From DDL Wiki

Client Comments on Report

We received your report. Your analysis and findings are impressive. Your summary suggests that your most important findings are that the design is already in good shape wrt manufacturing, assembly, and environmental impact, but that it has two important design flaws: (1) difficulty maintaining tune (in general, or during vibrato?) and (2) wear on the pivot points. These seem to be good areas for further study and improvement.

Detailed comments:

• Why does presence of variety in the market have you believe that "any major changes or improvements could be adopted competitively"?
  • With a market as broad as the music industry, there is a lower level of the entrenched product loyalty that in seen in other markets, such as Mac vs PC in computers. The division still exists, but customers will be more willing to experiment with an innovative design when they are used to a wide variety of options. Breaking into the bottom end of the market is very hard, since it is flooded with very cheap designs, and beginner guitarists who could care less about the type of bridge they have. The intermediate to advanced guitarists also represent a large percentage of the market, and they care much more about the features/quality of the bridge than the cost. Breaking into the mid to high end is easy as long as your bridge has features that make it stand out.

• Good observation that the springs are very difficult to remove or install - but doesn't this contradict your finding that the design is already optimized for DFMA?
  • The springs are the most difficult part in the guitar to install and remove, despite the fact that they are under low tension. This is especially true for the end user who will rarely need to deal with them. Like all tasks requiring manual dexterity, installing the springs is much easier for laborers who repeat the process hundreds of times a day. Creating an easy-to-remove spring assembly was one of our brainstorming ideas, but was ruled out because it would increase the cost and complexity of the bridge enough to negate the advantages of the new design. In practice, the average end user will probably never remove the springs from the bridge. This makes the weight on this factor very low.

• You suggest that professional users would all choose a Floyd Rose over a Fender. Does this imply that the only advantage to the Fender is cost?
  • The Fender bridge is also easier to use on a maintenance level. It has a simpler design without the string clamps and other added functions. Installing and removing the tremolo bar is easier on the Fender bridge. Changing the strings on a Fender bridge takes 15 minutes, while changing the strings on a Floyd Rose can over an hour. All of these effects are secondary to the guitar’s primary function, which is to play music. The Floyd Rose is the more high-performance model, and most musicians are willing to put in a little more maintenance work to get that added quality. That said, yes, the main advantage of the Fender bridge is that it is cheap.

• You didn't mention palm muting in your report, but this may be a potential issue with the Floyd Rose bridge, since forces from the wrist on the bridge may detune. Can you comment?
  • The hand position of guitar users varies. Some users rest their hand in front of the bridge, where it does not cause any problems. Others rest it far back, where it may cause the bridge to detune. However, the force required to push the bridge down (and raise the pitch of the strings) with a moment arm of only an inch or so is pretty immense (think 30-70 lbs). Few guitarists get quite so spirited. Ignoring the frequency of occurrence, it certainly is a design flaw of the Floyd Rose that we did not think of during our first report. This issue would be common to all types of floating bridges, but would not be a problem on Fender style bolt on bridges (because they only bend up, not down). Since we chose to pursue cartridge saddles on a Fender style bridge, this won't be an issue.

• You never explained why the floating bridge is better at keeping the guitar in tune. Is this only because the Floyd Rose has clamps at each end? Why can't clamps be added to the Fender design?
  • There are two main reasons why the Floyd Rose offers superior tuning. The first is the string clamps. These eliminate string slippage at the nut and bridge, which improves things immensely. The other improvement is the "Floating" mechanism the Floyd Rose design uses. Since the Floyd Rose floats on a pivot between a spring and the string tension, the spring forces on it are close to that of an ideal spring, and it is more likely to return to its original resting place when pushed and released. The Fender bridge pivots on 6 screws instead of two precision pivots and knife edges. The screws are much less precise, and there is wiggle and slippage when the bridge moves. This means that the bridge rarely returns to exactly its starting position. Clamps can certainly be added to the Fender bridge. The problem for us is, they already have been. There are quite a number of different Fender style designs with improved string retention mechanisms, so that it would be hard to create a new design that didn't infringe on a patent already in existence. We did manage to come up with one, though, and that is our cartridge design.

• In your "product function" section you explain use, rather than how the mechanism functions. However, we see that you explain the mechanism later in your mechanical analysis.
  • The "product function" section contains a description of the basic mechanism, as well as a section on the use of the bridge. A more quantitative description is given in our Analysis section.

• Part G7 seems to be an assembly with its parts listed later - why is it also listed as a part? Part F9 appears to be an assembly of multiple components. Please comment.
  • G7 was originally put on our list when we were measuring parts, so that we could know the weight of the assembled bridge. Looks like we forgot to take it off for the final report. Sorry! F9 will also be split into two parts. Thanks for the corrections.

• Good observation that the standardized fasteners simplify manufacturing and reduce costs. You also mention that the large number of fasteners increases assembly time. Are all of the fasteners in the design necessary? Could any of the functions be combined?
  • The number of fasteners has been reduced as low as it can be without impacting the function of the design. Where there is room for some improvement, at least to the end user, is to have all of the different fasteners use the same tool for installation, as opposed to the mixture of Philips head and several different sizes of hex screws in the current designs. The screws are of a variety of different sizes, require different amounts of torque to operate, and have wildly different expected duty cycles (some screws are used almost daily, others should never be unscrewed in the normal lifetime of a guitar), it could be a project in and of itself to find some sort of common screw head that would work in all the different situations. This would be an exceptionally dull project with very little user impact, so we decided to pursue something more exciting.

• Are DFA guidelines followed with this design? Are all parts inserted from the same direction? Is there potential for ambiguous placement or part mix-up? etc
  • As stated above, the design is fairly optimized. There could be a bit more tool standardization, but there are some function trade offs. The Fender bridge is especially optimized, assembly is two steps, and all screws are put in on the same side of the bridge. The Floyd Rose, being more complicated, has screws in many more places. Some of these locations are less than optimal for assembly purposes. However, having the less commonly used screws out of the way of the user probably takes precedence over ease of assembly.

• What scale are you using for FMEA numbers? You seem to have chosen 1 for "poor detectability", although it seems that it should be 10 to be in line with the RPN concept.
  • A score of one is given for a known design flaw, where no detection is required because every guitar bridge has the problem. Detection is very easy, not very hard, because you automatically know every part has the problem without any investigation. Should we have handled this differently?

• In your DFE, you suggest that very few guitars are scrapped, but in reality they all are eventually. Please comment. Your LCA analysis is quite good, and we understand that the CO_2 tax will not affect us significantly.
  • Guitars are more often left in a garage or basement than scrapped, but it does happen eventually. We feel that this is not a truly significant part of our analysis. (In part due to the fact that we are focusing on a sub assembly and not the main product.) The main body is generally a wood product and is biodegradable. The metallic parts will likewise eventually rust on steel bridged models. The only parts of a guitar with any potential environmental impact would be the small amount of solder on the electronics, and on some older guitars, toxic paint. In both cases, the amount of environmentally damaging material is very small. The relatively small amount of recyclable material combined with a very long product life make it impractical to design for end of life concerns.

• In your mechanical analysis, you examine a domain up to 12 degrees, where all strings are slack. Do guitarists use this range or any range beyond 6 degrees where some strings are already slack?
  • The range we considered was from 0 degrees (neutral position), to 12 degrees depressed. For the Fender and Floyd Rose designs, quick geometrical calculations show that the maximum travel of the guitar bridge (pushing the lever to the body of the guitar) is about 12 degrees, varying one or two degrees depending on the model of guitar and positioning of the bridge. At 12 degrees, all the strings are completely slack except for the High E string, which is almost completely slack. Results for bridge rotation about 12 degrees would be easy to perform (change one line of code in our MATLAB simulation files, and you can go up to 90 degrees), however, they would not be physically possible results. We did not simulate the behavior of the bridge when the lever is pulled up (raising the pitch), since this is not possible on the Fender bridge, only on the Floyd Rose.

• Your force equations seem to list F_pivot twice - should this be separated into x and y components?
  • Yes, this should be F_pivot_x and F_pivot_y. This force is just the force of the body holding the bridge in place, and is not used in any calculations, so we did not differentiate between the two.

• Do you have research that says performers would prefer the tremolo bar to change the frequency of all strings proportionally, or do they prefer to create dissonance? If some users would prefer chords to stay in tune, as you suggest, this could be a very interesting opportunity, indeed.
  • This isn’t something a lot of musicians think about – they tend to work with what they have. While this was not mentioned in our research, it can never hurt to put new options on the table for artists to play with. Just like people probably did not miss television during the 1850's, sometimes something has to be invented before users see how much better it makes their lives.

We are looking forward to seeing your market research and new ideas in the next report.