we use alternate positions and our B strings are used for something other than a 3rd. This isn't really a problem when we are playing single notes, because the dobro is fretless, and we are using our ears to play the note in tune anyway. When we play an alternate position of a chord, especially with an open B string (an E chord with an open B string, for example) the B string will sound flat (because it is). This is the compromise we need to live with if we want our major chords to sound pristine.
At the end of the day, you have to do what sounds best to you. If you're just starting out, you might want to stick to standard tuning, you have enough other things to worry about! When you're ready, try tuning your B strings by ear after you have the Gs and Ds perfectly in tune, and see what you think. I use a tuner that is programmable, and allows me to tell the tuner that I want my Bs 10 cents flat, and it makes it easier to deal with on stage. It's a Sonic Research Turbo Tuner, and I recommend it, but only if you have a pickup, you have to plug it in to use it.
Above are a couple videos to further explain how to tune the B strings. Check out the distortion demonstration, it makes it easy to hear the harmonics lining up to sweeten our major chords!