This article is based on common knowledge on this subject, it reflects many issues that have been covered on the Shriners' Convention e-list, the RMMP newsgroup as well as facts and pointers obtained from commercial sources, internet research and the writer's own experience of playing, tweaking and experimenting with drums.

What is a drum?

A drum is any cylindrical object (shell) or object with an open top that has a membrane normally called a head or skin stretched across it, this is known as a membranophone.  The drum is struck on the membrane to produce a tone. 

What are drums made of?

Drum shells can be made of any material that can be formed or carved to meet the above description, however in contemporary construction of drum shells of reasonable quality the main materials used are wood laminates commonly made from Maple, Beech, Birch or Mahogany; budget kits generally are made of lauan (normally called select hardwood); top end kits can use more exotic hardwoods such as jarrah, Ironwood etc.  Specialist drum makers can make shells constructed from solid pieces of wood either glued together as staves or in the case of true solid shell construction, hollowed from a single log.  Less commonly, drum shells can be formed from plastic or fibreglass.  Metal and metal alloys are also used for shell building but are more prevalent with snare drum building although some manufacturers do make drum kits using metal shells.

What causes the tone?

A drum is fitted with either one or two heads over the open ends of the shell, with drum kit this is Mylar, with drum corps Kevlar and on 'traditional' instruments any one of a range of animal or fish skins.  The head is struck which generates vibrations that are modulated within the drum and radiate out from it.  These vibrations are perceived by the ear as a fundamental note plus harmonics & overtones.  The shell and head properties dictate the timbre and tone respectively in a manner which will vary in line with many factors but mostly dependent on the properties of the shell design viz. bearing edge, diameter, thickness, depth, internal construction, number and type of laminate plies, internal shaping and also by your choice of heads and how you have tuned the drum.

Bearing edges

The bearing edge is the only part of the shell that the head touches.  The top of the shell is cut so that it comes to a point part way between the outer edge and the inner edge, with drum kits, most drum builders cut this angle to between 40 and 45 degrees and have this offset towards the outside of the shell.  Some contemporary builders cut this to a double 45 degree angle and/or towards the centre of the shell body.  The sharpness of this edge is an important determinant to the overall sound of the drum, a sharper 'point' will give a very accurate representation of the state of tuning of the drum and will make the resonance within the head greater, it also will allow more of the vibration to be passed to the hoop which will give it more contribution to the overall drum sound.  A more rounded edge will be slightly less 'bright' in tone and a more 'woody' sound as more of the vibration is able to be absorbed into the drum, there will also be less of the hoop effect in the sound.

The condition of the bearing edges should be checked every time you change heads.  These edges are fragile and any dips or divots, bar very minor damage, will show up in the overall tonality of the drum.  If a drum's bearing edge becomes more significantly damaged it will be difficult to tune properly and the only remedy is to repair or re-cut the edge.  Re-cutting bearing edges is a highly specialised woodworking activity and should only be undertaken by someone who knows exactly what they are doing.

Rack Toms and floor toms

'Rack toms', 'tom toms' or just plain 'toms' are the drums that are normally seen mounted above the kick drum usually with head sizes in the ranges 6" - 18." Floor toms are, as the name suggests, toms that sit on the floor, they are supported by legs.  Generally floor tom sizes vary from 14" to 20".  Rack and floor toms are constructed in the manner outlined above with a cylindrical shell having one or two heads stretched across the open ends.  they are generally used for fills or patterns.  Toms may be tuned melodically..

Bass drum / Kick drum.

The Bass or kick drum, is usually the largest drum in the set with sizes usually in the range 18"-24" however drums much larger than this are available.   It sits on the floor with the heads in a vertical plane, construction is the same as tom toms, and it may be viewed (particularly in jazz) as another tom tom, left untreated and tuned to a highly resonant pitch.  Generally, though for most drummers' applications the drum is tuned to just above its lowest tuning point.  The front head has a small (< 6") hole in the resonant head to facilitate mic'ing and the insertion or adjustment of some form of treatment to reduce resonance and increase attack.  The bass drum is played by a foot pedal with a beater generally striking the centre of the head.   It is common to see an additional patch attached to the batter head at the point of impact to counter the effect of constant striking in the one place.  Bob Gatzen in his excellent tuning video points out that the constant impact in the same area causes a build-up of heat at this point and a head without a patch of this nature will have a significantly decreased lifespan.

Snare drum

A snare is the heart of the drum kit, head sizes fall generally in the range 10-15" with the majority of drums being 14", although 12 & particularly 13" drums are becoming increasingly prevalent as main snares.  Depths fall generally in the ranges 3"-4-5" (Piccolo), 5" -5.5" (standard), and 6" - 12" (deep) although custom drum builders can cut any depth if required.  The snare almost always is played with a single ply head on the batter side, occasionally heavier hitters wishing to extend the lifespan of the head at the expense of tone, may use a head with a dot or similar appliqué.

The resonant underside side of the drum (reso head or snare side head) is where the three main differences lie between the snare and any other drums in the set.  Firstly the snare has a number of wire coils stretched across it, these vibrate and snap against the resonant head in response to the batter head being struck and give the snare its distinct sound; secondly, the bearing edge has a shallow flat spot cut into it at two opposite points falling between tuning nodes, this is known as the snare bed and is there to accommodate the snare wires or cords being held flat against the reso head, were it not to be there, the snare wires would sit slightly above the head and would give unwanted rattles and buzzes.  Finally, the resonant head itself is only 3-4/1000ths (3-4 mil) of an inch thick, this head is this thin to make it more responsive to the vibrations caused by hitting the drum's batter head.

One head or two?

The choice of using a single (batter) head or two (batter and resonant) heads on rack and floor toms is a personal decision.  Using the batter head only will give you a sound that is very clean and bright with a shorter sustain, the emphasis on attack rather than tone.  Toms with a single head are known as concert toms and are less common than two headed toms.  Concert toms may be seen in orchestral applications, within larger drum set-ups or as drums for that specific sound, however the decision to use single headed toms should be based on suitability for your own musical requirements. 

Using two heads creates a synergy within the drum which gives an output greater than the sum of the parts.  With two heads  you have a surface parallel to the batter head against which the vibrations caused by striking the drum are reflected back against the batter head and then back to the resonant head etc etc.   Secondly, as the vibrations are retained within the drum for a longer period, the drum shell is 'excited' to produce vibrations also which in turn add the existing vibrations.  The other main advantage and the most important aspect of using two heads is the level of control that the drummer can exert over the movement and duration of the tone.  This is a tuning consideration and is covered in the tuning section of the site.  Basically, with both heads tuned identically, the waves are continuously reflected in phase with each other with each wave slightly quieter than the previous until they are dissipated sufficiently to have decayed below the point of hearing, this gives maximum resonance for that drum in that tuning.  With the heads tuned differently to each other, they will be out of phase, giving a tone that decays faster and a greater attack.  On lower toms and/or at lower tunings this gives a 'pitch bend' effect.

Most drummers opt for two heads for all the above reasons.

Thick or thin?

The density of the shell has a significant impact on the sound of a drum.

A very thick drum will, in relative terms, hardly resonate at all and will tend to project a clear bright version of the head-tone imparting few of its own qualities into the sound, this is because the vibrations from striking are reflected by the shell more than they are absorbed by it (although a certain amount of absorption will always take place with a wooden drum) At lower tunings, they deliver a 'fat' or 'round' sound.  At elevated tunings they tend to choke up more easily, or as Bob Gatzen describes them, a 'Blunt' or 'Sticky' sound.

A thinner drum on the other hand will act like a type of membrane, vibrating and resonating in greater harmony with the heads, in this scenario, because it is absorbing vibration, it starts to vibrate itself and imparts its own vibrations and therefore sound into the overall tone of the drum.  At higher tunings, they are very clear in pitch and cut well through the music, they deliver greater volume than thicker shelled drums and lower tunings this may be considered a more 'woody' and warmer sound, overall a thinner shell will deliver a more pure tone than a thicker drum.  In general a thinner shelled drum will accept all head types and thicknesses and will deliver the optimum tone for that head type.

One caveat about using thinner shelled drums is that at high volumes, the vibrations within the shell of a drum itself can cause the sound to distort.   Pick your shells to match the music you aim to play

Construction variations

Because by far the majority of drums are of laminate construction, manufacturers also have the option of using 'cocktail laminates' in their drums whereby they construct the shells from different types of woods sandwiched together.  This an attempt to address the tone/resonance trade-off situation.  The choice is a subjective one and the major considerations are the number / thickness of plies and the types of woods used.  Different materials impart different qualities of vibration into the sound of the drum (see shell design) and therefore giving different qualities or timbres of sound.  As a rule of thumb, the softer the construction material the more 'mellow' the sound, e.g. Maple is 'warmer' than Birch, and because the softer wood will have more movement and vibrate more easily than a drum made from harder wood.  Maple will also be louder and more bass-resonant, whereas a harder material such as birch will have a quieter and more focused sound. 

A limited number of manufacturers construct drums using solid shells, these fall into two types.  Stave drums are constructed in a barrel-like manner with vertical blocks of wood glued together to create a shell, some 'high end' snare drums use this construction method.  The other and true solid shell construction involves taking a solid log of wood and machining it to size.  In general solid shell drums are thicker than laminate drums usually 1/2" (10-12mm) as opposed to 5/16 (7-8mm) are heavier and deliver a bright sound balanced with an impressive low end.

Reinforcements?

If you look inside the interior of a drum you may see that there is a second layer of plies at the top and bottom 3/4" - 1"of the shell usually angled to match the bearing edge cut, with the central vertical area of the shell remaining at the 'proper' shell thickness.  These are known as reinforcement rings.  primarily these are used for maintaining roundness and tune .

With the on-going development of drums, manufacturers have created product lines that are very thin-shelled to produce warm and woody sounding drums, although structurally sound, these drums, particularly larger sizes, may distort with the vibration of being struck, the reinforcement ring acts as a shock absorber and keeps these excessive vibrations to an acceptable level.

Reinforcement hoops therefore, by restriction, counter the tonal effect of thin shells to an extent, however as John Van Ness from DW drums says in his article on re-inforcing hoops on this site, they taper "off the highs because the column of air is physically blocked by the re-inforcement hoops at the inside edges." Certainly you should expect less resonance a more low frequencies from a drum with reinforcement rings.

Internal surfaces

The interior surface finish of a drum will also have an effect on the overall sound of the drum, some drums are manufactured with the same glossy lacquer inside as out and this will give a more reflected sound, very clean and crisp and because of the reduced absorption into the shell will be less woody.  A drum with a satin finish, i.e. not a high gloss lacquer, will start to deliver more of the woody sound and a drum with no interior finishing will have a porous surface and will deliver even more of the wood sound into the drum.  Some high end custom drum builders carve intricate designs into the internal shell to dissipate the internal harmonics. These can be pretty subtle differences!

What difference does the depth of the drum make?

The depth of a drum has an effect on the overall sound of the drum, not on the pitch but on the quality of the tone.  A longer drum will have a more full and rounded tone because the wavelengths generated will have more distance in which to develop, they will also be louder.  However with that in mind, longer drums require more effort to excite them as you are shifting a longer column of air with a greater resistance or backpressure.  A longer drum will have less attack, it will be slower to respond but will have a fuller tone and longer resonance, a shorter drum will have the reverse, again it is a trade off that only you can apply to your own drum-buying decision making processes.  Most off-the-shelf manufacturers provide only a limited number of depths for each diameter made, however custom makers can cut shells to any size.

How is the head attached to the drum

The head should lie horizontally and centred on the drum and extend beyond the bearing edges where it sits inside and under a metal or wooden rim which is attached by adjustable vertical tension rods to lugs that are fitted to the drum shell.  There are several variations on this such as 'free floating' drums where the tension rods attach to a lug that is not fixed to the shell, or less commonly drums that are adjusted at one single point with the aim of giving even tension all round.  Rims come in three main flavours. 

Hoops

By far the most common type of hoop is the flanged hoop (normally triple flanged) which is rolled into shape from a single strip of metal, made circular and welded. Equally spaced holes made to accept the tension rods are punched into the rim.  This type of hoop has two main advantages, firstly it is cheap and secondly it has a degree of flexibility which allows it to provide good contact all around with both head and shell, particularly where a drum is not exactly round or where some lateral torsion is evident.  Generally this type of hoop is found on toms and when playing gives a 'soft' strike and increased rebound.  Flanged hoops are available made out of metals of differing thicknesses, a thicker hoop will act more like a die-cast hoop (see below)

The second type of hoop is die-cast.  As the name suggests this is cast from molten metal into a mould (die) which is the exact shape and size of the finished rim.  This is a very solid piece of hardware and it resonates a a unit which gives greater attack and a sharper more 'brittle' sound to the drum  There is limited flex within the hoop and it is more inclined to show up any inconsistencies in the bearing edge, head and your tuning than you would find with a flanged hoop.  When the drum is struck, lateral vibrations move across the head and hit the hoop, as it is constructed from a solid piece of metal the sound is not absorbed and is reflected back in towards the centre of the drum again, giving increased overtones and clarity.   Die-cast hoops are a love hate thing, many drummers love the extra ring and bite that it gives them, it certainly facilitates high tuners who want that high more ringy sound, others find them too cutting, it is very much a matter of personal taste.  The other point to consider is that Die-casts will have less of a rebound than a flanged hoop, the head will feel 'harder' requiring increased control by the player.  It is most common to see Die-cast hoops on snare drums as they lend themselves to this type of sound more than rack toms, however some manufacturers use die-casts all around the kit.  

The third main type is wooden hoops.  These are constructed from plies of laminate and are about 3/4" thick.  If you think of a very shallow but very thick-shelled laminate drum shell you get the idea.  The plies give the hoop strength to withstand the battering they will take and they are much more durable than you would imagine.  They are the opposite of the die-cast hoops, as they impart a 'warmer' tone into the drum by absorbing vibration instead of purely reflecting and by vibrating themselves and imparting that vibration in a manner not dissimilar to how a shell does.  These are the most expensive type of hoop available with the exception of gold plated hoops.

The hoops sit horizontally across the drum and along the edge of the hoop is a number of evenly spaced holes that co-incide with the number of tuning points of the drum, typically the number of points will vary from 6 for a smaller tom up to 10-12 for snare drums and bass drums.  generally the larger the drum the more tuning points it will have, the more tuning points a drum has the easier it is to tune and the better it maintains tune.

Rods and lugs

Placed vertically through the holes in the hoops are tension rods which are basically bolts, threaded at one end and sporting a square top at the other to accept a drum tuning key.  Older kits tended to use slotted tops (like the top of a screw) however these are not generally manufactured for modern drums.

A tension rod fits into a 'lug' or 'nut box' that contains a threaded barrel into which the tension rod is screwed.  The nut boxes are attached directly to the shell of the drum, the exception being free-floating shells where the lugs fix to a ring on the bottom edge of the drum.   Over recent years as players become more demanding and the understanding of how drums operate is becoming increasingly applied, manufacturers have been seeking to reduce the amount of lug contact points and the 'footprint' of each lug contact point.  This is working towards permitting the drum shell to resonate more freely and put more of the sound of the wood into the drum.  Many manufacturers have developed 'low-mass' lugs expressly for this purpose.

Mounting

With a view to the overall sound of the drums, there are also decisions to be made regarding the way that you mount the various elements of your drum kit.  A snare drum for example normally sits in and on rubber in a cradle, drummers tend to tighten the cradle around the bottom hoop of the snare in such a manner that the snare and stand can be lifted as one unit by just lifting the snare.  Doing this can 'choke' the bottom head of the snare and the shell itself, making the drum less responsive and not representing the snare sound that you tuned it to deliver.  A snare should rest on the protective rubber and the basket claws tightened sufficiently so that it will not fall out of the cradle but enough that it will still be held in place.

If bringing out the full sound of the drum kit is a priority then the kick drum should not be used as a holder for the rack toms, instead they may be mounted on a rack or on stands.  The front of the bass drum should be off the floor slightly (1"-2"), this will raise the whole base of the kick off the floor so that it is not being muffled by the carpet or other floor surface that the kit is placed on

It used to be the case that all toms had a mounting attached directly to the shell or worse, had a hole cut in the shell and had a suspension arm entering the body of the drum itself as well as having a mounting bracket on the shell.  If you have spent a long time searching for your drum kit and evaluating shell woods and thicknesses, depths, head selection and assuming that you want your drums to deliver the tones that you have tuned them to generate then you will want the drums to resonate as freely as possible.  For rack toms there are essentially two variations that do this, both are based on the same principle.  RIMS are suspension mounts that fit to half of the the drum's tension rods, under the hoop so that there is no contact with the shell, the second type is the ISS mount that fits to the hoop itself, my own personal preference is the ISS mount as it is smaller and more easily changed (with RIMS you are obliged to de-tune the drum and remove the tension rods to take the mount off).  I have one set of ISS mounts that I exchange between my two primary kits. 

Floor toms should also be freely mounted instead of having leg mounts attached to the shell, RIMS mounts again do this, but this time they fit to the bottom of the drum between the hoop and the lugs and floor tom legs fit to the rim.   One word about the RIMS floor tom mounts though, you will need to buy a case about 2" bigger than the diameter of the drum as they increase the physical diameter of the drum's footprint, I have my 14" tom in a 16" case.

Summary

So there you have a reasonably detailed introduction into some of the science behind how drums work and hopefully an increased understanding enabling you know what some of the considerations are when considering purchasing or upgrading a kit.  Much of the detail and choices here apply equally when looking at drumsets at all levels.  Kits above entry level standard right up to custom made kits will have an increasing level of attentiveness to these details and will offer an increased selection from which to choose.  Selecting the right drums for you is an extremely personal matter based on your own preferences and the types of music that you will be playing, but spending money on quality equipment is, in my opinion, well worth the short term pain.

One final point is that all of the above is worth absolutely nothing unless you learn how to tune your kit, tuning aids such as torque measuring devices or drum dials are at best a rough guide, if you want to do it right, there are no quick fixes , your ears are the best and most accurate tuning mechanism, the rest is practice, practice, practice.

Paul

Drumset / Drum kit

1. Drumset / Drum Kit - A collection of different percussion instruments generally including but not limited to bass drum, operated with a foot pedal, snare drum, cymbals, and toms. It is generally meant to be played by one person, although at times can be played by more than one.

2. Snare drum - the drum that generally sits between a player's legs. A Snare drum is constructed,  drum heads of mylar, kevlar or natural skin are stretched across the opening attached to the drums drum head sizes generally vary from 10" to 14" and depths from 3" to 12".  The bottom of the drum is home to a set of wires that resonate when the top head is struck giving the distinctive snare sound.  Snare drums are generally played with sticks or brushes, however mallets and rods (collections of small sticks) are also used.  

3. Toms/Rack Toms -  The small to medium/large drums that are mounted on top of, or to the side, of the Bass drum(s), sizes generally vary from 6" rack toms to 18" Floor toms in varying depths although there are no hard and fast rules as to tom numbers and placement. 

4. Bass drums - for purposes of the FAQ, the largest of drumset items will be termed the bass drum. It is commonly referred to as 'kick drum' or simply 'kick', especially in the rec.pro.audio arena, so as not to confuse it with bass guitar during mixing, recording, etc.  The bass drum is mounted with the head vertical to the floor and is hit by a pedal operated beater.  Sizes vary from 28" down to 16" generally although drums on either side of this range are not unknown

5. Cymbals - Member of the Bell family of instruments, Circular discs (except rocktagons) of metal alloy that are shaped by various processes to provide an instrument that provides emphasis, texture, or effect.  Cymbals are played with the implements described at snare drums.

Paul & son Conor