Audio Systems: diy PA-system for outside

Question
QUESTION: Hello,

This is the deal: I’m thinking of and learning how to build my own PA-system and found this website very inspiring
http://www.instructables.com/id/Battery-Powered-Mobile-Party-Sound-Systems/?ALLS

The questions are:
- For a public space and an audience of 100-300 people in a circle, what kind of speaker makes sense? How much watts do you recommend for a single speaker, maybe for 2?

- With an amplifier of 2x100watts – can I power a speaker that has higher watts? Does the mixer do that for me? That's what I learn from the instructable, where they use this kind of amp and speakers with 400w.

Thanks! I look forward to hearing from you!
Have a good weekend,
Matthias

ANSWER: Yes, the URL you mentioned is a good one.  Pay particular attention to the section on efficiency.  But, most loudspeaker specifications refer to 'sensitivity' as it relates to the efficiency of its ability to convert electrical energy to acoustic or sound output.  Sensitivity is the sound level that will be produced with one watt of input, generally.

Therefore, if one speaker is rated at 3db greater than the other it will require half the audio power to produce the same level.  So, sensitivity will be a key spec for you to consider.

You will need more power and speakers if you want good coverage for audiences of 300 and it depends alot on the acoustics of the space.  If outdoors you need much more power than inside a building because outdoors you get no reflections off the walls.

with 400 watts vs 200 watts you get twice power but that is only 3db increase in acoustic power. Just to give you and idea, to increase the sound output to what most people would say is twice as loud as before takes about 9 db increase in power.  A 10db increase represents a power increas of ten times! So, 9 db is nearly ten times more power needed.

Therefore, in PA work you are always trying to optimize speaker sensitivity and audio power output to keep the levels as strong as possible.  And if you are amplifying music you will probably need subwoofer assistance to keep fidelity up.

Let me know if you have further thoughts.


---------- FOLLOW-UP ----------

QUESTION: Hello again,

Thank you so much for your quick response! I'm very amazed!

It's indeed mainly music that I would like to amplify in a street. To give you the whole picture. It's not for a performance, rather a spontaneous dance to which we invite spectators. The music comes from an mp3-player. So, a full bass would be nice.
The location doesn't have walls on the back side, but we direct the sound to a large building opposite of us. So, that should help with the sound.
A subwoofer might make sense for the lower sounds and bass?!

Being outside, playing the music "stereo" doesn't make too much sense, does it?
How to I switch the amplifier or mixer to mono?

And can I use speakers with higher watts than the amp?

I'm toying with the idea of getting this amp, that the instructables recommended: "2x100W @ 4 Ohm TK2050 Class-D Audio Amplifier Board"
with the mixer "Rolls MX51 Mini 4 Channel Mixer"

Or do you recommend buying a prefab PA like the "PYLE-PRO PPHP159WMU 15-Inch 1600-Watt"

Thank you so much for your help!
Matthias

ANSWER: The higher the wattage rating of the speakers the better.  Wattage ratings on speaker systems is somewhat fanciful anyway as there is no universally  accepted way of measuring power ratings and specifying them.  As before, sensitivity is one of the most important details - unless you are dealing with powered speakers wherein the power is generally pretty well matched to the speakers by the design engineers.  Powered speakers make sense in an environment where moving the systems around alot is part of the business.

Outdoor systems take lots of power. You can't have too much.  If you've ever been to an outdoor concert by rockers you will find they use kilowatts of power on multiple channels.  For your street affair as you have described it you will need more power than you have originally planned for a good effect with crowds over 200 or so; at least in my opinion.

I think you are headed the right direction and you'll be okey except for the power; after you get started you will likely find yourself wanting to go to more powerful system; both amps and speakers.

Stereo/mono - won't make much difference in outdoor venues.  But you can always switch your mixer to mono and all is well.

Cheers.


---------- FOLLOW-UP ----------

QUESTION: Hi,

I'm getting it slowly. Question about a prefab battery powered PA:

If I get the amp and mixer plus a couple 12V batteries and cables and recharger as described in the instructables, that cost around 120+ $.
With a speaker an additional 100 (http://www.bax-shop.nl/passieve-fullrange/devine-artis-15-400-watt-passieve-luid - 400w/98 dB is good, right?) - maybe even two for more coverage of a large space/lots of people in a wide semi-circle.
We are talking about 320+ $.

How does that compare to a prefab PA like the "PYLE-PRO PPHP159WMU 15-Inch 1600-Watt" that I can get for 300$ (instead of 730$) from amazon?

Thanks for your responses! They have been great and I learn a lot here!

Answer
Sounds good to me.  But, as in all sound reinforcement systems one never knows until it has been installed and used for a few times.  So, my advice is go slow but leave the possibility that you may want to upgrade or change one or another of the elements of the system as you tweak and improve.  Seems to me you are headed the right directions.

Cheers.