Karaoke Forums

The speakers are fine.
The amp is a good match.
It's SPL or loudness is that for modern equipment.
It's good to go.



Keith you are right.
For the human ear to perceive a doubling it is 10db.

Once again, I feel compelled to caution folks, especially those less experienced with pro-audio gear, against over thinking and putting themselves in a worse situation. Kevin's technique will work (although I personally recommend a slightly different approach) but most of the time is not necessary.

If your speakers and amps are well matched power wise (i.e. your amp can deliver 200% of the speakers' RMS rating) you'll be fine. Yes, the gain structure zealot in me says you should match all points in your signal path but often times its more work than it's worth. Personally, I'm a big proponent of using your ears, after all that's what an audio professional's job is all about. I turn the input sensitivity on my Amps all the way up and just go with it. I generally don't drive the amp hard, my signal peaks from the board are typically somewhere around -18 to -12 dBu (even lower on the dBfs scale used on my digital desk). If I do decide to push it, I back off if I hear distortion, it's that simple.

This is where having spent the money to get high power handling equipment is key. Underpowering speakers, by itself, does not cause damage to speakers. When folks like Kevin talk about underpowering being the leading speaker killer, it's because of this. Distortion kills speakers. People with underpowered amps typically end up trying to drive them to their max. Well the harder you push an amplifier, the more distortion is created and the more likely you are to hit clipping on transient peaks creating additional distortion. So if you have an amp that peaks at 400W and you're driving it at 300W (over-simplified I know but go with me here) or 75% power, that's going to be far worse for your speakers than an amp capable of 1200W that you're driving at 300W or 25% power. This is what headroom is all about and why it is so important.

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DJ Tony
Let It Rip Karaoke

I'm not Kevin, but I'll speak for him.

Clipping occurs when your amp, or another device in your signal chain up stream of the amp, hits the rails and you then send pure DC voltage to your speakers, not ac voltage.

AC is a wave form(alternating current)...it goes up, and it goes down...the further it goes up n down in the window is called amplitude. The spaces between the up n downs is called frequency. When it goes up and down until it hits the rails at the top and bottom of the window, the top and bottom of the wave flattens and therefore is said to be clipped off... it then becomes pure DC current which does not alternate.

Alternating current pushes and pulls on the speaker cones...Direct current throws the cone in one direction and holds it there till the coil fries or the clipping stops.

Clipping is first heard as distortion. Continuous clipping is then heard as silence when the coils smoke in the woofers, or as crackling when the diaphrams burn in the horns.

Clipping cannot occur with proper gain structure and a fat amp....All that might happen then is the speaks smoke from too much power, so that is why you trim input on a fat amp, and always establish proper gain structure thru any stack no mater the amp.

Keith you describe how clipping and distortion occurs very well.
While the clipping creates short durations of DC it is still AC.
It would have to be at a very low frequency to do physical damage.
More like hearing damage.
Could possibly damage sub's.

Thanks....Won't do damage? Er, wanna see my old diaphrams?

Excuse me, let me make that clearer, not the diaphram my ex wife used, but the ones that came out of my horns?

You never mentioned horns.
I don't know how horns fry so much.
Mackie's have a rep. for it.
Really though, it should not happen at an AC of 1k and more.

Feedback will fry your horns too, fersure....Feedback can drive an amp to clip almost instantly. It will hit the rails and it's all over before you can lift a finger sometimes.

Subsonic feedback is a really sneaky devil. It's made up of bass freqs that are too low for your ears to hear, but your system hears it thru open mics. You can't hear it usually until it goes sonic, but when subsonic, it eats up head room and can cause clipping in your woofers and subs at mid power levels.

You get lots of warning with sonic bass feed back. Your woofers and subs get muddy, dull and droney sounding, but before that with subsonic you got no spank in your mains and the vocals seem dull.

I came back to edit this a couple days later because i failed to decribe how to prevent things you can't hear like subsonic feedback.

Preventing subsonic feed back is almost like preventing regular feedback where the speaks scream a high shrill sound....You know all about that, you don't point a mic at the speaks and you maybe turn down the mic gain, right? Right, except with subsonic feedback not only do you do all that, you also have to be mindful of more.

Bass freqs are not at all like higher freqs. Bass freqs are not near as directional and they tend to carry many time farther than higher freqs...That's why you hear a car stereo bass first and last as it passes. Seldom will you hear the horns in a passing car, but you fersure will hear the bass.

So ok, being that is the way bass behaves, then you can accept that your venue will fill with bass in every direction and reach farther, and the highs and mids will be more directional and taper off more father away from speaks than bass does......

So here you got your open mics in a room full of bass freqs and those freqs are entering the mics and getting reamplified over and over again as they go from speaker to mic and back to speaker....Yeah, you can see where all the amp power can get wasted cause bass freqs are the first to draw power and they tend to use the largest share anyway.

So what to do?

Install a 31 band EQ......Then cut everything below 60HZ. Cut it flat out.......Oh, and mute any unused open mics!

Every DJ knows that girls rumps don't bump until 65HZ, and guys chests resonate at 85HZ.....So cut all below 60 HZ and focus bass tight at 75-90 HZ.....The dance floor will fill up, the girls skirts will flip and the guys will thump their chest and they will all feel like Tarzan and Jane, and you will not have to worry much about subsonic feedback.

Yes...
On reflection a square wave going into a speaker
is going to heat up the voice coil.

Not only that....You see sub freqs eat amp power, unlike mids and highs....if you suck up amp power with invisible subfeedback you will get amp clipping way before you normally would, then the horns go sizzle at only mid power levels and you wonder if those are cheap speaks.

Then you look at your strips and sliders and say, "I can't be clipping, wtf?

yep, thats another term for it, "Square Wave" Everyone knows a wave is supposed to look like an ocean wave, right? but if the top and bottom of the wave hit the top and bottom of amp limits then it goes flat or square.

The neat thing about all amps is they are going to amplify whatever you input....If you clip at the mic pre coming into your board, then that square wave is going to end up at the input of your speaker amp and the amp is going to amplify it......goodbye speakers. Same goes for anything in the signal stream up to the input of the power amp. You can attenuate the amp inputs, but if you clip the board, guess what?-square wave to amp-then DC to speaks.

Therefore, clipping occurs whenever you overdrive any amp in the signal chain starting with the mic pre and ending at the power amp input gains. if you consider all input gains like they were doors, then you will learn to open each just far enuff because too far open will allow too much in, and too much input is called overdriving and that results in clipping.

sorry Keith and Kevin for confusing the two of you. Anyway, I'm extremely familiar with everything you just went through, however remember the situations we're talking about here. We're talking people with little to no pro-audio experience working in an environment where there is very little time for setup and tuning. Most of these folks do not have the proper tools to measure and get the correct match at the amplifier anyway. I agree with you in the ideal world, every gain stage would be perfectly matched, however that's not the real world.

The easiest way, and way very often employed by many a professional audio engineer, is crank up the input sensitivity and use the far more advanced meters of the console and these really cool tools we all have, called our ears, to manage the rig's levels. In my many years of doing this, I've yet to kill a voice coil or horn in this method.

Again, the purist in me is all for taking the time and effort to match gain stages but in the real world that is seldom something the majority of us have the luxury of time and equipment to do correctly.

As far as clipping/distortion, yes I oversimplified the description for purposes of the less experienced, so thanks for providing the detailed SE-101 less for everyone that might have interest in the science behind it.

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DJ Tony
Let It Rip Karaoke

Oh, I'm fersure not trying to come off as an 'expert' here, just contributing what I know and glad the rest are too.

It's the FORUM thing in me...I use forums like this all the time to get answers to things I know little about.

Someday a newby will search for 'lesson in sound' or something close and this thread will pop up....from there he will have a lot available in just one thread. Saves lots of searching, huh?

That's why in threads like this it's good to have counter veiws and others describing how and why they do it differently.

As long as it don't turn into an argument, it's all good

Oh believe me, I understand, no hard feelings here. I tend to be the same way and I agree totally on the value of having completely accurate information available. Many here can probably speak to horror stories of me being decidedly pedantic in certain threads.

I do have to admit though, one thing this forum has taught me is that not everyone cares to understand the deep details and in order to help them you have to speak in terms that are more easily understood by "non-techie types". Often times for me this includes using common terms incorrectly, just for the sake of understanding.

I hope this isn't coming off as condescending as it seems to me right now, I don't mean to be, but sometimes you just gotta be matter of fact about things.

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DJ Tony
Let It Rip Karaoke

"pedantic"

I just heard a new word...cool!

I gotta go look that up. Ain't forums the bomb?

One of theses days this idiot is going to wanna learn home recording and you can believe I'll be here asking lots of stupid questions and looking for threads that have tons of info even if much of it is over my head at first.

I fit the "no pro-audio experience" category. I am not quite "getting it" yet so let me ask some questions for clarification. First some facts:

My amp Power Output Level @ 8 ohms (stereo) = 525 watts x 2

@ 4 ohms (stereo) = 750 watts x 2

@ 8 ohms (bridge) = 1500 watts x 1

My Speakers: Noise/PGM/MAX = 250W/500W/1000W

1. In stereo mode @ 8 ohms, if I turn up my amp all the way (or nearly all the way) and adjust the mic/music levels with the mixer (console/desk), am I putting about 500 watts to the speakers? In my mind, I wouldn't be doing that unless I turned the volume up all the way. My thinking may be way off here though so please correct me.

2. In stereo mode @ 8 ohms, if I turn the amp up a little over half way and adjust the volume's with the mixer so that it sounds the same, am I putting out nearly the same volume? This is the way I have been doing it for more than two years now but if I am hurting the speakers I want to do it right.

3. In bridge mode @ 8 ohms, do I need to NOT turn the amp up all the way for my speakers as not to harm it or does it matter?

Where is the book, "Sound Engineering For Dummy's"?

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Kevin

Here is a manual that was recommended to me on this forum a couple of years ago:

http://www.amazon.com/Sound-Reinforceme ... 0881889008

It covers from the basics on up.

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Music speaks to the heart in ways words cannot express.

1&2, crank amp to max....at really high SPL's roll off bass till it tightens up.

3, why bridge? if you want mono, feed L&R into mono strip on board and leave amp connected as is and cranked to max. If bridged, yes, cut way down on amp input gain(only left will be active) and watch very close for feed back cause amp will still hit the rails should clipping occur upstream of amp.

You have excellent amp speaker match in when running parallel off amp in mono or stereo. no need to bridge

Yes turn the amp up full and throw the knobs away.
Your volumes will be set on your board.
Your board is the MG82cx.
I need a bit of help here, I'm not sure where 0db is on this board.

Turn your channel gains down.
Turn your master volume's and channel volumes to about two thirds up.
Start your sound check.
Turn up your channel gains till you are hearing the volume and mix you like.
Once that is set do not touch the gains again in that venue.
Work with the volume knobs.

Thanks RLC. I have it in front of me and have had it for over a year now. I still cannot find the answers to my questions in it though.

Keith - Just discovered Parallel for Mono.

I still do not know what the difference is in turning the amp up all the way or not. Am I putting 500 watts through to the speakers even if I am not maxing the volume on the mixer?

Just trying to understand what is happening in very basic terms.

Thanks Jerry.

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Kevin

The amp will only output 500W at it's loudest.
Watts is an equation of Amps x Volts.
Absolutely no indication of loudness.