The design of active crossovers- Douglas Self wants your opinions - Page 2 - diyAudio
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Old 30th December 2010, 07:44 PM   #11
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Hello,
480 that is a lot of pages, perhaps a few more regarding the application of low noise discrete JFETís.
Zero feedback JFET circuits would be of interest to me. Shame on me I bought 2K 2SK170ís
Thanks to you, your website and books I have built many circuits with 5532 Op-Amps.
DT
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Old 30th December 2010, 08:29 PM   #12
_Wim_ is offline _Wim_  Belgium
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Hi,

The book looks very promising, and will be on my shopping list when available. What I miss in a lot in many of the current audio books available, is measurement examples actual of actual loudspeakers and a written description on how these measurements need to be interpreted. Nowadays it easy to make high resolution measurements with low cost gear (pc + soundcard), but it as before to interpret these correctly.

The ideal book for me would place the focus on how to select between different types of cross-over/filters (based on measurements), rather then on the implementation details of active cross-overs.
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Old 30th December 2010, 08:38 PM   #13
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Doug,

The TOC of your book looks promising. I wish you all the best for the writing stage.

As filter design is a complex topic (one need only take a look at the "handbook" by Wai-Kai Chen to understand this), you will need to cut out relevant material somewhere.

Important things that are often, IMHO, wrongly omitted:

1. Related to section 3.1 of your book, the definition of "adequate flatness" often does not take into account that at the crossover point, two drivers are connected to the room, meaning that the effective total driver efficiency is actually slightly higher, so we would often like an amplitude dip in the summed filter outputs. I'm not sure you planned to cover this; anyhow, I think it's important.

2. From the TOC, I cannot see a reference to baffle step diffraction. I think it's relevant.

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.

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.

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.

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.

7. Perhaps series-filter prototype simulation is relevant. I love passive series-filters and I think under some circumstances it could make sense to have an actively simulated version.

8. An important topic in industry is to have good PSRR of the filter. Perhaps this is also relevant for the book (tricks such as referencing a dummy AC coupling cap on your filter input differential pair to a supply rail to make PS ripple turn into common-mode).

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MatchASM
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Old 30th December 2010, 08:50 PM   #14
sreten is offline sreten  United Kingdom
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Originally Posted by MatchASM View Post

2. From the TOC, I cannot see a reference to baffle step diffraction. I think it's relevant.


Greetz,
MatchASM
Hi, "Diffraction compensation equalisation" is in there, rgds, sreten.

What I don't like is a complex chain of EQ dealing with this and that separately.
Very often the whole thing could be far simpler, but not as easy to adjust.
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Last edited by sreten; 30th December 2010 at 08:55 PM.
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Old 31st December 2010, 12:17 AM   #15
Pano is online now Pano  United States
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This looks like it will be a good a thorough book. I especially like chapters 14, 16 & 17. Interfacing it with the real world and keeping an eye on gain structure is a vast area that not many people seem to understand, and it can make a huge difference.

However, to be a real party pooper, I don't see why a crossover book to be published in the 2011 would be so opamp centric. Who would use them for an active crossover in the 21st century, except as input and output buffers? In this day of ever cheaper and better DSP, who would build an active crossover with opamps? It seems so 1980s. Not that it can't be done well, but who would? Some hobbyists or students, perhaps, but that's all.

DSP and biquads are the flavor of the future. Learning how to use those to achieve the filter slopes laid out in your major chapters should be the interest of the forward looking crossover designer - IMO. Opamps make good examples, but I can't see them making very many crossovers in the future.

Sorry for the downer.
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Old 31st December 2010, 12:27 AM   #16
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Originally Posted by panomaniac View Post
DSP and biquads are the flavor of the future. Learning how to use those to achieve the filter slopes laid out in your major chapters should be the interest of the forward looking crossover designer - IMO. Opamps make good examples, but I can't see them making very many crossovers in the future.
Sure DSPs are more interesting, especially for high-end use.

But consider: Price NE5532 ~$0.10, Price TMS320VC5501 ~$5.00. Op-amps will be around for a long time.

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Old 31st December 2010, 12:43 AM   #17
cuibono is offline cuibono  United States
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I agree with Pano - DSP is the way of the future, and to leave things in the analog domain would encourage early obsolescence of the book. I've been designing active crossovers for a couple of years now, and would never consider doing them analog anymore, primarily because of the cost, and secondarily because of the lack of flexibility. I've designed/built complex analog crossovers that cost over $300, and are totally fixed in their design, and take many many hours from start to finish, and are prone to circuit errors. Nowadays, I can spend $200, and get an extremely flexible DSP board, and within minutes be listening to different crossover variations. That is a huge difference.

Not only that, but DSP can do things that analog can't, like time and phase corrections. I guarantee that the future of loudspeakers will be heavily influenced by DSP - it is the only new technology that is making a significant differences to what is currently possible.
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Old 31st December 2010, 12:59 AM   #18
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Originally Posted by DouglasSelf View Post

I would be very glad to know about it if anyone thinks that anything is is missing.
What about shelving high-pass filters? Shelving low-pass seems to be there for diffraction compensation equalisation

Last edited by Drew Eckhardt; 31st December 2010 at 01:02 AM.
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Old 31st December 2010, 01:29 AM   #19
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Quote:
Originally Posted by DouglasSelf View Post
I'm not however planning to get into any details of digital implementation.
In my view a wise decision. Digital XOs would require a whole book.

Quote:
Originally Posted by MatchASM
But consider: Price NE5532 ~$0.10, Price TMS320VC5501 ~$5.00. Op-amps will be around for a long time.
That's hardly an apples-apples comparison - where can you get a 5532 for 10 cents incidentally? The opamp will certainly remain for simple XOs in cheap active speakers. For even something like the Linkwitz Pluto ASP it takes many opamps - the DSP solution might well be more cost-effective.

A common or garden DSP nowadays has 100's of MMAC/s performance - that's a hell of a lot of bi-quads at 44k1. A dual opamp can do a pair of 2nd order stages. If the DSP needs 5 MACs per bi-quad then it'll do roughly 5 stages per MMAC of performance. At 100 MMACs and $5 that makes just 1c per stage - five times cheaper than the opamp.
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Old 31st December 2010, 02:14 AM   #20
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The opamp will certainly remain for simple XOs in cheap active speakers.
= many X-overs. This is the only point I was trying to make (please read the post I quoted previously). BTW, if you order a couple tens of thousand 5532s, I'll bet you Fairchild will cut you a deal in the order of $0.10 a piece.

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. I omitted those for simplicity. The point is: simple 2nd order filter, go opamp!

@doug: I'm sorry for taking up so much space in your thread defending the validity of the book. I'll try to come up with a simpler example next time.

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