Thoughts about amplifiers at 3/4 volume.

Re: Thoughts about amplifiers at 3/4 volume.

I'm not going to contrdict Meyer engineers, but if you are using the M1-A processor there are sense lines that connect from the amplifier output terminals back to the processor. I'm not sure what the amp gain has to do with it. The processor should just be looking for a peak voltage (or other undesirable condition) to begin limiting or corrective EQ. For instance, older Nexo processors that have sense lines also have a amp gain adjustment (26, 32, or 38 dB) but the manual states that this has no bearing on the limiting or protection, it just helps to adjust the output of the process to be more inline with the amplifiers gain (i.e. pad to correct gain structure).

Additionally, I don't think using XTi amplifiers which have a DSP stage (and AD/DA stages) with a processor that has amp sense lines is a good idea. The delay in the audio processing incurred inside the DSP of the amplifier will throw off the calculations/comparisons being done by the external speaker processor (if sense lines are being used). I've never set up UPAs myself or used the M1-A processor and I don't know which Meyer processor you are using for certain, but these are just some friendly warnings for you.

In Meyer Sound Design Reference they specify that all amplifiers should have a voltage gain between 10 an 30 dB. I guess they did that for a reason :)
 
Re: Thoughts about amplifiers at 3/4 volume.

I think you have that backwards. I own a Crown iTech and in the application guide it talks about attenuators and input sensitivity. Unlike most amps, the iTech's input sensitivity is adjustable. It also has attenuators like most amps. It talks about the best way to reduce maximum output power being adjustment of the input sensitivity because that will result in better SNR. This is especially useful when using it with a speaker with a lower than recommended power rating. The 8000 produces 4000w @ 4 ohms per channel and I use it to power an SRX728S on one channel and a pair of SRX712M's as mains on the other channel. Both present a 4 ohm load and are both rated at 1600w RMS/3200w program so I adjust the input sensitivity and leave the attenuators at 100%.

Technically, with the Itech, you would use the same knob to adjust both input sensitivity and attenuation with it's menu driven system but it doesn't have a level marking on the knob for obvious reasons and when not in menu mode, the knobs adjust attenuation.

Most amps though, like I said, have fixed input sensitivity.

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Re: Thoughts about amplifiers at 3/4 volume.

I think you have that backwards. I own a Crown iTech and in the application guide it talks about attenuators and input sensitivity. Unlike most amps, the iTech's input sensitivity is adjustable. It also has attenuators like most amps. It talks about the best way to reduce maximum output power being adjustment of the input sensitivity because that will result in better SNR. This is especially useful when using it with a speaker with a lower than recommended power rating. The 8000 produces 4000w @ 4 ohms per channel and I use it to power an SRX728S on one channel and a pair of SRX712M's as mains on the other channel. Both present a 4 ohm load and are both rated at 1600w RMS/3200w program so I adjust the input sensitivity and leave the attenuators at 100%.

Technically, with the Itech, you would use the same knob to adjust both input sensitivity and attenuation with it's menu driven system but it doesn't have a level marking on the knob for obvious reasons and when not in menu mode, the knobs adjust attenuation.

Most amps though, like I said, have fixed input sensitivity.

The I-Techs do have adjustable input sensitivity as well as several stages of attenuation, in both the analog and digital realms. I have the schematic around somewhere, I might post an excerpt of the input stage.

However, there is absolutely nowhere in the user manual that Crown tells you to limit your power output by lowering the input!!!

The I-Techs have some of the best output limiters anywhere with both peak voltage and RMS power limiters available independently.
 
Re: Thoughts about amplifiers at 3/4 volume.

The I-Techs do have adjustable input sensitivity as well as several stages of attenuation, in both the analog and digital realms. I have the schematic around somewhere, I might post an excerpt of the input stage.

However, there is absolutely nowhere in the user manual that Crown tells you to limit your power output by lowering the input!!!

The I-Techs have some of the best output limiters anywhere with both peak voltage and RMS power limiters available independently.

Actually, I got that information from the iTech Application Guide, not the user manual.
http://crownaudio.com/pdf/amps/137327.pdf

See page 9. Setting Sensitivty partially quoted below (including a typo)

With other amplifi ers, it is often necessary to apply attenuation
in order to achieve the desired sound pressure level.
Large amounts of attenuation are not necessary with I-Tech
amplifi ers and can, in fact, degrade performance. The
attenuation adjustment should only be used for small (3 dB) or temporary adjustments
in amplifi er gain. Instead, set the sensitivity/gain of your I-Tech amplifi er so that you
can achieve the desired output output with the attenuators at or near 0 dB.
 
Re: Thoughts about amplifiers at 3/4 volume.

Actually, I got that information from the iTech Application Guide, not the user manual.
http://crownaudio.com/pdf/amps/137327.pdf

See page 9. Setting Sensitivty partially quoted below (including a typo)

It says set the sensitivity such that desired output can be achieved with the attenuators at or near 0dB...that has everything to do with signal to noise ratio (and gain structure), and nothing to do with maximum output.
 
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Re: Thoughts about amplifiers at 3/4 volume.

Actually, I got that information from the iTech Application Guide, not the user manual.
http://crownaudio.com/pdf/amps/137327.pdf

See page 9. Setting Sensitivty partially quoted below (including a typo)

Be careful about reading too much into what manufacturers say "that" other manufacturers do.... :)

The Crown amplifier is very likely operating at a fixed gain with a variable pad just before that amp stage to provide the appearance of variable sensitivity. This is mostly semantics, unless you are an amp designer, but they would probably love for variable amp sensitivity to become a "must have" feature.

Good independent slow-average and fast-peak limiting are far more powerful features IMO. The multiple gain trims are perhaps somewhat useful to optimize noise floors between amp and processing, for best internal gain structure management, but I wouldn't lose any sleep over it.

JR
 
Re: Thoughts about amplifiers at 3/4 volume.

I used to drive a Volkswagen Passat. Great car, roomy, and the 2 liter turbo engine got it going pretty well while returning fuel economy in the low 30MPG range (7.8 l/100Km+). The only problem is that it was front wheel drive, and the differential must have been a very generic type as in any sort of low traction environment it resorted to spinning one wheel.

Now, on the dash was a little button that allowed one to disable the traction control. By doing this, and with careful control of the throttle, brake, and steering, I could get that car through pretty much anything in short order. Enabling traction control, on the other hand, retarded the engine so extremely and applied so much braking that while the car might worm its way out eventually it was such slow going you'd have to be an idiot to put up with it. Of course if you're the sort of person who is an idiot, and when encountering a situation where the car isn't traveling at the expected speed mash the accelerator pedal to the floor, traction control is a must since it overrides your stupidity. Turn it off and mash the accelerator and you'll sit all day until either the wheel digs into so much dirt that you're truly stuck, or spins on ice long enough to catch fire.

So the traction control is there for people who don't know how to operate a motor vehicle. People who grew up driving on dirt and ice can pretty much leave it off, but the vast majority of drivers desperately need it to save them from themselves.

Or, at least, that seemed like a decent analogy in my head.

Maybe a better auto to audio analogy might be that downshifting doesnt mean your car cant go as fast, it just means your engine has to work that much harder to get it going that fast. Oh, and it might clip - er, I mean redline...
 
Re: Thoughts about amplifiers at 3/4 volume.

Silas and John Roberts, perhaps I did read too much into this. Maybe getting two types of db mixed up?

I understand that the watts from an amp increase the SPL db and reducing the sensitivity by x db sounded like the same thing. Well I think you get my drift. So would you say that even with the sensitivity turned down I'm risking speaker damage?
 
Re: Thoughts about amplifiers at 3/4 volume.

dB is dB. A 4dB reduction in any place will have the same effect on the output.

Even if your amp is turned down, it can still "put out" full power-you just have to drive it harder.

So yes-you can still damage your loudspeakers-even with your amp turned way down.

The level control is NOT a wattage control-as many people mistakenly think.
 
Re: Thoughts about amplifiers at 3/4 volume.

dB is dB. A 4dB reduction in any place will have the same effect on the output.

Even if your amp is turned down, it can still "put out" full power-you just have to drive it harder.

So yes-you can still damage your loudspeakers-even with your amp turned way down.

The level control is NOT a wattage control-as many people mistakenly think.

Hmmmm... maybe I need to trade with someone an iTech 8000 for a 6000? I guess I'm more confused than ever... is input sensitivity on an amp roughly equivalent to input level on a mixer or processing equipment?
 
Re: Thoughts about amplifiers at 3/4 volume.

Hmmmm... maybe I need to trade with someone an iTech 8000 for a 6000? I guess I'm more confused than ever... is input sensitivity on an amp roughly equivalent to input level on a mixer or processing equipment?

Sensitivity is exactly the same thing as voltage gain, but it is stated in terms of N input voltage to make Nx output voltage.

JR
 
Re: Thoughts about amplifiers at 3/4 volume.

Okay - not to belabor the point, but I was thinking some more about the input sensitivity thing. Tell me if I'm completely off my rocker here.

My speakers have program rating of 3200w @ 4 ohms. amp is rated 4000w @ ohms per channel.
Sensitivity on the iTech displays as db reduction but of course translates to input voltage.
With less power available, am I not effectively turning a 4000w amp into a 2000w amp if the setting is adjusted to -3db from -0db?
My thinking is, with the sensitivity turned down (whether I go with -3db or something more conservative like -6 or even -10 db. the amp will clip earlier.
If proper gain structure is set using full bandwidth pink noise so I never see red, I won't run into clipping short of some sort of malfunction or major accident and thus my speakers will be seeing 2000w (with -3db set) which is 1.25x RMS, well within stated guidelines.

My trig skills are rusty, so I'm not sure how to figure out what decrease in db would result in a 800 reduction which is what I would really like. I read the bit posted in this thread in the opening paragraphs of the Shure publication about setting gain structure and it seems to me if my amp power is at program rating I still have a bout 3db of room for error based on following the procedure outlined. I've known about the recommendation of 1.5x to 2x over RMS for some time but didn't know the technical explanation why.

I guess bottom line is this... does turning down my input sensitivity in effect reduce the power input into the amp and thus reduce the power output by the amp? If it does then I think I am fine and maybe I just don't have my terminology down pat. Oh, and part 2 of that would be... does the iTech really reduce the input power by the number of watts one would expect as I've outlined (3b = 1/2 power or 2x depending on your point of view) which I borrowed from the explanation of speakers' sensitivity ratings where 2x the power = 3db increase in SPL.

Thanks for bearing with a relative noob.
 
Re: Thoughts about amplifiers at 3/4 volume.

Okay - not to belabor the point, but I was thinking some more about the input sensitivity thing. Tell me if I'm completely off my rocker here.

My speakers have program rating of 3200w @ 4 ohms. amp is rated 4000w @ ohms per channel.
Sensitivity on the iTech displays as db reduction but of course translates to input voltage.
With less power available, am I not effectively turning a 4000w amp into a 2000w amp if the setting is adjusted to -3db from -0db?
My thinking is, with the sensitivity turned down (whether I go with -3db or something more conservative like -6 or even -10 db. the amp will clip earlier.
If proper gain structure is set using full bandwidth pink noise so I never see red, I won't run into clipping short of some sort of malfunction or major accident and thus my speakers will be seeing 2000w (with -3db set) which is 1.25x RMS, well within stated guidelines.

My trig skills are rusty, so I'm not sure how to figure out what decrease in db would result in a 800 reduction which is what I would really like. I read the bit posted in this thread in the opening paragraphs of the Shure publication about setting gain structure and it seems to me if my amp power is at program rating I still have a bout 3db of room for error based on following the procedure outlined. I've known about the recommendation of 1.5x to 2x over RMS for some time but didn't know the technical explanation why.

I guess bottom line is this... does turning down my input sensitivity in effect reduce the power input into the amp and thus reduce the power output by the amp? If it does then I think I am fine and maybe I just don't have my terminology down pat. Oh, and part 2 of that would be... does the iTech really reduce the input power by the number of watts one would expect as I've outlined (3b = 1/2 power or 2x depending on your point of view) which I borrowed from the explanation of speakers' sensitivity ratings where 2x the power = 3db increase in SPL.

Thanks for bearing with a relative noob.

Turning down the gain DOES NOT REDUCE THE OUTPUT CAPABILITY in any way. That has been stated a good number of times in this thread. You keep thinking it will, will not somehow start to make it so.

All you are doing is changing the input drive level needed to achieve FULL output power.

There is no need for Trig in this. Just basic math.

In a way a compressor/limiter- if properly set -can "reduce" the maximum output capability of the amp-in a "kinda" way.
 
Re: Thoughts about amplifiers at 3/4 volume.

I regret it's all a little more complex than that.

Amplifier sensitivity is the same thing as voltage gain, just stated a different way. It simply means that X volts at the amp input will result in Y volts at the amp output. Power in the loudspeaker is the result of a the voltage at the amplifier output, divided by loudspeaker impedance. i.e. 4 ohm speaker makes twice the power as 8 ohm speaker at same voltage.

The amplifier output voltage, or power, is only limited by two things. the amplifier power supply rail voltages which define the max voltage (power) the amp can possibly make. The other limit involves the amp's sensitivity (for amps like this that make sensitivity adjustable) or more typical amplifiers that use pad/attenuates, to vary the effective amplifier voltage gain or ratio from input to output voltage "and" the max voltage possible at the input.

This may be easier to follow if I use some specific (rounded off for my convenience) numbers... Suppose the amplifier PS allows it to make a maximum of 100V at the output. Working backwards with a sensitivity or voltage gain of 33x, means 3V at the input will drive the output to full power. Now if we change the sensitivity (gain) from 33x to say 16.5x, the amplifier can still make the same output power, but now it needs 6V at the input to reach full power. Since the typical line level devices driving the power can easily make 6V or more, the amp's max power is unchanged, while you will just be be driving it a little harder, perhaps noticeable on the console meters.

We can use adjustable amplifier gain to crudely limit power if we throttle back the gain so much, that the line level gear driving the amp clips or runs out of swing before it can drive the power amp to full output.

It is possible to put a limiter in front of the amp, and dial back this limiter threshold so it limits the drive voltage so it can only put out say 3V, then dial in the sensitivity of the amp so that agrees with your desired output power.

But it seems that it would be far simpler to just use one of the power limiters built into that power amp...

So long story short, sensitivity (gain) only limits output power if the input voltage is also limited or hard clipped such that it is incapable of driving the amp input any harder. Changing the amp gain while you still have extra drive capability in front of it will limit nothing.

I hope this helps

JR
 
Re: Thoughts about amplifiers at 3/4 volume.

Turning down the gain DOES NOT REDUCE THE OUTPUT CAPABILITY in any way. That has been stated a good number of times in this thread. You keep thinking it will, will not somehow start to make it so.

All you are doing is changing the input drive level needed to achieve FULL output power.

There is no need for Trig in this. Just basic math.

In a way a compressor/limiter- if properly set -can "reduce" the maximum output capability of the amp-in a "kinda" way.

The basic math needed to calculate the db change for an increase in power, unless that increase happens to be a power of 2 (2x, 4x, etc.) involves a log10. That's a moot point though because I just remembered I have both Excel and OpenOffice which have scientific functions so this wouldn't be too hard to figure out.

As far as the concept goes, I think I understand. Sorry for being dense. Tell me if I'm wrong in this scenario...

I find that when setting gain structure, as I lower the amount of attenuation on the amp, starting with full attenuation, it goes into clipping at 50% attenuation. In order to get a better SNR, I adjust the sensitivity downward to the point that now, I get clipping right at the point where I also have zero attenuation. This gives me better SNR plus the peace of mind of knowing nobody can turn up the "gains" when I'm not looking driving the amp into clipping and ruining my speakers. HOWEVER, at that point, the amp is still putting out it's full rated power (assuming it was before).

Now assuming that is true, is not also true that I could measure the output and continue turning down the sensitivity with the attenuation at zero and achieve a lower output assuming the same input signal? At this point, adjusting the sensitivity would be in effect changing the input drive level need to achieve a CERTAIN output level... the level I am hoping to achieve.
 
Re: Thoughts about amplifiers at 3/4 volume.

Okay - not to belabor the point, but I was thinking some more about the input sensitivity thing. Tell me if I'm completely off my rocker here.

My speakers have program rating of 3200w @ 4 ohms. amp is rated 4000w @ ohms per channel.
Sensitivity on the iTech displays as db reduction but of course translates to input voltage.
With less power available, am I not effectively turning a 4000w amp into a 2000w amp if the setting is adjusted to -3db from -0db?

No, for a couple of reasons. First, amplifiers increase VOLTAGE, not watts; second all you did was double the required input voltage to drive the amp to full output. Also, you can change in the input sensitivity in actual volts for full output.. it's in the Advanced menu, IIRC.

My thinking is, with the sensitivity turned down (whether I go with -3db or something more conservative like -6 or even -10 db. the amp will clip earlier.
If proper gain structure is set using full bandwidth pink noise so I never see red, I won't run into clipping short of some sort of malfunction or major accident and thus my speakers will be seeing 2000w (with -3db set) which is 1.25x RMS, well within stated guidelines.

My trig skills are rusty, so I'm not sure how to figure out what decrease in db would result in a 800 reduction which is what I would really like. I read the bit posted in this thread in the opening paragraphs of the Shure publication about setting gain structure and it seems to me if my amp power is at program rating I still have a bout 3db of room for error based on following the procedure outlined. I've known about the recommendation of 1.5x to 2x over RMS for some time but didn't know the technical explanation why.

I guess bottom line is this... does turning down my input sensitivity in effect reduce the power input into the amp and thus reduce the power output by the amp? If it does then I think I am fine and maybe I just don't have my terminology down pat. Oh, and part 2 of that would be... does the iTech really reduce the input power by the number of watts one would expect as I've outlined (3b = 1/2 power or 2x depending on your point of view) which I borrowed from the explanation of speakers' sensitivity ratings where 2x the power = 3db increase in SPL.

Thanks for bearing with a relative noob.

Your amp isn't too big. All you need to do with the I-Tech is set your peak voltage limiters and your RMS power limiters.

Have fun, good luck.

Tim Mc