This is a project I was prompted to work on by a forum member on a forum I frequent, and an idea that had been kicking around in my head for a while.

The main design points I wanted to explore were the effect of mass in different places, resonance control, mass centralisation and the pivot point height. Firstly the pivot height. Ideally the pivot point should be on the same plane as the stylus, the reason being, that as the arm traverses warps the geometry is subtly altered as the stylus moves in an arc. It doesn't go straight up or down. Hence, the effective length of the arm is not what you would think. It is measured in one dimension, from the pivot point to the front of the arm, say for example a rega rb250 is 237mm. Or whatever it is. I forget.... The actual effective length is the distance between the pivot point and the stylus. If the pivot point is higher or lower than the stylus, you are measuring in three dimensions, i.e a diagonal line. Think of a right angled triangle, the quoted effective length being one side, the offset between the stylus and the pivot point being the side at 90 degrees to the first. The actual effective length being the longest side that comes down at an angle. A squared (quoted effective length) + B squared (offset between stylus and pivot point) = C squared (actual effective length).

The difference isn't a great deal, but does removing that offset make a blind bit of difference? I wanted to find out. (hint: yes it does)

Secondly, mass centralisation. Honda made a big deal of this when they released the CBR600 RR. What they did was to try and get as much of the mass of the bike as they could centred around the rider to make the bike handle better. By effectively reducing the gyroscopic force the rider has to overcome when getting the bike to turn, they made the bike easier to turn and in turn this made the bike more stable when cranked over. Anyone who has ridden one will tell you they did a good job of this. Looking carefully at this point made putting the pivot point in line with the stylus possible.

A unipivot is inherently unstable, and the usual plaster for this trait is to raise the pivot point higher so that the mass of the arm is lower than the pivot point. However, this is at odds with the first design point of keeping the pivot on the same plane as the stylus. So I had to get as much of the mass as close in to the pivot as possible to reduce this tendency to fall over.

Thirdly, mass in different places. I wanted to try to see what effect mass has when it is placed in different locations. A chance comment about adding mass to a headshell improving bass tone and texture by a forum member put this in my head. Put simply, mass around the cart allows the stylus to traverse the groove more faithfully as the stylus is acting against the mass at the headshell rather than acting against the mass of the counterweight hanging off the back of the arm .

Basically, whatever the stylus does is transferred in part to the arm itsself. The counterweight reacts to this after a delay and muddies the next thing the stylus does by introducing an 'echo' of the previous thing that the stylus did, that the counterweight is just reacting to. Imagine a sink filled with water. Drop something in and you get a ripple which spreads. When the leading edge hits the side of the sink it bounces off and comes back, interfering with rest of the still travelling ripple. This is the oscillation that is introduced by the counterweight. The stylus in turn reacts to this 'echo' and on and on it goes. The mass at the headshell effectively shields the stylus somewhat from this oscillation that is introduced by the counterweight, and makes it more difficult for the wildly waggling stylus to shift the headshell itsself in the first place.

Leading on from mass in the right places, is resonance control. We know that the arm is, from the point of view of the cantilever, waggling all over the place. We cant stop it doing this, but can we control it in such a way that its effect is reduced from the point of view of the cantilever?

With careful use of materials, probably. Now i made this arm from stuff I have lying around, but this issue was a prime consideration.

To this end the wand is copper tube. I chose the copper for 2 reasons. I had some carbon fibre, copper and aluminium tube, so i cut them to equal lengths. Then dropped them on a granite chopping board. Why? to see what sound they made. The carbon fibre made a high pitched noise which decayed away quickly. The ally made a lower pitched noise but rang on for quite a while , and the copper made a lower pitch noise and shut up very quickly. I wanted the decay as low as possible and a lower pitch so it fit the bill. Plus it was 2 quid a metre so quite abit cheaper than the others.

The bearing housing is walnut, I like to use wood as it has good damping properties. This can be made better by soaking it in danish oil to further damp it too. The oak I had was a little too heavy so i chose walnut. The 'mass block' behind the cart is the same, again for its damping properties and lower weight. I didn't want too much mass there. The headshell deck is acrylic as plastic has different damping properties again and little to no ringing when dropped on the chopping block. And it looks nice.

There is a full thread on audio talk forum about the building of this arm, and the evolution from mk 1 to mk 2.

I am very happy with the way the arm turned out, and keeping the design goals in mind has been a real advantage. Chopping and changing between the m1 and mk2 wands proved the evolution between the 2 was for the better.

a really enjoyable project

The main design points I wanted to explore were the effect of mass in different places, resonance control, mass centralisation and the pivot point height. Firstly the pivot height. Ideally the pivot point should be on the same plane as the stylus, the reason being, that as the arm traverses warps the geometry is subtly altered as the stylus moves in an arc. It doesn't go straight up or down. Hence, the effective length of the arm is not what you would think. It is measured in one dimension, from the pivot point to the front of the arm, say for example a rega rb250 is 237mm. Or whatever it is. I forget.... The actual effective length is the distance between the pivot point and the stylus. If the pivot point is higher or lower than the stylus, you are measuring in three dimensions, i.e a diagonal line. Think of a right angled triangle, the quoted effective length being one side, the offset between the stylus and the pivot point being the side at 90 degrees to the first. The actual effective length being the longest side that comes down at an angle. A squared (quoted effective length) + B squared (offset between stylus and pivot point) = C squared (actual effective length).

The difference isn't a great deal, but does removing that offset make a blind bit of difference? I wanted to find out. (hint: yes it does)

Secondly, mass centralisation. Honda made a big deal of this when they released the CBR600 RR. What they did was to try and get as much of the mass of the bike as they could centred around the rider to make the bike handle better. By effectively reducing the gyroscopic force the rider has to overcome when getting the bike to turn, they made the bike easier to turn and in turn this made the bike more stable when cranked over. Anyone who has ridden one will tell you they did a good job of this. Looking carefully at this point made putting the pivot point in line with the stylus possible.

A unipivot is inherently unstable, and the usual plaster for this trait is to raise the pivot point higher so that the mass of the arm is lower than the pivot point. However, this is at odds with the first design point of keeping the pivot on the same plane as the stylus. So I had to get as much of the mass as close in to the pivot as possible to reduce this tendency to fall over.

Thirdly, mass in different places. I wanted to try to see what effect mass has when it is placed in different locations. A chance comment about adding mass to a headshell improving bass tone and texture by a forum member put this in my head. Put simply, mass around the cart allows the stylus to traverse the groove more faithfully as the stylus is acting against the mass at the headshell rather than acting against the mass of the counterweight hanging off the back of the arm .

Basically, whatever the stylus does is transferred in part to the arm itsself. The counterweight reacts to this after a delay and muddies the next thing the stylus does by introducing an 'echo' of the previous thing that the stylus did, that the counterweight is just reacting to. Imagine a sink filled with water. Drop something in and you get a ripple which spreads. When the leading edge hits the side of the sink it bounces off and comes back, interfering with rest of the still travelling ripple. This is the oscillation that is introduced by the counterweight. The stylus in turn reacts to this 'echo' and on and on it goes. The mass at the headshell effectively shields the stylus somewhat from this oscillation that is introduced by the counterweight, and makes it more difficult for the wildly waggling stylus to shift the headshell itsself in the first place.

Leading on from mass in the right places, is resonance control. We know that the arm is, from the point of view of the cantilever, waggling all over the place. We cant stop it doing this, but can we control it in such a way that its effect is reduced from the point of view of the cantilever?

With careful use of materials, probably. Now i made this arm from stuff I have lying around, but this issue was a prime consideration.

To this end the wand is copper tube. I chose the copper for 2 reasons. I had some carbon fibre, copper and aluminium tube, so i cut them to equal lengths. Then dropped them on a granite chopping board. Why? to see what sound they made. The carbon fibre made a high pitched noise which decayed away quickly. The ally made a lower pitched noise but rang on for quite a while , and the copper made a lower pitch noise and shut up very quickly. I wanted the decay as low as possible and a lower pitch so it fit the bill. Plus it was 2 quid a metre so quite abit cheaper than the others.

The bearing housing is walnut, I like to use wood as it has good damping properties. This can be made better by soaking it in danish oil to further damp it too. The oak I had was a little too heavy so i chose walnut. The 'mass block' behind the cart is the same, again for its damping properties and lower weight. I didn't want too much mass there. The headshell deck is acrylic as plastic has different damping properties again and little to no ringing when dropped on the chopping block. And it looks nice.

There is a full thread on audio talk forum about the building of this arm, and the evolution from mk 1 to mk 2.

I am very happy with the way the arm turned out, and keeping the design goals in mind has been a real advantage. Chopping and changing between the m1 and mk2 wands proved the evolution between the 2 was for the better.

a really enjoyable project