Math question - Speaker in parallel
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 PA Systems A forum for discussion of all parts of a sound reinforcement or DJ system: loudspeakers, mixers (desks) etc.

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 8th February 2018, 07:29 PM #21 Pano   diyAudio Moderator     Join Date: Oct 2004 Location: SW Florida The clipping light is a good indication, but you can also measure. Since your amp is rated at 1200 watts into 4 ohms, that means it should be able to supply 69 volts RMS to your speakers before, or maybe right at, clipping. If you wanted to limit the amp to 350 watts RMS into 8 ohms, you could dial it back to a maximum of 53 volts RMS when your source (mixing desk) is maxed out with a sine wave. You know the amp will never clip, but you might not have enough volume for your PA. It's a safe place to start, at least. With a volt meter you can st those levels. __________________ Take the Speaker Voltage Test!
JMFahey
diyAudio Member

Join Date: Mar 2009
Location: Buenos Aires - Argentina
Quote:
 Originally Posted by livingtool I'm putting together a medium **PA system**. 4 x 350watts full range, 8 ohms, passive speakers (2 for each channel, in paralell) Digital Power Amp with a 1200watts per channel at 4 ohms. As I understand it, each channel will have a load of 4 ohms and add to a maximum of 700 watts.
Not "add to" because they re not producing power, a more accurate word would be : "they stand up to 700W RMS"

Quote:
 That will leave a 500 watts headroom, taking into account the "rule" of "1.5 to 2 times the amp".
That is a much misunderstood and misquoted statement.
It has meaning in a home Hi Fi environment, where you listen to pre recorded Music and typically at about 10% average level relative to maximum.

But you are talking a *live sound* PA system (a DJ would have similar problems), presumably used in a large place (definitely not your own Living Room, even less your Bedroom) and with presumably a sizable amout of people, not Family and a couple friends.

In that scenario you **will** clip your amp and damage speakers.

Unless you are obsessive controlling the peak signal and turning it down all the time, acting as a sort of Human Limiter, the normal solution is to add a limiter between preamp and power amp and set it up so it can not go beyond *average* 700W RMS per channel.
Narrow higher power peaks (cymbal crashes, acoustic guitar strumming, etc.) won´t hurt, of course.
Quote:
 Is my math ok? Thanks for the help.
Maqth is fine, just this idea does not apply to Live Sound, where the opposite is right: speakers at least 50% stronger than what amps can deliver.
Quote:
 PS: sorry if my english isn't so good.
Conmigo zafaste Hermano
Igual está muy bien
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Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.

 8th February 2018, 09:06 PM #23 nigelwright7557   diyAudio Member     Join Date: Apr 2008 Location: Carlisle, England In the 1980's I used to run a mobile disco. I had four 50WRMS Fane speakers running off a 225 watts RMS amplifier. It was incredibly loud and sounded very good. I never used to drive it into clipping. __________________ PCBCAD51 pcb design software. 2018 version out now with lower prices >> http://www.murtonpikesystems.co.uk
conanski
diyAudio Member

Join Date: Mar 2013
Quote:
 Originally Posted by livingtool The full range speakers are 350 watts RMS at 8ohm.
Ok, that means they most likely can handle 700w program and 1400w peak.

Quote:
 Originally Posted by livingtool Since I first posted, I have added a fairly powerfull subwoofer, so the full range are now only for mids+highs.
Did you also add a crossover?

Quote:
 Originally Posted by livingtool Anyway, I'm aware that if the amp is bigger than the speakers I can blow them. I just don't know if there is a way I can limit the power.

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 Originally Posted by livingtool I asked before if the red light means the speakers are clipping or the amps are insuficient for the speakers
Neither. And speakers don't clip but amplifiers do so when you see the red clipping light flash it is indicating that you have reached the peak limits of the amplifier. It is usually safe for this indicator to flash occasionally too but you don't ever want to see it illuminated constantly, that means you are heavily over driving the amp.

JMFahey
diyAudio Member

Join Date: Mar 2009
Location: Buenos Aires - Argentina
Quote:
 Originally Posted by nigelwright7557 In the 1980's I used to run a mobile disco. I had four 50WRMS Fane speakers running off a 225 watts RMS amplifier. It was incredibly loud and sounded very good. I never used to drive it into clipping.
You should have scoped it

Then you would have been surprised
__________________
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.

Sonce
diyAudio Member

Join Date: Jan 2014
Location: Macedonia
Quote:
 Originally Posted by nigelwright7557 In the 1980's I used to run a mobile disco. I had four 50WRMS Fane speakers running off a 225 watts RMS amplifier. It was incredibly loud and sounded very good.
I remember those times, that power was enough, indeed. But times changed... Now it is not loud enough unless blood is dripping from ears.

 9th February 2018, 10:23 AM #27 livingtool   diyAudio Member   Join Date: Jan 2018 Location: Argentina Thank you for all the responses! Let's see if I can reply correctly: * That my speakers can handle 700 program is something I don't get. The peak value I grasp. Program, not so much. * I added a "crossover" on my XR18 mains EQ, using Aux to Sub at 100Hz. That is what sounded better in my ears. Found a tutorial for the X32 by Behringer, and duplicated it as closely as I could on my XR18. I managed to make an outdoors test, and it was quite loud and no amp was clipping. I guess by substracting the bass from the main speakers they can boost the mids and highs a bit more, but that is just an assumption. As you can see by my postings, I don't know much. * I don't know what a limiter is. Is it just bringing down the volume on the amps channels or the amps have to have a limiter? Mine sure don't. Thank you all for your time!
conanski
diyAudio Member

Join Date: Mar 2013
Quote:
 Originally Posted by livingtool * That my speakers can handle 700 program is something I don't get. The peak value I grasp. Program, not so much.
RMS, Program, and Peak are just terms commonly used to rate speaker power handling. Sometimes you will also see Continuous substituted for RMS. In all cases Program is 3dB above RMS and Peak at 6dB above. The bottom line is a speaker can handle remarkably high power levels for very short periods of time(miliseconds), but only a relatively small amount of steady state power over an extended period of time.. minute or hours. Fortunately most music types are very dynamic with a relatively low continuous energy levels so it works out well.

Quote:
 Originally Posted by livingtool * I added a "crossover" on my XR18 mains EQ, using Aux to Sub at 100Hz. I guess by substracting the bass from the main speakers they can boost the mids and highs a bit more, but that is just an assumption.
Yes, you effectively transformed your system into a 3-way and in doing so you do get cleaner mids and highs.

Quote:
 Originally Posted by livingtool * I don't know what a limiter is. Is it just bringing down the volume on the amps channels or the amps have to have a limiter? Mine sure don't.
What amps do you have? As the name suggests a limiter stops a signal from getting any stronger. A DSP processor like the Behringer DCX would give you adjustable limiters, crossovers, and some very good EQ all in one package, this type of thing isn't really optional if you want to be able to use a system like this and not have to worry about accidentally blowing something if a mic or guitar is unplugged or some feedback happens.

 10th February 2018, 03:53 AM #29 Pano   diyAudio Moderator     Join Date: Oct 2004 Location: SW Florida Or you can just turn down the volume on the amps so that they don't clip, or don't go above a certain level. __________________ Take the Speaker Voltage Test!
dotneck335
diyAudio Member

Join Date: Dec 2012
Quote:
 Originally Posted by conanski RMS, Program, and Peak are just terms commonly used to rate speaker power handling. Sometimes you will also see Continuous substituted for RMS. In all cases Program is 3dB above RMS and Peak at 6dB above.
WHERE did you get these figures?

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