Technical Questions

[Bandieramonte 10+ year member]

I got some questions regarding some technical specifications for amps, specially the ones that affect the sound quality. The questions are the following:

1) Regarding the signal/noise ratio, some amps have their manual describing as:

Signal-to-noise ratio: 85dB (reference 1W into 4 ohms)

Signal-to-noise ratio: 104dB (reference rated power into 4 ohms)

That confuses me a lot. What is finally the final signal/noise ratio in that case?

2) Regarding the THD factor, some amps have their manual describe it this way:

100W RMS x 4 channels @ 4 ohms and ≤1% THD + N*

THD + N: 0.05% (rated power @ 4 ohms)

But when will the THD be 1% and when will it be 0.05%?

3) How do I know if an amp is capable of doing a bi-amping setup with a set of comps? Can all 4 channel amps may do this?

4) If I bi-amp an amp being 100 rms x 4 to a set of comp, does that necessarily means that it will be sending the whole 100 rms to each driver of the comp without possibility to lower the amount of power the amp sends per channel? (in other words, can bi-amping be flexible regarding the amount of power it sends per channel)?

5) What would be better SQ wise for powering a set of comp SR6500: the JBL GTO1004 or the Focal Solid 4? Why?

Thanks.

Click to read more...

 

[Ctesibius 10+ year member]

I got some questions regarding some technical specifications for amps, specially the ones that affect the sound quality. The questions are the following:
1) Regarding the signal/noise ratio, some amps have their manual describing as:

Signal-to-noise ratio: 85dB (reference 1W into 4 ohms)

Signal-to-noise ratio: 104dB (reference rated power into 4 ohms)

That confuses me a lot. What is finally the final signal/noise ratio in that case?

The problem is that there isn't a "final" SNR. Signal to noise ratio is exactly what it says; It the ratio of the signal to the noise. Guess what? When you have less signal (1w) then the ratio of signal to noise will be lower (85db) than when you have a large signal (rated power output, 104db).

This is one of the reasons you need to know the measurement method used to establish the published SNR between two different amplifiers before you can meaningfully compare them.

Good reading on the subject; http://www.bcae1.com/sig2nois.htm

One of the most important things to know is that SNR is one of those measurements that doesn't really mean a whole lot as the differences will be inaudible in when comparing any two amplifiers worth owning.

2) Regarding the THD factor, some amps have their manual describe it this way:100W RMS x 4 channels @ 4 ohms and ≤1% THD + N*

THD + N: 0.05% (rated power @ 4 ohms)

But when will the THD be 1% and when will it be 0.05%?

The first indicates that the amplifier is capable of 100w of power output while maintaining less than or equal to 1% THD.

The second indicates that the distortion at rated power was .05%

Look at the second chart in this picture; http://www.wjjeeps.com/jl_3004_chart.jpg (for example purposes only, as this was simply one of the first I could find quickly)

It's the THD+N vs Power output chart. What happens? Well, as power increases from near zero to 100w, the THD+N is gradually decreasing. Why? Because "N" is "noise", which is generally a fairly steady figure. Now go back to what we said before about SNR; as power increases the SNR improves, right? Well, this is the reason for the decline in the chart. The level of the signal is increasing, but the THD is very low and "N" is a relatively steady figure.....so as power increase the percentage of THD+N decreases (i.e. improves just like SNR improves as we increase the level of the signal). But then what happens at about 200w? It jumps up fairly quickly! Look on the left hand side, find the 1% line and follow it across. Where does it intersect with the charted line? That would be similiar to the "≤1% THD + N" rating. Then find the .05% and trace it across. That would be similar to the ".05% THD+N" rating.

3) How do I know if an amp is capable of doing a bi-amping setup with a set of comps? Can all 4 channel amps may do this?

Bi-amping is more a function of the crossover than the amplifier. If the crossover is capable of being bi-amped, then you can do so with basically any 4 channels of amplification be it a 4-channel amp, two 2-channel amps, etc.

4) If I bi-amp an amp being 100 rms x 4 to a set of comp, does that necessarily means that it will be sending the whole 100 rms to each driver of the comp without possibility to lower the amount of power the amp sends per channel? (in other words, can bi-amping be flexible regarding the amount of power it sends per channel)?

No. Due to the dynamics of music and other various factors, your speakers will almost never receive 100w from a 100w rated amplifier. But you can also use the gain control, volume knob and other level adjustments to affect the amount of power the speakers will receive.

5) What would be better SQ wise for powering a set of comp SR6500: the JBL GTO1004 or the Focal Solid 4? Why?

I would go with which ever was cheaper as long as they both offered the features I needed, since they both have pretty close to the same rated power output.

 

[dB-r 10+ year member]

Good reading on the subject; http://www.bcae1.com/sig2nois.htm.

You know, you actually are pretty smart. I didn't get that from your posts over in the now infamous sundown vs aq thread... Nothing personal dude.

And I see you linked bcae1.com, not sure if you know Perry or not, but he is actually the one who trained me. He is the "master" as far as I am concerned. Great guy too.

 

[Ctesibius 10+ year member]

You know, you actually are pretty smart. I didn't get that from your posts over in the now infamous sundown vs aq thread... Nothing personal dude.
And I see you linked bcae1.com, not sure if you know Perry or not, but he is actually the one who trained me. He is the "master" as far as I am concerned. Great guy too.

I have no idea who Perry is, other than knowing he's been a blessing to car audio for atleast the past 5 years for designing, writing and hosting the bcae site.

If I did ever meet the man, I would definitely shake his hand //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[dB-r 10+ year member]

He's been repairing amps for like 25 years now... amazing amount of knowledge in that mans head..... I hope he stays around for another 25 years.

 

[Bandieramonte 10+ year member]

Thanks Ctesibius! Your post really helped me understand a bunch more about those indicators for amps. Though, I been left with some doubts, whose clarification would definitely help me more:

- Let's suppose the amp is 100 rms x 4 @ 4 ohm and its max power is 600 watts. Its manual says that S/N ratio is Xdb and THD + N is Y% at reference rated power into 4 ohms, and I connect the amp to a set of comp. This means that such S/N ratio and THD will be Xdb and Y% respectively when I send exactly all the 100 rms to the 4 channels? Or must I send all the 600 watts of max power the amp has?

- The second chart from http://www.wjjeeps.com/jl_3004_chart.jpg, you said it was only for example purposes. But how does it empirically fit the real data? I mean, how close is that chart to the reality for 4 channel amps, as for example the amp I described in my previous point? That chart is very interesting and revealing, thanks for such info.

- You said that bi-amping actually depends on the crossover. But you meant on the amp's crossover? And how do I know if the crossover has this function? For example, does JBL's GTO1004 crossover support this?

- Is it possible to do biamping with a 100 rms x 4 amp, whilst almost 100 rms on two channels, while sending 85 rms on the rest two channels?

 

[Ctesibius 10+ year member]

- Let's suppose the amp is 100 rms x 4 @ 4 ohm and its max power is 600 watts. Its manual says that S/N ratio is Xdb and THD + N is Y% at reference rated power into 4 ohms, and I connect the amp to a set of comp. This means that such S/N ratio and THD will be Xdb and Y% respectively when I send exactly all the 100 rms to the 4 channels? Or must I send all the 600 watts of max power the amp has?

Max power is utterly meaningless. When (respectable) companies site "rated power" they are referring to "RMS power" and not max power.

If you connected a 4ohm resistive load to the amplifier and caused the amplifier to output 100w, then the SNR would ideally be Xdb and THD+N would be Y% (assuming the amplifier was accurately rated).

- The second chart from http://www.wjjeeps.com/jl_3004_chart.jpg, you said it was only for example purposes. But how does it empirically fit the real data? I mean, how close is that chart to the reality for 4 channel amps, as for example the amp I described in my previous point? That chart is very interesting and revealing, thanks for such info.

Well, it is the real measured THD+N vs Power for a JL 300/4.....so I would say it's about as empirically real data as you're going to find //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

The general shape of the graph will be fairly consistent across most solid state amplifiers. Power levels and THD+N values will of course vary from amp to amp. The reason I said it was for example purposes was more to indicate that we didn't need to consider what amplifier was measured for that graph. I was using the graph to demonstrate my point. If that makes any sense ?

- You said that bi-amping actually depends on the crossover. But you meant on the amp's crossover? And how do I know if the crossover has this function? For example, does JBL's GTO1004 crossover support this?

No, I meant the component set's passive crossover. Whether or not you can bi-amp the speakers through the passive crossover is going to depend on whether or not the passive crossover accepts separate inputs for the woofer and tweeter.

- Is it possible to do biamping with a 100 rms x 4 amp, whilst almost 100 rms on two channels, while sending 85 rms on the rest two channels?

I don't follow your question. If you're asking if, for example, the front two channels can be made to output less power than the rear two channels....then the answer is yes.