One more point. DURRL's video turned many of us on to using the weight of the forearm to get a bigger tone/sound.
Strictly speaking if you think about pure physics:
Force = Mass X Acceleration
To which you could interpret as:
Big Sound = Mass X Pull Strength
So if you want to play loud without increasing the amount of strength to pull the string, then you have to somehow bring in more mass into how you pull the string. It explains why pulling with the side of your fingers gets a better sound - you're using the mass of the hand and fingers.
I think this is why many teachers also espouse pulling strings from the larger muscle groups (back muscles, leg muscle). You get not only more strength, but also more mass into the game. My previous post is just the discovery that I can throw the mass of the bass into the mix.
If you can bring a ton of mass into the game, you might even be able to reduce on the amount of strength needed.
You explained the science behind it much better than I did in the video. But yes, playing from the body is way more effective than playing from the hand or arm. I think of it as a progression from least effective/relaxed to most effective/relaxed:
1) Finger/Hand/Forearm (squeezing)
2) Elbow/Shoulder
3) Chest/back
4) Torso/Hips
The farther down the list you go, the bigger the muscle groups get, and therefore the less stress is applied to the muscle group(s) to produce the required amount of force to get the job done. I've finally made it to stage 3 and am transitioning into stage 4.
Interestingly, I think this formula applies to the technique of both hands. It's a large part of the reason I sit when playing, and always seemed like a compromise for a long time: to me, sitting seemed to improve the leverage of the left hand immensely, which improved stops, sound, and intonation, and also gave me an immovable reference point from the torso to any point on the bass. It took a while to adjust to the right hand portion of the equation, since sitting at first seemed to limit the range of motion. I've overcome that by now, but when people say they want to play standing for this reason, I totally get what they are saying and don't won't argue with it.
I'm proud to say that I've never coerced a single student to sit when they prefer to stand, and I hope I can still say this 20 years from now. For players who prefer to stand, I notice that the better ones all seem to have some provision in place to allow them to leverage more body power into the left hand; sometimes it's the Karr "vertical approach", sometimes it's the bent endpin which allows the bass to anchor better, and sometimes it's another connection to the body, usually on the hip. Different strokes, as long as the leverage is there.
The third video in the series I've been working on is about leverage and the left hand, and I expect it to be less well received than the first two because of some details that not everyone will agree with. But that's life. The big lesson is that full stops are essential, that playing with different parts of the finger surface produces different sounds and requires somewhat different amounts of force; as long as enough force can be applied to the string to produce the desired tone and allow the player to still be relaxed, I call that "good technique".
Slightly off topic, since you seem to have some knowledge of/interest in the physics involved, I'd be interested in learning what the formula is as regards applying pressure with various sized surface areas. Specifically, since the very tip of the finger is smaller and harder than the pad, it requires less force to achieve a full stop with it. If tips and pads sounded the same, that would be the end of the story; but since they don't it, would be interesting to see the ratios of force needed as relates to size/hardness of the area applying the force to achieve the same result, if only as an intellectual illustration.
Last, the Klinghoffer video series is great!
