The design of active crossovers- Douglas Self wants your opinions - Page 3 - diyAudio
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Old 31st December 2010, 03:01 AM   #21
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Quote:
Originally Posted by MatchASM View Post
Regarding apples-apples comparison, it's not meant to be. The DSP still needs an ADC, a DAC + reconstruction filter for every output, more board space, more test time (also lower yield due to higher transistor count and pin count), more supply rails, additional clock circuitry, etc.
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.

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I omitted those for simplicity.
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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The point is: simple 2nd order filter, go opamp!
Undisputed.
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Old 31st December 2010, 04:54 AM   #22
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I've been very happy with a tri-amped system using 4th order crossovers from Marchand for many years. I find them far better sounding than 3rd order or less. Anything you can include on making the decision on order and type is certainly useful.

There's an old Burr_Brown book on Opamp Function Circuits that has a nice treatment of filters and offers some numerical solutions to single op-amp 4th order filters that I find useful. Some complain of component sensitivity, but I've never had a big issue with it. They work great. If you don't have the book, I can get you the ISBN number. I know there are a lot of them available used for very little.

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Conrad
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Old 31st December 2010, 07:23 AM   #23
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Imho, something that would be a very good idea to add is to say something about "all" the things that are not covered in the book. Why? Well, the book is likely to be widely read especially by those DIY'ers who are not already EE types. They will tend to take such a book as something of a "bible", a sole or primary reference. To some extent, it would be... but it is still important to illustrate (albeit in relatively shorthand terms) that the book covers a subset of the options and implementations. I'd want to show brief examples of some of those options, and maybe just list others. It's important, I think, that the reader be made aware and have a good sense of the length and breadth of the "playing field", even if the plan is to march right down a wide swath of the middle!

Hope this makes some sense...

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Old 31st December 2010, 07:29 AM   #24
Calvin is offline Calvin  Germany
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Hi,

as I understand from the TOC the book concentrates on HiFi-Filters.
As such IŽd expect to see something more than just the usual OP-amp based filters. If one want to use OP-amps one can google and find myriads of similar designs on the net. But hardly anyone builds filters any more with tubes or discretes,even though such filters can sound much better.
What I like is, that the book seems to take the driver into account. Most filter design handbooks focus on the filter, all to often completely ignoring the speaker. So while the filter performs perfectly the desired electrical transfer function, the output of the speaker doesnŽt perform the desired acoustic transfer function. Better crossovers allow for additional equalizing. But while passive filters usually combine filter functionality and equalizer functionality in one circuit, active filters most often divide the functionalities. This leads to an increase in filter stages and parts number count. But an active filter may also be designed like a passive filter. This of course leads to filters which are none of the standard types. The acoustic transfer function may be the same in the end, but the parts number count of the filter is reduced and it sounds better.
Will the book deal with this issue?

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Old 31st December 2010, 01:39 PM   #25
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Good points Bear & Calvin.
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Old 31st December 2010, 01:54 PM   #26
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Quote:
Originally Posted by sreten View Post
Hi,
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.
Interesting but not really the job of a crossover. I wanted to include motional feedback but there just isn't room
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Originally Posted by sreten View Post
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 ?
That's all in Chapter 14.

Thanks for your input
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Old 31st December 2010, 02:34 PM   #27
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I didn't see DSP explained in the chapters.
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Old 31st December 2010, 02:37 PM   #28
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Quote:
Originally Posted by MatchASM View Post
Doug,
2. From the TOC, I cannot see a reference to baffle step diffraction. I think it's relevant.
Me too, but I've called it diffraction compensation

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3. Multiple-feedback or "Rauch" filters are convenient especially in integrated active crossover designs, as the resulting capacitor values are often small (=convenient in integrated filter design). This is often omitted; I think it's important.
They are in Chapter 8

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4. Antoniou's General Impedance Converter is IMHO a very relevant synthesis tool. I think the difference between series-L and shunt-C ladder prototypes w.r.t. dynamic range is relevant..
No GICs, are not planned for inclusion. Looks like there will just not be space.

Quote:
5. Perhaps Voltage-Controlled Filters (VCFs) are relevant to mention, as they have special properties. They are mainly (and very scarcely) mentioned in older books, I can dig in my library to provide you with at least one reference, if you like. I find it remarkable that modern equipment such as Allen&Heath mixing consoles still use such filters..
If you mean filters with voltage-controlled cutoff frequency, as used in analogue synths, why would you use them in a crossover? I think we are not communicating here.

Quote:
6. I see you plan to cover time delay filters. I hope LC time-delay filter prototypes deserve a mention... they are especially hard to wrap your head around, due to their nonplanar topologies..
No LC filters are included. It's a very expensive way of getting a delay. Nonplanar topologies?? What are they?

Many thanks for your input.
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Old 31st December 2010, 03:08 PM   #29
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Default Minimising topic overlap

Having quickly scanned the chapter list and compared the contents with your 'Small signal Audio Design' there does look to be considerable overlap - one or two chapters look to be almost identical in both. One way to minimize this and free up a little space for more crossover-centric topics would be to omit the chapter on outputs completely (since that's one that looks like its mostly a duplicate) and change the title to something like 'Crossovers for active speakers' - implying that the crossover and power amps are integrated.

Building a stand-alone active crossover box I don't think is going to appeal to many diyers and it seems a bit of a shame to use up valuable book space on material which you've already published when other interesting topics are being squeezed out (like GICs for example).
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Old 31st December 2010, 06:18 PM   #30
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Quote:
Originally Posted by abraxalito View Post
Having quickly scanned the chapter list and compared the contents with your 'Small signal Audio Design' there does look to be considerable overlap - one or two chapters look to be almost identical in both.
I assume you mean the line input and line output chapters; since they are finished I can speak confidently about them.

I agree that they may look from the ToC to be not very different from those in SSAD, but this is not actually the case. The sub-headings certainly look similiar but it is hard to see how else they could be phrased with equal clarity.
The line input chapter has had some of the more specialised input configurations pruned and there is now more emphasis on low-noise design. Much of the chapter has been rewritten with additional information added. The line output chapter is much extended compared with the SSAD version, with a lot of important material on reducing output transformer distortion added, and is at least twice the size.

I never have and never will simply cut and paste chapters between books. I always aim to give value for money.
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