Second opinion on Watts and Ohms for my PA set up

RicPlaya · #1 10-07-2009, 03:46 PM

So I have a gig this Saturday. Question I have is I have a Crown amp 402, that puts out 300 watts @ 8 ohms or 900 watts bridged @ 8 ohms. My speakers are Yammie club SV115's that handle 500 RMS/1000 peak at 8 ohms. Any damage running them in stereo at 300 watts per speaker? I don't think bridging is an option, according to the Crown website the 402 does not do 4 ohms bridged, only 8 and daisy chaining the speakers will give me a 4 ohm load if I am not mistaken. Better to be safe then sorry!! Thanks!!

modulusman · #2 10-07-2009, 03:53 PM

Should not be a problem since you will not be overpowering them.

RicPlaya · #3 10-07-2009, 04:24 PM

Worried about underpowering them. You should use 1-2X the RMS for the speakers. So optimal usage should be betweeen 500-1000 watts per speaker, not 300 watts.

GregShadoan · #4 10-07-2009, 04:59 PM

Keep the amp out of clip, (the little red lights), and you should be ok. RicPlaya has it right though.

modulusman · #5 10-07-2009, 05:20 PM

From what I have read from guys who actually design Pro audio underpowering is a myth. You do want to be careful that you are not running your amp into clipping because this could fry your horns. Check out this thread http://acapella.harmony-central.com/...ring+PA&page=2

RicPlaya · #6 10-07-2009, 06:10 PM

Yeah it's a little gig, not going to be really all that loud so I hope it will be OK, just looking for a little reinforcement.

JimmyM · #7 10-07-2009, 07:51 PM

Underpowering is a complete myth. Nothing true about it at all. It was once used to explain why tweeters blow, and it's been bastardized over the years to include woofers, which isn't true and never has been. Only overpowering blows speakers, not underpowering them. And even tweeters are built better and crossed over properly in most cases these days, so it's not even much of a risk with them anymore.

This 2x power nonsense...where does it come from? You don't put 32 ounces of water in a 16 oz cup. And you shouldn't put 2x the power in a cab rated for far less.

projectMalamute · #8 10-07-2009, 08:29 PM

Quote:

Originally Posted by JimmyM

Underpowering is a complete myth. Nothing true about it at all. It was once used to explain why tweeters blow, and it's been bastardized over the years to include woofers, which isn't true and never has been. Only overpowering blows speakers, not underpowering them. And even tweeters are built better and crossed over properly in most cases these days, so it's not even much of a risk with them anymore.

This 2x power nonsense...where does it come from? You don't put 32 ounces of water in a 16 oz cup. And you shouldn't put 2x the power in a cab rated for far less.

You are applying information relevant to bass amps here to a different situation.

point 1: An under powered amp driven in to clipping absolutely can and will fry tweeters. You really don't want to be overdriving the amps in a PA. Which leads to:

point 2: Rule of thumb is you want double the RMS rating of the speaker box. The most common mode of failure with bass amps is over excursion, in a PA with a crossover and subs this is less of a problem. Momentary bursts of power above the thermal limits of the woofers(where most of the power is going) are not going to burn out the voice coil. Using a marginal amp which is often clipping can send huge amounts of energy to the tweeters, blowing out the diaphragm or melting the voice coil.

A lot of PA stuff has a 'program power' rating. With a reputable company this is generally what the manufacturer is recommending you use with that system, and is usually about twice the RMS rating.

edit:

All that said, you can run that system, just listen and pay attention. The situation is not ideal but if you really only need 150 or so watts with peaks hitting the 300 watt capacity of the amp you should be fine. Where you will get in to trouble is if you need every ounce of that 300 watts and the loudest transients are clipping the system and putting out 600 or so watts, much of it going to the tweeters.

modulusman · #9 10-07-2009, 08:44 PM

Quote:

Originally Posted by projectMalamute

You are applying information relevant to bass amps here to a different situation.

point 1: An under powered amp driven in to clipping absolutely can and will fry tweeters. You really don't want to be overdriving the amps in a PA. Which leads to:

point 2: Rule of thumb is you want double the RMS rating of the speaker box. The most common mode of failure with bass amps is over excursion, in a PA with a crossover and subs this is less of a problem. Momentary bursts of power above the thermal limits of the woofers(where most of the power is going) are not going to burn out the voice coil. Using a marginal amp which is often clipping can send huge amounts of energy to the tweeters, blowing out the diaphragm or melting the voice coil.

A lot of PA stuff has a 'program power' rating. With a reputable company this is generally what the manufacturer is recommending you use with that system, and is usually about twice the RMS rating.

They reccomend twice the rms rating so you will buy one of their bigger {more expensive} power amps.

JimmyM · #10 10-07-2009, 09:03 PM

Right, and then they don't tell you that the quoted power handling rating of their cabs is a lot higher than it works out to in real life. And that's why people blow their 400w rated 112 cabs with their 800w amps.

And Malamute, that 2x is for pro situations with experienced soundmen who know how to run systems without blowing them. It's not for people who are inexperienced with PA who might be prone to blow out speakers because they turned up too loud because they didn't hear distortion.

walterw · #11 10-07-2009, 10:14 PM

the "myth" part of underpowering speakers (learned this on PSW) is the idea that distortion is what blows up speakers. if that were true, no guitar players could finish a gig.

the real problem is that when you drive a power amp into clip trying to get more volume than it's supposed to give you, that clipped amp actually puts out way more power than in its unclipped state. if that power is too much for the speaker, it kills the speaker.

(to the OP) put that amp into parallel, run one speaker off of each side so you get 300w into each speaker rather than the 225w you'd get by putting both speakers into one side, and keep too much low end out of them. that means vocals and maybe a little kick drum, and for everything else use stage volume.

RicPlaya · #12 10-08-2009, 12:33 PM

I have always heard the 1-2 time RMS to power PQ equipment. It's industry standard, my Yammie SV15's are 500 watts continuous 1000 peak accoring to specsheet. That fit's nicely into the 1-2 times RMS thoery. I found running PA speakers 1.5-2 times the RMS like bass amps/cabs really opens them up and they sound much better. There is a lot that goes into it. If the gain structure is set up correctly with the right power a PA sounds excellent and clean. PSW is a great resource for this stuff, as is that book Yamaha put out about sound reinforcement.

RicPlaya · #13 10-08-2009, 12:35 PM

Quote:

Originally Posted by walterw

.
(to the OP) put that amp into parallel, run one speaker off of each side so you get 300w into each speaker rather than the 225w you'd get by putting both speakers into one side, and keep too much low end out of them. that means vocals and maybe a little kick drum, and for everything else use stage volume.

Yeah I am running it in stereo for sure!

JimmyM · #14 10-08-2009, 01:01 PM

Quote:

Originally Posted by RicPlaya

I have always heard the 1-2 time RMS to power PQ equipment. It's industry standard, my Yammie SV15's are 500 watts continuous 1000 peak accoring to specsheet. That fit's nicely into the 1-2 times RMS thoery. I found running PA speakers 1.5-2 times the RMS like bass amps/cabs really opens them up and they sound much better. There is a lot that goes into it. If the gain structure is set up correctly with the right power a PA sounds excellent and clean. PSW is a great resource for this stuff, as is that book Yamaha put out about sound reinforcement.

Well it ain't for amateurs, that's all I'll say about it.

RicPlaya · #15 10-08-2009, 01:07 PM

Quote:

Originally Posted by JimmyM

Well it ain't for amateurs, that's all I'll say about it.

With a little research us amateurs can become pretty darn good at it!

**KJung** · #16 10-08-2009, 01:10 PM

Quote:

Originally Posted by RicPlaya

Worried about underpowering them. You should use 1-2X the RMS for the speakers. So optimal usage should be betweeen 500-1000 watts per speaker, not 300 watts.

You cannot underpower speakers. Also, cabinet power ratings are, at most, a loose guideline as to the maximum power they can safely handle, not in any way a 'requirement' or suggestion for how much wattage to apply to the cab.

You should be fine.

You are correct that you can typically put more 'amp rated spec' power into a speaker than its maximum rating, since power amps don't put out their full power in typically (i.e., you rarely have them dimed over long periods of time). However, it is not a requirement.

JimmyM · #17 10-08-2009, 01:15 PM

Quote:

Originally Posted by RicPlaya

With a little research us amateurs can become pretty darn good at it!

I should have used "the inexperienced," maybe not "amateurs." Sounds like you have the experience to handle it.

RicPlaya · #18 10-08-2009, 02:07 PM

Quote:

Originally Posted by KJung

You are correct that you can typically put more 'amp rated spec' power into a speaker than its maximum rating, since power amps don't put out their full power in typically (i.e., you rarely have them dimed over long periods of time). However, it is not a requirement.

Headroom does a lot of tone and clarity IMO

RicPlaya · #19 10-08-2009, 02:09 PM

Quote:

Originally Posted by JimmyM

I should have used "the inexperienced," maybe not "amateurs." Sounds like you have the experience to handle it.

Enough to get by and sound good, but I need to upgrade me amps to get back to that 1-2 time rms rating I am accoustomed too. Unity and and gain structure goes a long way and I would start there if you feel you have more to learn. Just my .02

**KJung** · #20 10-08-2009, 02:21 PM

Quote:

Originally Posted by RicPlaya

Headroom does a lot of tone and clarity IMO

+1 That's a different issue. I was responding to your concern about damaging your speakers with too few watts. That is not an issue. The only problem you would have there is if you were running a cab with an unprotected tweeter (like an Epifani cab without a fuse), and you drove a low powered amp into clipping, you might fry the tweeter diaphragm. That's about the worst that can happen, and your ears will tell you to turn down long before that!