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PostPosted: Fri Mar 25, 2005 6:37 pm 
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Lonman,  Up to what point however ?  Naturally there'd be a point where you hit the diminishing returns concept. Spread the sound thin rather than fill it out.


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PostPosted: Fri Mar 25, 2005 7:17 pm 
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Steven Kaplan @ Fri Mar 25, 2005 6:37 pm wrote:
Lonman,  Up to what point however ?  Naturally there'd be a point where you hit the diminishing returns concept. Spread the sound thin rather than fill it out.


How many hard rock concerts have you been to?  Check out an old Van Halen speaker stack behind Eddie or the main pa for that matter.  I don't see where it can start sounding thin with more - provided everything is wired correctly.

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PostPosted: Fri Mar 25, 2005 7:40 pm 
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Lonman,

   I likely made an incorrect assumption. I assumed that these stacks of speakers at concerts are driven proportionately by calculated power amp settings, and wattage that matches and optimizes the configuration.
   I wasn't aware that a person could Keep adding stacks to a 30 watt head, and not at some point start sounding thin, since the output wattage can't drive or fill-out the sound, or effectively drive the speakers. My understanding about THIS discussion of headroom, was we were talking about ONE head driving a 1X12, 2X12 vs 4X12 speaker configuration.  I was asking you about the perceived doubling regarding THIS type setup. IOW,  If I use a full stack 2x(4X12) I realize the perceived sound will be louder than the 2X12 configuration using a 100 watt head.  Will perceived loudness increase REGARDLESS of the number of cabs added to this one 100 watt head ?  or will there be a point of diminishing returns, or thinner sound in a somewhat larger venue if I try powering a wall of amps with this ONE 100 watt head ?  (no power amps added).   I'm asking how the "headroom" principle works, and up until what point, using one amp head of say 50 or 100 watts only.    

   As I've mentioned,  I don't deal with these aspects of audio.  Just for kicks however I did put the pignose portable amp once into a marshall 1/2 stack, and it did sound louder than expected.  Yet my assumption is this concept was limited. At some point you got sound loss, due to inefficiency.

    Just one other point. There are bands and musicians that have dummy cabs setup.  Setups for visual effect.  Granted this isn't very common these days.  Yet in the 60's and 70's it wasn't  uncommon for rock bands to have Marshall cabs setup with perhaps two speakers or even NO speakers operating in a 4x12 cab.  "Drool factor" of BIGGER is better was pretty common.  Again,  this is ONLY an area where I'm a little familiar with what *I* used firsthand, in the venues I played in.

    I don't know theory behind how a series of class A-type 5150 heads would get matched for optimal efficiency with speaker cabs to fill a say, 100 acre outdoor venue.  Yet my assumption was EVH can't use a standard 200 watt 5150 amp and effectively drive MANY stacks with just one 200 watt head.

    I think in the old days EVH used a Marshall 100 watt head that went into effects and a variac, and than a 200 watt power amp.  Not sure.  Pre- Peavey days. Yet since EVH also at one point used a bomb-shell casing to house some of his equipment, and was a HUGE endorsor of Peavey equip. Not sure what would be functional vs Visual affect with his stacks, or towers.


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PostPosted: Sat Mar 26, 2005 8:47 am 
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It amazes me the amount of power they are using especially at small venues...I ask them how much power was used at Woodstock69 Pics and get a wide range of answers up to hundreds of thousands of watts.. and the fact of the matter is it was less than 3500 watts... The last Woodstock was in the millions..... Dont quote me but I think these were Marshalls at least the bass bins maybe didnt make that party.......

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PostPosted: Sat Mar 26, 2005 10:04 am 
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Karyoker..I spent years on the road gigging, and opening for larger acts.... Weird thing is,  (like with a car, I don't care to look under the hood. I assume there's an engine)  I never got into the technical aspects of all this.  Paid others to worry about this stuff..LOL.   We can't all know about, or be good at everything I suppose.

Yet the basics I have to worry about, such as replacing 7027's in the ampeg B-25B head  (replacement tubes),  or knowing how to run my Eico tube tester I bought on Ebay  (because I love tube amp tech).  Eventually perhaps biasing my own amps...etc.  Yet unlike most of you, my mind doesn't work well regarding technical aspects.


As to woodstock.... Thousands of watts obviously were used.  Look at it this way.....I recall a rough rule of thumb for moderate outdoor rock music...something like 100 watts for 500 sq ft.     300 watts for 1000 sq ft. etc.  (and I think this was for backyard stereo apps.)  Outdoors you can get alot of sound loss.

I don't know about this stuff.  Yet I enjoy learning about it.


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PostPosted: Sat Mar 26, 2005 10:44 am 
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LOL   Ive forgot most of what I ever knew but I grew up in the tube days worked on missle radars with tubes and and an old RCA tv xmitter with tubes... Im too busy singin and havin fun now  Here is a good read on the 7027's tho

[Here

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PostPosted: Sat Mar 26, 2005 11:04 am 
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ROFLAO,  I printed out "Help Uncle Ned my ampeg has 7027's" about 5 years ago.
Yet thanks...

Btw,  I think another consideration when looking at the wattage needed for these two Woodstocks is massive difference in area.  Yasgurs land was a little over 600 acres.  Those sound towers were said to have been deafening to anyone within 10 feet of them. For some reason the specs that the sound guys wanted for woodstock 69 would've translated to MANY MANY more watts in terms of todays specs.

Griffiss AF base in Rome NY however was about 3,550 acres... Weren't the two stages close to two miles apart during the 1999 Woodstock ?

Look at the layout of Woodstock one.   Sloped land.... Perhaps more conducive to trapping some sound in a smaller area.

Woodstock 3 was completely flat.  Sound would've had to fill a HUGE flat area allowing for alot of loss.


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PostPosted: Sat Mar 26, 2005 3:50 pm 
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What missile radar did you work on?  I did HAWK Cont. Wave Radar myself a long time ago...

As for this discussion, underpowering can overload an amp, causing it to run hotter and distort.

Distortion can come from a variety of sources.  There is electrical distortion that can be induced when an attempt to amplify a signal beyond the normal capabilities of the electrical circuit.  This can happen in nearly any electrical equipment that performs amplification.

There is also physical distortion that occurs when the speaker reaches incursion or excursion.  This causes the speaker to distort and can damage the voice coil.  You can sometimes actually hear this when the speaker reaches incursion and the speaker smacks the backing plate.  A similar thing can happen when the speaker reaches excursion and the speaker cone can distort or tear away from the speaker surround.

Just trying to point out that distortion can have multiple sources - not all of them are electrical.

On a side note, some speakers have a minimum power requirement.


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PostPosted: Sat Mar 26, 2005 4:52 pm 
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The crackling was the cone of the speaker.  Only took place at loud volumes when I struck the electric piano keys.... Lower the note, more noticeable the crackling.


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PostPosted: Sun Mar 27, 2005 3:43 am 
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Crackling like what you're mentioning sounds like incursion on the speaker.  When the voice coil smacks the backing on the magnet it often causes a 'crackling' sound.

When this happens enough it causes the tube the voice coil(s) is/are wound on to rub on the magnet causing it to heat up and fail.  It's easy to diagnose by pushing gently on the speaker cone and you'll hear it rub as it moves back and forth.  It the late stages just before complete failure you can actually feel it rubbing.


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PostPosted: Sun Mar 27, 2005 5:09 am 
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I suppose there's no way to know if matching the head to the cabinets would lesten this event ?   or if the speakers just can't take this type of input.


Here's the latest.  I looked at specs.  My speaker cabs each are rated at 300W program 600W peak.  8 ohm cabs.

The QM-6 powered mixer is 200 watts at 4 ohms, yet only 65 watts going into 8 ohms.  

This isn't good :/     Even at very low volumes is this a source of trouble ?


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PostPosted: Sun Mar 27, 2005 12:25 pm 
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Steven Kaplan @ Sun Mar 27, 2005 5:09 am wrote:
Here's the latest.  I looked at specs.  My speaker cabs each are rated at 300W program 600W peak.  8 ohm cabs.

The QM-6 powered mixer is 200 watts at 4 ohms, yet only 65 watts going into 8 ohms.  

This isn't good :/     Even at very low volumes is this a source of trouble ?


At low volumes it wouldn't be a problem, it's when you need to get out & above crowd noise is when you start turning up the system to compensate & your power rating will max out pretty quickly from clean to distortion.

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PostPosted: Sun Mar 27, 2005 12:35 pm 
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Thanks Lonman,

   If I do wish to match this mixer to the speakers, Is it possible to do-so using a power amp ?   Or would I need to buy a more powerful mixer ?   For my purposes, I'm satisfied with the features this mixer provides. I went with the 15 cabs because of the keyboards. I could save money not having to buy a new powered mixer that allows me 600W@ 8 ohms per channel.


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PostPosted: Sun Mar 27, 2005 12:52 pm 
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Steven Kaplan @ Sun Mar 27, 2005 12:35 pm wrote:
Thanks Lonman,

   If I do wish to match this mixer to the speakers, Is it possible to do-so using a power amp ?   Or would I need to buy a more powerful mixer ?


You can add an external amp only if your mixer has pre-amp outputs.  Sometimes it's labeled Main Out.  Don't connect it to speaker outputs but i'm sure you know that, you'd be surprised how many people i've seen do that.  If it doesn't have these, then you pretty much need to replace/upgrade.  I did not see one on there when looking at the documentation.  It pushes 200 watts PEAK into 4 ohms, 100 watts RMS into 4 ohms 65 into 8.
BTW you are running at 4 ohms as this is not a stereo mixer, you are basically connecting 2 8 ohm speakers in parallel dropping the overall load to 4 ohms.  Still a little under rated for the speakers since the peak rating of the mixer/amp is below even the program rating of the speaker.

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PostPosted: Sun Mar 27, 2005 1:13 pm 
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Quote:
What missile radar did you work on?  I did HAWK Cont. Wave Radar myself a long time ago...


Rogers on the long time ago...I worked on the Anspw-2 guidance radar for about 4 years and the Anspg-49 tracking radar for a couple and the guidance computer if u can call it one.  It was full of 30 volt motors and mostly analogue. It took about 12 hours to run a complete systems check and hardly ever  made it thru without something breaking...
These were for the Talos surface to air shipboard.


 One radar had 1 transistor in it for a master oscillator and I had just came out of A school and was the only one who knew what it was or how it worked......

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PostPosted: Sun Mar 27, 2005 1:14 pm 
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Thanks again.  Actually I did NOT know this Lonman.  Power amps are an area I never touched.  I know nothing about this area.  After slaving amps and frying them as a kid.  I decided to leave this type of thing to those of you that know what you're doing.  I'm looking (as we speak) for something online that can give me a basic idea of do's and do nots regarding adding external power.  


Another deterrant whenever I questioned amp techs about boosting power (for guitar purposes) using another power source was having them say, "You will likely not retain the tone of the amp" if you run thru another power source.  Yet in the case of a tranny PA head.  I'm not really concerned about this.

On the output jacks it states of the QM-6

Speaker outputs
2 ohm capability
100W@4 ohms

There appears to be no preamp out.  ONLY 1/8 inch in RCA phono's,
EFX, and EFX return


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PostPosted: Sun Mar 27, 2005 1:26 pm 
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Steven Kaplan @ Sun Mar 27, 2005 1:14 pm wrote:
On the output jacks it states of the QM-6

Speaker outputs
2 ohm capability
100W@4 ohms

There appears to be no preamp out.  ONLY 1/8 inch in RCA phono's,
EFX, and EFX return


Yeah like I said I didn't see any on the documentation for the mixer.  This unit isn't expandable in the respect of adding more power, what you see is what you get.  
I wouldn't trust it at a 2 ohm load either although you weren't questioning it, you did state thats what it claims on the speaker outs.  Most amps aren't even very stable at 2 ohms though they claim they are.  The only amps I would allow a 2 ohm load is Crown Macro or K series, Peavey CS series & the QSC PLX series.

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PostPosted: Sun Mar 27, 2005 1:27 pm 
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Actually,  I'm not overly concerned about upgrading,  I just looked in AMS and some of the Behringer heads look REALLY affordable.  Haven't checked Carvins prices yet, that's next.  Maybe I'll just get another mixer,  sell this on Ebay.


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PostPosted: Sun Mar 27, 2005 1:29 pm 
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My assumption was a 10 channel, 300-600 watt mixer would run me closer to 1K.  Naturally, I was pleasantly surprised to find otherwise


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PostPosted: Sun Mar 27, 2005 1:33 pm 
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Steven Kaplan @ Sun Mar 27, 2005 1:29 pm wrote:
My assumption was a 10 channel, 300-600 watt mixer would run me closer to 1K.  Naturally, I was pleasantly surprised to find otherwise


Want a good quality VERY expandable powered mixer, take a look at the Mackie 808 series.  It's worth every bit the extra you'll put out.   The 808M (mono model) is rated 300 watts into 8 ohms for the mains & 300 watts for the monitors.  The 808S (stereo model) 300 watts per channel plus another 300 watts for monitors.  
Don't trust Behringer amps as far as I could throw one.

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