How many WATTS are needed for a band's PA ?

paulphoenix

As per the title really. I am looking for a little guidance in FOH sound levels please.  

I am just about to start rehearsing for a new project playing pop and rock covers and, as the only member with any amount of equipment other than that of their own musical discipline - I have become the "PA guy".

Some info for reference that might help: 

We are currently a 4 piece (but looking to add keys asap): 
Drums
Bass 
Guitar - I intend to put my HX Stomp through the PA (or at least mic a cab for spread)
female lead vox 
male backing vox 

I'm sure we'll begin by playing the usual small to medium size pubs to very small numbers of ( <50?) punters.  

I own a couple of small behringer mixers with just enough XLR inputs to cover everything, plus 

2 x 8ohm 15" subs with eminence 2 way passive crossover  
2 x 8ohm 12" tops with upgraded passive crossover and compression horns 

The specs of my power amp are: 

Peak power 1200W @ 4ohms
600W program power @ 4ohms
300W RMS @4ohms ;

My main concern in all of this is - will my power amp be enough to: 

run as a vocals only PA (plus guitar & eventually keys) using only the tops? - obviously 300w into 4ohms becomes more like 150w into 8ohms

run as a full band PA with the subs - guitar, (eventually keys), DI the bass, and mic a few drums? 
 
Or will I need to invest in a few extra watts under the hood?

I used to run the same speakers (in a 3 piece pub rock covers band) with a yamaha emx512 (2x500W @ 4ohm) and could never turn up past half way in most of the local pubs we played!   

TIA 

Danny1969

Although the loudness of a PA isn't actually down to the wattage of the amp completely  ... Generally a power amp with more power and thus clean headroom will be better. Something like a Peavey PV series if you don't have the Yamaha anymore. 
Some cheap power amps are really the equivalent of a souped up small car revving it's nuts off to achieve the speed a larger car could do relatively untaxed. Also smaller amps distort earlier and this taxes the speakers more than a higher power clean signal would. This is why you choose a higher power amp than the rating of the speakers.

maltingsaudio

Model numbers would help, but from what you’ve said your under amped and likely in my opinion to burn out your speakers because as @Danny1969 says you’ll be running the amp very hard to power the speakers which will result in it chucking out square wave distortion which will fry the cones. The only power rating for an amp to take note of is it’s rms rating, the others really are marketing blarney in the real world. 

Look for an amp which at least matches the total power rating of your subs and tops at the impedance the amp is going to see. So for example, if your tops are 300 watts at 8 ohms and your subs are 500 watts at 8 ohms, if you go from amp to sub to top, the amp will be seeing 800 watts at 4 ohms and your amp needs to have a minimum rating of 800 watts at 4 ohms rms. 

Nb this also depends on the type of amp you have, an old 500 watt with a toroidal power supply would probably be ok , an old 800 watt amp with switching power supply would probably struggle, due to the way they do things

paulphoenix

Thank you gents., I much appreciate your help and the benefit of your knowledge. 

My tops are 200W rms @ 8ohms so I should be ok powering these on their own. 

The only info on my subs that I can find, is that the crossover is rated 600W @8ohm. ;;

So I probably need somewhere nearer 800W a side to drive the subs and tops. 

maltingsaudio

paulphoenix said:

Thank you gents., I much appreciate your help and the benefit of your knowledge. 

My tops are 200W rms @ 8ohms so I should be ok powering these on their own. 

The only info on my subs that I can find, is that the crossover is rated 600W @8ohm. ;;

So I probably need somewhere nearer 800W a side to drive the subs and tops. 

Doubt they are 600 w , as the crossover should be rated higher than the speaker, but if you work to that you should be ok, 

if you can take a pic and post it , pic of the actual driver would be good too

ESBlonde

If the subs are 8ohm then run them in parallel for a 4ohm load, then get a big power amp like. PV2600 and run that in bridged mono (1600w"?) that should light up the bottom end. If you can get a behringer DSP as an active crossover between sub and tops and bypass the sub crossover. Run the 300w at 8ohm into the tops stereo and that will be adequate as long as the desk never clips it will be loud and clean for the venues you suggest.

paulphoenix

Thanks to all. 

I had a peak inside the speaker cabinet this morning and my subs are (Red Label) Eminence Delta 15LFA 8ohm.

There was nothing on the product labels I could find that stated the power handling -but current LFA specs suggest 500W. 

Rocker

I honestly think this is one situation where you need to talk to a company that sells or hires PA gear.  Otherwise you are only guessing that the kit you have can be adapted to your new situation. It may well be so but it would be a pity/tragedy to damage good working kit by using underpowered amps.  A £50 consultancy fee might be numbered amongst your best ever buys.

maltingsaudio

Rocker said:

I honestly think this is one situation where you need to talk to a company that sells or hires PA gear.  Otherwise you are only guessing that the kit you have can be adapted to your new situation. It may well be so but it would be a pity/tragedy to damage good working kit by using underpowered amps.  A £50 consultancy fee might be numbered amongst your best ever buys.

Ahem!

maltingsaudio

Delta 15,s great speaker, rated about 400 watt @8ohm shove 6 or 700 watts into them at 8 ohms and they will run really sweetly