so when you are testing your tweets by ear do you only listen to the tweets? Same for the mids and subs?
A tutorial on gain setting and amplifier power usage
Let's start with some simple concepts. Your source, whether it be a tape player, dvd, or a cd player has a maximum rated output voltage. That output is too weak to directly power a speaker, so in turn it's sent to an amplifer, which well... amplifies that signal and sends that along to your speaker.
What the "gain knob" does is matches the amplifier's input sensitivity to the maximum output of your source. Simply put, it prevents your headunit from overdriving your amplifier by telling your amp what is the max voltage/signal that it can expect from your headunit. At that point, your amp will achieve maximum power output without being overdriven into distortion/damage.
So if your headunit is capable of 4v, and you set the amp's gains to 4v then your amp will make max power when your headunit sends it a 4v signal. Sending it anything more than 4v will cause excess distortion and heat, since you're now exceeding the maximum power rating for your amp. On the other hand, setting the gains to 8v when you're headunit's max output is only 4v will cause your amp to never reach maximum power output.
Now, take a look at the following song:
![]()
This shows you the amplitude levels of the song over time. Notice that it fluctuates quite a bit, with some parts obviously much louder than others.
The ratio between the average level of the entire song and it's loudest point is called the "crest factor".
You can see that there's a problem here. If we were to set our amp's gain to the max output of our headunit, the only time our amplifier would be making it's max power output would be during those few, brief moments in the song when the amplitude is at it's peak. We can clearly see that for most portions of the song, the average amplitude is considerably lower than it's peak resulting in a large portion of our amp's power output being wasted. Remember that a doubling of power is equivalent to 3db of gain. Imagine that your typical song has a crest factor of 12db or more, and you can easily imagine the considerable waste of power if your gains were to be set in such a manner. For a 16w amp, you would only be outputting an average 1w... with volume set to max on your headunit.
So what can we do? Generally, I prefer to set my gains by ear. I set the gains at a lower output level than what my headunit is capable of producing, up until the point I can "hear" the amplifier distorting. At that point I back off a bit. Now the amplifier is still going to distort, but only on those very brief high amplitude peaks in the music. Everyone's ears are different. It's best to choose a song with a high crest factor to ensure the least amount of amplifier distortion with the widest range of music, and to let your ear be the judge of what distortion levels are audible to you. This way, you can be sure to utilize as much of our amp's power output as possible.
Also consider the practical fact that as you turn up the gains on your amp, you generally begin to pickup more hiss/noise. Having a more powerful amp will allow you to keep the gains down, and thus reduce noise.
Regardless, with music it's fairly obvious that your amp does not constantly output it's maximum continuous power output. Looking at the example song above, the amplitude fluctuates quite a bit. So when people claim their speakers are taking the full rated output of their amp's on a continuous basis, it's probably not true.
Also, bear in mind that we rarely use one speaker in our setups. We have mids, tweeters, and subs. Generally, the power output to tweeters and mids is fairly low. Those huge spikes you see in the music are bass tones. This is because our ears are less sensitive to bass frequencies, so when recording a low frequency and a higher frequency tone of the same spl, the low frequency tone is going to have much higher amplitude.
For anyone curious to get a more realistic measure of how much power is needed or used, I suggest using 0db sine waves to test your system. Hook up a voltmeter across the terminals of your tweeter or mid and play the sine wave. You'll be surprised to find how little power it takes to get your speaker extremely loud above 200hz. Usually a few watts at 1m on your typical tweeter at 3khz is enough to cause pain.
What the "gain knob" does is matches the amplifier's input sensitivity to the maximum output of your source. Simply put, it prevents your headunit from overdriving your amplifier by telling your amp what is the max voltage/signal that it can expect from your headunit. At that point, your amp will achieve maximum power output without being overdriven into distortion/damage.
So if your headunit is capable of 4v, and you set the amp's gains to 4v then your amp will make max power when your headunit sends it a 4v signal. Sending it anything more than 4v will cause excess distortion and heat, since you're now exceeding the maximum power rating for your amp. On the other hand, setting the gains to 8v when you're headunit's max output is only 4v will cause your amp to never reach maximum power output.
Now, take a look at the following song:
This shows you the amplitude levels of the song over time. Notice that it fluctuates quite a bit, with some parts obviously much louder than others.
The ratio between the average level of the entire song and it's loudest point is called the "crest factor".
You can see that there's a problem here. If we were to set our amp's gain to the max output of our headunit, the only time our amplifier would be making it's max power output would be during those few, brief moments in the song when the amplitude is at it's peak. We can clearly see that for most portions of the song, the average amplitude is considerably lower than it's peak resulting in a large portion of our amp's power output being wasted. Remember that a doubling of power is equivalent to 3db of gain. Imagine that your typical song has a crest factor of 12db or more, and you can easily imagine the considerable waste of power if your gains were to be set in such a manner. For a 16w amp, you would only be outputting an average 1w... with volume set to max on your headunit.
So what can we do? Generally, I prefer to set my gains by ear. I set the gains at a lower output level than what my headunit is capable of producing, up until the point I can "hear" the amplifier distorting. At that point I back off a bit. Now the amplifier is still going to distort, but only on those very brief high amplitude peaks in the music. Everyone's ears are different. It's best to choose a song with a high crest factor to ensure the least amount of amplifier distortion with the widest range of music, and to let your ear be the judge of what distortion levels are audible to you. This way, you can be sure to utilize as much of our amp's power output as possible.
Also consider the practical fact that as you turn up the gains on your amp, you generally begin to pickup more hiss/noise. Having a more powerful amp will allow you to keep the gains down, and thus reduce noise.
Regardless, with music it's fairly obvious that your amp does not constantly output it's maximum continuous power output. Looking at the example song above, the amplitude fluctuates quite a bit. So when people claim their speakers are taking the full rated output of their amp's on a continuous basis, it's probably not true.
Also, bear in mind that we rarely use one speaker in our setups. We have mids, tweeters, and subs. Generally, the power output to tweeters and mids is fairly low. Those huge spikes you see in the music are bass tones. This is because our ears are less sensitive to bass frequencies, so when recording a low frequency and a higher frequency tone of the same spl, the low frequency tone is going to have much higher amplitude.
For anyone curious to get a more realistic measure of how much power is needed or used, I suggest using 0db sine waves to test your system. Hook up a voltmeter across the terminals of your tweeter or mid and play the sine wave. You'll be surprised to find how little power it takes to get your speaker extremely loud above 200hz. Usually a few watts at 1m on your typical tweeter at 3khz is enough to cause pain.
1 - 20 of 41 Posts
I just had an addition to suggest for setting gains on sub amps - because I definitely also like to set my gains by ear as well:
With all my amps, I set my gains using test tones - you can pick up CD's with test tones recorded at the maximum -0dB level, and I find this real easy to pick out when distortion starts, with pure tones.
Anyway - with subwoofers-
Bearing in mind that the lower you go in frequency, the less sensitive your hearing is to distortion (did you know with subwoofers, most people can't hear distortion until it reaches 5%-10% levels - even trained ears?
), I like to use a frequency that's actually well outside my subwoofer's normal playing range... but not too terribly high, because the sub's own inductance will start to roll off higher frequencies...
My sub amp gain setting usually goes like this:
1) turn off the sub amp's low-pass filter (or whatever LP filter is engaged, for the sub's signal)
2) play a 200hz-300hz test tone, adjust the gains listening for distortion
3)turn the low pass filter back on and call it a day
Of course your sub isn't going to ever play 200hz-300hz (outside of this test), but this doesn't matter, since all we're doing is adjusting the size of the doorway that we are allowing the signal to pass through on the way into the amp... and the amp has a frequency response (power output) that's flat across this whole range.
With all my amps, I set my gains using test tones - you can pick up CD's with test tones recorded at the maximum -0dB level, and I find this real easy to pick out when distortion starts, with pure tones.
Anyway - with subwoofers-
Bearing in mind that the lower you go in frequency, the less sensitive your hearing is to distortion (did you know with subwoofers, most people can't hear distortion until it reaches 5%-10% levels - even trained ears?
), I like to use a frequency that's actually well outside my subwoofer's normal playing range... but not too terribly high, because the sub's own inductance will start to roll off higher frequencies...My sub amp gain setting usually goes like this:
1) turn off the sub amp's low-pass filter (or whatever LP filter is engaged, for the sub's signal)
2) play a 200hz-300hz test tone, adjust the gains listening for distortion
3)turn the low pass filter back on and call it a day
Of course your sub isn't going to ever play 200hz-300hz (outside of this test), but this doesn't matter, since all we're doing is adjusting the size of the doorway that we are allowing the signal to pass through on the way into the amp... and the amp has a frequency response (power output) that's flat across this whole range.
I set by ear and spectrum analysis. And I may get flamed for this.... I could give two ****s if I get a little clipping. On large coil drivers (larger mids and subs) the inductance is such that any upper harmonic content of a clipped signal will see a very high impedance load thus not be translated into real power. A little clipping is not bad, as long as it's distortion characteristics don't exceed that of the drivers distortion, which is a bunch!
Those who have observed clipping indicators in action need to understand a couple things. 1. They are delayed to stay on for a while after the actual incident if simple peak clipping is occurring. If they were not timed out this way you would barely if never see them. 2. Sometimes they are set up using a comparator circuit, meaning that it looks for a different signal from the input to the output sans gain and illuminates the device when a difference is sensed. This is the best type. Others are simply a single ended design where the engineer assumed that the amp would clip at a preset voltage level be it input or output, those suck because they don't take into the account of complex output loading or voltage variations on the mains inputs.
I've been doing this long enough that I don't mind seeing a little flicker of the clip light on lows, some mids and all tweets is a different story, if you are clipping your HF amplifier then something is wrong, you are deaf, or you are about to be My Sub and low amps in my PA flicker the clip lights every night and have been doing it now for almost 15 years without ever having a failure. Most LF failures I have had were suspension and lead wire failures and the coils looked great after being removed from service. I have never blown one of my JBL subs. But I did tear up 8 of the "research" Peaveys before we got it right, I've been on this set of peaveys now for a while, all have survived. The new sub project cold prove interesting
Set them by ear, or a SA, then tweak from there. if you are clipping amps bad then take it as a lesson learned and buy bigger amps
Chad
Those who have observed clipping indicators in action need to understand a couple things. 1. They are delayed to stay on for a while after the actual incident if simple peak clipping is occurring. If they were not timed out this way you would barely if never see them. 2. Sometimes they are set up using a comparator circuit, meaning that it looks for a different signal from the input to the output sans gain and illuminates the device when a difference is sensed. This is the best type. Others are simply a single ended design where the engineer assumed that the amp would clip at a preset voltage level be it input or output, those suck because they don't take into the account of complex output loading or voltage variations on the mains inputs.
I've been doing this long enough that I don't mind seeing a little flicker of the clip light on lows, some mids and all tweets is a different story, if you are clipping your HF amplifier then something is wrong, you are deaf, or you are about to be
My Sub and low amps in my PA flicker the clip lights every night and have been doing it now for almost 15 years without ever having a failure. Most LF failures I have had were suspension and lead wire failures and the coils looked great after being removed from service. I have never blown one of my JBL subs. But I did tear up 8 of the "research" Peaveys before we got it right, I've been on this set of peaveys now for a while, all have survived. The new sub project cold prove interesting Set them by ear, or a SA, then tweak from there. if you are clipping amps bad then take it as a lesson learned and buy bigger amps
Chad
1 - 20 of 41 Posts
