Modifying drivers (split from markmck's Tang Band mods)

[Bill F.]

Mark,

I'd sure be interested in your responses to posts 18 and 19.

Pretty Please?

 

[rcavictim]

When I responded with the below, I assumed the question referred to the W3-881S.



I now recognize the possibility that it might have referenced the W4-656SB. The magnetic circuit design of the 656 is more conventional. It would be better served by a faraday ring (field modulation/eddy current control), but to optimize the corrective technique you have to get inside the gap and not be above it. Hard to do on an already assembled driver. Field strength drops quickly outside of the gap. In this low flux environment, I am uncertain of the possible gains of a shorted turn technique.......

Still, in the case of the W4-656SB, there is an experiment that can be conducted by shortening the plug length and using a copper ring spacer to bring the total assembly back to 1.5 inches. In this case, the only variable in play is the copper faraday ring sitting just in front of the gap. If the diameter of the plug and ring match, then any differences in response (transient response, frequency response, or distortion) can, with a high degree of certainty, be assigned to the presence of the shorting ring. Anyone want to conduct the experiment?

Good designing and good building,



Mark

Mark,

Thank you or answering my question on the W4-656. Yes I was discussing the conventional motor driver, not the neodymium job.

You suggest that to operate best the shorted turn must be positioned in the max field strength area of the gap produced by the magnet assembly. It is my thinking that as long as one had a shorted turn magnetically coupled to the voice coil at all points in it's travel (and one mounted on the outside front of the existing pole piece would do this if the VC was substantially longer than the magnetic gap), you would benefit fom the VC inductance reduction (through transformer action) which is as I understand it, the desired effect. This has nothing to do with the static magnetic field in which these components are bathed if my understanding is correct.

I agree that by making the added bullet out of soild aluminum you may benefit from this effect but copper is actually a measurably better conductor and a well placed copper ring of substantial cross section for good coupling and low ohmic loss would be the method of choice IMO.

I would be happy to give this trick and your other modifications a try but at the moment have no way of testing the performance changes. My computerized testing suite is not as sophisticated as yours and I rely on my ears/brain as much as my test instruments in these challenge cases now.

Rob

 

[MarkMcK]

Rob,

To be more precise, the best way to conduct the experiement is to use a shortened wooden plug and then two spacers of identical dimensions; one of wood and one of copper (or aluminum).

Also, FEMM 4.0 allows the insertion of non magnetic conductors into magnetic circuits with or without electrical currents. While I haven't conducted the experiment based upon your idea, I do have a fairly good idea of variable tolerance and impact. I still stand by my statement that out of gap shorting rings will be of little value.

Still, the experiemental design is complete and all that has to be done is to do the experiement and the question may be answered. Until then, I am more than willing to place the question into the "metaphysical pending tray."

Bill F.,

The questions in the two posts have already been addressed. Although my responses are in different threads, I have talked about how I do what I do and how you "read" dirac responses and how you interpret frequency response, onset response, and decay responses.

I have also talked to Dave about the article. He even tried to convince me to send him the manuscript. Dave, however, posts so much he rarely remembers his conversations. No offence meant Dave. When the article is published, if someone doesn't beat me to it, I will announce its availability.

The main reason I did not respond to your "how" question was the truly huge volume of knowledge that is required to do it. It is like asking an artist how they create or a scientist how they invent. It falls into the realm of what is called tacit knowledge. It is much easier to talk about the how of what I do to someone who already understands the physical processes that produce the signal and signs in response graphs and who knows about material vibration modes and structures. Some degree of understanding of chaos and turbulence is also helpful.

While I am sorry I cannot provide a "simple" answer to your question, the reason I am posting is to make it more likely that others will be able to duplicate and even extend my work. From my perspective, by giving examples of before and after and explaining what is going on in the before and after, I am explaining how I do what I do. In sum, while my work follows a consistent theory and I hit more than I miss, in the end all thought must be tried in the world of experience.

Mark

 

[Bill F.]

Although my responses are in different threads, I have talked about how I do what I do and how you "read" dirac responses and how you interpret frequency response, onset response, and decay responses.

Sorry Mark, I've searched and browsed your older posts, and I do not find anything about how you move from response graphs to cone mods. Perhaps I overlooked something. Can you supply a link?

The main reason I did not respond to your "how" question was the truly huge volume of knowledge that is required to do it. It is like asking an artist how they create or a scientist how they invent.

Sorry, I was not suggesting that you supply a magic pill that would convey the sum total of your skills, just that you comment on the basics. For example, a landscape artist cannot encapsulate how he creates a masterpiece, but he can tell you, "Start with the sky and water washes, move to palet knife for stone and wood, then sponge on the greenery."

It is much easier to talk about the how of what I do to someone who already understands the physical processes that produce the signal and signs in response graphs and who knows about material vibration modes and structures. Some degree of understanding of chaos and turbulence is also helpful.

The assumption that such knowlege is nowhere to be found among the readership of this thread may not be entirely correct...or appreciated...

From my perspective, by giving examples of before and after and explaining what is going on in the before and after, I am explaining how I do what I do. In sum, while my work follows a consistent theory and I hit more than I miss, in the end all thought must be tried in the world of experience.

Granted, experience is the best teacher, but what is this consistent theory? How does one move from measuring to cone mods?

I'm not trying to be tiresome here, I'm just inviting you to fill in a wide gap for those who might be, in fact, interested in extending your work.

For example, a good first step might be: How do you target a specific cone radius for modification? Noting a troublesome resonance at a certain frequency, do you infer its position on the cone using the cone material's dimensions and Young's modulus to derive the wavespeed and likely antinodes? Or do you use a simpler "close enough" approximation of some kind? Etc, etc.

Cheers,

Bill

 

[MarkMcK]

Bill,

The thread is about Tang Band modifications. I feel that you are taking it off topic. I have noticed how thread size is directly related to being off topic. Apparently this is a common problem in on line communities. Your concerns might be better addressed in a thread on "learning loudspeaker transducer design."

As a writer and editor (as you claim in your bio), you know how to use language in both positive and negative ways. Emoticons aside, what is your intent here? It seems to me you have an agenda that is different from my intent in starting this thread.

Late in your last post you use some of the words of mechanical engineering, but do you understand them? Are you able to work with them? If you do and can, then you should be able to tell from the frequency of vibration and locations I treat to squash them if the material characteristics you list fit what I report. If they do, then you can check to see if they also can be used to predict vibrations in other drivers.

Last, I hope you did not pay to be told those things about painting a landscape. With those directions, forget about a masterpiece. Even a "starving artist sale at the local hotel" quality of work would be unlikely. In art as in transducer design, a broad knowledge base is essential. Both artists and transducer designers study and work for long years before they hit their peak. Perhaps in response to one of my comments you have started along one path that will help you to your destination. The study of the mechanical properties of materials is a useful part of the knowledge base to do what I have done here. I will also recommend a book that Dan recommended to me when I was confused about the relationship of frequency to Xmax, Fundamentals of Acoustics by Kinsler, Frey, Coppens, and Sanders. I wish you well in your pursuits.


Mark

 

[Bill F.]

The thread is about Tang Band modifications. I feel that you are taking it off topic. (snip) Your concerns might be better addressed in a thread on "learning loudspeaker transducer design."

You are right. I apologize. I didn't set out to threadjack...

Would a passing mod be kind enough to please move my opening question and the following pertinent posts into a thread titled "Learning transducer design?" Many thanks. Mark, I'd of course appreciate any further contribution you'd be willing to make to that thread.

Late in your last post you use some of the words of mechanical engineering, but do you understand them? Are you able to work with them? If you do and can, then you should be able to tell from the frequency of vibration and locations I treat to squash them if the material characteristics you list fit what I report. If they do, then you can check to see if they also can be used to predict vibrations in other drivers.

Like many on these forums, I am merely a dabbler in many things. Transducer design happens to be one of them. Yes, I have a little formal engineering training, but it has remained my avocation, not my vocation. (Though I know for a fact that honest-to-goodness engineers do haunt these parts.) I feel I am reasonably equipped to answer many of my own questions on resonance control, but I am always seeking wisdom from those with more experience--like yourself--both for myself and my fellow DIYers.

Regarding the painting thing... Alright--perhaps I am justly guilty of using a bad analogy. And perhaps I was asking the impossible of you, short of me going back for another degree. Although I have to admit I prize the mental exercise of reaching for something over my head. It beats getting talked down to, for example.

I'll continue to read this thread with interest. Thanks for sharing.

Once again, sorry to intrude on your thread.

Onward and Upward.

Bill