What is causing Excess Group Delay?

[JStewart]

I have a new sub and placed it where the old sub was. I was comparing measurements of the two when I stumbled upon this bit of mystery:

Here's the room and location info:

Sub 1 is not pictured but is Symmetric to Sub 2

I first looked to see if former sub in same spot had same issue and it does.

Next looked to see if the symmetrically placed front wall left sub has same result and it does:

Finally looked at Sub3 behind and left of MLP and it does not:

Here is the SPL response of the sub in postion 2. There is a dip at the frequency of the Excess GD but what was revealing was looking at more of the direct sound using a frequency dependent window. (I used 4 cycles). The peak of the dip of the FDW spl chart aligns perfectly with the peak of the Excess GD.

I use Dirac room correction and Dirac will mostly mitigate this dip. Despite that I have subjectively preferred using Sub 3 phase aligned with the others and then applying Dirac room correction. Using Sub3 phase aligned (as best as possible) partially fills the dip AND reduces the Excess GD by about 20ms vs Sub (position) 2 alone:

I've read that Group Delay above 1.5 cycles is supposed to be audible, but I've not found anything describing what it sounds like. This would be about 2.7 cycles.

It's clearly related to MLP location within this room relative to the subs in positions 1 and 2, but I'm at a loss to identify it beyond that rudimentary observation.
Am I even looking at this right? Does it even matter?

Help is much appreciated!!

Rew .mdat attached,

 

[Sonnie]

No help here, but I'll follow along. I may want to test my subs.

 

[CAAudiophile]

Not sure of what is the problem ..
And what trying to achieve.

 

[JStewart]

@jtalden , would you mind looking at this? I think what's going on is late arriving sound from the E15 which can be eq'd but then there's just more late arriving sound so it does not sound as good to me as using a second sub that does not have late arriving sound in the area of the E15's excess group delay. Your expertise to confirm or set me straight will be much appreciated.

 

[CAAudiophile]

My first reaction is what frequency is the sub xover sat at?
Whenever the phase response is linear with the respect to the frequency then the group delay is always constant, however according to the photo the 270 HZ is way too high for a sub of this caliper to be sat, since the group delay is the amount of time delay introduced by the system of a group of samples having the same frequency, this 270 HZ delay is independent of the input signal frequency, therefore it is err-respected of the input signal then it will have a different amount of delay.
It seems very likely the delay at ~270 HZ of 70 ms be a soundcard/mic issue.

 

[JStewart]

My first reaction is what frequency is the sub xover sat at?
Whenever the phase response is linear with the respect to the frequency then the group delay is always constant, however according to the photo the 270 HZ is way too high for a sub of this caliper to be sat, since the group delay is the amount of time delay introduced by the system of a group of samples having the same frequency, this 270 HZ delay is independent of the input signal frequency, therefore it is err-respected of the input signal then it will have a different amount of delay.
It seems very likely the delay at ~270 HZ of 70 ms be a soundcard/mic issue.

Thanks! The XO was set to 200 and the amp for the mains off for these measurements. Sweep signal directed to a single front channel. I use an XO of 80Hz when not measuring.

 

[jtalden]

@jtalden , would you mind looking at this? I think what's going on is late arriving sound from the E15 which can be eq'd but then there's just more late arriving sound so it does not sound as good to me as using a second sub that does not have late arriving sound in the area of the E15's excess group delay. Your expertise to confirm or set me straight will be much appreciated.

I'm not sure I understand the main question, but here are some general thoughts in case it helps:

There are room effects for the 3 different positions. There are very differing phase responses for the direct sound of the different 3 SWs. This doesn't necessarily mean a favorable alignment can't be found though.
Are you just looking for a favorable alignment of 3 SWs together prior to IIR PEQ? If so, do you care which SW is in which position? I can see what I would recommend if you like.

The GD result shows the major early room effects that causes a non minimum phase condition at some frequencies. These event cannot be eliminated by IIR PEQ. We can often improve the measured SPL, but the sound will arrive later than the direct sound. I would tend use the spectrogram to determine the delayed time of the sound arrival rather than using the GD, but am not sure how to best represent it as the measurement depends on the smoothing/FDW settings used.

Multiple SWs do often help to improve the overall situation making more the range minimum phase as thus easier to EQ.

I showed and example of this type problem in my system recently. It can be found in this thread.

 

[JStewart]

We can often improve the measured SPL, but the sound will arrive later than the direct sound.

I think that answers the main question and what the charts in post 1 were telling me. Related to that is my observation that adding and a 2nd sub in a different position, aligned with the first, that does not have delayed sound in the same frequencies sounds better to me vs. just applying eq to the sub with the delayed sound. I was wondering if this was because using a second sub provided more direct sound. Or in other words, is delayed sound audible?

This doesn't necessarily mean a favorable alignment can't be found though.
Are you just looking for a favorable alignment of 3 SWs together prior to IIR PEQ? If so, do you care which SW is in which position? I can see what I would recommend if you like.

I appreciate the offer. You've been a great teacher, so with your prior help I'm able to do this and get a good result!!

 

[jtalden]

I think that answers the main question and what the charts in post 1 were telling me. Related to that is my observation that adding and a 2nd sub in a different position, aligned with the first, that does not have delayed sound in the same frequencies sounds better to me vs. just applying eq to the sub with the delayed sound. I was wondering if this was because using a second sub provided more direct sound. Or in other words, is delayed sound audible?

I just choose a favorable setup of the SW group and then apply SW EQ to the group. I don't apply EQ to any individual SW.
I don't know if the initial delay itself is audible. In my situation, I'm guessing it is not as harmful to sound quality as the resulting extra decay time that occurs at the boosted frequency.

 

[JStewart]

I just choose a favorable setup of the SW group and then apply SW EQ to the group. I don't apply EQ to any individual SW.

Yes, that’s the way I do multi subs. Align first then eq the group.

I don't know if the initial delay itself is audible. In my situation, I'm guessing it is not as harmful to sound quality as the resulting extra decay time that occurs at the boosted frequency.

That makes sense. Thanks again.