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-   -   The design of active crossovers- Douglas Self wants your opinions (http://www.diyaudio.com/forums/analog-line-level/180090-design-active-crossovers-douglas-self-wants-your-opinions.html)

DouglasSelf 30th December 2010 05:17 PM

The design of active crossovers- Douglas Self wants your opinions
 
Hello all:

I am in the process of putting together a book, on active crossover design. This is planned as a weighty tome of 480 pages or so, and I am trying to make it as comprehensive as possible. To this end I have put the provisional Table of Contents on my website at The Douglas Self Site

I would be very glad to know about it if anyone thinks that anything is is missing. Even in 480 pages I cannot hope to cover the whole field, but I want to make sure that nothing important is left out. I would also be glad to hear any opinions that anyone may have on this project. In particular I would like to know if anyone is aware of any other book on the topic- I am not.

I would stress that this post is not an advertisment- publication is many months away. This is going to take time!

SY 30th December 2010 05:25 PM

Looks like a great book! I assume from the table of contents that you'll be dealing with the excess distortion issues of Sallen-Key (e.g., the Billam paper in JAES)? Will you be talking about the use of GICs/gyrators and the like in quasi-passive filter implementations?

I'll be diplomatic and not ask about showing vacuum tube versions...:D

DouglasSelf 30th December 2010 05:37 PM

Quote:

Originally Posted by SY (Post 2415506)
Will you be talking about the use of GICs/gyrators and the like in quasi-passive filter implementations?

I have to say it seems unlikely. I have sketched out the chapter on highpass & lowpass filters, dealing just with S&K and MFB types, and it looks like it is already the longest in the book. But thanks for the input- if I can squeeze it in I will.

jackies 30th December 2010 05:39 PM

Sounds like a great book! Looking forward to see it published!
The other book like that (that I know of) is Active Filter Cookbook by Don Lancaster. 1975
There's another one, Moshits, G., Horn, P. Active Filters Design 1981 - I only have it in russian translation, though it seems to be originally from the same US publisher as the previous one.

P.S. - Now that I think of it, these books aren't about Active Crossovers per se, but they discuss very similar topics anyway...

DouglasSelf 30th December 2010 05:48 PM

Quote:

Originally Posted by jackies (Post 2415526)
Sounds like a great book! Looking forward to see it published!
The other book like that (that I know of) is Active Filter Cookbook by Don Lancaster. 1975
There's another one, Moshits, G., Horn, P. Active Filters Design but I only have it in russian translation, but it seems to be from the same US publisher as the previous one.

Ah yes, but they are books on general active filter design, not specifically active crossover design.

Saurav 30th December 2010 05:48 PM

Any chance of getting some discussion on digital crossovers? Maybe just highlighting what's different when doing crossovers in the digital domain?

DouglasSelf 30th December 2010 06:07 PM

Quote:

Originally Posted by Saurav (Post 2415538)
Any chance of getting some discussion on digital crossovers? Maybe just highlighting what's different when doing crossovers in the digital domain?

Much of the book will be on the basic crossover and filter concepts, which can be applied in both the analogue & digital domains. I'm not however planning to get into any details of digital implementation.

Many thanks for your input.

jerome69 30th December 2010 06:09 PM

Hi Douglas,
I have read the TOC, it's very dense and seems cover the essential about analog active filter. This book is promising :).

For a first impression, you don't talk about amplification with chips amps, often used in this kind of design.
The second thing is about numerical XO ? It will be an other book :D
But can you talk a little about this ? For me it is very logical to talk about numerical processing because the source is numerical, now amplifiers become numeric (class D) and the process between the two (source and amplifier) should be ?

Third, when we design loudspeakers we use measurement tools, simulation tools ... A chapter on these ? I think you cannot avoid this. How can you evaluate time delays ? could be a very instructive chapter
For a more general design of active filter how to trace transfer response.

Some more precises impressions :
Chapter 2 : Can you talk about open baffle ? Very useful to use active XO. I have seen this in chapter 11

Chapter 13 : The AOP survey, i will curious to see the list ;) You have in the TOC at least five generation of AOPs ;)

Hope this helps if I notice other things, I will post later.

Rodolphe.
:)

DouglasSelf 30th December 2010 06:15 PM

Quote:

Originally Posted by SY (Post 2415506)
Looks like a great book! I assume from the table of contents that you'll be dealing with the excess distortion issues of Sallen-Key (e.g., the Billam paper in JAES)?

I have just tried to download the Billam paper (been on my list of things to do for a long time) but the JAES server is down until Jan 4th. I suppose you don't have a copy?

sreten 30th December 2010 06:36 PM

Hi,

The contents look very comprehensive and I'm sure will cover lots of filter theory.

However loudspeakers are not electrical circuits, and I've read too many articles
by electrical filter designers about designing loudspeakers that are fairly clueless.

I'm not saying that is applicable here, that is presumptious, but its the acoustic
responses that matter, and the required electrical filters, just like passive c/o's,
usually have nothing much to do with any classical electrical filter parameters.
That may seem obvious, but far too many want to assume perfect drivers,
and/or ignore the fact that that might be only true into infinite halfspace.

An area of interest worth exploring in such a tome IMO :

Incorporating the the power amplifiers as active devices in the schema,
not many people know how to go about doing this, and what can be done.
e.g. its easily possible to build the treble c/o into the treble amplifier.
(i.e. high pass is easy, but not low pass due to stability issues.)

Its really about combining flexible gain with filter functions.

That might lead on to another interesting practical issue :
Varying the amplifiers output impedance via feedback. That leads on to
the Stahl ACE bass or similar principles using complex output impedances.

An extension of your previous work regarding the statistical distribution
of the dynamics of a musical signal might be to extend this to the
seperate band limited sections of an active speaker, unlike the
former I'd expect different distributions with different music types.

Say you ~ knew this for each typical 1/3 octave. What is ~ the
relative powered required for each section ? How to derive it ?

There is so much nonsense about the active amplifier capabilities
required on the internet, a sensible analysis would be really good.

rgds, sreten.

A 3rd order elliptical lowpass filter and a 2nd order highpass
used in reality to produce 4th order L/R lowpass and highpass.
http://www.zaphaudio.com/audio-speaker17.html


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