Per Channel PEQ results

[slartibartfast]

Well, maybe I don't know what you don't know.

Even if you don't have per channel EQ you can still make measurements L+sub, R+sub and L+R+sub to compare them.

 

[Wiimer]

Perhaps you are asking me to do that?

Okay,
No PEQ, with Sub






I think your problem is caused by the room or the setting, but I don't know the details.

 

[slartibartfast]

Perhaps you are asking me to do that?

Okay,
No PEQ, with Sub
View attachment 10101
View attachment 10100

View attachment 10102


I think your problem is caused by the room or the setting, but I don't know the details.

I'll try without the sub to see if that makes a difference. Where is your sub positioned?

 

[Wiimer]

I'll try without the sub to see if that makes a difference. Where is your sub positioned?

next room.

Just kidding a little, but I am testing a strange use right now.
I have different systems in room A and B, with a sub in the middle point C.

There is no wall between A and B. Ultra is placed in A , Amp in B, and Pro is connected to the sub in C. A and B share sub C.

 

[Wiimer]

Briefly, the distance between the left and right speakers is 2m and the sub is 2m to the right of the right speaker. The distance from me is about the same (2m).
The sub is placed 0.4m above the floor.

 

[TimWiim]

Judging by the lack of posts I guess nobody knows why a flattish response for (Left+sub) and (Right+sub) produces a peak below the crossover frequency when all speakers are playing. I am not surprised as I am stumped.
I have the sub set to +5dB in the WiiM amp settings to avoid needing any boost at subwoofer frequencies. When I measure all speakers together without any EQ that boost is clearly seen in the frequency response. As seen in the curves above I don't see that boost when measuring (Left+sub) or Right+sub).
Any theory however daft is welcomed .

 

[slartibartfast]

View attachment 10103

Good idea. I will try something similar

 

[slartibartfast]

I've repeated my measurements and starting to think I did something stupid the first time. Maybe I had EQ turned on.



Now I do see the peak in the single speaker measurements. Now the only thing confusing me is the 6dB difference between the response for both speakers and a single speaker at low frequencies but 3dB at high frequencies. Maybe this link explains it.

https://gearspace.com/board/live-sound/793829-why-does-stacking-2-speakers-create-3db-loudness.html

 

[harkpabst]

I've kept very quiet so far (as you might or might have not noticed ) because that first measurement didn't make any sense.

For lower frequencies one would expect ~6 dB gain for two speakers vs. one speaker because these sources have a high correlation at low frequencies. For higher frequencies there is little correlation, so the gain should be ~3 dB. That's exactly what the new measurement shows in my view.

Now, the concept of correlated sources isn't too popular a topic in the Hi-Fi world, but it's well known in acoustics in general and (hopefully) by audio professionals. There are a couple of ways to think about it to get a grasp (unless you already have it). Let me start with a typical and not too technical example.

• Imagine a violinist in a room playing just one note with as constant a level as possible for a human being. We and our microphone are in the same room, at some distance.
  This will create a certain sound pressure level (SPL) in this room and in particular in our listening position. Reflected sound from the walls will contribute to the overall SPL, of course. There will be a slight variation with time but we can measure an average SPL and the deviation from that average will be small, because we are listening to an experienced musician.
• Now, a second violinist will enter the room, playing the exactly same note, standing close to the first violinist.
  Question: Will the resulting sound in our listening position be louder than before?
  Answer: Yes, it will.
  Question: Will it be "twice as loud" as before?
  Answer: No, it won't. While both violinists are playing the same note, the sound pressure wave from both instruments will not be exactly identical at each point in time. Sometimes they will be very similar and mostly in phase, sometimes not so much, but on average the sound will still be louder, of course.
• The violinists went home, but we managed to do a close up mic recording of the single violinist. We put a speaker in the original position of the violin and replay that recording at exactly the same absolute level the violin did create.
  Question: Will the resulting sound in our listening position be as loud as when the single violinist was playing before?
  Answer: Yes, at least mostly. It depends on the directivity of the loudspeaker and the fidelity of our recording, but if both are good, the SPL will be about the same.
• Finally, we place two loudspeakers in the position of the violinists, close to each other, but we feed both the exact same recording of the first violinist. Each loudspeaker on its own will emit the same SPL as before, if only one of them is switched on. But now we switch on both speakers simultaneously.
  Question: Will the resulting sound in our listening position be louder than before?
  Answer: Yes, it will.
  Question: Will the resulting sound be as loud as that played by two violins??
  Answer: It will be louder. Both speakers are reproducing the exactly same sound wave at every point in time. There is (about) 100% correlation between the sources, the signals are coherent.

Now on to the numbers:
How much louder will two violins be than a single one? How much louder will two speakers be than a single speaker?
Coherent signals can be summed up directly, for incoherent sound sources we need to sum up the acoustical power.

Luckily, we don't have to do all that on our own, because the late engineer and Tonmeister Eberhard Sengpiel left us with a whole bunch of useful calculators and fundamental articles on acoustics and recording technology. Luckily, his son Alexander (who is not a sound engineer) is dedicated to preserving his father's legacy, a truly invaluable source of information, so we can still take advantage.

Here's the calculator for coherent signals (correlated sources):

Total dB level adding of coherent correlated sound sources combining decibels or SPL sound pressure level audio logarithmic decibel scale loudspeaker add signal noise levels incoherent noncoherentt - sengpielaudio Sengpiel Berlin

Total dB level adding of correlated coherent sound sources combining decibels or SPL sound pressure level audio logarithmic decibel scale loudspeaker add signal noise levels incoherent noncoherent - Eberhard Sengpiel sengpielaudio

sengpielaudio.com

And here's the calculator for incoherent signals (uncorrelated sources):

Total dB level adding of incoherent or noncoherent uncorrelated sound sources signals combine sound levels two sources resultant level audio logarithmic decibel scale decibels or SPL sound pressure level add signal noise levels noncoherent incoherent

Total dB level adding of uncorrelated incoherent noncoherent sound sources signals combine sound levels two sources resultant level audio logarithmic decibel scale decibels or SPL sound pressure level add signal noise levels incoherent random phase acoustic - Eberhard Sengpiel sengpielaudio

sengpielaudio.com

For those who prefer to not follow these external links immediately: The SPL of two violins is ~3 dB higher than a single one. The SPL of two speakers is ~6 dB higher than a single one.

But wait!

Didn't I just state that the two loudspeakers reproducing exactly the same signal are coherent sources? Shouldn't the SPL be up by 6 dB all over the frequency range then?

No, not really. These two speakers can be seen as correlated only at low frequencies with long wavelengths. At higher frequencies and with both speakers spaced noticeably apart (compared to the wavelength) there are all kinds of different room reflections adding up. Those acoustic signals are no longer perfectly in phase (although the electrical signal is). The result is still louder than a single speaker playing, but due to room reflections with vastly differing run times to the microphone we no longer have two distinct correlated sources.

As a result the total SPL at higher frequencies with both speakers replaying the same signal is different from the SPL at low frequencies.

 

[slartibartfast]

I've kept very quiet so far (as you might or might have not noticed ) because that first measurement didn't make any sense.

For lower frequencies one would expect ~6 dB gain for two speakers vs. one speaker because these sources have a high correlation at low frequencies. For higher frequencies there is little correlation, so the gain should be ~3 dB. That's exactly what the new measurement shows in my view.

Now, the concept of correlated sources isn't too popular a topic in the Hi-Fi world, but it's well known in acoustics in general and (hopefully) by audio professionals. There are a couple of ways to think about it to get a grasp (unless you already have it). Let me start with a typical and not too technical example.

• Imagine a violinist in a room playing just one note with as constant a level as possible for a human being. We and our microphone are in the same room, at some distance.
  This will create a certain sound pressure level (SPL) in this room and in particular in our listening position. Reflected sound from the walls will contribute to the overall SPL, of course. There will be a slight variation with time but we can measure an average SPL and the deviation from that average will be small, because we are listening to an experienced musician.
• Now, a second violinist will enter the room, playing the exactly same note, standing close to the first violinist.
  Question: Will the resulting sound in our listening position be louder than before?
  Answer: Yes, it will.
  Question: Will it be "twice as loud" as before?
  Answer: No, it won't. While both violinists have be playing the same note, the sound pressure wave from both instruments will not be exactly identical at each point in time. Sometimes the will be very similar and mostly in phase, sometimes not so much, but on average the sound will still be louder, of course.
• The violinists went home, but we managed to do a close up mic recording of the single violinist. We put a speaker in the original position of the violin and replay that recording at exactly the same absolute level the violin did create.
  Question: Will the resulting sound in our listening position be as loud as when the single violinist was playing before?
  Answer: Yes, at least mostly. It depends on the directivity of the loudspeaker and the fidelity of our recording, but if both are good, the SPL will be about the same.
• Finally, we place two loudspeakers in the position of the violinists, close to each other, but we feed both the exact same recording of the first violinist. Each loudspeaker on its own will emit the same SPL as before, if only one of them is switched on. But now we switch on both speakers simultaneously.
  Question: Will the resulting sound in our listening position be louder than before?
  Answer: Yes, it will.
  Question: Will the resulting sound be as loud as that played by two violins?
  Answer: Will it be louder or softer than two violinists playing?
  Answer: It will be louder. Both speakers are reproducing the exactly same sound wave at every point in time. There is (about) 100% correlation between the sources, the signals are coherent.

Now on to the numbers.:
How much louder will two violins be than a single one? How much louder will two speakers be than a single speaker?
Coherent signals can be summed up directly, for incoherent sound sources we need to sum up the acoustical power.

Luckily, we don't have to do all that on our own, because the late engineer and Tonmeister Eberhard Sengpiel left us with a whole bunch of useful calculators and fundamental articles on acoustics and recording technology. Luckily, his son Alexander (who is not a sound engineer) is dedicated to preserving his father's legacy, a truely invaluable source of information, so we can still take advantage.

Here's the calculator for coherent signals (correlated sources):

Total dB level adding of coherent correlated sound sources combining decibels or SPL sound pressure level audio logarithmic decibel scale loudspeaker add signal noise levels incoherent noncoherentt - sengpielaudio Sengpiel Berlin

Total dB level adding of correlated coherent sound sources combining decibels or SPL sound pressure level audio logarithmic decibel scale loudspeaker add signal noise levels incoherent noncoherent - Eberhard Sengpiel sengpielaudio

sengpielaudio.com

And here's the calculator for incoherent signals (uncorrelated sources):

Total dB level adding of incoherent or noncoherent uncorrelated sound sources signals combine sound levels two sources resultant level audio logarithmic decibel scale decibels or SPL sound pressure level add signal noise levels noncoherent incoherent

Total dB level adding of uncorrelated incoherent noncoherent sound sources signals combine sound levels two sources resultant level audio logarithmic decibel scale decibels or SPL sound pressure level add signal noise levels incoherent random phase acoustic - Eberhard Sengpiel sengpielaudio

sengpielaudio.com

For those who prefer to not follow these external links immediately: The SPL of two violins is ~3 dB higher than a single one. The SPL of two speakers is ~6 dB higher than a single one.

But wait!

Didn't I just state that the two loudspeakers reproducing exactly the same signal are coherent sources? Shouldn't the SPL be up by 6 dB all over the frequency range then?

No, not really. These two speakers can be seen as corellated only at low frequencies with long wavelengths. At higher frequencies and with both speakers spaced noticeably apart (compared to the wavelength) there are all kinds of different room reflections adding up. Those acoustic signals are no longer perfectly in phase (although the electrical signal is). The result is still louder than a single speaker playing, but due to room reflections with vastly differing run times to the microphone we no longer have two distinct correlated sources.

As a result the total SPL at higher frequencies with both speakers replaying the same signal is different from the SPL at low frequencies.

Your reply was worth waiting for . You probably can't get much better correlation than when combining the same L and R signals in a subwoofer.

 

[noise]

@slartibartfast so in the end, what procedure for calibrating two separate channels with a subwoofer did you find most effective?

 

[slartibartfast]

@slartibartfast so in the end, what procedure for calibrating two separate channels with a subwoofer did you find most effective?

I measured L + sub and R + sub and corrected each one separately. I don't know if that is the best way to do it. I suppose it could result in a bass boost of 3dB if those frequencies are always correlated but many people use target curves with boosted bass anyway.

 

[Smartplug]

I measured L + sub and R + sub and corrected each one separately. I don't know if that is the best way to do it. I suppose it could result in a bass boost of 3dB if those frequencies are always correlated but many people use target curves with boosted bass anyway.

I will only find independent peq once it become part of rc where you just point and click.

 

[Wiimer]

Hi, @harkpabst,

My speakers don't have 3dB of bass boost, is there something wrong with them?

Can you please let me know if you find a possible cause?

Thank you in advance.

 

[slartibartfast]

Hi, @harkpabst,

My speakers don't have 3dB of bass boost, is there something wrong with them?
View attachment 10234
Can you please let me know if you find a possible cause?

Thank you in advance.

Are you using a subwoofer?

 

[Wiimer]

Are you using a subwoofer?

Yes,
Is the problem that the main and sub are controlled by two WiiMs?
I really like the sound, but I could be doing something wrong.

 

[Mr Ee]

I really like the sound

So what's wrong?

 

[Wiimer]

So what's wrong?

It could be better.

 

[slartibartfast]

Yes,
Is the problem that the main and sub are controlled by two WiiMs?
I really like the sound, but I could be doing something wrong.

Maybe the position of the sub makes a difference. I wouldn't worry about it. I'll do some measurements with Sound Analyser Pro when I get a chance. Were you playing pink noise? If so what was the source?

 

[Wiimer]

Maybe the position of the sub makes a difference. I wouldn't worry about it. I'll do some measurements with Sound Analyser Pro when I get a chance. Were you playing pink noise? If so what was the source?

Thanks.
I used WiiM's Room correction audio file.