Well, because the truss rod only applies counter-bending load to the neck in the zone from about the 1st fret to around the 14th. The truss rod applies no load or reinforcement to the headstock or the neck/body joint. And those are the more fragile areas.
When the strings are up to full tune, they are applying compression and bending loads to the whole instrument frame, including the main length of the neck plus the headstock and the neck/body joint.
So, if you drop the bass with the strings up to tune, the headstock, neck, and neck/body joint will see the shock load in addition to their normal string load. They are added together.
With the strings slack, headstock and neck/body joint will see only the shock load.
That's the rationale for slacking the strings: To reduce the peak loads that the headstock and neck/body joint will see in the event of a high impact drop. Basic physics and engineering.
Is it necessary to slack the strings before shipping? No, obviously not, if you go by statistics. Millions of instruments are shipped up to tune and make it there safely. Fine & good. But I slack the strings before shipping my basses because it's a simple no-cost extra measure of protection against impact drops.
Hey Bruce
Obviously, I have a lot of respect for you and all you do. You are an accomplished luthier and I have had the pleasure of seeing your fine work first hand. We all appreciate that you take the time to give us your considered opinion and your feedback here on this forum. I must say, one of the things that prompted this thread, is that when I got my Fender Performer build from you and Keith, the strings were loosened. Never have I been shipped a bass where that was the case and it concerned me. I didn't mention it, but when I first got it - the action was really off after I tuned it up. I figured I would let it settle in before I did any set up work. I also noticed that after a couple of days or so the action seemed fine. I suspect that it had settled in on it's own - but it seems like something that - given the choice - I would rather not have put the bass through.
As far as I can see, the only way to settle this debate on your side - is to get a handful of identical basses, detune some, leave some in pitch and start dropping them. I really wish we had a sample or actual statistics on how many instruments actually sustained damages over the years - with the strings tightened that wouldn't have been damaged if the strings were loosened. Could be enlightening. It wouldn't be that hard. Buy a few SX or equivalent identical $100 basses, tighten some to pitch and loosen some - and pack them back in their original packaging. Then you can start dropping them from pre-measured heights and see which one gets damaged first. What fun. Too bad Letterman isn't still in business. He would love this.
Bruce your argument is convincing - much more convincing than anything else that has been offered up on the "loosen" side of the fence. But I can't help but think that minimizing shipping damage is all about packaging. I am thinking long and hard about how I want Keith to ship back to New York the other 8 basses I have coming.
So as the OP, I would like to entertain the concept of a little tangent here. We have kind of beat this horse to death already, and I think it's fair to say that your point of view is diametrically opposed to Gard's - who I also have the ultimate respect for.
True Confessions.
When Paul Reed Smith made PRS#7 for me in 1976, it was only the second or third bass he had ever made. He was experimenting with truss rod designs and in retrospect, Paul would tell you that his early bass truss rods simply were not heavy duty enough. I had chosen a mapleglo Rickenbacker prior to the PRS build - among about a dozen or so - and it was the one with the widest thinest neck I could find. I mean that neck is super thin! I told Paul how much I liked the Rickenbacker neck and he told me to bring it over and he would measure it up and duplicate it for me on PRS #7. So I did.
We had booked a winter tour mostly in the NorthEast in'77 and I had a huge road case made for the PRS Bass. Well the winter was brutal in the NorthEast and we were playing all the northernmost New York cities like Buffalo and Oswego and well - you get the idea. We hit a cold spell where the temperatures were at zero or well below for an extended number of days.
When the weather got cold, our stage manager started taking the tension off my bass strings before preparing it for the ride in the very cold truck. He had a physics background and this made complete sense to him due to the extreme cold temperatures. I didn't know he was doing it at first, but even if I did I probably wouldn't have argued about it - it seemed to make sense to me. But when I found out he was doing it I probably should have called Paul and asked him about it. I didn't.
Well, a couple weeks after the tour - the neck on PRS #7 began to bow and change and became unplayable. After a couple of weeks with it, Paul proclaimed the neck on the bass as unfixable, and since it was a "set" neck the bass became firewood.
Now, was the damage caused by the thinness of the neck? Was the cause the light duty truss rod Paul was using at the time? Was the cause the loosening and tightening the strings an a daily basis over many weeks? Was the cause subjecting the bass to the extreme cold temperatures and the shock of bringing it into the heat every day? My guess would be a combination of all four. After I settled in on PRS #11, I never took the tension off the neck all at once. Nope, not once, not ever, mostly out of superstition I think. And, I bought a very pricey Reunion Blues leather bass bag for the bass - and on future tours the bass never left my side or at least my sight. No more trucks for the PRS after that.
So, in trying to bring this full circle - one of the things that caught my attention was that the cargo holds, while pressurized - are not always heated. One gentlemen even mentioned that he had seen pets perish in unheated cargo holds - when the pilot forgot to flip the heat switch.
So here is the tangent question. Is extreme cold a reason to loosen the strings? At what temperature should one be concerned? Below freezing? Below zero? Inquiring minds want to know....
