Announcement

Collapse

HUG - here for all audio enthusiasts

Since its inception ten years ago, the Harbeth User Group's ambition has been to create a lasting knowledge archive. Knowledge is based on facts and observations. Knowledge is timeless. Knowledge is human independent and replicatable. However, we live in new world where thanks to social media, 'facts' have become flexible and personal. HUG operates in that real world.

HUG has two approaches to contributor's Posts. If you have, like us, a scientific mind and are curious about how the ear works, how it can lead us to make the right - and wrong - decisions, and about the technical ins and outs of audio equipment, how it's designed and what choices the designer makes, then the factual area of HUG is for you. The objective methods of comparing audio equipment under controlled conditions has been thoroughly examined here on HUG and elsewhere and can be easily understood and tried with negligible technical knowledge.

Alternatively, if you just like chatting about audio and subjectivity rules for you, then the Subjective Soundings sub-forum is you. If upon examination we think that Posts are better suited to one sub-forum than than the other, they will be redirected during Moderation, which is applied throughout the site.

Questions and Posts about, for example, 'does amplifier A sounds better than amplifier B' or 'which speaker stands or cables are best' are suitable for the Subjective Soundings area.

The Moderators' decision is final in all matters regarding what appears here. That said, very few Posts are rejected. HUG Moderation individually spell and layout checks Posts for clarity but due to the workload, Posts in the Subjective Soundings area, from Oct. 2016 will not be. We regret that but we are unable to accept Posts that present what we consider to be free advertising for products that Harbeth does not make.

That's it! Enjoy!

{Updated Nov. 2016A}
See more
See less

Refurbish capacitors inside speaker crossovers?

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • #31
    Almost too good to be true?

    Originally posted by Gan CK View Post
    ...The M40.1 crossover does not have a single electrolytic cap in view. In contrast, it has plenty of polyester caps, a total of 19 if i counted correctly. Obviously, the cost of manufacturing a M40.1 crossover is higher than the M40 one. Therefore, we can all conclude that the M40.1 was designed with durability as a primary concern.
    Exactly. Now, again, being scrupulously fair to the reversible electrolytic, I guess that it is the principle capacitor used in speaker crossovers even on the most swanky 'boutique' speakers*. And again, the reversible electrolytic has been around for over forthy years and presumably today's is a highly developed great grandson of the original concept. But, to me, it seems almost too good/too cheap to be true using such a tiny amount of material (the can is almost significantly empty).

    Do you take my point in my previous post about the moist electrolyte? Why would that be a concern?

    *Again, can you see how a photo of the speaker crossover in a review is so hugely informative?

    [My first post at The Old Barn, Harbeth's new R&D place].
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

    Comment


    • #32
      Deterioration of electrolytic capacitor?

      Originally posted by A.S. View Post
      Do you take my point in my previous post about the moist electrolyte? Why would that be a concern?

      *Again, can you see how a photo of the speaker crossover in a review is so hugely informative?

      [My first post at The Old Barn, Harbeth's new R&D place].
      Congratulations Alan, on a new "cradle" for the Harbeths :)
      I hope the R&D will benefit and even better models (if possible!!) will emerge :)

      To the quoted question; I guess eletrolytic moist will be substansially detoriated exposed to heat so for use in hot amplifiers it will need replacement a lot quicker than a dry film type.

      When at use in a colder environment as a loudspeaker crossover my guess is that it will last a bit longer but nevertheless it will be detoriated over time?

      Comment


      • #33
        Just how suitable are non-polarized electrolytics?

        Alan - a most fascinating insight. I really had no idea that non-polar electrolytics were widely used in commercial crossovers - I'd always assumed that the problems outweighed the advantages. So how does the designer address the following issues?

        1. Tolerance is typically poor (+/- 20%). Filters, in general, require greater accuracy than this.

        2. Inductance is high - again, a problem in filter design.

        I recall being taught "always make sure your electrolytics are well-polarized". In other words, get a decent DC bias (of the correct polarity) on 'em, for a long and reliable life. Now how do you reconcile this view with an electrolytic capacitor whose life is the AC environment where a nice stable polarization is impossible. Bear in mind that a non-polar electrolytic is, in reality, little more than a pair of 'normal' electrolytics back-to-back so they are unlikely to operate very differently to their polarized siblings.

        Prior to this little tutorial, I assumed that non-polar electrolytics were really not suitable for serious loudspeaker crossover use.

        Comment


        • #34
          Capacitor construction and durability under load

          Originally posted by Pluto View Post
          Alan - a most fascinating insight. I really had no idea that non-polar electrolytics were widely used in commercial crossovers - I'd always assumed that the problems outweighed the advantages.... Prior to this little tutorial, I assumed that non-polar electrolytics were really not suitable for serious loudspeaker crossover use.
          Well you don't have to look too far to find examples of supposedly high-end speaker brands whose PCBs are bristling with reversible electrolytics.

          Whilst the tolerance issue is as you say, typically +/- 20% and the inductance high, that's only the start of the issues the designer has to be aware of. Did you know that capacitance test meters work by applying a fixed frequency to the capacitor under test. The inexpensive meters are typically set to one frequency, about 120Hz. The better ones have two (or more) frequencies. We have a top of the range HP capacitance meter that can analyse every parameter of a capacitor you would ever wish to know. The worrying thing about electrolytics is that the capacitance value (i.e. whatever is printed on the case +/- the tolerance) is not the same at 120Hz and 1kHz. It is with dry-film capacitors. If you consult the suppliers data sheet for reversible electrolytics you will note in the small print a caveat that the capacitance value is at a certain test frequency. The difference can be quite significant. For example, the 150uF reversible tested at 120Hz has a value of xxxx uF. The same capacitor at 1kHz has a value of yyyy uF. At other higher frequencies it will be even further from the 'base' value. That means, when designing a loudspeaker crossover using a software simulator (as I have done for over twenty years) it is not possible to make a reliable simulation if you use reversible electrolytics. You simply cannot describe the frequency-variable behaviour of what should be a fixed, invariant component in enough detail for the simulator to calculate the resulting circuit functionality. That's a degree of variation beyond the simulator's capability - or need.

          In addition the loss factor (i.e. how much the capacitor behaves like a resistor and/or inductor at different frequencies) is extremely complex. Undoubtedly those who make reversible electrolytics thoroughly understand their technology, but that information is too complex, too proprietary to share with their customers. Indeed, since the first reversibles appeared there have been two grades in use in the speaker industry: low loss and the cheaper high loss variants. The low-loss ones have a more sophisticated chemical construction and can take more current - they'd be used in bass sections (presumably). The high-loss ones would tend to be used where little power flowed 'through' them: say, in a tweeter or in what is anyway a cheap speaker system. They can become warm to the touch if used in bass filters. So reversible electrolytics are complicated components that, depending upon applied frequency will behave as partly resistor, partly capacitor, partly inductor.

          Someone commented a few posts ago that I'd remarked that one 'probably couldn't hear a difference between reversibles and dry-film capacitors'. Actually that's not what I said or if I did, sorry: it's not what I intended to convey. I'd be surprised if, bearing in mind the extreme electro-chemical complexity of the reversible electrolytic capacitor, that it sounded the same as the dry-film variant. I was saying that I'd be surprised to hear a difference between dry-film polyester (the ones we use) and polypropylene, both are dry-film types.

          The first instance of a reversible electrolytic in a BBC speaker (as far as I can tell) was as a tweeter LF-breakthrough protection in the active LS5/8 - see picture. Designed and built in the mid 70s, this HF-tap board evidences three high-value hermetically sealed reversibles, of a type long disappeared, but popular at the time, and certainly used by KEF. The first use of a reversible in a passive conventional BBC monitor (as far as I know) was in the Harbeth LS5/12A - see picture. This speaker had a very large port that occupied 40% of the rear panel and that blue 40uF electrolytic rather than four 10uF dry-film capacitors was mandatory due to space limitations. You can also see my clip-on polyester dry-film block comprising 14 x (nominally) 10uF plus one 2u2 giving an exact total of 150uF - see picture. This clip-on capacitor block allowed me to make direct comparisons between between one 150uF electrolytic and the alternative 150uF dry-capacitors in the M40.1 prototype circuit.

          Electrolytic reversible capacitors are the mainstay of the speaker industry. They are the only solution where very high capacitance is required at reasonable cost in a confined space. My primary concern is that they work because the electrolyte is moist, and providing it remains so for five, ten, twenty years than no problem I suppose. But we know that in the real world damp washed clothes pegged onto the washing line will dry in a few hours. The only thing that prevents the magical electrolyte from evaporating is the quality of the air seal around the legs, in what is by nature a low-cost component.

          So finally we are at the answer to the original question:

          The manufacturer of my audio (electronics) equipment advices to refurbish the capacitors inside the amplifier every ten years or so. To let the amplifier sound again just like "new-recap" they call it- Now I wonder since there are caps to be find inside the crossover filter of Harbeth speakers -I guess-is it wise to change these caps also once in a? Or does this not apply to speaker crossover filters?
          And the answer has to be: ... if your speakers use reversible electrolytics in the crossover, and they are good quality ones (how to be sure?), and they are not under strain, and they do not carry high currents and become hot (which accelerates evaporation) and the wire lead-outs are and remain perfectly sealed, and no corrosion/breakdown has or will occur in the capacitor with time due to the intimate proximity of liquids and metals, then you should not need to replace them.

          Without taking you along this inside-story journey I could have just answered your question as ...

          ... if your speakers use reversible electrolytics in the crossover, and they are good quality ones (how to be sure?), and they are not under strain, and they do not carry high currents and become hot (which accelerates evaporation) and the wire lead-outs are and remain perfectly sealed, and no corrosion/breakdown has or will occur in the capacitor with time due to the intimate proximity of liquids and metals, then you should not need to replace them.
          but knowing what you now know, that would have been an opaque and quite useless answer, in my opinion. Now you are empowered. Hope you have found something useful here

          >

          P.S. I have been on a mission to design-out reversibles from our products for some years, regardless of cost implications. The P3ESR (see PCB design video here) has none, although the P3ES2 used some low-loss ones.
          Attached Files
          Alan A. Shaw
          Designer, owner
          Harbeth Audio UK

          Comment


          • #35
            Low loss caps

            This has been a very interesting & fascinating thread. Thanks once again to Alan for all of his valuable insights. I notice that the crossovers in the SHL-5 & M30 still has one reversible electrolytic cap each & i assume that these are low loss caps similar to the ones found on the P3ES2 crossover?

            Comment


            • #36
              Informative

              For me, this has been one of the most educational and interesting threads I've read on the forum. Now I hold Harbeth speakers in even higher regard. Thanks.

              Comment


              • #37
                Awesome!

                AWESOME THREAD!!!

                thanks,
                delgesu
                Harbeth M40.1-Naim NAC52-Supercap-NAP 135-CDS2-XPS

                Comment


                • #38
                  Thanks!

                  Many thanks Alan for this wonderful lesson. I am grateful and feel even more proud as a Harbeth speakers owner.
                  "Bath with Music"

                  Comment


                  • #39
                    Insightful.

                    Originally posted by Will View Post
                    one of the most educational and interesting threads...
                    I agree. A significant insight into a little known aspect of one of the subtleties that goes into the creation of a quality loudspeaker. Bravo!

                    Comment


                    • #40
                      Capacitors repair to my preamp

                      Excellent information, before I knew nothing of what those odd things with wires coming out of them were, now, it makes a lot of sense. The repair work done on my pre-amp also makes sense and I know that it will now work for a good 5-10 years! Sadly, I think that most components in my own body use wet capacitors, and that most need replacing...

                      George

                      Comment


                      • #41
                        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.

                        Comment


                        • #42
                          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?"

                          Comment


                          • #43
                            Load and its effect on component SIZE

                            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 Files

                            Comment


                            • #44
                              The ideal solution?

                              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?

                              Comment


                              • #45
                                Choice and more choice ...

                                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

                                Comment

                                Working...
                                X