Crossover capacitor for Maplin tweeters A64GY

Discussion in 'Home Cinema Speakers' started by ROZ, Feb 27, 2013.

  1. ROZ

    ROZ
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    Hi All,
    I've got 2 pairs of the tweeters below for my vehicle. Cheap and cheerful. Not understanding why I should add 4.7uF capacitors to the wiring, and went looking and now understand much more of the wonderful world of crossovers.

    The thing is these are rated at 2000 - 20K. But looking at the crossover calculators, the 4.7uF would drop out everything below 8500Hz, somewhat above 2000Hz.

    Also, the leads supplied with the speakers also include 3.3uF caps wired in already! This equates to a crossover of an even higher 12KHz, meaning these would only be poppping out some high frequency and nothing else.

    But of course (I now know) adding both these in series as instructed by Maplin actually creates an effective capacitance of even less, and a resulting crossover more like 13KHz. The way I look at it, these speakers will only be able to be heard by dogs at this rate!!!!:rolleyes:

    Am I working this out all wrong?
    Has anyone experience with all this?

    1.5-Inch Car Tweeters : Speakers : Maplin Electronics
     
  2. Cliff

    Cliff
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    It could be that they have labelled them 4 ohm meaning that they are suitable for 4 ohm car system when in fact the impedance is higher?
    That would limit the power as they are small.
    Just a thought- could be wrong.
     
  3. BlueWizard

    BlueWizard
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    With a 1st Order or 6db/octave crossover, you can not crossover at the rated low end. Typically this is true of just about every crossover.

    Even crossing at 4khz would mean the response would only be down by -6dB at 2K, that is a very slight attenuation.

    Here is one of many crossover calculators found on the Internet -

    Crossover Design Chart and Inductance vs. Frequency Calculator(Low-pass)

    Put in the speaker impedance, and the required frequency, and it will give you the needed values.

    Assuming 4 ohms speakers and a 4khz crossover, you would need roughly a 10uF capacitor. Also, you want Audio Capacitors, not general purpose capacitors.

    To cross at 5khz, you would need 7.95uf. I'm not sure what the closest value would be to that, but about 8uF.

    Best are Metalized Film capacitors, next best are Film capacitors, least are Non-polar Electrolytic, but the non-polar electrolytic are also dirt cheap and are typically found in low end systems.

    Capacitors add when placed in Parallel. So rather than one 8uf, you could put two 4uf in parallel and get the same final working value. They don't have to be equal either. For example, if you need 7uf, you could put a 4uf and a 3uf in parallel.

    Steve/bluewizard
     
  4. Cliff

    Cliff
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    I think the answer to this puzzle is to do with the cost and low power rating of the tweeters. They will not be very efficient at 2kHz and the coil will get hot. At 10kHz they will be much more efficient and will not overheat. That is why they are recommending 4.7uF.
    I would most definately not recommend a 10uF in series regardless of the calculation (which is fine by the way) as voice coil will burn out at high levels.

    I would either leave the 3.3uF in and connect direct. If the crossover is too high then take these out and put in 4.7uF. At least if they blow you can take them back as you have not abused them.
     
  5. BlueWizard

    BlueWizard
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    Keep in mind, there are no fundamental notes above about 4khz. That is roughly the highest note on a Piano. The Piano cover pretty much the entire orchestral range. Crossing over at 10k or above, will add very little.

    But you are right, with only a -6dB/Octave (single component) crossover, you are probably going to have to be at about 8khz.

    Still, there is always the option to use a two component crossover (-12dB/Octave or 2nd Order) which uses a coil in parallel, and a capacitor in series. The Internet Crossover Calculator I link to can help you determine the correct values.

    At 10k, the Tweeter is going to supply NO fundamental notes (1st Harmonic) and few 2nd harmonic. So mostly 3rd and 4th Harmonics. You can give it a try, basic low cost Non-polar Electrolytic capacitor only cost a Pound or two. See how it sounds. If you want to bring the crossover down below 8khz, then I recommend using a two component (12dB/octave or 2nd Order) crossover. If you get down real close to 2khz, then probably a 18dB/octave or 3rd order crossover.

    These are all shown at the link to the Internet Crossover Calculator I gave you.

    Steve/bluewizard
     
  6. ROZ

    ROZ
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    Cheers guys, you're all stars!
    I'd already used those calculators Steve, thanks. I'm still not au fait with the orders/dB per octave terminology. If these were actually expensive hifi I might do something more involved, but the fact is they are, as Cliff rightly infers, cheap, and I'm mounting them in my 1988 VW camper - hardly an audiophyllic environment :D

    I've actually had a response from Maplin. Usually this is rare, usually very late, or non-existant, or useless. However, Luke sent me an email stating, "These items have been changed and now come with the Capacitor built in already."

    So great. Use what they come with, and ignore the instructions we send, and the Q&A on our website. You've got to laugh. :s
     
  7. BlueWizard

    BlueWizard
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    Orders and Stages - simply refers to the number of crossover components.

    If you look at the Diagrams at the link I provided -

    6dB/Octave = 1st Order has a SINGLE Capacitor on the Tweeter.

    12dB/Octave or 2nd Order uses TWO components on the tweeter; one series capacitor, one parallel coil. Because there are two components working together, the slope of the roll-off is twice as steep.

    18dB/Octave or 3rd order, as you can see from the Diagram uses THREE components in the shape of a "T". Three components roll of three time steeper than one component, so 3x 6dB = 18dB/Octave.

    An Octave change is a doubling or halving of the frequency, so here is a series 10hz, 20hz, 40hz, 80hz, 160hz, 320hz, and so on; 1khz, 2khz, 4khz, 8khz, 16khz, etc....

    These are the natural increments of music. If you look at frequency response graphs, to our ear, the space between 100hz and 1000hz sounds the same to us as the space between 1000hz and 10,000hz.

    The full range of a piano, and therefore the full range between all natural instruments is -

    Interactive Frequency Chart - Independent Recording Network

    here you can see the Fundamental Frequencies (Red) and the range of Harmonics (Yellow) for various instruments, as well as see various facts above the Audio Frequency Range.

    For example, male and female voices go up to about 1khz, but harmonics go up to about 8khz.

    A Piano is roughly 27hz up to about 4.2khz. Synthesizers and Pipe Organs go a bit higher and a bit lower than that. (20hz to 7.1khz)

    Instruments like Piccolo and Violin have harmonics that reach as high as 16khz. But a Picolo's highest fundamental is no higher than a piano at about 4Khz. The Violin highest fundamental is only about 1.3khz.

    Guitar is 82hz to 1.2khz with harmonics up to about 5khz.

    Steve/bluewizard
     
    Last edited: Mar 1, 2013
  8. ROZ

    ROZ
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    Nice one Steve,
    That's clearer. I am (kinda) musical, although it's mostly singing and recording these days. I leave teaching piano and arranging music to the GLW. But I did get to the heady height of grade 3 in theory and violin back in the day. One of my pieces had a harmonic on the e string - more piercing than usual - lol.

    But the thing we really do is relate the music speak to the physics, so this is brill. Thanks.
     

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