Andy
Honorary Member
Another Andy "infothread", let's see where this goes
I'll kick off with describing some features, how they apply, & what they achieve. For the sake of removing terminology confusion, I'll describe the three edge features as follows: From the outside inwards - outer cut - crest - inner cut. Please use this terminology in questions & replies.
Angles:The most commonly used means of differentiating one edge from another, but angles in themselves, how relevant are they? The answer is, far less than you'd imagine in terms of general playing & sonic characteristics, but there are some finer aspects to this. One person's double 30 degree edge can be quite different to another's. Back in the day, the outer & inner cut angles were used as an indication of sharpness. A trend that continues through to today. Typically, a 30 degree angle would be regarded as less sharp than a 45 degree angle. Given little control over the crest form, this has some truth to it, as a more shallow angle will typically offer a larger crest radius when sanded to finish.
The crest:This is where the action is. It's the bit that interfaces dynamically with the head. It's by far the most critical aspect of a bearing edge, yet there's often little - no information revealed about it in drum specifications. No matter how sharp or how rounded the crest is, it has a radius, & that radius can be controlled & measured if time is taken to do so. The only exception to this is a totally flat crest. In essence, the smaller the radius, the more the head will sustain its movement when excited. As you move to a larger radius, this effectively puts the brakes on the head, right through to a full roundover (baseball bat edge) that cuts the head sustain pretty short.
If you look at how a head actually behaves in slow motion, the amplitude of the waves in the head, once excited, is very significant. So much so, that the edges of the head actually momentarily lift away from the inside edge of a big radius edge. This varies the head contact point across the peak of the radius, & in doing so, stifles continued resonance of the head. So, the smaller the radius, the less "braking" is applied to the head.
A flat crest works in the same way. Same physics apply, only there's a distinct step between reaction at low & high dynamics. Edges with a totally flat crest tend to have a very narrow crest. Typically no more than 1/8" across, but more usually less than 1/16". Imagine the same head dynamics, under low dynamic playing the head remains mostly in contact with the inner edge of the flat crest. Play harder, & the head starts to reciprocate between the inner & outer edge. This has the affect of promoting fairly long head sustain at low dynamics, but puts the brakes on at high dynamics. How pronounced the affect is depends on the depth of the flat.
The outer cut:This controls three basic elements:
1/ The static element of the amount of contact between the head & the shell.
2/ The orientation of the crest to the head.
3/ The head orientation directly prior to the crest.
So, breaking this down:
1/ The theory is that additional contact of the outer cut drives vibrations into the shell, & we've proved that to be the case in our A-B comparisons. This aspect matters more on some constructions than it does on others. For example, a very thick drum will gain almost nothing from this feature, as it's unable to respond to stimulus at such low dynamic levels. An exception to that is stave construction that uses the vertical grain structure to directly excite both the shell & the reso head. Equally, many less resonant forms gain little additional shell excitement from this feature. Highly resonant forms gain a noticeable additional level of excitement with full contact. The more rounded the outer cut, the more contact area is achieved. A straight cut 45 degree outer cut only contacts on the crest & the very outer edge of the angle intersection with the outer shell wall. A 30 degree outer cut achieves slightly more contact, but not much. Even the introduction of a gentle radius increases contact considerably.
2/ The outer cut depth dictates the crest position in relation to the shell thickness & ultimately the head itself. Moving the peak inward of the outside of the shell typically achieves seating the crest away from the formed area near the rim of the head, depending on make/model of head used. With some heads, this gets the peak away from that "crinkle" area thus promoting a more consistent contact.
3/ This matters to some degree, especially with respect to greater ease of tuning, but can also form part of the very high dynamic behaviour results on a very shallow & rounded crest.
Of course, in the case of a full roundover, all this information still applies, it's just that the divisions between the three edge elements merge into one.
The inner cut:least important of the three edge elements, or so you would think. The inner cut form can play a part in the sharpness of transition in a flat crest form, & that can dictate head sustain characteristics to some extent. The biggest affect however is how higher overtones are managed near the outer edge of the head. Getting that right, or even knowing where to start, is a bit of a black art TBH. Clearly, it's more important on a thicker shell where that inner cut is fairly generous. Only experimentation can dictate the best inner cut form, as it's affects vary widely from construction to construction.
As a footnote to all this, I cannot emphasise too strongly how big the affect of correctly specified & executed edges are. Outside of heads & tuning, it's the biggest every day affect on your drum's sound, & indeed, the biggest element that's beyond the control of most players to adjust. Standard double 45/30 degree edges are a most valid edge choice, but they are often specified because they're cheaper/faster to achieve in a production scenario, & control of that all important crest radius is more difficult in a fast finish environment. Ultimately, there's no substitute for taking time & multiple checking. A quick spin around the router & cusory hand sand or flat to finish will get you what you paid for. Even edges cut completely by CNC are a way away from guaranteed correct, for reasons I won't bore you all with now. Finally, edges are just one aspect of a drum's design, & must always be considered in the context of the overall instrument design.
I hope you find this basic edges breakdown of some use.
Andy
I'll kick off with describing some features, how they apply, & what they achieve. For the sake of removing terminology confusion, I'll describe the three edge features as follows: From the outside inwards - outer cut - crest - inner cut. Please use this terminology in questions & replies.
Angles:The most commonly used means of differentiating one edge from another, but angles in themselves, how relevant are they? The answer is, far less than you'd imagine in terms of general playing & sonic characteristics, but there are some finer aspects to this. One person's double 30 degree edge can be quite different to another's. Back in the day, the outer & inner cut angles were used as an indication of sharpness. A trend that continues through to today. Typically, a 30 degree angle would be regarded as less sharp than a 45 degree angle. Given little control over the crest form, this has some truth to it, as a more shallow angle will typically offer a larger crest radius when sanded to finish.
The crest:This is where the action is. It's the bit that interfaces dynamically with the head. It's by far the most critical aspect of a bearing edge, yet there's often little - no information revealed about it in drum specifications. No matter how sharp or how rounded the crest is, it has a radius, & that radius can be controlled & measured if time is taken to do so. The only exception to this is a totally flat crest. In essence, the smaller the radius, the more the head will sustain its movement when excited. As you move to a larger radius, this effectively puts the brakes on the head, right through to a full roundover (baseball bat edge) that cuts the head sustain pretty short.
If you look at how a head actually behaves in slow motion, the amplitude of the waves in the head, once excited, is very significant. So much so, that the edges of the head actually momentarily lift away from the inside edge of a big radius edge. This varies the head contact point across the peak of the radius, & in doing so, stifles continued resonance of the head. So, the smaller the radius, the less "braking" is applied to the head.
A flat crest works in the same way. Same physics apply, only there's a distinct step between reaction at low & high dynamics. Edges with a totally flat crest tend to have a very narrow crest. Typically no more than 1/8" across, but more usually less than 1/16". Imagine the same head dynamics, under low dynamic playing the head remains mostly in contact with the inner edge of the flat crest. Play harder, & the head starts to reciprocate between the inner & outer edge. This has the affect of promoting fairly long head sustain at low dynamics, but puts the brakes on at high dynamics. How pronounced the affect is depends on the depth of the flat.
The outer cut:This controls three basic elements:
1/ The static element of the amount of contact between the head & the shell.
2/ The orientation of the crest to the head.
3/ The head orientation directly prior to the crest.
So, breaking this down:
1/ The theory is that additional contact of the outer cut drives vibrations into the shell, & we've proved that to be the case in our A-B comparisons. This aspect matters more on some constructions than it does on others. For example, a very thick drum will gain almost nothing from this feature, as it's unable to respond to stimulus at such low dynamic levels. An exception to that is stave construction that uses the vertical grain structure to directly excite both the shell & the reso head. Equally, many less resonant forms gain little additional shell excitement from this feature. Highly resonant forms gain a noticeable additional level of excitement with full contact. The more rounded the outer cut, the more contact area is achieved. A straight cut 45 degree outer cut only contacts on the crest & the very outer edge of the angle intersection with the outer shell wall. A 30 degree outer cut achieves slightly more contact, but not much. Even the introduction of a gentle radius increases contact considerably.
2/ The outer cut depth dictates the crest position in relation to the shell thickness & ultimately the head itself. Moving the peak inward of the outside of the shell typically achieves seating the crest away from the formed area near the rim of the head, depending on make/model of head used. With some heads, this gets the peak away from that "crinkle" area thus promoting a more consistent contact.
3/ This matters to some degree, especially with respect to greater ease of tuning, but can also form part of the very high dynamic behaviour results on a very shallow & rounded crest.
Of course, in the case of a full roundover, all this information still applies, it's just that the divisions between the three edge elements merge into one.
The inner cut:least important of the three edge elements, or so you would think. The inner cut form can play a part in the sharpness of transition in a flat crest form, & that can dictate head sustain characteristics to some extent. The biggest affect however is how higher overtones are managed near the outer edge of the head. Getting that right, or even knowing where to start, is a bit of a black art TBH. Clearly, it's more important on a thicker shell where that inner cut is fairly generous. Only experimentation can dictate the best inner cut form, as it's affects vary widely from construction to construction.
As a footnote to all this, I cannot emphasise too strongly how big the affect of correctly specified & executed edges are. Outside of heads & tuning, it's the biggest every day affect on your drum's sound, & indeed, the biggest element that's beyond the control of most players to adjust. Standard double 45/30 degree edges are a most valid edge choice, but they are often specified because they're cheaper/faster to achieve in a production scenario, & control of that all important crest radius is more difficult in a fast finish environment. Ultimately, there's no substitute for taking time & multiple checking. A quick spin around the router & cusory hand sand or flat to finish will get you what you paid for. Even edges cut completely by CNC are a way away from guaranteed correct, for reasons I won't bore you all with now. Finally, edges are just one aspect of a drum's design, & must always be considered in the context of the overall instrument design.
I hope you find this basic edges breakdown of some use.
Andy