Page 3 of 4 FirstFirst 1234 LastLast
Results 41 to 60 of 62

Thread: Refurbish capacitors inside speaker crossovers?

  1. #41
    Join Date
    Oct 2010
    Location
    Singapore
    Posts
    48

    Default Understanding capacitors

    Even though I lack the, er, capacity to fully understand all the technical details of this thread, I'm nevertheless grateful for the little understanding I've gained from reading it. Many thanks.

  2. #42
    Join Date
    Feb 2010
    Location
    England and Cyprus
    Posts
    357

    Default Active v. passive

    Just browsing around the forum and I notice I have a a question pending:

    "To what extent, Alan, are line level (active) crossovers advantaged over passive (post amplifier) crossovers because of the value and type of capacitor that can be used?"

  3. #43
    Join Date
    Aug 2007
    Location
    Harrow, UK
    Posts
    457

    Default Load and its effect on component SIZE

    Quote Originally Posted by Labarum View Post
    To what extent are line level (active) crossovers advantaged over passive (post amplifier) crossovers because of the value and type of capacitor that can be used?
    The problem with traditional passive crossovers is that they need to operate at a rather low impedance. The drive unit's voice coil will be the loading impedance, typically around 4-10 ohms. Consider a typical, basic, high pass filter - about the simplest filter you could make:


    Let's obtain a response suitable for a hypothetical tweeter: the frequency (Fc) is given by 1 / (2*pi*R*C). If we use values of 10nF and 10kΩ the 3dB point of this filter will be 1.6kHz.

    You can see that the load needs to be in parallel with R, so unless the load impedance is high compared to R, the very existence of the load will affect the turnover frequency of the filter. Lets assume that the impedance of our hypothetical tweeter is 10Ω - this means that R in our filter will be, near enough, 10Ω - we are stuck with it because that is the impedance of our tweeter. You can see from the formula that if you decrease the value of R by a factor of 10, you must increase the value of C by the same factor to maintain the same result (Fc). So, having reduced R to 10Ω (the figure - like it or not - that we're stuck with) C has to be increased to 10μF to retain our 1.6kHz value for Fc.

    So the answer to your question is that passive crossovers, with their inherent need to operate at a low impedance, require large values of capacitance and inductance and these parameters are only achieved by bulk. Such components are therefore large and expensive, all the more so if quality and stability are desired.

    An active crossover, by definition, operates at a much higher impedance (because its output load is an amplifier's very high input impedance - perhaps 47kΩ) and therefore the necessary frequency discriminating components can be physically far smaller.
    Attached Images Attached Images

  4. #44
    Join Date
    Feb 2010
    Location
    England and Cyprus
    Posts
    357

    Default The ideal solution?

    Quote Originally Posted by Pluto View Post
    An active crossover, by definition, operates at a much higher impedance (because its output load is an amplifier's very high input impedance - perhaps 47kΩ) and therefore the necessary frequency discriminating components can be physically far smaller.
    Smaller, cheaper, more accurate, less lossy, and with a specification closer to that of an ideal component.

    So, in these days when amplification is or ought to be cheap, what is the conclusion?

  5. #45
    Join Date
    Jan 2006
    Location
    South of England, UK
    Posts
    3,809

    Default Choice and more choice ...

    Quote Originally Posted by Labarum View Post
    Smaller, cheaper, more accurate, less lossy, and with a specification closer to that of an ideal component.

    So, in these days when amplification is or ought to be cheap, what is the conclusion?
    I think you have to ask yourself who would benefit from going active. The essential point is that it binds the consumer to a particular active [speaker+internal amp] combination. We all know from the vast rhetoric that drags around hi-fi amplifiers like Marley's ball and chain, that the last thing the audio consumer will vote for is less flexibility in his speaker/amp arrangement.

    So the argument pro/against active speakers is 1% techical and 99% emotional. If the consumer won't buy it, it's a concept without a market. And that is the only conclusion you need reach.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  6. #46
    Join Date
    Jun 2009
    Location
    Canada
    Posts
    758

    Default Counter-intuitive actives

    Quote Originally Posted by A.S. View Post
    .... We all know from the vast rhetoric that drags around hi-fi amplifiers like Marley's ball and chain, that the last thing the audio consumer will vote for is less flexibility in his speaker/amp arrangement.

    .... If the consumer won't buy it, it's a concept without a market. And that is the only conclusion you need reach.
    Mystifying but undoubtedly true, or there'd be a lot more active setups out there, given the technical advantages.

    I have sometimes wondered if an active setup that looked more like a conventional amp/speaker combination - that is, with all electronics, including the crossover, contained in a single box that looked like a conventional integrated amplifier, with dual wires out to the speakers - might have more appeal to the audio purchaser. The longer speaker wires might not be technically optimal, but the more "normal" appearance (plus the preservation of the all-important "choice" of the wires) might make it a commercially more viable proposition. Maybe.

  7. #47
    Join Date
    Feb 2010
    Location
    England and Cyprus
    Posts
    357

    Default A Bettter Way?

    Quite so, Eric. Did someone say choice? When it comes to domestic active speakers I have very little choice, which is a great frustration. I can buy actives in industrial or star wars styled boxes, or I can buy nicely veneered passives. A most unsatisfactory situation. But how to turn the market! And how to beat some sense into consumers.

    Now if there were an agreement on a standard for a DAC-DSP four channel amp, at least it would drive all common two ways with crossovers removed, or two way speakers designed to work with the new range of DAC-DSP four channel amps. Program in the crossover parameters, set the room correction, make minor adjustments to taste (like in tone controls!) and there you have a modern choice with maximum flexibility using better technologies.

    But I guess you would never get the producers to agree a standard, and you would never remove the ball and chain from the ankles of the hifi enthusiast consumer.

  8. #48
    Join Date
    May 2009
    Location
    England
    Posts
    781

    Default Some terrible actives

    Quote Originally Posted by Labarum View Post
    Smaller, cheaper, more accurate, less lossy, and with a specification closer to that of an ideal component.

    So, in these days when amplification is or ought to be cheap, what is the conclusion?
    My conclusion, having listened to many active and countless passive speakers, is that there are good and bad of each. Some of the worst speakers I have heard were active, so it's obvious (to me) that it isn't the 'be all'.

  9. #49
    Join Date
    Dec 2012
    Location
    UK
    Posts
    166

    Default It totally depends upon the designer's skills

    Douglas Self published a good book about active crossovers:

    http://www.google.co.uk/search?clien...-_LsaW0QXGh4Ag

    http://www.amazon.co.uk/Design-Activ.../dp/0240817389

    For those not familiar with Self, he's famous for his no-nonsense approach to audio, and for his rigour and insight - his analysis of the complexities of power amplifiers is really quite something. Yet he has a very accessible writing style that appeals to less technical readers too - have a look at the opening chapter via the preview on Amazon...

    As I've said before, active operation is no guarantee of performance: an average designer might not be able to exploit the potential benefits, leaving a product that is out-performed by passive designs from top-class designers. In the pro world, where active operation is much more commonplace, I can think of plenty that don't come close to, say, an M30, and I know that I couldn't improve the M30 by making it active (but can't help but wonder what Alan would do?).

    Mark

  10. #50
    Join Date
    Feb 2010
    Location
    England and Cyprus
    Posts
    357

    Default Science or art?

    Quote Originally Posted by mhennessy View Post
    I know that I couldn't improve the M30 by making it active (but can't help but wonder what Alan would do?).
    Neither could I. For that reason I would not contemplate buying a passive speaker, ripping out the crossover and doing a DIY activation. I would get it horribly wrong.

    I am convinced that skilful voicing is essential to any design, and that is more art than science; but if the voicing is of a better basic technology, and by a master, the active ought to pull ahead.

  11. #51
    Join Date
    Jan 2006
    Location
    South of England, UK
    Posts
    3,809

    Default A re-active M30.1?

    Quote Originally Posted by Labarum View Post
    ...the active ought to pull ahead.
    Well, an active M30 did exist, and could again. In 1999 I designed such a beast, and we sold a few pairs. But the cost were against us, because at that moment the cheap foreign active speakers started to appear at a retail price below our manufacturing cost. So that was that.

    I have all the notes (of course, amongst my PDF archive!) and I went straight to the active M30 folder. All carefully documented, step by step so that, if the market conditions return, we could reactivate that project with ease. I don't want to give too much away, but attached you will find a snap from one page where the tweeter filter (or to use fancy clever clog language, the tweeter's transfer function) in the passive circuit is carefully overlaid with the active circuit. You can see that, for all intents and purposes, the two curves were within the pen thickness from 3-20kHz and the phase around crossover frequency (about 3.5kHz) within just a few degrees. The bass filter was just as close a match.

    So, the idea to leave you with is that the passive design should be completed first, and then the active speaker filters cloned from the frequency response shape of the passive filters. How you do that is up to you as the designer but what I did was to overlay the active onto the passive and simulate and then hand tweak until they are as close as possible. There is nothing really magical about active filters; they just do the job that a passive filter does using (many more) smaller components. The weakness of actives is that they need a power supply and that opens up all sorts of issues including electrical safety and - you will never have even thought of this - a huge hike in public liability insurance.

    Note: this is not the frequency response of the speaker. It is a plot of the voltage that appears at the tweeter's terminals, which cannot and does not indicate the sound output (speaker frequency response).

    >
    Attached Images Attached Images
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  12. #52
    Join Date
    Feb 2010
    Location
    England and Cyprus
    Posts
    357

    Default Why passive first?

    Quote Originally Posted by A.S. View Post

    So, the idea to leave you with is that the passive design should be completed first, and then the active speaker filters cloned from the frequency response shape of the passive filters.
    Can you tell us why you would do it that way, Alan; unless your sole purpose was to mimic a well loved and proven passive loudspeaker?

    With all the power and control of a DSP crossover you could manage your proven voicing practices in minute detail, and without the tiresome need to swap components in and out of the crossover board.

    Does mimicking the curves of a passive crossover produce the same audio output in the active version; or do the drivers behave differently when driven directly from an amplifier, and without inductors and capacitors close by which must act like mechanical springs and dampers on the drivers?

    I agree that active speakers can lead to more rather than less cable-clutter, especially if the master speaker has a multi-input DAC.

    However, if the electronics is, as I was suggesting, in a separate box - (ADC)+DSP + DAC + 4 power amps - a four (maybe three) core cable is all that is needed to each loudspeaker.

    Could be an extremely neat solution.

  13. #53
    Join Date
    Jan 2006
    Location
    South of England, UK
    Posts
    3,809

    Default The Faraday Method ....

    Quote Originally Posted by Labarum View Post
    Can you tell us why you would do it that way, Alan; unless your sole purpose was to mimic a well loved and proven passive loudspeaker? With all the power and control of a DSP crossover you could manage your proven voicing practices in minute detail, and without the tiresome need to swap components in and out of the crossover board.

    Does mimicking the curves of a passive crossover produce the same audio output in the active version; or do the drivers behave differently when driven directly from an amplifier, and without inductors and capacitors close by which must act like mechanical springs and dampers on the drivers?....
    Good question, very conservative answer coming up.

    The cardinal sin committed by most or even all DIY speaker makers (and I assume more than a handful of professional loudspeaker designers) is to fail to consider what we hear at our sweet-spot as a inextricable combination of the 'sound' of drive units plus the 'sound' of the crossover. Every drive unit is at its best only with a certain crossover circuit driving it. Whether that circuit is stumbled across by accident or the result of some deep and meaningful (and repeatable) insight is irrelevant: the fact is that you can hurl out of a high window every text book touching on crossover design because not one of them will steer you towards that magical crossover + driver combination.

    In fact, you would be far wiser to ignore the text books as if they were never written, get yourself a bucket of resistors, capacitors and coils of the sort of values used in passive crossover filters, a reliable microphone and measuring system and plenty of listening time and your selected drive units. You will need a rod-of-iron willpower to document every experiment to avoid going around in circles. I call it 'The Faraday Method': discipline is much more important than a deep understanding of what is going on at a molecular level. Once you have experience as a reliable observer of circuit topography that sounds best (and worst) then you are in a position to postulate your own mini-theory, and that theory can guide you until such time as a combination predicted as bad sound good or good sound bad. Then you need to revise your theory.

    When you no longer need to revise, you have a hypothesis which although not comprehensive, creates a certain working orbit: keep within that orbit and you will not be caught out: stray beyond it, and you go back to square one. Perhaps.

    Prof. Faraday and observational physics at its very approachable best, here.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  14. #54
    Join Date
    Feb 2014
    Location
    France
    Posts
    4

    Default Big mistake! Changed capacitors in speaker

    Hello!

    I'm new here!

    I've just renewed the treble electrolytics on my Beovox M70, for testing purposes.

    I replaced with high quality MKT cap, and it certainly was a big mistake!

    The sound of the speaker is different! There is less treble, it is less focussed, and I was wondering whether the lower series resistance of the old electrolytic was not showing here.

    I opened the old cap and it was not dry at all! The rubber cap (ah polysemy) was actually on its way, starting to transform into goo, but being one cm tall, the seal was still perfect.

  15. #55
    Join Date
    Jan 2006
    Location
    South of England, UK
    Posts
    3,809

    Default Chemistry

    Quote Originally Posted by chartz View Post
    Hello!

    I'm new here!

    I've just renewed the treble electrolytics on my Beovox M70, for testing purposes.

    I replaced with high quality MKT cap, and it certainly was a big mistake!

    The sound of the speaker is different! There is less treble, it is less focussed, and I was wondering whether the lower series resistance of the old electrolytic was not showing here.

    I opened the old cap and it was not dry at all! The rubber cap (ah polysemy) was actually on its way, starting to transform into goo, but being one cm tall, the seal was still perfect.
    I'm curious as to why you though that you could "improve" your speakers by changing a capacitor in its crossover. What led you to that idea?

    No doubt the "MKT" capacitor is a dry-film type (polypropylene, polyester or similar) and you have used that type to replace a wet-film electrolytic. Since you presumably do not have capacitor measuring equipment, you do not know the true capacitance value of the original electrolytic cap or its replacement. The tolerance for this type of capacitor could be printed value on the side plus or minus 20%, let alone the differences in electrical characteristics due to the internal chemistry.

    Your only solution is to order an official original replacement from the manufacturer. Everything else would be guesswork.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  16. #56
    Join Date
    Feb 2014
    Location
    France
    Posts
    4

    Default I did measure!

    Thanks for your reply Alan. I do have a measuring device, so I got a batch of 8 F+/- 5% - as per service manual - and I replaced with exact same value, discarding out of tolerance caps. I actually measured anything from 7.7 to 9.2 F!

    M70Xover.jpg

  17. #57
    Join Date
    Jan 2006
    Location
    South of England, UK
    Posts
    3,809

    Default

    Quote Originally Posted by chartz View Post
    Thanks for your reply Alan. I do have a measuring device, so I got a batch of 8 F+/- 5% - as per service manual - and I replaced with exact same value, discarding out of tolerance caps. I actually measured anything from 7.7 to 9.2 F!

    M70Xover.jpg
    9.2uF is +15% up on the target value of 8u0, a value change, let alone a chemistry change, enough to make a very audible difference.

    What about the loss factor, reflecting the chemical/physical reality of the two types? Could your test equipment measure that?

    A very odd circuit indeed.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  18. #58
    Join Date
    Dec 2007
    Location
    Suffolk, UK
    Posts
    283

    Default Fearless

    Hope I can chip in with this...

    Many passive B&O speakers used electrolytic caps that can and do age and change in value over the decades, if not fail altogether (I've seen this). It's a 'done thing' with this brand to update all the electrolytic caps in their crossovers as well as to re-foam many of the drivers using this material for cone suspension. The Beopeople ;) are totally fearless in this, although I believe they tend to use sensible modern replacements, rather than OTT 'boutique' parts here. For some of the models from the early to mid 70's, this can be well worthwhile as the 'heart' of so many of these models was definitely in the right place, especially before the 'phase corrected' models came along and threw another iffy spanner in the works.

    My old Spendors use pre-selected film-caps in their crossovers and I've been advised NOT to replace them, as it's unlikely they'd have drifted too far from original settings, unlike the bass drivers, which had to be replaced. They image very clearly (a strength in the BC1 and BC2), so have 'gone off' the same on each one :lol:

  19. #59
    Join Date
    Feb 2014
    Location
    France
    Posts
    4

    Default Loss factor?

    Quote Originally Posted by A.S. View Post
    9.2uF is +15% up on the target value of 8u0, a value change, let alone a chemistry change, enough to make a very audible difference.

    What about the loss factor, reflecting the chemical/physical reality of the two types? Could your test equipment measure that?

    A very odd circuit indeed.
    I did replace the tweeter cap with an MKT of the proper value. However other parameters such as loss factor I haven't measured. Will a 10 kHz waveform signal do?

    I must say that those Phase-link speakers sound really good!

    Thanks,

    Jacques

  20. #60
    Join Date
    Jan 2006
    Location
    South of England, UK
    Posts
    3,809

    Default Cannot advise

    Quote Originally Posted by chartz View Post
    I did replace the tweeter cap with an MKT of the proper value. However other parameters such as loss factor I haven't measured. Will a 10 kHz waveform signal do?

    I must say that those Phase-link speakers sound really good!

    Thanks,

    Jacques
    Since these are not Harbeth speakers, I think you'd better take the advice of their manufacturer. Our advice would be to back track to the original components and leave well alone. Any other strategy is going to leave you in with a nagging doubt, and if great music is your objective, that's the last thing you want.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

Page 3 of 4 FirstFirst 1234 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •