Doped drivers, why?

[Simon Hickie]

Ithilstone, if you'd like me to contribute, I'd be happy to. I have coauthored the UK's best selling undergraduate textbook in my field, so know a bit about proof reading, making things clear and understandable etc. PM me if interested.

[Dr Bunsen Honeydew]

Is there a book in this - the nva way or something similar. I have written at least a book full in the last 30 years. A lot lost now I am sure.

[Ithilstone]

well the way i see it we can make it as simple as possible with help from this forum
make it only about " why and how" and no opinions pure knowledge and know how - opinions always bring heated responses
lets open a new topic that first post can be constantly edited I will start digging in the archives and start to build compendium based on most common questions then we can go and start answering thise not so common ones. i am sure i will have some questions myself so Doc and other more knowledgeable users can chip in.
if i get something wrong you can correct me etc and i will edit the main post and if we get to the bottom of this Doc can then close the topic and Siomn can help turn it into a professional looking and sounding pdf

if we do it right it will help Doc to spent more time building amps and speakers and not get constantly wind up with silly or repeatable questions

sounds good?

[Dr Bunsen Honeydew]

Sounds good you start the thread

[Ithilstone]

as soon as i am back home and fill my belly

[TheMadMick]

I've used a photography analogy before and here's another couple. Some lenses 'measure' extraordinarily well but for whatever reason might render images in a less pleasing way than perhaps an older or 'technically inferior' one. I now buy lenses based on how they render an image with real life subjects not how they measure in MTF tests or shooting USAF test charts. I buy lenses to photograph people, places and things, not test charts. On the issue of lens filters, the less glass you put in front of your lens and the higher quality the glass and coatings the better. Filters degrade the image unless they are extraordinarily good and even then light transmission is affected even if only fractionally. The only filters I use are for protection - somewhat analagous to the simple cap and resistor approach to tweeter protection. You cannot make a poor lens better by sticking loads of filters on it or compensating for the poor results somehow by fiddling around in Photoshop for an eternity. However, lens manufacturers make money from the mass market by concentrating on style and marketing and perceived (but not actual) functionality over and above image and build quality.

If something can be configured simply to produce a superior result (like a prime lens with just a few elements or a speaker with just a capacitor and resistor in addition to the drivers) it seems daft not to - unless of course commercial considerations involve selling something for as high a price as possible for minimal materials costs.

William Bruce Cameron said: "Not everything that counts can be counted, and not everything that can be counted counts". I am also reminded of my inorganic chemistry teacher who said "all this fancy theory is there to explain what goes on at the bench". I don't dismiss theory (and the associated measurements) but if the observation and the theory don't agree - guess which one is wrong? This is most powerful when those using the measurement understand what it means!!! There are many out there who don't understand.

Hope this helps.

[Simon Hickie]

Good stuff. Despite virtually all of my career being in information systems and information management (as practitioner and educator), it never ceases to amaze me as to how knowledge is (a) lost and (b) becomes impenetrable for whatever reason.

It occurs to me that one way to convince (too strong a word for some, I know) the doubters is support what we know from empirical evidence with a bit of underlying science and theory where appropriate. We know that empirical evidence is derived from practical experience rather than theories. Theories without empirical evidence are just that - theories. However, empirical evidence which is then used as a basis for theory building is much more relevant. The risk is that it descends into a 'measurist vs. subjectivist' debate which tends to be pretty destructive.

By way of example, my Doc Mod project has broadly settled on the recommended 3.3uF cap with 12ohm resistor on the tweeter. This has been suggested by the Doc on the basis of empirical evidence and is borne out by my personal experience. Is there any science or maths to support this? I suggest there probably is. I've guesstimated that the roll-off from by doped woofer starts from around 2.8khz. I've also guesstimated that the efficiency reduction from the driver doping is in the order of 4-5db. This puts it on around the 81-82db mark. My tweeter is around 91db efficient and has an impedance of 5ohms at 2800hz, a difference of 9-10db. Lo and behold: a 10 db tweeter padding with a -3db roll-off at 2800hz gives us a cap value of 3.3uF and resistor value of 12ohms.

But here's the thing. It was the empirical evidence from listening that let me to what sounded best from which I then went back to look at the underlying theory, not the other way round. When I tried it the other way (theory first), I just ended up in a bit of a mess. But if the empirical evidence can then be used as a basis for theory building, then you are much more likely to be on to a winner.

As they say on Marvel's Agents of Shield: Knowledge Requires Experimentation.

[Toontrev]

I had a similar question to that of jonty's a few months ago. I can understand why the doc gets p'd off having to repeat the same thing time after time. However if it were possible to have the technical explanations and insights located in one place I for one would find it fascinating. In my case the question can be found on page 4 of the thread I had on my Goodmans Magnums, I particularly enjoy the historical aspects that make me wonder if we really do learn from experience.

[TheMadMick]

I had a similar question to that of jonty's a few months ago. I can understand why the doc gets p'd off having to repeat the same thing time after time. However if it were possible to have the technical explanations and insights located in one place I for one would find it fascinating. In my case the question can be found on page 4 of the thread I had on my Goodmans Magnums, I particularly enjoy the historical aspects that make me wonder if we really do learn from experience.

In a former life I did knowledge management (KM) as one of my work themes. KM is not re-learning and spreading the learning around an organisation. The problem with this, good though it is, it can tell you what to do but not necessarily, how to do it. I have to say, I wouldn't fancy trying to dope speaker units (especially more expensive ones) without a bit of practice and, possibly, a few mess-ups as well.

But don't let that stop you. It's a first step.

[Dr Bunsen Honeydew]

It seems I am in good hands