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Bronze Member Username: DrumsuckSt. johns, Newfoundland Canada Post Number: 33 Registered: May-04 | Anybody every tried using a wrist saver (one of those gel-like keyboard things) as a method of turntable isolation? They're cheap and I was thinking it would be worth a try to cut one up into 4 pieces and place it under the turntable feet to see if it does anything. |
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J. Vigne Unregistered guest | Let's talk about isolating a turntable from the outside world of acoustical and mechanical vibration. How you go about isolating your turntable from the effects of vibration are determined by the type of table you own. In the world of turntable design there are essentially two types of tables on the market; a suspended table such as the AR and Linn Sondek designs and a nonsuspended table such as the Rega and it's derivatives. The two types of design will require different methods of isolation in some key areas and similar methods overall. One of the first things almost every table manufacturer agrees upon is the need for rigidity in the support system and in the table's structure. This is required because a turntable is an electromechanical design. In other words the only way a turntable works is by mechanical motion of the record past the stylus of the cartridge to produce an output voltage. If the stylus modulates in reference to a movement that is not in the original groove then the result is distortion. Any outside motion can swamp the signals of a record groove which are created by movement of the stylus in the grooove to a dimension that is smaller than the width of a human hair. To that end the first point of reference is to make certain the surface the table sits upon is a rigid as possible. This precludes the use of the rattan boookcase and the hand me down coffee table as suitable surfaces for a turntable. If you look at the megabuck tables on the market you will see that, at the top most price range, the turntable is actually part of a structure that supports the table in an extremely rigid environment. If you can't afford $80,000 for one of these tables you can at least take a few ideas from them and bring them down to the DIY market. Unsprung tables particularly and most suspended tables will almost always perform best for the least amount of money on a wall mounted shelf. These are available from various manufacturers and are designed to screw into the studs that support the wall. This is about as rigid as you can find as long as you do not mount the table to the drywall alone. Make certain the wall you are using is not subject to vibration from a fan or air conditioning motor that will add vibration to shelf. If you would like to start out with less financial investment you can buy shelf brackets at the hardware store and mount these to the wall with a shelf on top. When mounting a shelf to any surface for a suspended turntable it is usually best to isolate the shelf from the surface it will sit upon. This can be done several ways but the most common is a spike of some type. When using a spike you will normally be trying, in the case of a turntable, to drain any vibration in the equipment chasis away from the device and to keep vibration from entering the equipment from the surface it is resting upon. This means the large end of the spike will be against the equipment and the small end will be on the supporting surface. This places a very small contact area at the support surface and little energy can move up the path to the table. Another way to isolate the table is with ball bearings. The surface of the table and shelf will touch the surface of the bearing only at a tangent to each surface. This provides a small contact area similar to a spike. With either a spike or bearing it is usually a good idea to place a hard surface, such a penney, under the tip of the spkie or the bearing to assure as small a contact area as possible. To maintain the rigidity of the support it is often a good idea to use a blob of a substance called BluTack or photo mounting plastic to the bottom of the structure sitting on the spike. DO NOT use a compliant material such as sorbothane or gel inserts as this will defeat the idea of rigidity and possibly add unwanted motion in the playback system. You effort is to lock the support system in space while isolating it from the outside environment. With an unsprung table you will normally find it best to attach the shelf to the brackets. Make this surface as level as possible and remember three points of support are the most stable as the system will become self stabilizing. ANY spring type surface will change the resonant frequency of the system and may defeat the entire purpose of what you want to accomplish. Unless you are well enough versed in physics that you can determine the frequency with which the system you are creating with compliant materials will oscillate you should stick to making a rigid support system and leave the compliant material selection to the table manufacturers. Once you have a support system in mind it is a good idea to look at what you are going to create and decide if you are looking for high mass or low mass. Different tables will respond to each system differently and it is best, if you don't already know, to find out if you are going in the right direction for your particular table. A call to the manufacturer is the best way to find out what they have found to be the best way to use their product. The down side to high mass it the energy storage of most high mass materials/structures will delay the transmission of vibration in time. This means whatever does get through to the table will be delayed in time similar to an echo and, in extreme cases this is exactly the sound you might hear through your system. The advantage of low mass is the vibrations are shifted upward in frequency and are released more quickly. The down side of low mass is the difficulty in making a rigid structure and the likelyhood that the structure will ring and still have a delayed effect on the system. If your table is one that prefers a low mass system, such as a Linn Sondek, you are almost home free at this point. Tables such as this can be mounted on a shelf that is sitting on a rigid support structure and at most a set of spikes will be sufficient between the shelf and the table. If you are using a free standing shelf it should be mounted on spikes and filled with a material that will dampen the vibrations of the structure. Cat litter is one of the best materials for this purpose. If, on the other hand, your table is one of the many that will perform better on a high mass system then you still have work to do. If you are using a free standing shelf you will want to fill it with lead, sand (or concrete) and some people like to finish off the top with cat litter to create several layers of material that all absorb different frequencies. Shelves should have no enclosed spaces such as a bookshelf or the racks sold with systems. These spaces act as acoustic collectors that will increase the amount of vibration in the support structure. Once you have managed to construct or purchase a support system that works well with your table you can proceed to how to place the table on the support. In most cases the more isolation you can provide here is beneficial. The easiest support is a simple piece of solid wood. Not plywood since you want to keep the surface the table sits on as light as possible so it will dissapate energy as quickly as possible. The best choice for this surface is a maple cutting board. You can usually find these in the dimensions necessary to support a table and it will be a solid surface that will not move in separate directions. If you are going the high mass route all the way through the system you will want to use several layers of MDF, the material your speakers are most likely made from. MDF is available at any home improvement center but if you go to a limber yard you might be able to find High Density Fiberboard which will be stiffer and more resistant to vibration. Several layers of MDF with a SINGLE layer of paper towel between them is a good choice for a support system. To get more sophisticated you can vary the materials and/or use a damping material sold at car stereo shops to dampen panels in between the layers. If you go the damping material route make certain you have a material that will not convert vibration into horizontal energy. For more sophistication use a constrained layer damping material. This can be purchased from various suppliers on the web, usually scientific supply houses or large elctrical/mechanical suppliers. Try: http://www.mcmaster.com/. Some good combinations of materials to build upon one another are MDF, marble or granite topped with glass. If you go this route you want to make certain the structure doesn't get unstable with weight at the top so it will tend to oscillate as the table spins. This will require redoubling your efforts to make a rigid structure. In the end this surface must be absolutely level. (If you use MDF and have a router you can scribe an undulating pattern on the bottom of the panel going about 1/3 the depth of the panel. This will help breakup vibration patterns.) If you wish to go further before you place your table on this surface you can purchase diver's weights at any scuba supply store and place these under the feet/spike of your table. These are weights made of lead that will further deaden your system. Again make certain you are not creating a system that will oscillate from all the weight at the top. The table itself can be made less prone to react to vibration if you dampen the panels of the table. You can use the automobile damping sheets, I coated the inside of the frame to my VPI HW19 with epoxy and then built up consecutive layers of lead shot, sorbothane would work on a "boxed" table or there is a ceramic based paint sold at paint centers that is used for insulation purposes that will deaden the panels. (If you go this route buy enough to coat the inside of your speaker cabinets also.) On all tables make certain the frame of the table is stiff. On a Rega there is no other option but on a table like the VPI HW19 put diagonal braces across all four corners to eliminate flexing. Once you have the table supported properly you can move on to isloating the motor from the plinth. The motor is going to want to vibrate and now your job is to keep that vibration to a minimum and keep it from entering the playback system. If you want to simply put some sorbothane between the motor and the plinth this will help as long as you don't change the geometry of the belt riding on the (sub)platter. If you want to go further you can again look at the high priced tables and see they use a motor assembly that is isolated from the main plinth. The motor is placed in a heavy mounting sytem and has no connection to the plinth. You can begin by simply keeping the vibration of your motor down to a minimum. This can be accomplished by placing a weight (either a diver's weight or a weight from a barbell) under the motor and attaching it to the motor with BluTack or epoxy. The weight has to be supported or else you will create a rotational mass that will defeat your purpose. Layers of sorbothane or damping material will do to raise the weight sufficiently and will keep the vibration from entering into your support shelf. You can also take a can or some other container that is stiff enough and, after detaching the motor from the plinth, you can place the motor in the can, afix it with BluTack and fill the rest of the space with lead shot. Get a size of shot that will not enter any openings in the motor casing. If you go this route, epoxy three ball bearings to the bottom of the container to act as spikes to the motor assembly. As before you do not want to change the geometry of the motor spindle/belt/platter. Most spindles will have a set screw that will allow some height adjustment. If your table has a presed on spindle you will have to adjust the height of your newly isolated motor assembly to accomodate the needed height of the spindle/platter. Dust covers are a major source of feedback since they act as collectors of mechanical and airborne vibration. It is best to remove the dustcover when playing a record. If your table has a sprung chasis you will normally find a small piece of open cell foam inside the springs. If you table doesn't have these you can use a piece of foam from a corrogated mattress pad or go to shop that sells musical instruments and buy a foam wind screen for a microphone. Use enough to slip inside the spring without impeding its motion. (Use foam in the port of your speakers to tighten the bottom end on reflex and ported designs.) Platter mats and record weights are a matter of taste and whether your turntable can use these accessories. More often than not they make an improvement that is worth the money. If you can't go the expense of an aftermarket mat try a piece of rice paper between your mat and the record. Rice paper can be purchased at art supply houses or they are the heavy record sleeves sold to audiophiles. Cut it to fit your platter and you may have a cheap fix for the sound of a thin mat or a glass platter. Tonearm damping can be added to many arms and will improve tracking and give a more solid presentation. There are articles on the web on how to accomplish this. The method is too long to be included in this article. It is, however a simple DIY project. The same methods normally apply to isolating a CD player or a tube pre amp. The difference is in the selective use of compliant materials in those applications. One way to judge the effectiveness of your efforts is to rap the surfaces of the turntable with your knuckle with the stylus sitting in the groove of a record that isn't spinning. The volume on your pre amp should be at a low level to begin until you are certain your efforts have been successful. If you begin to hear noise transmitted throught the system, stop and reasess your design. |
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Bronze Member Username: DrumsuckSt. johns, Newfoundland Canada Post Number: 34 Registered: May-04 | that was a far more detailed response than i could have envisioned. thanks. 80) |
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Bronze Member Username: DrumsuckSt. johns, Newfoundland Canada Post Number: 35 Registered: May-04 | currently i have a piece of 1" think MDF laid atop of two concrete bricks on top of my MDF utility cart which is acting as an equipment rack at the moment. the utility cart has no back or door, but it's on wheels and is generally wobbly. I realize that I would do well to replace it when I purchase my new turntable. |
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New member Username: FlaxtonPost Number: 1 Registered: Nov-04 | I have a rega planer 3 on an atikarma platform which is on a sound organisation stand. Is this ok or would a shelf on the wall be better. |
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J. Vigne Unregistered guest | Normally the Rega tables do better on a wall mounted shelf but that is a matter of your room and system set up. If the floors are not shakey and the S.O stand seems to give good isolation then you may not find much benefit to a wall shelf. Many time a wall shelf will respond to other vibrations such as air conditioners or fans that will not affect a floor stand equally. |
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New member Username: FlaxtonPost Number: 7 Registered: Nov-04 | J.v.. The sound organisation is on a concrerte platform so it is very solid. Thanks for the advice. |