The purpose of this thread is to review the idea of how difficult it is to maintain precision with completed DIY designs, or any speaker for that matter, over a long period of time. A lot of the designs on the web are getting pretty old now, including even some of the Mission Accomplished speakers. What happens is product tolerances change significantly over time- sometimes from batch to batch; including resistors, inductors, and caps. I recently tested my friend's completed DIY project based on a DIY design and the final measurements were a bit different than the original design. Since I have measuring capabilities, it was no problem correcting the problem, which ended up being a slightly hot tweeter. Clearly, this was the result of production tolerance of the components used. Some DIY designers offer different L-pad variances to deal with this issue, but as a perfectionist, there are many limitations of giving someone a schematic and hoping that their response will measure like the "reference" FR plot.
So, I guess I'll just have to relax and accept that there is no perfect for everyone in DIY if you are using someone else's design. For example, if one is using electrolytic caps with a fairly large value tolerance difference, that can alter the final response quite a bit too. Some tweeters, even though they might be the same model have slightly different FR (see my vifa D26 thread). I've noticed with with the D26 in particular. I'm sure there are many other tweeters that show the same issue. Someone once posted that he's tested a bunch of RS28s, some with flat top end... some without it. So, combine the diffences in resistance from someones choice to use a 18gauge instead of a specified 19-20 gauge, and in conjunction with a slight hotter tweeter than the original, and we might have +/- 3 db differences over or under the references model. This bugs me to tell you the truth, but as long as DIYers are aware that they might not get the exact thing that is posted... and rely on their ears to judge the balance of the FR... I guess that's all one could hope for.
Ideally, a designer of a particular DIY speaker should check the design with new drivers periodically. This is a rather expensive endevour to ensure the end user is getting exactly what is shown in the thread, but it hardly makes much practical sense from a financial standpoint, given the designer probably already has the completed speaker from years past, in stock.
So, just some thoughts I've been having as I look on some of my designs that are going on over a year old now.
cheers
Jed
So, I guess I'll just have to relax and accept that there is no perfect for everyone in DIY if you are using someone else's design. For example, if one is using electrolytic caps with a fairly large value tolerance difference, that can alter the final response quite a bit too. Some tweeters, even though they might be the same model have slightly different FR (see my vifa D26 thread). I've noticed with with the D26 in particular. I'm sure there are many other tweeters that show the same issue. Someone once posted that he's tested a bunch of RS28s, some with flat top end... some without it. So, combine the diffences in resistance from someones choice to use a 18gauge instead of a specified 19-20 gauge, and in conjunction with a slight hotter tweeter than the original, and we might have +/- 3 db differences over or under the references model. This bugs me to tell you the truth, but as long as DIYers are aware that they might not get the exact thing that is posted... and rely on their ears to judge the balance of the FR... I guess that's all one could hope for.
Ideally, a designer of a particular DIY speaker should check the design with new drivers periodically. This is a rather expensive endevour to ensure the end user is getting exactly what is shown in the thread, but it hardly makes much practical sense from a financial standpoint, given the designer probably already has the completed speaker from years past, in stock.
So, just some thoughts I've been having as I look on some of my designs that are going on over a year old now.
cheers
Jed
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