Connect with us

Public address system

Discussion in 'Electronic Design' started by Andrew Edge, Oct 7, 2009.

Scroll to continue with content
  1. Andrew Edge

    Andrew Edge Guest

    Hi to everybody
    I'm designing a public address system for a work place .The
    loudspeakers I'm using have an internal amplifier and use up to 25W
    at maximum power. I'm wondering what specs to look for the power
    supply which will power the speakers. Apart from the total power
    which should be about 100W for each position as they will be about 2-4
    speakers ... what type of Power supply? SMPS , linear or mixed? What
    S/N , distortion figures should I be asking from the supplier? What
    other specs are important.
    Thanks to all in advance.

    Martin.
     
  2. Charlie E.

    Charlie E. Guest

    Sorry, but your question does not compute. What voltage? What
    current? What source are you using? If you are an engineer, you must
    be either in software or digital design... ;-)

    Charlie - who has designed many PA systems and never used power
    speakers!
     
  3. Joerg

    Joerg Guest


    I haven't used power speakers either. However, from experience I'd say
    I'd try it. The main reason are the power volume controls. Even
    expensive ones don't last. At our church they begin to crackle after 1-2
    years, later the audio cuts out across large chunks of potmeter range.
    Powered speakers fit the same 8" ceiling tile cut-out:

    http://www.cambridgeaudio.com/summary.php?PID=79&Title=Summary

    Then you don't have to string fat cable around, CAT5 suffices. Some have
    IR controls, others can be controlled by regular low-power potmeters and
    not those failure-prone wirewound rheostats. Another nice feature on
    some active PA speakers is that you can individually adjust the
    frequency response so it acoustically matches the furnishings of each
    room area. Most are now class D so heat isn't an issue.

    Of course, the fire marshall will have a word as well here and that
    could make commercial installations of powered speakers quite
    cumbersome, because of the power cable.
     
  4. Charlie E.

    Charlie E. Guest

    Hi Jim,
    I assumed that. But, it is so much easier in a PA situation to have a
    single power amp, and have multiple un-powered speakers, that only a
    newbie or amateur would even consider it. If he has many stations, he
    just uses 100V or 70V transformers for the line. To have a powered
    speaker at each location means you have to have separate power
    supplies at each location, or run a power feed with your audio feed,
    unless you get really crazy and decide to run power over the audio
    line! :cool:

    Charlie
     
  5. Charlie E.

    Charlie E. Guest

    Yeah, power in a plenum needs to be in conduit, or at least armored
    cable.

    Charlie
     
  6. Joerg

    Joerg Guest

    Some are LV-powered, for example at 24V. But yeah, it's a hassle to do
    proper power runs up there. The reward comes later, by not having to
    replace rheostats all the time. According to Murphy's law this stuff
    dies at odd times like when pastor just starts his sermon. BT :-(
     
  7. Joerg

    Joerg Guest

    120ft? That must be one heck of an entertainment room.

    It becomes non-trivial in public buildings because the fire marshall and
    his opinion is law. If he thinks something looks odd it gets written up
    no matter how safe it is :-(

    Luckily he wasn't there when I hauled in my electric saw and connected
    it via a cable that had a NEMA plug on one end and a Euro outlet at the
    other.

    Just do diff pairs with true line level (or more) and you'll be fine.
     
  8. Joerg

    Joerg Guest

    Euww ...

    Might want to invest in shielded CAT5 then, depending on whether you
    must cross paths with some huge mains trunk. And keep the code distance
    from that ;-)

    But this is America ...
     
  9. Joerg

    Joerg Guest

    Yeah, the speakers I mentioned can also take power over CAT5 but it's
    about an amp max per speaker. That gets old when you must install a dozen.

    We also use the speakers for overflow area sound at our church. It's
    best to have the least amount of digital stuff in the way, too much
    delay, we do it all analog.
     
  10. Charlie E.

    Charlie E. Guest

    Ok, so you aren't talking about a PA system, but a custom paging and
    other use system. If you have a lot of other equipment at each
    location, and cabling that involves a lot more than just the PA
    signal, then locally power amplification is just another feature. If
    you are talking PA, then having to install and power multiple
    amplifiers is usually a lot more trouble than necessary. Using a
    single, inexpensive amplifier connected by 16 guage speaker cable is a
    lot easier than even CAT5.

    Charlie
     
  11. Andrew Edge

    Andrew Edge Guest

    Hi thanks for the replies.
    The loudspeakers have an amplifier incorporated in them as I said in
    my earlier post. Its not a HiFi system but a Public Address system or
    as some of you prefer calling it a paging system to call operators to
    an Intercom line for urgent communications or warn them of dangers to
    the environment like poisonous gases , fire and the like.

    The loudspeakers each have an amplifier incorporated I repeat ... and
    each one of these amplifiers absorbs 25W, though the data sheet says
    the maximum value is 40W. The input voltage to each loudspeaker is 24
    to 48Vdc but looking at the loudspeakers specs I prefer using 48V as
    distortion at 24V(2% versus1.5%) is high as is the quiescent current
    through the amplifiers (45mA versus 25mA). Input impedance of the
    loudspeakers = 10kOhms, S/N is about 90dB. The amplifiers are Class D
    type.
    I prefer a power supply with a 230V to a 115V input option.

    I can't use a single amplifier because with the number of speakers
    we're dealing with it would need more then a 1000W speaker with huge
    distances involved its complicated. The source is an intercom system
    so at a first estimate 0.6mm telephone wire should suffice.

    The source amplifies the input voice to 7 dB but I reverse engineered
    that with an inductor coupling to 0 to make it OK for the
    loudspeakers amplifiers.

    Till tomorrow.

    Martin
     
  12. Andrew Edge

    Andrew Edge Guest


    And hey I forgot to include inj my last post the question is about
    powering these things :

    what type of Power supply? SMPS , linear or mixed? What
    S/N , distortion figures should I be asking from the supplier? What
    other specs are important.
    Thanks again to all in advance.

    Somebody was asking about the reliability of powered speakers. These
    are robust things ... cost a small fortune a bit but they blare out
    louder then the work environments background noise and are in
    conformity with the norms for Industrial environments where they will
    be fitted.

    Martin
     
  13. Joerg

    Joerg Guest

    I would certainly go for SMPS (primary switchers). Linears become
    toasty. Try some out, to see if they cause any serious noise. Modern
    ones should not be much of a problem in that respect as they operate
    well above the audio range. Best to find an "international power" type
    that takes anything between 90VAC and 260VAC without a need to
    re-configure. Most contemporary SMPS will be like that. That way you can
    sell to just about anywhere, from Japan with its 100VAC grid to the UK
    with their 240V grid.

    It's a pity that the speakers don't work with a voltage around 18VDC
    because then you could possibly use cheap laptop brick supplies if code
    and safety regulations allow that. 24VDC or 48VDC is industrial, meaning
    expensive.

    It will be important to distribute the audio feed differentially.

    [...]
     
  14. Joerg

    Joerg Guest

    That's why I suggested to try it out first, before issueing a large
    purchase order. I found it can be done. You might need to use a couple
    wee ferrites and a capacitor but Martin could cross that bridge when he
    gets there, and if he can't get it quiet ask here again.
     
  15. Nico Coesel

    Nico Coesel Guest

    You've got to be joking...
    Sorry, but the only way to do this right is using 100V speakers which
    are fed by several amplifiers at strategic places. There is no sense
    in designing such a system. It is already available as an off-the
    shelf product. Go ask at the local football stadium or an amusement
    park. They deal with long distances as well. Besides, I don't know if
    you want to design a safety critical system. I'd see if I can buy such
    a system so I can blame someone else if things go wrong.
     
  16. [...]
    Is there any requirement for the system to continue to work if the mains
    fails? If you need emergency battery backup, a centralised system or
    one with a few large amplifiers will be much easier to install and to
    maintain over the years.
     
  17. Ross Herbert

    Ross Herbert Guest

    :
    :Hi thanks for the replies.
    :The loudspeakers have an amplifier incorporated in them as I said in
    :my earlier post. Its not a HiFi system but a Public Address system or
    :as some of you prefer calling it a paging system to call operators to
    :an Intercom line for urgent communications or warn them of dangers to
    :the environment like poisonous gases , fire and the like.
    :
    :The loudspeakers each have an amplifier incorporated I repeat ... and
    :each one of these amplifiers absorbs 25W, though the data sheet says
    :the maximum value is 40W. The input voltage to each loudspeaker is 24
    :to 48Vdc but looking at the loudspeakers specs I prefer using 48V as
    :distortion at 24V(2% versus1.5%) is high as is the quiescent current
    :through the amplifiers (45mA versus 25mA). Input impedance of the
    :loudspeakers = 10kOhms, S/N is about 90dB. The amplifiers are Class D
    :type.
    : I prefer a power supply with a 230V to a 115V input option.
    :
    :I can't use a single amplifier because with the number of speakers
    :we're dealing with it would need more then a 1000W speaker with huge
    :distances involved its complicated. The source is an intercom system
    :so at a first estimate 0.6mm telephone wire should suffice.
    :
    :The source amplifies the input voice to 7 dB but I reverse engineered
    :that with an inductor coupling to 0 to make it OK for the
    :loudspeakers amplifiers.
    :
    :Till tomorrow.
    :
    :Martin
    :
    :
    :
    :On Wed, 07 Oct 2009 21:55:57 +0200, Andrew Edge
    :
    :>
    :>Hi to everybody
    :>I'm designing a public address system for a work place .The
    :>loudspeakers I'm using have an internal amplifier and use up to 25W
    :>at maximum power. I'm wondering what specs to look for the power
    :>supply which will power the speakers. Apart from the total power
    :>which should be about 100W for each position as they will be about 2-4
    :>speakers ... what type of Power supply? SMPS , linear or mixed? What
    :>S/N , distortion figures should I be asking from the supplier? What
    :>other specs are important.
    :>Thanks to all in advance.
    :>
    :>Martin.


    Andrew, I don't wish to be overly critical, but I fear that you are embarking
    upon a project about which you have little real-world knowledge.

    From your description you are dealing with a large number of speakers over a
    huge distances. My first recommendation would be to ditch the idea of powered
    speakers. Each powered speaker is a fault liability in its own right due to the
    individual electronics in both PSU and amplifier, and fault isolation may not be
    as easy as simply saying "oh, speaker number 123 is faulty". Your statement that
    each speaker "absorbs 25W" tells me you are new to this subject and I really
    think you need to talk to a PA specialist who is conversant with covering large
    areas such as sports stadiums or college campuses.
     
  18. Andrew Edge

    Andrew Edge Guest

    I make a living designing these things ... so just answer my question
    if you can ... same goes to Tuddenham and Herbert.

    Thanks to Joerg and Vladimir for their constructive comments.

    Martin
     
  19. Charlie E.

    Charlie E. Guest

    Martin,
    Are you saying that you design PA systems for a living? Or industrial
    systems for a living? And, are you an electronic designer? Or
    mechanical? I have to ask because your question is so basic, and
    wrong, that I suspect that you have little to no electronic or
    electrical experience, unless it is in a field such as digital design
    or software where practical problems are far from reality.

    As to the answer to your question, it is quite simple. Where are
    these units located. What is the spacing? Is power available at each
    location? If they are relatively close, you get one really beefy
    power supply, and run a cable from there to the units in parallel. If
    they are far apart, then you buy smaller power supplies, and put one
    at each unit. If some are far, and some are near to each other, you
    use a separate power supply for each area. You also get to find out
    what a ground loop eliminator is... ;-)

    In other words, your question is meaningless. There is not enough
    information to give a reasonable answer, and it seems that most of the
    assumptions you have are wrong.

    Charlie
     
  20. Nico Coesel

    Nico Coesel Guest

    FYI: We are in the same business. I'm not saying the old way is the
    good way and I endorse to think about new ways of doing things instead
    of following old habbits. But in this case the 100V systems make a lot
    of sense. I'm quite sure if you do the math on a 100V system and your
    system, the 100V system will be 4 times cheaper and much more
    reliable.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-