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Revised technical question:

Discussion in 'Misc Electronics' started by Shawn Sutherland, Jan 3, 2004.

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  1. What is the best capacitor value for audio frequencies between 100 HZ and
    6000 HZ into an impedance of 1K ohms?

    Please let me know.

    Shawn
     
  2. Myron Samila

    Myron Samila Guest

    1k ohm for audio? as in where in the circuit?? speaker? active part of the circuit?
    passive crossover?

    A capacitor cannot limit bandwidth on the top end, you'd need a bandwidth limiting
    crossover network to limit frequencies between 100hz and 6khz.

    We need the following information:

    Application?
    What you are trying to achieve??
     
  3. Brian Oakley

    Brian Oakley Guest

    A cap cant limit on the high end?? Are you sure about that? If you take an
    appropriate cap across a speaker, doesnt that short out some of the high end
    freqs?
     
  4. Myron Samila

    Myron Samila Guest

    You wouldn't use a cap to limit bandwidth in parallel in audio.

    You'd use a coil to limit high frequencies at a rate of 6db/octave, in series. A cap in
    series with the speaker will filter low frequencies.

    Passive crossovers are horrible anyhow, bi-amping or three way (active xovers) work best.

    Yes, the OP won't get his question answered because it is too vague.
     
  5. Brian Oakley

    Brian Oakley Guest

    It depends on his application. As I said in my post "across the speaker"
    will roll off the top end. As you stated in your post, a cap in series will
    roll off the low end. We dont know what kind of circuit application he is
    using, hifi, mono, etc. He may be looking for a filter for his ham radio
    reciever for all we know so a crossover may not even be what he needs.
    Anyway, until he is more specific, we wont be able to answer.
    Brian
     
  6. Switch

    Switch Guest

    How does a cap across the speaker roll off top end? I believe that is incorrect. Hifi,
    mono, 5 channel, it doesn't matter. A passive filter is a passive filter, period, ham
    radio or not (I have friends who are operators and I've built many bandwidth filters for
    them. The only way to roll off high frequencies to a speaker is to put a coil in series
    with the speaker or resistor across the speaker (high value resistance will absorb
    frequencies at a specific attenuation, as 6db/octave typical). Putting a capacitor across
    a speaker is the same as putting it in parallel. Trust me, it won't work, even when a
    12db/octave filter is used, the cap goes in series with the load, the coil goes in
    parallel to the load for low-pass applications, reverse for high pass applications.



    A crossover is a filter, exactly that, highpass vs lowpass vs... bandpass..... all
    crossovers (a term used in the audio field).

    Top posting is bad, stop it.
     
  7. Brian Oakley

    Brian Oakley Guest

    I will accomodate your wish about top posting. And dont be telling people
    what to do.
    A cap does roll off the frequencies when placed across the speaker. If you
    study filter design, the coil in series does what a capacitor in parallel
    does. The point is the capacitor needs to be the correct value to do so.
    Granted, it may be a large capacitor, but it does work. Try it. Also, the
    ARRL Handbook has some good theory on filters.'
    Brian
     
  8. Brian Oakley

    Brian Oakley Guest

    Someone that understands!
    B.
     
  9. Switch

    Switch Guest

    Usenet rules.... read the FAQ and rules and regulations of usenet, it is in black and
    white.

    Brian, in my time of designing filter networks, reading books, using crossover/filter
    design software, there is no where that suggests the use of a capacitor in parallel to a
    speaker to limit frequency. If so, what is the predictable filter slope??

    Anything less than 6db/octave is useless in audio.
     
  10. Switch

    Switch Guest

    Why would that be considered rash? if you are trying to limit bandwidth (lets say low
    pass) from 250hz up to 20khz, then at anything less than 6db/octave, you will still hear a
    great deal of program material at the next lower octave. The slope is too great,
    typically, in home audio filter networks employ a minimum of 6db per octave, and then
    higher quality ones use 24db/octave, Butterworth, Linkwitz, Bessel, Bec... depending on
    the desired Q.

    Look, if you want to limit bandwidth in audio, I am simply suggesting that your method is
    not practical and not used.

    ie: 8ohm speaker, bandpass 500hz-6000hz, use a 40mF (non polarized) cap in series with a
    coil of .212 mH, this will bandpass at an effective slope of 6db/octave on the upper and
    lower end of the shelf.

    What now?? Qualify yourself, otherwise your posts aren't of any use.
     
  11. Switch

    Switch Guest

    We are talking audio (AC), not any other type of AC coupled circuit. You are clearly (not
    to you though) missing the point.

    Someone suggested you can bandpass audio using only a cap, how?(bandpass passively on the
    output of an amp) Where does it filter the low end? Are you going to put a 100,000 mF
    capacitor at 200V to cut out frequencies at 8 ohms? Practical? ummmmmm.......

    The suggestion of bandpass came up regarding ham radios........ that is why we are on the
    topic of audio, nothing to do with the OP.
    I was responding to someone who said you can use a capacitor across a speaker to achieve
    bandpass, not the OP.
    We're talking electronics here.....I'm not in the alt.shakespear.chat.forum, his rants are
    about as out of date as your theorems.


    You're still incorrect unless you can prove otherwise. Show me an example using ONE
    capacitor how you would filter frequencies between 100hz and 5000hz with an 8ohm speaker
    load?? we are assuming the signal is audio, from an amp. That is what I was arguing, it
    is incorrect and cannot be done, period......

    Lets stop the misinformation here. I wasn't referring to the OP at all, all previous
    posts have snips of the question I was answering.


    Do you own a stereo? ;) Do you understand what I'm talking about at all??!?! That is my
    only question. If there is any other way of doing what I'm suggesting, why doensn't
    anyone else do it?

    Just like the thread about 50hz vs 60hz motors, oh my, don't even get me started on that
    one. So much WRONG information, I only wish I jumped in on that one.
     
  12. Myron Samila

    Myron Samila Guest

    Hate to say it Richard,

    This person is right........ You cannot create a bandpass audio filter with just a cap
    across a speaker load as was mentioned that you could in a previous post. If you put a
    cap in series with the speaker load, you create a filter. (filtering out low frequencies).

    I think you missed the initial point that I brought up in this thread a while back.

    And you don't need to study schematics to understand how a speaker crossover or bandpass
    filter works. Usually, there are no more than 4 components (in a 24db/octave slope
    passive crossover), this is the only component between a speaker and an amplifier.

    I think I also talked about the ham radio application and such, but whatever. Points get
    missed, heheh.

    All I do is live and breathe professional audio, have done so for the past 10 years, wind
    my own air core coils, built hundreds of passive and active crossover networks ;). I've
    never put a cap in parallel (across) a speaker load to achieve what you guys are arguing
    about, ?!?! heheh. If a cap could be used as a bandpass device in audio, that would be
    great, since then I would start to wonder why we use coils (which are expensive, power
    robbing, expensive, oh and did I mention expensive?, high quality audio air core coils can
    reach upwards of $400!!!! or more (Cnd), for only 100Watts power dissipation!!!

    Anyhow, great discussion!! A lot can be learned here!
     
  13. Brian Oakley

    Brian Oakley Guest

    Doesnt matter, its not your job to tell people what to do. You can explain
    the rules, but assuming to be the boss doesnt make you someones boss kid.
     
  14. Brian Oakley

    Brian Oakley Guest

    I think the question that Switch asked was how does a cap across a speaker
    roll off frequenceis at the top end. He didnt say anything about bandpass. A
    bandpass filter consists of several poles made up of caps and coils. But a
    cap across an 8 ohm load can roll off frequencies at the top end. Like I
    said it depends on the size and type of the cap. Xc =2pi*f*C. This is the
    formula one would use to calculate the capactive reactance to frequencies
    with a given capacitance. Plug in the frequency in question with the
    reactance in question and it will give you a capacitance that you need. Find
    a good electronics book and a physics book. it does work.
     
  15. Brian Oakley

    Brian Oakley Guest

    No I think he understands the point as it was originally described in the
    original post.
    The original post about filtering in ham radios was my post. It doesnt
    mention bandpass, nor 8 ohm load for that matter. The original post says
    1000 ohm impedence. There are a lot of things you can do with audio at 1000
    ohms that may not be practical at 8 ohms. We are not talking hi fi audio
    here. We are more than likely talking about a lowpass filter using a cap
    across the speaker leads of a 1Kohm speaker (or headphones).
    Im not sure where you keep getting the idea about bandPASS. BandWIDTH was
    what was mentioned, and a cap can effectively limit the bandwidth by rolling
    off the high end frequenceis. We were talking about a rolloff filter, one
    that rolls off the higher frequencies. Theres a big difference.
    alt.shakespear.chat.forum, his rants are
    Again, 8 ohms was not mentioned in the original post. 1000 ohms was the
    load. For all you kids out there that dont know it, there is a lot of older
    equipment that use higher impedence output audio. It can range from 6k ohms
    on down to 8 these days. If Im not mistaken, PA systems use higher impedence
    loads to limit the current drawn from the system.
    Like I said above, youre thinking high end hifi, not high impedence
    communication audio amplifiers.
    Not gonna comment on that.
    Brian
     
  16. Switch

    Switch Guest


    Yep, you'd be mistaken

    PA systems run in very low impedance

    2 ohms is common thru to 8 ohms. Only high frequency drivers use 16ohms as nominal
    impedance. Series Parallel is never used on low frequency transducers.

    Qsc Audio, Crown, Carver, Bryston, Crest, BGW, Peavey, all manufacturers of power amps for
    PA use. All have minimum impedance of 2ohms, and typically, a dual 18" subwoofer has a 4
    ohm impedance (2 8ohm 18" drivers in parallel)

    Ever put a cap across a speaker load? Introduces harmonics that aren't supposed to be
    there, even at low power levels. Ummmm??
     
  17. Switch

    Switch Guest

    Contrary:

    abuse of the usenet can be reported to your isp for traceroute. Everyone (even dynamic)
    IP addresses get authenticated.

    Usually fill in your isp. (ie: someone posting illegal material in
    newsgroups can't get away with it, hate mongerers etc...)

    Please understand that your post appears to not only this newsgroup, it gets posted on
    almost every electronics website with a forum, that means, MILLIONS of people get to see
    your top post.

    http://www.faqs.org/faqs/usenet/posting-rules/part1/ (just an example, try google)

    Read up sometime, not following the rules doesn't mean you're better than anyone else.
     
  18. Switch

    Switch Guest

    These are not musical equipment, they are power amplifiers, the SAME type of amp you can
    drive a 70V speaker system with, just put a transformer on the output of the amp!!!!! duh.

    read below, 200watts at 2ohms is quite low power, several hundred feet with the
    appropriate AWG wire. I've installed ElectroVoice MTL-4 (2ohm sub cabinet uses 4 18"
    woofers in a manifold/bandpass box), with a 1800W/ch power amplifier using 10AWG wire in a
    nightclub over 200 feet. The damping was only slightly affected because the amplifier had
    a damping factor of >2000, amplifiers with low damping factors cannot dampen the speakers
    over a long distance of wire. Read below for an explanation of damping.

    A 70 volt system would be 5000/200 or
    impedance matching is all done in parallel, each speaker down the line is on a transformer
    that has tappings.

    You're absolutely correct, except the way a 100V or 70V system works is if you have a 100W
    amp, you can run (10) 10W speakers. Impedance isn't typically necessary to calculate,
    wire size isn't even a factor, you can use 16AWG, 18, heck, even 24AWG will do it!!

    Yes, the wire length does make a difference, my company happens to install the stuff on a
    regular basis into hotels, restaurants, banquet halls, etc...

    The impedance of a 70V system is irrelevant because of how high the impedance is, as well
    as there won't be any noticable difference when you remove or add speakers in the line.

    70V is pretty much the standard for North America. I buy 100V systems from Europe, same
    difference, just higher voltage.

    The speakers are still 8-16 ohms on the other end, the matching transformers are tapped so
    you can select the W, typically .5,2,4,8,20 watts being the highest as most transformers
    start to saturate at high power levels (including those being produced by the amp).

    A Crown MacroTech 3600 (which is a stereo power amp typically driving 2-8ohm loads) in
    bridge mode can run 100 10W tapped speakers without worry about the "head" transformer
    getting saturated, because it can run right off the amp into all your tapped speakers down
    the line.


    70V and other transformer speaker loads are not capable of playing full range (20-20Khz).
    They are low power.

    You can typically drive a 2500W/ch stereo amp at 2ohms using 10AWG wire about 200feet. At
    this distance, the damping factor is way out of wack, which means the amplifier has very
    little control over what the driver is doing. A short wire run from an amp creates the
    highest damping possible, when the music stops playing (bass hit), the amp will control
    the speaker and it will not 'flop' around.

    In this case of high power, it is desirable to put the amplifier behind the speaker
    stacks, run balanced XLR signal cable out to the amps (up to a maximum of 1000 feet
    without distribution amplifiers), and voila.

    200 watts is super low power. A Crown MacroTech 5000 is 5000W bridged into a 4ohm load
    using a 220V/30A supply and has such a high damping factor, that if you use 8AWG wire, you
    could literally blow up any speaker load you put on it.
    The use of such an amp is strictly for driving low frequency cabinets.

    I've been doing professional audio in North America for the past 25 years.


    PA means public address, 25,000 screaming concert goers, or a million people at the
    Million Man March still need to hear, heheh, I don't think we'd use 70V systems in that
    case.

    Little known fact, 70V and similar audio systems make up for 80% of the sales of
    professional audio equipment, may even be more now!
     
  19. Brian Oakley

    Brian Oakley Guest

    anyone else.

    As I said in my last post, its not your job to tell someone what to do. You
    may explain the rules but youre attempting to be the boss is inappropriate.
    If you dont like the way I post, youre free to complain to whomever you
    wish, but you dont have the right to tell anyone what to do.
    Brian Oakley
     
  20. Switch wrote...
    This is wrong. There are many uses of 6dB/octave or lower
    response slopes, such as in areas of feedback stabilization,
    line equalization, signal processing, etc. And a -3dB/octave
    filter is the easiest way to make pink noise from white noise.
    Although it may not seem so to some, pink noise generation is
    an important capability to many audio experts. Plus it makes
    a great background-masking sound for sleeping.

    Thanks,
    - Win

    whill_at_picovolt-dot-com
     
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