Public address system

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.

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.

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.

: :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 : wrote: : :>

:>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.

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

What an ass! "I make a living designing these things". Really? No one would ever guess. You're clearly incompetent, and likely to royally screw it all up... your boss will love it ;-) ...Jim Thompson

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

Here's how it will look...

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.

Two wannabe smart guys/ engineers on Fri, 09 Oct 2009 ,called Jim Thompson and, Charlie E. spewed rubbish on this thread of which edmondson said

If you know so much ... Why not give an answer... Its probably beacuse you're both too incompetent to give an intelligent answer. I've seen some people giving it a try without any real certainty but I'm sure you believe everybody is stupid except you ... just shut your mouths. If you don't have anything to do with your life ... I'm sorry for you man as I am for Jim Thompson whose posts are useless.. Run run guys ... before i catch you.

Martin

OK I understand your reasoning ... but sorry I don't have as much time as you people do to give explanations ... There is more fun in life then debating on these issues ... . But did it ever cross your mind that it is a need of the client? Did it ever cross your minds that the Industry where these things are going to be placed have conformity issues that only the above mentioned Loudspeakers satisfy ... and a whole lot of other reasons accompany my decision.

Martin

Yikes! For some reason I think this is not a trick photo...

You can tell they're not too intelligent because they're in a wading pool on a cloudy day?

Cheers

Phil Hobbs

Ok, you are an idiot. Believe it or not, I HAVE (and do!) designed PA systems for a living, as well as do electronic and embedded design. I even answered your question. You must just be a stupid troll, with nothing better to do than waste people's time.

Charlie

It must be a small church then. Usually some digital delays are used to feed speakers further away so the sound from the front speakers is in phase with the half-way speakers.

Ok, so you post a dumb question that you seemingly don't understand, don't tell us half of the requirements, act like a little baby when we ask for more info and cry that we don't understand, don't listen when we DO answer your wrong question, and it is all our fault. You're a democrat, aren't you???? ;-)

Charlie

I'm a troll because I ask a question.? That sounds very stupid , doesn't it Charlie. You can't even understand what I ask and you claim you can design a PA system? The instinctive reaction was to laugh one's head of but a careful consideration of your words as well as those of the other answers on this thread ... convey the message that you suffer from some deficiency, or is it something physical? Which is all very sad. As I said before my deepest pity for you and the company.

Martin

Compared to European cathedrals it is small, holds about 300 people max plus maybe another 50 or so in the overflow area (narthex). But in contrast to European ones it fills up twice every Sunday and that's what really counts :-)

Our Yamaha mixer does have a DSP with delay features in there but that part of the mixer has died many years ago, along with the VU meters.

Charlie The requirements had nothing to do with the technical aspects. My answer was atechnical one. To illustrate ... A man gets a fracture ... and calls his doctor and asks ... Doc what should I do if I have a broken leg ... and the Doctor says don't be stupid enough to break your leg. Now what would you call the doctor? Dumb as hell. You put yourself in the situation of the Doctor.

Martin