Noise floor eats up headroom, am I right?

Richard Stringer

Sophomore
Jan 13, 2011
124
0
16
Boston, Lincolnshire, UK
Am I right in saying that the amount of noise a system has, can eat up precious headroom? The reason I ask is, i'm kinda confused, a little. I used to have a QSC RMX2450 and a QSC PLX3002, and used to power 4 JBL MP418S subs. Now I used to power them by putting 2 subs on each channel of the PLX3002, running it into 2 ohms per channel, and at that impedance the PLX3002 can output 1,500 watts average power into 2 ohms per channel. I tried the same with my RMX2450, which at 2 ohms per channel can output 1,200 watts average power. I could clearly hear how the PLX3002 was louder, or definately seemed louder, and the difference was only 300 watts per channel. Do you guys think that, say for example, an amplifier with a S/N ratio of 107db can sound louder than an amplifier with the same power output per channel which has a S/N ratio of 100db? Am I right in thinking that with the amplifier which has the 107db S/N ratio, the noise floor is lower so not so much precious headroom is being taken up by the noise it suffers from?

My way of thinking and also confusion about this idea is because the way I see it is, if I set gain structure of my system (so I can accurately know how close i'm getting to clipping), and use an amplifier which has horrendous noise, say for example, an S/N ratio of 70db, and if the noise was so bad that it maybe registered on the vu meters without a signal coming through the system, and if for example the noise was so bad that I only had about (only for example not in real world terms) about 3db of headroom before clipping, that would mean most of the sound coming out the speakers would be mainly noise wouldn't it? And if I used an amplifier of the same power output with a brilliant S/N ratio, say 110db, would the music levelk be louder out the speakers because not so much noise would be taking up the headroom?

Or am I totally wrong, and a system can only output what it can output regardless of whether it's noise or music or whatever?
 
Re: Noise floor eats up headroom, am I right?

Am I right in saying that the amount of noise a system has, can eat up precious headroom? The reason I ask is, i'm kinda confused, a little. I used to have a QSC RMX2450 and a QSC PLX3002, and used to power 4 JBL MP418S subs. Now I used to power them by putting 2 subs on each channel of the PLX3002, running it into 2 ohms per channel, and at that impedance the PLX3002 can output 1,500 watts average power into 2 ohms per channel. I tried the same with my RMX2450, which at 2 ohms per channel can output 1,200 watts average power. I could clearly hear how the PLX3002 was louder, or definately seemed louder, and the difference was only 300 watts per channel. Do you guys think that, say for example, an amplifier with a S/N ratio of 107db can sound louder than an amplifier with the same power output per channel which has a S/N ratio of 100db? Am I right in thinking that with the amplifier which has the 107db S/N ratio, the noise floor is lower so not so much precious headroom is being taken up by the noise it suffers from?

My way of thinking and also confusion about this idea is because the way I see it is, if I set gain structure of my system (so I can accurately know how close i'm getting to clipping), and use an amplifier which has horrendous noise, say for example, an S/N ratio of 70db, and if the noise was so bad that it maybe registered on the vu meters without a signal coming through the system, and if for example the noise was so bad that I only had about (only for example not in real world terms) about 3db of headroom before clipping, that would mean most of the sound coming out the speakers would be mainly noise wouldn't it? And if I used an amplifier of the same power output with a brilliant S/N ratio, say 110db, would the music levelk be louder out the speakers because not so much noise would be taking up the headroom?

Or am I totally wrong, and a system can only output what it can output regardless of whether it's noise or music or whatever?
So much to say about this-but 2 comments.

The noise floor has NOTHIGN to do with headroom The "headroom" (assuming you are talking about how loud a system can get) of a system is solely determined by the size of the amplifier and the sensitivity/capability of the loudspeaker system.

Noise floor will affect the DYNAMIC range of a system-ie how QUIET it can get in relation to how loud it can get.

What you are hearing is NOT the difference in the noise floor, but simply rather the gain of the amplifer. Turn the "louder" amp down to match the same level as the other amps and see what you think.

And NOT (before you ask) the knob on the front is NOT a wattage control, simply a gain control. The amps will still be able to deliver full power when turned down quite a bit.
 
Re: Noise floor eats up headroom, am I right?

Am I right in saying that the amount of noise a system has, can eat up precious headroom? The reason I ask is, i'm kinda confused, a little. I used to have a QSC RMX2450 and a QSC PLX3002, and used to power 4 JBL MP418S subs. Now I used to power them by putting 2 subs on each channel of the PLX3002, running it into 2 ohms per channel, and at that impedance the PLX3002 can output 1,500 watts average power into 2 ohms per channel. I tried the same with my RMX2450, which at 2 ohms per channel can output 1,200 watts average power. I could clearly hear how the PLX3002 was louder, or definately seemed louder, and the difference was only 300 watts per channel. Do you guys think that, say for example, an amplifier with a S/N ratio of 107db can sound louder than an amplifier with the same power output per channel which has a S/N ratio of 100db? Am I right in thinking that with the amplifier which has the 107db S/N ratio, the noise floor is lower so not so much precious headroom is being taken up by the noise it suffers from?

Honestly, who knows. Maybe the PLX sounded louder. However, S/N ratio has nothing to do with the capability of an amplifier to make a speaker get louder - which is really what we are talking about here. Maybe there is some crazy psychological/perceptual effect where increased noise causes our perception of loudness to change, but I highly doubt it.

I'm actually surprised that, all else being equal, the PLX sounded louder. With gain knobs at maximum, the RMX has 34dB of gain while the PLX (all first gen models) are 32dB. If your are describing your perception of "loudness" at the point where the clip indicators are flashing I'd believe you if you said the PLX sounded louder. That observation could be due to many factors. Increased distortion, a compression of the signal due to clipping, or yeah, just an extra 300 Watts (though I really doubt the latter, it's only a 0.97 dB difference). I wouldn't have been surprised if you said the RMX was louder. Why? Because I see no method to your measurement and observations and the difference between these amplifiers (audibly speaking) is very very small.

My way of thinking and also confusion about this idea is because the way I see it is, if I set gain structure of my system (so I can accurately know how close i'm getting to clipping), and use an amplifier which has horrendous noise, say for example, an S/N ratio of 70db, and if the noise was so bad that it maybe registered on the vu meters without a signal coming through the system, and if for example the noise was so bad that I only had about (only for example not in real world terms) about 3db of headroom before clipping, that would mean most of the sound coming out the speakers would be mainly noise wouldn't it? And if I used an amplifier of the same power output with a brilliant S/N ratio, say 110db, would the music levelk be louder out the speakers because not so much noise would be taking up the headroom?

Or am I totally wrong, and a system can only output what it can output regardless of whether it's noise or music or whatever?

Indeed, you are wrong. Irregardless of the SNR specification, the power produced will be the same, but at some threshold it may "sound different." One thing you should note: typically amplifiers are the best performing piece of equipment in the signal chain of a typical sound system. I rarely see SNR specs above 100dB in most electronics, and 100 or greater is fairly common in amplifiers. Unplugging the input from an amplifier connected to a speaker with the gain knobs WOT confirms this to my ears... most functioning amps are dead silent. Your mixer will be the biggest noise source, and in practice if you can achieve 80dB SNR from a mixer whilst in operation you are doing OK IMO. This varies greatly with the number of microphones connected and the gain required on each.
 
Re: Noise floor eats up headroom, am I right?

Ah right a bit of confusion cleared up then thanks guys.

Ryan,
When you said "If your are describing your perception of "loudness" at the point where the clip indicators are flashing I'd believe you if you said the PLX sounded louder", that's exactly what I meant yeah, at the point of clipping, the PLX3002 sounded a little louder than the RMX2450.