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Author Topic: Voltage Gain new to me; well, kind of...  (Read 1586 times)

Dennis Wiggins

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Voltage Gain new to me; well, kind of...
« on: January 20, 2012, 04:41:59 pm »

Read this first:  Marty Explains Voltage Gain

http://peavey.com/support/technotes/soundsystems/Voltage%20Gain.1.pdf

For many years (10-15 perhaps), I have been running my amps at about half throttle. 

I do this because I almost never need to be that loud (except outdoors), need to minimize idle noise, and like to drive the mixer so that I hit 0dB (or max of +6) on peaks. 

I always run a sub crossed over to a 2-way (not bi-amped) top, and I always use the same brand and model amplifiers for the subs and the tops. 

Typically, as the night progresses and things ramp up to my target of 95-100dB on the dance floor, I end up setting the attenuators of the sub channels about 3-6 "dB" higher.  Picture 12:00 for the top amp channels, and 2:00 for the subs.  Outdoors, it would be 3:00 for tops and wide open for subs.

I can then drive the board the way I am comfortable. 

Here's the revelation.  After ready Marty's explanation of amp gain, I realize that I am introducing a non-linear response that increases gain for the subs with respect to the tops.  In other words, as I push the volume up, the subs get more gain than the tops.  This, to me, is exactly what I want to happen and is probably what my ears have been telling me; thus, the amp settings I have migrated to. 

I have tried running with the amps "wide open ", but it becomes uncontrollable both in sheer volume levels at low mixer output, and the tops outrun the subs, making the system too "in your face" (top heavy - not good) sounding. 


Am I all wet here, or can this non-linear approach be useful?

-Dennis
« Last Edit: January 20, 2012, 04:45:20 pm by Dennis Wiggins »
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John Roberts {JR}

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Re: Voltage Gain new to me; well, kind of...
« Reply #1 on: January 20, 2012, 07:52:11 pm »

Read this first:  Marty Explains Voltage Gain

http://peavey.com/support/technotes/soundsystems/Voltage%20Gain.1.pdf

Do I have to....  8)
Quote

For many years (10-15 perhaps), I have been running my amps at about half throttle. 

I do this because I almost never need to be that loud (except outdoors), need to minimize idle noise, and like to drive the mixer so that I hit 0dB (or max of +6) on peaks. 
The amp attenuator setting doesn't really limit how loud the system can go unless you pad down the amp input so much, the mixer clips before it can drive the amp to clip.

I don't recognize half throttle as a precise gain structure term... Half power is -3dB. 
Quote
I always run a sub crossed over to a 2-way (not bi-amped) top, and I always use the same brand and model amplifiers for the subs and the tops. 
That's a good customer...
Quote
Typically, as the night progresses and things ramp up to my target of 95-100dB on the dance floor, I end up setting the attenuators of the sub channels about 3-6 "dB" higher.  Picture 12:00 for the top amp channels, and 2:00 for the subs.  Outdoors, it would be 3:00 for tops and wide open for subs.
Sorry I can't picture what your clocks express in dB terms, but +3 to +6dB on the input attenuators is 2x to 4x the power.
Quote
I can then drive the board the way I am comfortable. 

Here's the revelation.  After ready Marty's explanation of amp gain, I realize that I am introducing a non-linear response that increases gain for the subs with respect to the tops.  In other words, as I push the volume up, the subs get more gain than the tops.  This, to me, is exactly what I want to happen and is probably what my ears have been telling me; thus, the amp settings I have migrated to. 
?? Yes you are pushing the subs relative to tops.

If it's what you want then be happy.

It should be the opposite of what your ears tell you. Our hearing is more sensitive to mid range than LF at low levels, so in general you would have to turn up bass at low level to sound flat, or turn the bass down when you increase the system up to still sound flat, if it sounded flat at low SPL. .
Quote
I have tried running with the amps "wide open ", but it becomes uncontrollable both in sheer volume levels at low mixer output, and the tops outrun the subs, making the system too "in your face" (top heavy - not good) sounding. 
Gain structure is six of one half dozen another, if you need different gain for bass and mids the amps, or crossover are where to do that... It is the sum of all the gain in tha path so mixer gain + crossover gain, + amp gain.
Quote

Am I all wet here, or can this non-linear approach be useful?

-Dennis

I am not sure that non-linear is the right term for this...

I am still unclear what you are correcting for... You mid gig tweak seems opposite fletcher-munsion constant loudness curves, so perhaps your bass speakers are experiencing some power compression (you have to push them harder to get same output), or you just want to change the mix.. kind of unclear to me.

JR

PS: Another minor point, when using power amps with clip limiting (like Peavey's DDT) the amount of still relatively clean headroom, past amp clipping threshold depends on the amp input attenuator.. The more the amp is padded down the sooner you run out of mixer headroom.  Note: I do not advocate using the full limiting capability available by driving that hard past clipping, just splainin the way it is interrelated.   
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chuck clark

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Re: Voltage Gain new to me; well, kind of...
« Reply #2 on: January 21, 2012, 08:08:18 am »

For many years (10-15 perhaps), I have been running my amps at about half throttle. 
Am I all wet here, or can this non-linear approach be useful?


Answer: Yes.
If it sounds good, your acheiving the volume you need and not blowing stuff up, your ahead of lots of systems/people. So obviously the "if it ain't broke don't fix it" rule should be in effect here. (I've done the same thing for about 20 years!)

Now TECHNICALLY speaking, you should double your low end so the power compression at higher levels better matches the output of the tops for better overall system linearity. Nice if you can afford it and have the extra space and muscle to haul it around. No more amp knob setting differences neccesary.
The main thing it tells you is where to best spend your money going forward to have a system with well matched output capabilities between the hi/mid and low portions of your system.
Happy sailing! Chuck
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Dennis Wiggins

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Re: Voltage Gain new to me; well, kind of...
« Reply #3 on: January 22, 2012, 12:15:04 pm »

A little clarification:

JR - "I don't recognize half throttle as a precise gain structure term... Half power is -3dB. "

Attenuator knobs straight up (-6dB) on a CS3000.

JR - "Gain structure is six of one half dozen another, if you need different gain for bass and mids the amps, or crossover are where to do that... It is the sum of all the gain in tha path so mixer gain + crossover gain, + amp gain."

Can I change the voltage gain for each output in the VSX? Hmmm... that would be a good feature.  I do adjust the balance between highs and lows in the VSX, but as I move from 85-90 dB into 95-100, my ears tells me to add more bass to keep things nicely balanced. 

*** 
Does changing the output level in the VSX have the same effect as turning the attenuator on the amp?  That is the question, and why I asked if I was "all wet" in the OP. 

***

JR - "I am not sure that non-linear is the right term for this..."

What I mean here is: After reading Marty's explanation, I am driving the tops with a voltage gain of roughly x20, and the subs are roughly x30.  If I were to run either of the amps wide open, the gain would be x40.  Backing off the attenuators does flatten the dynamics (which I like the sound of), but it does not do it by compression or limiting (which I don't like).  I have tried tweaking the sub ouputs in the VSX mid-show, but turning the attenuater knob seems to have a different effect. 

JR - "PS: Another minor point, when using power amps with clip limiting (like Peavey's DDT) the amount of still relatively clean headroom, past amp clipping threshold depends on the amp input attenuator.. The more the amp is padded down the sooner you run out of mixer headroom."

Except outdoors, I am not running anywhere near limiting on my CS3000s.  I am able to hit +6 on the mixer without tickling DDT.  At +6 on my mixer, I am well above 105dB (way too loud, for me) on the dance floor.

-Dennis
« Last Edit: January 22, 2012, 11:03:24 pm by Dennis Wiggins »
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Re: Voltage Gain new to me; well, kind of...
« Reply #3 on: January 22, 2012, 12:15:04 pm »


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