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Double Bass Total pull at tail piece?

#3
That depends on a bunch of factors -- string type, bridge height, and, I'm sure, countless factors that are above my head.

IIRC, Spiro Reds on a Kay will apply about 250 pounds of downward pressure onto the bridge. How that translates to pull on the tailpiece I'm not sure, but is probably around that number.
 
#5
Fogducker said:
I checked the various threads to make sure this ground hasn't been plowed, so at the risk of getting my axx chewed, how much pull is there on the tail piece with the various strings, gut metal etc?

Fog
Click to expand...

The pull on the tailpiece wire is the total tension of all the strings. See the 'Double Bass String Tension' Sticky on the 'String' page and multiply at will! ;)
 
#6
Jake, it's a long time since I did maths at school but I think the theory of vectors comes into play here. Part of the total tension of the strings is directed down into the bass by the strings bending over the bridge and part goes through to the tail wire. If my maths was better I could calculate each proportion because I could measure the angles of deflection. Do we have a math whizz who can help here?

DP
 
#7
David Potts said:
Jake, it's a long time since I did maths at school but I think the theory of vectors comes into play here. Part of the total tension of the strings is directed down into the bass by the strings bending over the bridge and part goes through to the tail wire. If my maths was better I could calculate each proportion because I could measure the angles of deflection. Do we have a math whizz who can help here?

DP
Click to expand...

Ah... Well, that's beyond my meagre arithmetical skills! I think I see what you're saying about the 'diversion' of the tension down through the bridge.
 
#8
If there were a little pulley under each string as it crossed the bridge, then the tension on the playing portion of the string, and on the afterlength, would be equal. There's no pulley, but probably enough sliding that the tensions equalize themselves pretty well. So, the pull on the tailpiece is equal to the pull on the strings. Most string brands have tables of the tensions for their different varieties of strings.

Where vectors come into play is not in the tensions, but how all of the forces add up (to a net of zero) on the bridge, neck, etc.
 
#9
Jake deVilliers said:
Ah... Well, that's beyond my meagre arithmetical skills! I think I see what you're saying about the 'diversion' of the tension down through the bridge.
Click to expand...

The downforce on the bridge is a separate issue from pull on the tailpeice.

One observation is that even if you do the math it's a purely theoretical calculation that may not be indicative of the actual measurement of tension at the tailpeice on a particular bass. Theoretical measurements are good when spec-ing a build but next to useless when you want to know what's actually going on in an up and running system.

Second the when you do take a measurement of the real tension on the string at the tailpeice it will tell you how hard the string is pulling on the tailpeice. Right? It's one way you can calculate the actual static load on the chainplate of a sailboat and the fact the rigging (which=the string) is passing over a [Invalid or Expired Link Removed] (which=the bridge) is not of any consequence. Even when you're doing a theoretical static load calculation (the first step in a theoretical dynamic load calculation) you don't need to consider the spreaders.
 
#10
fdeck said:
If there were a little pulley under each string as it crossed the bridge, then the tension on the playing portion of the string, and on the afterlength, would be equal. There's no pulley, but probably enough sliding that the tensions equalize themselves pretty well. So, the pull on the tailpiece is equal to the pull on the strings. Most string brands have tables of the tensions for their different varieties of strings.

Where vectors come into play is not in the tensions, but how all of the forces add up (to a net of zero) on the bridge, neck, etc.
Click to expand...

+1. You don't need any physics here, just addition.

On this chart (from the string tension sticky) you can quickly sum up the four strings of most popular sets. Ex. Helicore medium: 62+65.9+69+70=266.9. That means you can't use kite string for the tailpiece gut, and should avoid those nylon fasteners as well. However, you don't need bridge cable either. The TP is held effectively by two ropes, so anything with a break strength well over half the total string tension should be fine.

The idea that this force is independant of bridge height and afterlength is counterintuitive to many, and some bassists and even luthiers absolutely refuse to accept it. If you are in this camp, I recommend looking up your old high school physics teacher or a former classmate who went on to become a mechanical engineer, and invite him out for a beer. I bet with the help of a crayon and some bar napkins he will set you straight in a few minutes:)
 
#13
At the top of the bridge three forces must be in equilibrium - the tension of the strings, the front table's reaction to the downward pressure of the bridge and the endpin's reaction. Since energy can neither be created or destroyed and part of the tension (latent energy) of the strings is deflected down onto the belly the remaining (reduced?) tension must be counteracted by the tail wire.

Then again, if you are lifting a weight with a rope over a single pulley your pull must equal the weight that you are lifting if the weight is to stay still. The equal and opposite reaction comes from whatever the pulley hangs from.

Help!! Hasn't anyone got a tension gauge? Perhaps D'Addario could help solve this conundrum?

DP
 
#14
It's actually a simple bit of physics... the tension is what determines the pitch at a particular scale length. If your bass has that scale length, that is what the tension on the strings will be, and therefore just add them up to get the tension on the tailpiece.

If your scale length is a little different, the tension will change in inverse proportion, so 1% longer scale length gives 1% less tension. But given the range of numbers we're talking about, that's insignificant. Also stiction in the bridge slots will make a small difference as the tensions on either side don't have to be strictly balanced... but it has to be fairly small, or else the bass is hard to tune and the bridge eventually falls over.

Certainly adding the string tensions up then doubling it will be adequate for sizing a tailwire... but most people would look at the result and say 'That can't possibly be enough' and double the strength again.
 
#15
Andrew McGregor said:
...

Certainly adding the string tensions up then doubling it will be adequate for sizing a tailwire... but most people would look at the result and say 'That can't possibly be enough' and double the strength again.
Click to expand...

I would say halving it, not doubling it. You're using two lengths of TP wire to hold the string tension, so I would say that any wire with a break strength of at least 150 pounds ought to do it. More can't hurt, of course.
 
#17
robobass said:
I would say halving it, not doubling it. You're using two lengths of TP wire to hold the string tension, so I would say that any wire with a break strength of at least 150 pounds ought to do it. More can't hurt, of course.
Click to expand...

I'm not an engineer but I work with wire rope for a living. I'm not following your logic here. Unless you are using two independent tail wires you are using only ONE section of wire rope. You are distributing the load over two halves of the same piece of rope. Therefor the complete load is being borne by ONE rope. If you size it to carry half the full load, the question is not IF it will fail but WHEN will it fail.

If you are using two independent pieces of rope they are not likely to divide the load evenly. The load borne by each rope will be proportional to the difference in tension between the two ropes. It will be nearly impossible to balance tension so one of them will always be carrying more than half the load. Again, not if, but when will it fail.

If I have missed the point somewhere and gone way off in left field please help me see your point.

Thanks
 
#18
So, what strength rope would you guys recommend?

I really think it's true that the tension in the rope will be half the total string pull, and unless you have some very unusual way of going around the socket, it should be pretty even across the two lengths. My number is kind of a theoretical minimum, but I bet it would work.

Besides, I bet those nylon hangers you see on many student basses wouldn't hold much more than 150 lbs., and they only rarely break.
 
#20
The tension is not being divided by the two halves of the tailgut. It's one rope and is holding all the tension by itself. Focus on the tailgut where it passes behind the endpin, not the two halves coming out of the tailpiece. There is force being diverted into the top, but the tension of the strings will constant throughout. I think most sets of strings are around 250 pounds, so I would want something with a safe holding strength of around 500 pounds as a measure of safety. I use some thin 1/16" stainless cable that has a safe holding strength of 480 pounds. I have also used the Pecanic tailgut which I don't have specs for, but it works well.
 

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