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Multi-Ply Hardwood Shells

There are several different ways of making a wooden cylinder, but5 today the great majority of shells are made from multi-ply hardwood. The multi-ply lamination process was perfected on drums, so it’s claimed, by Fred Gretsch Snr in 1927. Until that time, shells were made by steam bending a single plank or board of wood and then holding it in the round by fixing ereinforcing hoops’, or eglue rings’, inside the top and bottom edges.

The introduction of plywood was seen as a great advance over the single ply esolid shells’ of the day. Ludwig and Ludwig ran a famous advertising campaign for their so-called Aero-Kraft laminated bass drum shell, dropping it out of an aircraft into a cornfield to demonstrate that it would not break. And, I believe, it didn’t. During the 1940s, Gretsch improved their ply shells by cross laminating them.

This involved arranging alternating plies in opposing directions, vertically and horizontally, making the resulting shell much stronger. Cross lamination meant the shells no longer needed reinforcing rings, so the straight sided eunsupported’ shell was born. Straight sided, cross-laminated plywood shells are the commonest type available today. Shells are further strengthened and kept in the round by staggering the seams where the plies join so that there isn’t just a single butt join at one point around the shell’s circumference.

They also occasionally have scarfed joins, rather than butt joins: a scarf joint is a smoothly graduated, overlapping join covering a greater contact area. The thickness and number of plies in a shell generally varies from around 3mm (1/8”) three-ply to 12mm (1/2”) twelve-ply. The thickness of plies can vary though, so a six-ply shell might be 6mm, or it might be 5.5mm or 7.5mm. Thinner shells are traditionally favored, as they are with other acoustic wooden instruments, the shell being the resonance chamber that gives the drum its particular flavor or timber.

It has always been the goal of a drum maker to construct the drum that’s both light and strong. In far off times this was because drummers had to march into battle carrying their drums slung around their necks. Then in the early days of jazz, portability was still prized n first because the early jazz bands were also marching bands, then later because most drummers didn’t have their own transport.

They would drag their kit around on public transport. We still want lightweight drums today, but this has to be offset against the fact they must be strong to withstand the rigors of much louder contemporary drumming. A thin shell is fragile and liable to deform from the circular and go oval. So reinforcing hoops, or glue rings, are still sometimes fixed to the inside top and bottom edges for stability. This is something you will find with some of the professional level drums made by companies like DW, Premier, Pearl and Tama.

It’s a matter of personal taste whether you feel the advantage of having a very thin and resonant shell is negated by the cramping effect of the glue ring. Tama, for example, offer glue ring shells as an option on their Starclassic drums and they say that top endorsee Simon Phillips prefers them because he likes the slight imellowing or muting effect” they have on the sound. DW says that its reinforcing hoops both strengthen the shell at its weakest point and raise the shell’s pitch. DW uses reinforcing hoops of maple, which are egraduated’: i.e., they get bigger as the drum diameter gets bigger.

Premier do a similar thing with their Series Maple and Birch drums. A tom tom with a diameter of 8” glue ring of around 7/8” deep, while a 22” diameter bass drum has a glue ring of around 1.5” depth. Noble and Cooley, uniquely I believe, fix their reinforcement rings at what they call the enodal’ points of the shell. These are areas an inch or two in from the top and bottom edges where there is minimum interference with the shell’s natural resonance.

The effect of these rings is to create a iclean and dense sound”, according to N&C. Thicker shells don’t need this strengthening and so they are termed straight sided, or eunsupported’. The thicker the shell the higher the pitch and the shorter the sustain. So a thick shell will be very stable, with a bright sound, while a thin shell will have a deeper sound and more resonance. If the shell is very thick (rare these days except with occasional snare drums) the shell tends more towards becoming a passive chamber and the head does most of the talking. That is, the drum will be loud, while the character of the head will be less colored by the material of the shell. But with a thin shell the wood resonates more and absorbs more of the energy and overtones of the head.

So in this case the type of wood the shell is made from will color the sound more noticeably. Pretty well all budget and middle price drums have straight sided, medium thickness shells with six to nine plies. The Pearl Export’s shells are six-ply and 7.5 mm. Top line drums are mostly straight sided, but the fact they are made from harder, denser woods means they can afford to be a little thinner while being as strong or stronger. You’ll notice also that the plies themselves can vary in thickness, so, for example, Spaun’s maple shells are eight-ply and 5.5mm thick while Premier’s Birch and Maple Series drums are six-ply and about 5.9mm thick. Sometimes the bass drums and larger floor toms are thicker than the smaller toms. Noble and Cooley’s CD Maples small tom shells are six-ply and 1/8” (3.2mm) thick, whereas their bass drums are eight plies and o” (6.4mm) thick.

DW calls this eproportionate-ply’ configuration. Thus their small drums are thinner five-ply, medium drums are six-ply and larger drums eight-ply. Occasionally snare drums are also made with a large number of plies since thicker shells give a higher, brighter attack. British custom drum builder Jalapeno makes 1” thick snare drums with 45 plies, while Peavey’s unique Radial Bridge design snare drum is 1.75” (45mm) thick. These drums really do have a loud, piercing attack and they are very sensitive. But they weigh a ton. Incidentally, by complete contrast, Peavey uses the thinnest three-ply 1/10”(2.5mm) thick maple shells for its tom-toms.

For mainstream multi-ply drums, it seems to be the pattern that the European and Oriental drum companies largely makes their own shells while many American companies buy in their shells ready-made. American companies buy plywood tubes in all the diameters they need from large-scale specialist manufacturers like Keller and Jasper. The various diameter tubes are then sliced into individual shell lengths (depths). Each drum company takes these eblanks’, cuts bearing edges, drills them and finishes them as necessary. So although many companies may share the same supplier this certainly does not mean you get the same result from each.

The Europeans, like Premier and Sonor, and Orientals, like Pearl and Yamaha, have traditionally made their own shells, often using their own-patented processes. For example, Yamaha’s Air Seal System (also used by Premier) and Sonor’s eCross Laminated Tension Free’ (CLTF) system. These involve cutting sections of plywood and layering them up inside circular moulds. Each section must be an exact length so that it lines up correctly inside the mould. Sometimes you’ll see cheaper shells which have butt-joined plies with tiny gaps where the plies don’t quite reach around the circle. These gaps may have filler to disguise them.

High-end shells overcome this problem by using sloping butt joins, angled rather than vertical. The plies are espiraled’ into the fiberglass former moulds and microwaved, ensuring a very tight join. An alternative method is to use a scarf joint, as does Pearl with its Heat Compression Molding System (HCMS). The scarf joint also eliminates the gap problem, but again, the cutting of the long overlapping scarf must be very accurate or the shell will not be flat.

It will have lump or depression in the area of the join. You can safely assume that problems such as these have been eliminated in the shells of the major companies, which these days are excellent in their appearance and finish. The plywood itself often starts out as two- or three-ply board, which is already cross-laminated. Layering up two or three lots of three-ply gives us the six-ply and nine-ply shells we’re familiar with. As we’ve seen with budget kits, sometimes a single ply of better wood is put on the inside of a six-ply shell making seven-ply. And sometimes an extra outer veneer is applied for finishing, making eight-ply.

Some companies, the most prominent of which is Sonor, have the outer veneer and innermost ply running vertically top to bottom of the shell, which they say helps the projection of sound up and down the shell. Most other companies have the inner and outer plies applied with the grain running horizontally. The more plies there are in the shell the more layers of adhesive glue. Glue is an insulating material and it’s a major reason why solid shells with no glue except for the single join are said to resonate better.

However, the process of gluing the multi-ply shells and then curing them is usually done by microwave heating. This process bakes the wood and the adhesive together so they fuse as one and thus n in theory n resonate as one. However, there are those who say it’s better to construct the shell without baking it. I have to confess I have no opinion on this point. If you can hear a difference, your ears are better than mine.

drum_techniuqes/emails/multi-ply_hardwood_shells.txt · Last modified: 2007/07/26 12:19
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