The design of active crossovers- Douglas Self wants your opinions - Page 4 - diyAudio
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Old 31st December 2010, 05:59 PM   #31
dewardh is offline dewardh  United States
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This is, perhaps unfortunately, going to be a history book. Builders of the analog crossovers for Linkwitz speakers are already finding it difficult to source the necessary capacitors . . . a situation that is only going to get worse, since demand for such items is steadily falling. Meanwhile digital signal processing becomes ever better and less expensive . . . and ubiquitous. If the book is long on crossover theory (which can translate to the digital realm) it may have future use . . . but where is the market for a "new" analog crossover?
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Old 31st December 2010, 06:27 PM   #32
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Hi Douglas

I miss the chapter about the "blameless crossover".

Fun aside: Are you going to show how to take the driver transfer functions into account within the chapter dealing with the subtractive crossovers ?
These filters are by themselves almost useless if you don't resort to some tricks to include said transfer functions.

Regards

Charles
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Old 31st December 2010, 11:41 PM   #33
BrianL is offline BrianL  United States
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Douglas,

this looks like an interesting undertaking. I think the trick will be to walk the fine line between being a speaker 'system' design book and an active crossover design book.
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Old 1st January 2011, 12:45 AM   #34
DQ828 is offline DQ828  Australia
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Quote:
Originally Posted by abraxalito View Post
No ADC needed if the signal is already digital as is the trend nowadays. Board space and test time I dispute in the case of more complex designs. Testing analog filters is quite time consuming and requires fairly dedicated test equipment (like AP) and multiple test points whereas digital can largely self-test. So its not just a function of time in production, its machine hours where the machine's capital cost is significant. Yield I also dispute - its not just a function of transistor count, its also solder junction count - integrated gets better yields and DSP will always be higher integration. DACs (with reconstruction filters) already come on-board with some DSPs and this trend can only continue further.



I omitted the opamp support circuitry - SMT caps for audio performance (NP0) aren't too small and can be more expensive than the opamps they're connected to for the larger values. Alternatively, to use the smaller values the cost of the opamps goes up for the same performance levels (JFETs being more expensive than bipolars).



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MiniDSP $200.00 for 4w stereo+ two cheap PS (I used old phone charges) & away you go, 1hr & you making all of the changes you probably ever need.

David

PS: except some people might prefer it in a case
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Old 1st January 2011, 05:40 AM   #35
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Quote:
Originally Posted by DouglasSelf View Post
I assume you mean the line input and line output chapters; since they are finished I can speak confidently about them.
Yes, I was referring to those chapters. I look forward to the deltas when the book comes out. Is the Amazon date of May this year realistic incidentally?

Quote:
I never have and never will simply cut and paste chapters between books. I always aim to give value for money.
So I take it you had no clout over how your own contributions to Audio Engineering Know It All were presented? I find it hard to disagree there with the reviewer who gave it one star - a breathtaking hatchet job of a book. One of your chapters (12, p367) on 'Negative Feedback' looks to be an almost direct paste, beginning from the final paragraph of p49 of your earlier book 'Audio Power Amplifier Design Handbook, 5e'. Only the paragraph headings and some otherwise dangling cross-references appear to have changed. As the Amazon reviewer from Australia points out, the context provided by earlier paragraphs in the original chapter is notable by its absence.
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Old 1st January 2011, 07:30 AM   #36
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Hi Douglas,

Quote:
Originally Posted by DouglasSelf View Post
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
No offense meant, but that looks like it about covers the state of my knowledge of the subject in 1980's so and all relevant sections have weighty tomes published on them decades ago (from the filters including allpass filter use for time alignment to line-in/out circuits etc), most of which are now available freely for download.

To be honest, I cannot see why it would desirable to publish such a work as it essentially holds only historical interest.

We live in an age where we have:

1) mature modern digital crossover options (including crossovers that can be directly feed digital signals) and which handle time alignment, equalisation and many other functions rather well, are infinitly and instantly adjustable with a precision that state variable analogue filters can never manage, even allow dynamic filtering (to protect drivers against over excursion)

2) fully digital Amplifiers (as in digital input with no intermediate DA conversion except in the power stage) that could be used in active speaker applications fed directly from a DSP Crossover and which use power supply voltage adjustment for the first 24dB of volume adjustment, so no digital domain resolution is lost until more attenuation is applied

3) essentially exclusively digital media being available for the last almost 30 Years already and most historical material also archived only in digital form

Analogue in audio is rapidly becoming a stagnant and uninteresting backwater.

Now mind you, everything I do remains in the analogue for now (for various reasons), however a reference grade work on active speaker systems in this day and age e.g. the 21st century (and not in the 1980's) should probably limit the whole "analogue" section to 10 - 20 pages tops in the history part and focus on the current technologies and how to maximise the return from them.

Kind regards Thorsten
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Old 1st January 2011, 07:42 AM   #37
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Originally Posted by ThorstenL View Post
Hi Douglas,
Analogue in audio is rapidly becoming a stagnant and uninteresting backwater.
Kind regards Thorsten
That is "fighting words"..

I have auditioned Hypex class D amps. For a sub , yes. For the rest .. Ha ha

A modern class AB amp with all the "candy" (cap multipliers , TMC) is far more engaging than the best D amp. The Eagles (2009) , with their Class D amp stacks in concert ... the sound quality sucked !! Rush , in 1990 with 100.000 watts of class AB , sounded far better. This absolutely carries over to the living room , I would not trade my 250W "blameless" w/ TMC for any of the Hypex's. Not even subjective , but a analog output stage driving a analog loudspeaker is the ONLY way !!

I agree that digital sources RULE (with analog OPS's)


"UnInteresting" to corporate interests that only want to push garbage on the "sheeple" , who know not what good Hi-Fi sounds like!
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Last edited by ostripper; 1st January 2011 at 07:47 AM.
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Old 1st January 2011, 08:14 AM   #38
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Hi,

Quote:
Originally Posted by ostripper View Post
I have auditioned Hypex class D amps.
Now, I am not talking about slow switching, analogue input, looped feedback design in my post above, am I?

I am talking about open-loop system which use powersupply voltage adjustment for much of the volume control range and switch at much higher frequencies.

Stuff that is switching with analogue inputs does interest me in the least. It is counter productive to even consider. Such amplifiers are essentially low order delta sigma analogue to digital converters with very low sample rate (a few 100KHz at best) and so require first a DAC only to follow it with a poor Delat Sigma system.

On the other hand something like the TAS5518 plus correct power stage gives 8 Channels at 300W/4Ohm each with 110dB dynamic range at -24dB attenuation and includes a fair bit of DSP processing on board. Input is strictly digital data. Add the right DSP to it and you have enough to drive 8 individual drivers (so it becomes trivial to implement active radiation pattern control in the speaker, on top of any time alignment and crossover functions you could desire).

It is a whole other kettle of fish. The potential in this kind of technology is staggering.

I have heard partially active commercial systems (passive 2-Way satellites and active 2-way between sub and sats) that incorporate the TAS5518 modulator and fully digital crossovers, time-alignment and room correction.

It is one of the best commercial audio systems I know. Other very good ones I know use analogue crossovers and amps and others even tubes.

However with the CORRECT USE of current technology it is possible to match the performance of the prior art.

I would go further in saying that once we appreciate this kind of technology and actively push it's boundaries it can offer much that is simply infeasible using traditional analogue approaches.

Ciao T
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Old 1st January 2011, 08:25 AM   #39
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Originally Posted by ThorstenL View Post
Hi,
However with the CORRECT USE of current technology it is possible to match the performance of the prior art.
Ciao T
But the "correct use" will never be. profit margin will cater to the masses and give us the most perceived output/ quality, and the "masses" will reference to what they are given. Optimum is not compatible with a "made in china" profit margin.

Also , the "prior art" has been advanced to quite a high level recently. (still at 50% efficiency , can't get rid of that)

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Last edited by ostripper; 1st January 2011 at 08:30 AM.
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Old 1st January 2011, 10:38 AM   #40
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Gentlemen, much as we could debate digital vs analogue or amp topologies, Doug has made it clear this book will only cover the analogue side. What we should be doing is pressing him to write a sequel that covers digital, then we'll have the best of both worlds!
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