Hi! This "newbie" needs help with a PA system design

[jack.allwardt]

Hi there! I'm the local Lions Club projects director and have been tasked with replacing/updating/etc. the high school baseball stadium's PA system.

 

This system is 20 years old, and really stinks!

 

I'd like to chat with anyone that has experience or knowledge in this area. Most audio/amplifier/speaker forums don't wish to deal with this mundane subject.

 

Any takers?

Thnx!

[big314mp]

Well, I play around with speakers and amps a bit, so I may be able to help some.

 

The more relevant advice I can offer you is to try diyaudio.com, as they have been very helpful to me.

[tomgwyther]

I work in the entertainment industry as a musician and sound engineer, would be happy to help.

 

It all depend on how big the stadium is, (I assume it's an outdoor environment)

 

General rules are.

You'll need about 5 watts @8 ohms per person i.e a room which holds 100 people would require an amp of 50 watts RMS @ 8 ohms

better to have about 7-10 watts if budget will allow.

although this ratio deminishes with room size e.g massive stadium (80,000 seater) pa systems are about 20,000 watts

 

Your amps power output should match the speakers power handling

i.e 100w amp with 100w speakers. although there are two schools of though on this... either;

your speakers should be able to handle more power then your amp can generate, thus avoiding damaging your speakers

or

you amp should exceed you speakers power rating , thus avoiding overloading the amp.

 

the easiest way to over come this dilema is to buy powered speakers,

these have an amp build into the speaker cabinet which is perfectly matched to the speaker chasis and coil.

 

you will also need some kind of interface between the sound source and the sound produced - a mixing desk.

for your purposes an eight or even four channel desk should be fine.

e.g you can plug in a couple of microphones and a cd player etc.

 

because it's a stadium and the audience is situated 360 degrees around the source you would do best to have four speakers.

If indoors; do not put your speakers in the corners, have a flat wall behind them, preferably with something soft (Foam) on the wall behind the speaker. this help the acoustics and minimises feedback from microphones.

(in the UK and probably in the US ceiling or wall mounted appliances such an speakers must be secured with a chain as well as the mounting bracket: H&S law)

 

so. to sum up, for a 1000 seater, 360 audience stadium I would use

4X 500 watt powered speakers

or 4X 500 watt passive speakers with 2X 1000watt amps

and a 4 channel mixing desk.

a Shure SM57 microphone or two

or maybe even a radio microphone would be of more utility.

 

hope this is of some help. there are lots of other issues regarding this sort of thing, this is just a general overveiw.

Edited September 14, 2008 by tomgwyther

[jack.allwardt]

Hi folks--got some real good info so far. Let me add some facts about this problem I'm trying to solve:

 

It is an outdoor stadium, the seating runs nearly 100 feet in each direction from a press box directly behind and above home plate.

 

At the present--there is a 20 watt (yes--TWENTY!) amp driving two 15" horns on a 70 volt line. There is extreme distortion, and the coach who has beem there all this time told me that they really "cheaped out" when they got to the sound system. When we analysed the system, we tried plugging an MP3 player into aux inputs--very clear patriotic music--military marches, etc.--and at low levels of gain, was not good. Announcing with a NEW mic produced a distored, but understandable output--OK for scores, etc. but not a play-by-play.

 

My proposal so far is the following hardware all from parts-express (so far..)

Amp: http://www.partsexpress.com/pe/pshowdetl.cfm?Partnumber=300-218&FTR=300-218&CFID=9760487&CFTOKEN=96404083

Speakers (2) : http://www.partsexpress.com/pe/pshowdetl.cfm?Partnumber=300-069&FTR=300-069&CFID=9760487&CFTOKEN=96404083

with these drivers: http://www.partsexpress.com/pe/pshowdetl.cfm?Partnumber=300-190&FTR=300-190&CFID=9760487&CFTOKEN=96404083

 

My tentative decision was based upon speaking with one of their techs, and then I found this forum and am looking for validation or better suggestions.

 

Again, thanks to those who have responded so far, and please feel free to ask more questions--either on forum or at: jack@exeterlions.org

[Dudde]

It sounds like the equipment presented should work pretty okay for an outdoor stadium, where would you be placing the speakers in relation to the crowd, if I may ask?

[jack.allwardt]

Hi Dudde! Thanks for your response.

The original location was mid-way down each bleacher side about 6' higher that the upermost seats.

My plan is to mount them on the front corners of the press box (an 8'x12' structure, 9' high.)

My speaker wire runs will be 16' and 8', although I will most likely use the 70v line out and the transformers that come with the drivers.

 

OK guys, here's another question:

 

Although 90% of the use of this system will be announcing ball games, the stadium is used for several other activities, the most noteworthy being the 4th of July fireworks presentation. As the sound system was so poor, one member brought in his "home-brew" PA system and set it up just outbound of 2nd base. (Reason: The crowd "dead-line" as dictated by fire marshall) The audience has gotten used to having an announcer in the front of the field, folks come up with questions, requests for pages, music selections, and we do have our Chaplain give the invocation, the singer of the National Anthem, and the winner of the drawing all come to this location.

 

I'm thinking of a medium quality wireless microphone system(s) to interface with the power amp--about 150' away--OK you baseball fans probably know the exact distance from home plate to 2nd base--1) for voice, the other interfacing with an MP3 player for both music and pre-recorded announcements in other languages--yes, we're in THAT part of CA! Any suggestions on systems--trying to keep that cost to under $300 for both channels.

[Dudde]

I just did a random search on google for "long range microphones" and came up with a variety of results, a lot of them at a pretty affordable cost, my best advice would be to start with that -

[big314mp]

AFAIK, your choices look solid for announcing/scores/etc. It will be quite weak for music however. I would be careful about overdrawing the amp while playing music.

 

The people at PE are quite good, and if that is what they recommended to you, then I would be quite confident in it. I was just up there on friday, getting some parts for a new speaker, and they were extremely knowledgeable and helpful.