Why Do Drummers Have PlexiglassPosted by Mike Schuck
A drum shield is a tool used by audio engineers to avoid the sound control problem of the drums. This article will discuss why drummers use this and some tips for making your drums sound great.
The easiest way to remove the plexiglass from a drum head is to remove it without using a special tool, or a second hand.
A small screwdriver is sufficient to slide the cover to the side so it can be removed, or use a hot mallet. The plexiglass must be removed as this prevents sound from escaping through the bottom of the shell.
The problem with this approach is that sound can seep from the bottom of the plexiglass up the side of the shell.
This results in reflections and a thin layer of negative-sounding noise around the drum.
An alternative method of removing the plexiglass is to "cut" around it with a piece of wood, thus making it less thin and extending it to the bottom of the drum.
This gives you greater access to sound trapped inside the shell and is quicker than using a special tool.
However, this method has two limitations; firstly, it won't work if the drum is cracked, which will result in a thinner layer of sound loss; and secondly, it may result in damaging the finish.
The second method mentioned is to use a super-thin blade that allows you to slide the plexiglass with the same dexterity and speed as your fingers, so you can cut it with a single stroke.
The blade is thinner than the plexiglass, so there's no added force, and this method avoids damaging the finish.
Sound pressure and vibration
One reason for the extra thick finish of drum shells is to damp the sound so the drum sounds quieter inside the shell.
This is achieved by applying a finish to the top of the shell with a thin film of oil. This increases the thickness of the topmost layer of the shell, creating a "silencer" effect.
The thicker the top layer, the more air is compressed and the sound is muffled, which results in the drum sound sounding less powerful inside the shell.
So there must be a thinner layer of skin closer to the "skeleton" of the drum head, which allows more air to pass through the drum and creates more vibration.
We don't know the exact thickness of the extra layer of skin, but we do know it has a certain form that can be defined.
These finger-width-thick layers of skin are known as drum skins and are painted on with paintbrushes or applied with thin pencils.
It's best to do a thin layer of thin, even paint over the skin to establish the thickness of the layer closest to the drum surface.
When the drum is taken apart, the top layer of skin should be removed as well. This gives a small sample of the thickness of the skin, and it's easier to evaluate this accurately with a microscope.
The plexiglass itself, however, will usually require several thin coats of oil or epoxy to protect it from the corrosive chemicals in the drill and turntable.
The largest drum shell on the market, the Yamaha TR7, measures 92.5cm in diameter.
In other words, it's roughly half as tall as a barrel, meaning the tonearm is approximately one-third as tall as it would be in a single-deck system.
To offset this the Linn Sondek LP12 turntable uses a shorter arm to allow the lower tonearm pulley to be at a lower height relative to the top platter.
Because there's no tonearm buffer bar inside the shell to restrict the vibrations, extra attention must be paid to keep the tonearm bearings properly aligned.
This is an essential factor in the performance of a turntable, as not being aligned correctly will reduce the life of the bearings, and decrease the speed at which they can spin.
The damping system for the Yamaha VL-1 turntable is a key contributing factor in the manufacturer's claims that it's 30 percent quieter than a similarly priced rival turntable.
The decoupled system removes the tonearm’s center bearing to provide the required damping, whilst also reducing the vibrations that are felt from the tonearm to the turntable itself.
There is also no plinth bracket, which should be fitted to all high-end turntables to keep them as level as possible.
Also, there's no anti-skate or anti-skate reduction on the VL-1, so a larger and more expensive floor mat is recommended to prevent ‘kinking’ of the platter in the sander.
After taking a digital recording or a CD from a CD player, turning the turntable on is a simple process.
For example, turning it on with the bearing level at the lowest setting with no belt on the motor should put the platter in good condition.
If a belt is fitted, raising the bearing level slightly should raise the platter – although the best is to run without a belt and to take extra care not to wobble the platter.
Once a record or CD is inserted, it can be played at a high speed by hitting the on-off button with a rod fitted onto a pedal.
Playing at too fast a speed can be extremely fatiguing, particularly if used with a large caliber cartridge. Even a turntable that looks good to the untrained eye can fail quickly.
Turntables have to be serviced, and it's important to follow a particular procedure when diagnosing problems.
It can be very difficult to hear the 'still' sound from the needle, so any changes to the platter drive belt should be investigated before adjusting the tension on the belt pulleys.
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