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New member Username: Fredrico_alvarezPost Number: 7 Registered: Apr-08 | im fairly new to vinyl but am in love with the sound, its better than any other medium that ever existed. but i still dont know a lot of the technical side, which brings me to my question: how do tonearms affect sound and why, and what makes good ones good experience and knowledge appriciated |
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Gold Member Username: Frank_abelaBerkshire UK Post Number: 2875 Registered: Sep-04 | Jan will be better able to expound on this than me, so I'll keep this brief-ish. There are several parameters which will determine how well an arm works in a particular situation. The tonearm's effective mass, the quality of its bearings and its geometry. For example a typical arm is 9" in length (approx) but there such things as 12" arms and these show appreciably lower distortion figures by comparison to their almost identical 9" brothers. Why is it that the bearing tolerances are so important? Well, consider what is actually happening here. The cartridge drives the tonearm across the surface of the record. Friction introduced by the bearings is something the cartridge has to work against in order to drag the tonearm across the record. If a cartridge were the size of a small plough, the record diameter would be something like a couple of football pitches in length. The arm bearing would be a quarter mile away (for a 9" arm). So - any friction in that bearing, any movement whatsoever, has a major impact on the job of the cartridge. The tonearm's effective mass also has a major effect on how it works with your chosen cartridge. It and the cartridge's compliance add together and provided they're compatible, you'll get good results, but it is possible to buy combinations which are not compatible and therefore cause more grief, irrespective of how good the two components are. On another forum, I found some information regarding the characteristics of arms and cartridges which alows you to work out what combination makes a good combination: F (Hz) = 159/sqrt [Compliance X (Arm mass + Cart Mass)] There are several alternatives to this equation but they all yield similar answers to 2 decimal points. Dont forget to add something for the fastenings that attach the cart to the arm. If you dont know the mass of these just use 1 gram to get an estimate. Basically the ideal frequency is between 9 and 11 with anything from 8 to 15 being workable. Most modern carts are designed with medium mass arms in mind - but not all. Medium mass arms are about 10 to 12 grams of apparent mass. As a general rule the lower the compliance specified the higher the mass required. If you do not know the characteristics of your arm or cartridge you can find them out on line: http://www.cartridgedb.com/ http://www.cartridgedb.com/default_arms.asp Might make an interesting experiment to try your nujmbers out... Regards, Frank. |
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Gold Member Username: Frank_abelaBerkshire UK Post Number: 2876 Registered: Sep-04 | Oh by the way, in practice, most modern arms suit most modern cartridges and most older arms suit most older cartridges, but I thought you might be interested in the above. The calculations for my combination are as follows: My Dynavector XV-1S has a compliance of 10 x 10-6 Cu. My Naim ARO tonearm's effective mass is 11 grams. F (Hz) = 159/sqrt [Compliance X (Arm mass + Cart Mass)] F (Hz) = 159/sqrt [10 X (11 + 12.6)] (Note: the equation assumes that compliance is * 10-6, so remove this when plugging in the numbers.) The result of the numbers above is about 10.35. This is the harmonic frequency of the combination of arm and cartridge. I'm told that this wants to be at a lower frequency than might be reproduced on the record and a higher frequency than might be expected from motor/bearing rumble etc. Therefore a figure between 9 and 11 is ideal but anything up to 15hz and down to 7hz is workable. Regards, Frank. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 12445 Registered: May-04 | . "Why do good tonearms sound better?" A) 'Cause some designers are better than others. B) 'Cause someone else says this arm sounds better than that arm. I'm sorry but you are asking such a broad question it would take volumes to begin to scratch the surface of the topic. There is very little consensus amongst audio buyers and designers as to which type of tonearm is better. You must learn very quickly that all audio designs are a set of compromises and choices made which reflect the goals of the designer. There is no one perfect item in audio or else everyone would be making the same thing. A straight arm doesn't operate like a "J" or "S" shaped arm and neither operate like a linear tracking arm. A 9", 10", 12" and 16" arm will each have its own benefits and disadvantages. A gimballed bearing isn't the same as a ball and race which is neither a unipivot nor a knife edge bearing. Air suspended bearings are too way out there to discuss. Wood, aluminum, plastic, flat, round, square arms all reflect what the designer wanted at the time. There are very few low mass arms around today though a few decades ago they were very popular. Some vintage arms will kick a new arm down the block and into the emergency room. High mass arms are normally low compliance but not always. Damped counterweights do not sound the same as decoupled counterweights. I could continue but you should be getting the idea by now. There is no one or two or a dozen things which make a good tonearm "good". If you read enough about the various design techniques and decisions made by a designer, you'll learn what some people think makes their tonearm good. When you've read enough, you'll find what makes a good tonearm is the way it doesn't sound. . |
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New member Username: Fredrico_alvarezPost Number: 8 Registered: Apr-08 | Jan, i see you point. maybe the question I was trying to ask is more to the effect of: what do different designs lend to or take away from the sound? in other words, i understand essentially what cartriges must do well in order to do their job properly. if the stylus doesnt follow the groove well, then what comes out of the speakers is colored in some way. but what does the arm do besides hold the cartridge, what does it need to do well in order to give the listener what he or she is looking for? i am just looking for basics, i think better knowledge will just have to come with time, but I need to start somewhere. If my question is still too broad, then please let me know. muchos grasias |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 12452 Registered: May-04 | . Yep, still too broad. If you've reduced the "job" of the cartridge down to "follow the groove", then you've got the basics of the arm's task in "hold the cartridge" in place. |
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Gold Member Username: Frank_abelaBerkshire UK Post Number: 2885 Registered: Sep-04 | Here's a start. Look at the Rega RB300 arm. It's a relatively cheap, highly successful design OEM'd by loads of other brands. It's successful because it provides very high levels of performance for the money. It's a one piece aluminium casting with close tolerance bearings, very secure mounting and simplicity itself. This is why other brands take it and soup it up. Most simply rewire it with silver litz wiring. Some change the counterweight arrangement. A couple add a VTA adjustment wheel lock and one adds all those as well as lowering arm resonances by cutting holes into its underside. But underneath all that the arm remains the simple affair it is. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 12453 Registered: May-04 | . A few basic problems with tonearms is how they do their job. They do not follow the single groove of the record in the same fashion in which it was cut into the master disc. Therefore any deviation from that original path results in distortions and loss of information. A second issue is how they hold the cartridge. Ideally, they should not exist. But they must exist to do a job which is to hold the cartridge rigidly in space while not exerting any effect of their own. In this case think of the groove not as a spiral inward but as a straight line that pases underneath the stylus. The spiral just puts another "spin" on the problems a tonearn must face and we'll deal with that issue once we've thought about a few other more important requirements. The stylus of the cartridge is mounted on a cantilever which has free motion at the end where it enters the cartridge body and proceeds to the magnetic motor assembly. Since the stylus is vibrating in response to the modulation of the groove (and we hope that is all the stylus is responding to - which is a totally different set of problems), the entire system begins to vibrate being damped only slightly (in all but the Decca cartridges which have no damping device for the cantilever) by a small bit of elastomeric compound at the entrance to the cartridge body. So you have a canitlever wanting to vibrate and a damping block trying to stop the vibration. If the both ends of the cantilever don't respond in kind to the exact vibration of the stylus responding to the groove modulations, you loose information. See a problem yet? The cantilever's damping block must be stiff enough to supress "unwanted resonances" and wild @assed motion in the cantilever. The softer the damping material the more compliant the stylus can be to the groove but the more likely it will be to resonate at a higher frequency, for a longer time and at a higher volume. Stiffer damping compounds present other problems. This modulation between compliance and dampening places the semi-damped vibrations into the cartridge body at different rates at different times and from differnt parts of the cartridge structure. (For simplicity we'll assume the tonearm is built to only accommodate one specific type/brand/model of cartridge which alleviates the issue of how many variations of cartridges the user could eventually choose and expect good results with our one arm.) Depending upon the cartridge's design the movement of the cantilever in the magnetic field can - read most likely will - also create another set of resonances in the cartrige body. The entire cartridge body responds to these internal resonances by building another set of resonances based on the material body of the cartridge and how firmly it is attached to the device holding it in place and how frimly attached the motor of the cartridge is to the cartridge body. The more rigid the system, the less loss will occur from random motion but the most resonance will be transfered from the cartridge body to the device it is attached to. The higher the damping, the stiffer the compliance of the cartridge and the lower the resonant frequency of the system in most cases which pushes the problems of record warps into the picture. That, however, is another issue we'll deal with when we get to it. The resonance of the cartridge's systems generates resonances in the holding device unless the cartridge is decoupled from the headshell. Decoupling the cartridge almost always results in lost information and another set of damped resonances. For the most part decoupling is not used in modern arms and the arm is left to deal with the complex groud of constantly changing resonances coming from the cartridge which is firmly attached to its one end. The common way to mount a cartridge is to very rigidly attach it to a headshell which can either be permanently attached to the tonearm itself or detachable for the convenience of the user and manufacturer. How you make the connection between headshell and arm tube will affect the amounts and frequencies of resonance and loss at the junction between the cartridge body/headshell/tonearm. Press fit, cinch type, set screw, glued or one peice construction all affect how this headshell connection will be made and each presents another possiblity for loss and resonance along with complexity and cost of construction/machining the tonearm. One problem to consider here is stylus/cartridge azimuth. If the stylus is not absolutely perpendicular to the 45/45 groove walls, there will be mistracking. How the headshell attaches to the arm tube in large part determines how close to perfection you can get when mounting a cartridge. If you allow the the headshell any adjustment, you've broken the rigidity rule we want in an arm. If you build the arm without any adjustment, your cost and complexity of manufacturing the arm shoot up expotentially. More arms will be rejected due to machining errors than if you make the headshell adjustable. But the one piece headshell has more rigidity than an adjustable unit. More rigidity gains us what? And suffers from what? Allowing adjustability at the manufacturing end is not the same as allowing the user to adjust azimuth. One has a much greater success rate than the other in getting the stylus to sit in the groove without deviation from perpendicular. For some cartridges - not many in the present day - this would mean more cartridges sent back for misalignment of the cantilever or poor response from a user that just didn't get the stylus set right. A tonearm is the physical connection between the user and the turntable system. A manufacturer of any part of a turntable must realize the user has tremendous potential for error while trying to set the system up properly to the degree of a few microns making a vast difference in sound quality and life of the system. So the part of your system that requires the most precision in alignment must be designed with an acceptable amount of slop in the alignment procedure or made without any potential for error which will again raise the cost and complexity of the design. OK, let's skip over a lot of other considerations and just consider what happens when you set a resonant tube in motion through sympathetic vibration coming from the groove/stylus/cantilever/cartridge body/headshell. Very quickly, I'll tell you the bearing(s) of the arm at its mount must be very rigid to avoid slop and noise while being as close to zero friction as possible. So at the one end of the toenarm you have bearings which are attempting to hold the arm rigidly in place while not holding it at all. At the other end of the arm you have a resonating device attached which is mounted on a lossy, "springy" cantilever/damping block which is attached to the stylus which is in effect travelling at tens of miles per second while going over a rocky road that has potholes and ruts along with chunks of concrete sitting like uneven speed bumps. Consider loading your car's trunk with bags of sand until it is overflowing, disconnecting the rear suspension so it is more rigid and driving as fast as you can down a country dirt road that has not been maintained other than to place speed bumps along the way every few feet. If you understand the effects of wheelbase on the suspension and handling of a car, consider whether you are driving a Honda Civic, a Ford LTD or a Peterbuilt 18 wheeler under these same conditions. Open the hood of your car so it is free to bounce along on its springs and then consider the hood ornament is the stylus in your catridge and you are aiming it at that fly a 1/4 mile down the road. Step on the gas!!! Those are a few of the issues a tonearm designer must deal with to get just to the headshell portion of the arm. . |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 12454 Registered: May-04 | . I would suggest you read up on a few arms that are considered classics. Let's stick with pivoted arms for now. Place "Rega RB300" and "SME 3009/3012" into search engines. |
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Gold Member Username: Frank_abelaBerkshire UK Post Number: 2891 Registered: Sep-04 | Classic, Jan, classic! |
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New member Username: Fredrico_alvarezPost Number: 9 Registered: Apr-08 | Wow, this is obviously a much deeper topic than I thought. You post helped a lot though, Jan, thank you. The analogy at the end was effing hilarious. Once again, I appriciate your time. |
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Gold Member Username: Frank_abelaBerkshire UK Post Number: 2896 Registered: Sep-04 | Alex, Was there a reason behind your request for information? Are you looking at the subject academically, or are you interested in possibly buying smoething or what? The reason I ask is that, as Jan said, the subject is huge when looked at in a relatively esoteric conceptual way, but when it comes down to it, there are many less combinations of deck, arm and cartridge. You just need to bear in mind that manufacturers and dealers will tend to put together components which - in their view - deliver synergistic results. So, for example, let's say you were considering buying a new record deck and were trying to figure out what was so special about a tonearm that a cheap one should not 'sound' as good as an expensive one. Well, your choices depend on the deck you have and what are generally accepted as decent combinations. Even if you haven't bought a deck then the options offerred on your new deck are likely to be ones that work better. If, on the other hand, you're considering making your own tonearm, you'll have to bear in mind the deck you will be using as a platform. Incidentally, making a tonearm is far from easy - well, making a good tonearm is anyway! Regards, Frank. |
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New member Username: Fredrico_alvarezPost Number: 10 Registered: Apr-08 | Purely academic, Frank. I trust the dealers alot more than I trust myself anyway. I was just curious as to the workings of my turntable is all. |