Help a novice from blowing speakers
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Posted on Jun 04, 2009 06:13 pm
drumstruck
Member Since: Jun 03, 2009
Hello,
I was hoping to get a little schooling on how to work my band's PA. We recently upgraded from some misc stuff to a Gemini 750 power amp and Nady PS115 speakers - 250 watts RMS, 500 peak. I tried the amp in stereo, parallel mono, and bridged. And promptly blew out the horns. The speakers state they are 8 ohms. The amp specs for 8 ohms are 175 in stereo, 190 in parallel, 550 in bridged. So I guess they blew when the amp was bridged? But I only had the amp levels up about 2/3. I guess I don't understand exactly how to match the amp and my mixer, with my speakers to get max (safe) volume. I have read the amp should put out more watts to provide headroom (the Gemini manual says to crank the levels to FULL and slowly bring up the mixer levels). Is this safe? The Nady speaker guys says that this amp is TOO powerful. I would appreciate your thoughts. Thanks!
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Jun 04, 2009 07:24 pm Hummm. I think that you may have had something else that happened here.
Can you tell me how you had the amp connected to the speakers in all of the modes?
What I am after, is what type of speaker cable connectors did you have on them? And how did you have them wired?
The biggest thing, is how it was wired when you put it "Bridge" mode?
And how you ran them to each speaker?
Let me know how you did so, and we will see if what I think it was that damaged your horns.
And by the way, Welcome to the HRC. Hope you have a great time here.
Jun 05, 2009 04:28 pm Thanks for the quick reply!
The amp has Speakon connectors, the speakers have 1/4 inch. I have 2 new cables, decent guage, no adapters. In parallel mode, I had a left and right channel to each speaker. In bridged, the amp has a separate Speakon out, and I chained the speakers together with a 1/4 inch guitar cord.
I also tried parallel mode, out one channel and chaining the speakers together (theoretically leaving the other channel for some monitors).
I'm trying to get a handle on this "more amp wattage for headroom" vs. "too much amp wattage blows the speakers".
As an example, if I'm in parallel at 190 watts output, does that mean each speaker is getting 190 watts, or about 95 each? What if the amp levels are only half way up? Does that reduce the wattage to the speakers? Does chaining the speakers make them a "4 ohm load"? How does my (separate) mixer fit in to all this?
If you're still reading, thanks for your patience!
Jun 05, 2009 09:32 pm OK, I think that we found out why you speaker went up in smoke.
In "Bridge" mode, you have to have a special cable. You need a cable that is wired on the Speakon end.
The +1 and the +2 are used for bridge mode.
In all other modes, parallel, and stereo, the Speakon is wired +1, and -1.
So, for bridge, your using the +1 as the positive, and the +2 as the negative. The reason for this, is the fact the your are tieing both sides of the amp together.
Now I think I need to clarify something for you. When you are wiring in parallel, you do not need to put the amp in parallel.
What this means is, that you can wire in parallel to your speakers in all modes. Just by using the connections on the back of the speaker.
All speakers have their jacks wired in parallel. making this much easier. Just run a speaker cable from one speaker, to the other. And you have just wired in parallel. Ta Da!
When an amp is in parallel, you are tying the left channel to the right channel. Meaning that what ever signal that you put into the left, will show up on the right side as well.
So, if you wanted to put two speakers on one side of the amp. And you wanted to run the other for monitors, then you need to have the amp in stereo. That will do the trick for you there.
As for how the wattage runs out to your speakers. In parallel, the speakers see the same wattage. Now that's wired in parallel, not the amp mode.
Now, this does not mean, that if you have one 190 watt speaker, and you add another, you are not pushing 380 watts out of your amp.
It just means that you are pushing 190 watts out of the amp, and each speaker is seeing that 190 watts.
Hope this helped.
monmixrIf 50hz 60 will kill ya.Member
Since: Jan 08, 2009
Jun 06, 2009 04:51 pm Rob also wanted to say dont use a guitar cable for speakers, use a 1/4" speaker cable, but he forgot.
Jun 06, 2009 05:19 pm Cool, thanks. That helps a lot.
I still would like your opinion on setting the levels on the power amp. Set them all the way up and keep the mixer levels lower (as the Gemini manual instructs)? Or keep the amp levels low (as the Nady rep warned) and push the mixer near full?
Does adjusting the levels on the amp change how much wattage it is putting out?
Thanks again.
Jun 08, 2009 07:55 pm Sorry that I didn't get back to you on this right away. I've been giging and needed time to recover.
The dials that are on the amp are input gain, not output.
To find out what the output of the amp is, requires some math.
10 log the square root of P1 / P2 = V. V squared / ohm load = wattage.
P1 is the output of the board. P2 is the output of the amp.
It's a lot to go through for finding out what the amp is doing. The best is to have the amp input wide open. And then just adjust the board for the total volume. You don't need to know the exact wattage of the amp all of the time.
And you can always take the short cut of just measuring the output of the amp with a meter to find what the voltage is. Then do the last part of the equation. V squared / ohm load = wattage.
And to do so, you should run a 1K tone to the amp @ 0 dB of the output of the board.
Oh, and Monmixer is 100% absolutely correct on never ever ever use guitar cables for speaker cables. That will send your amp into the worst oscillations and destroy all in it's path!
Jun 30, 2009 11:32 pm Hi guys. I'm back for a follow-up. I discovered that the horns in my speakers were not bad. Actually the circuit boards (cross-over?) were completely burned up! So, can you help get some basics through my slow-moving brain?
What did I do and how can I make sure I don't do it again? Basic specs: amp appears to be 190 watts in mono, 470 bridged. speakers are 250 RMS (500 peak). I have read that if the amp is UNDER-powered it could cause speakers to "fry" due to clipping.
So what is the best setup? Crank the amp all the way up and go bridged and keep the mixer low? Or something else.
If you're so inclined, here are links to my amp (750) and speaker manuals:
www.geminidj.com/product_...50_1600_man.pdf
nady.com/manuals/audio/ps115.pdf
Thanks a lot for your responses.
Jul 01, 2009 09:44 am Ah, the dreaded square wave strikes again!
What you are seeing, is what a square wave does to equipment.
A square wave destroys all in it's path.
For right now, turn that amp all the way up. And make sure that you do not run it into the Red.
Whenever you get the chance, I would like to see you get another amp that is a little more horsepower then what you have now.
Feb 25, 2010 12:59 am This was a great discussion but I want to be sure I am clear on this. You guys are saying to max the poweramp then bring the master or main volume on the mixer up slowly.
I am asking this because I read that many years ago but I was reading today and an article said the opposite. It said to max the board (each channels attenuation to just before clipping for max output) then the mixing board masters also maxed...on most "0" then creep up on the power amp volume (input sensativity) until just befor clipping.
....I assume all of this is done before the audience comes so you can adjust for the feed back.
...in the real world we want the max volume before feedback.
so which will give us better results? max the mixer and creep up on the power amp just before feed back or a red meter on anything?
or
Max the amp and creep up on the mixer just before feed back or a red meter on anything?
thanx...you folks are great!
Feb 25, 2010 11:26 am Hey uriasmusic. Welcome to the HRC!
The reasoning behind our theory of raising the input of the amp all the way, has more to do with signal to noise ratio, then it does feedback.
With the amps inputs at full, you can run a lower gain structure out of the console. This will also reduce the amount of transistor noise (That persistent hiss) coming out of the speakers.
The added danger of running the console hot, and the amps low, is the dreaded square wave that I constantly harp about here on the HRC.
I can not stress enough about how deadly a square wave is. You do not want to ever run a console into the RED!
Now, manufactures did have enough sense to give you a chance to not clip your amp. What they did was to set the clip LED early for you. They give you a 6 dB warning before actual clip. So the LED will be Red before you hear the distortion.
Also, think about the word "Clip". This just does not mean that an LED will turn Red......... This really means CLIP. As in removing something. Like the top of the wave! As in the formation of a square wave.
If you remove the top of a rounded wave, your left with a flat top. Right? A flat top wave, is a square wave.
Feedback has more to do with your gain structure. It the chaos that comes about from the mic picking up the speakers, and re amplifying the signal over and over again. This is where a 31 band EQ is king. By reducing the the problem frequencies that the mic is picking up.
Also the low the gain, the better your chances of not having feedback to begin with.
Doug BabbittSound as good as you playMember
Since: Dec 23, 2008
Feb 25, 2010 07:33 pm Great thread .... I don't know how I missed it the first time.
Here's how I set gain structure in a soundcheck (I never get enough time to ring out the room properly):
1) Start with mixer main and monitor output gains at full off, amp input gains at full off, channel input gains full off, all mixer channel faders and GEQ at unity.
2) Solo channels one at a time, adjusting each input gain individually to meter occassional yellow and no red.
3) Bring up the main and monitor faders to about -5 dB.
4) With the band playing, ease open the amp input gain until it yields the desired SPL (usually between 1/3 and 2/3).
5) Monitor the GEQ throughout the show for problem frequencies and knock them down as necessary.
The reason that I do it this way is to keep all faders near unity, where it requires much more fader movement for a given amount of gain (i.e. they are less sensitive). Starting at -5dB on the mixer mains and monitors, I have the headroom I need to compete with the guitar heros at last call.
