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just1n

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Hey community,

I’m resetting my strategy for deploying multiple subwoofers in my setup. Information sources include fellow members' testing (@Nuyes I measured 10 Subwoofers) and spreadsheets (@sweetchaos Subwoofer Comparison). Also using Audioholics, Buttersworth, and Erin’s to identify those in my price and output ranges. Nuyes testing brought to my attention group delay and how varied it can be below 80hz. I really don't know anything about it and will certainly not be attempting to explain its significance. But it got me wondering at what point would measurements show "this is now a problem"? I have (tried) to understand posts and papers group delay that have been linked on other threads and I simply confidence in drawing my own conclusions. I did see one post on DIYAudio stating the ‘ideal’ is sub-one cycle at a given frequency. If true, the ideal group delays should measure less than:

20hz — 50ms
30hz — 33.33ms
40hz — 25ms
50hz — 20ms
60hz — 16.67ms
70hz — 14.29
80hz — 12.5ms

Ok, this is may not be the best rule of thumb and responders may quickly call out a 'general rule' error. If so, let's find something agreed upon to the best of our ability. Right now it's what I have found that I can run with. I want to learn more.

So why am I asking for help with this subject and possibly making knowledgable people on the forum tired of beating a dead horse? I want to sell my current subwoofer to find a more affordable unit to be able to scale up (2-4 subs). My current SVS 3000 micro nails the form factor, but there are less expensive options - namely the Kali WS-6.2. If I could afford them, I would be looking at the Paradigm MilleniaSub, Sigberg Inkognito, or continue with more 3000 micros. I'm not looking for crazy output or sub-20hz output. I just want to get the most for my money and be done with it with as much peace of mind as I can knowing I made the most educated decision I could.

The Kali looks viable. But what about group delay for a ported subwoofer like this one? Looks like there is a direct correlation between ported subwoofers and higher group delays. I don't mind the look of the WS-6.2 because my intention is to conceal them. Output looks respectable based on Erin's video review I stumbled upon through thread Anyone Tried Kali Audio WS-6.2 Subwoofer?. True it may not pass CEA-2010 below 25hz, and I'm ok with that.

20hz ≈ 45ms
30hz ≈ 42ms
40hz ≈ 26ms
50hz ≈ 16ms
60hz ≈ 12ms
70hz ≈ 10ms
80hz ≈ 9ms

Good, you just proved your own point, Justin. The Kali should fit the bill, so why post this at all? Glad you asked...

Presuming one cycle is the ideal, at what point would the group delay become audibly unacceptable? This isn't meant to put anything to bed, but to take my next subwoofer search and have a thread people can look back to in layman's terms, see how we got there, and what is reasonable and within an acceptable margin. Go easy on me.

Thanks!
 
Humans are not very sensitive to group delays at low frequency.

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Thank you.

Playing devil’s advocate, why would one measure group delay for subwoofers? What is to gain from them other than the act of measuring them?
Don't know. Group delay is not one of the tests in ANSI/CTA-2010-C, so I'd consider it as an indicator of its importance. Probably because when you take a frequency response measurement the software will automatically calculate it, so there is no extra effort required.
 
The room has massive influence on group delay. Therefor the room and sub placement should be considered jointly with the sub. EQ for a flat or slowly sloping down in-room response, and the group delay will be good as well.
 
At the moment, the evidence for audible group delay thresholds for bass frequencies is lacking. The only good study seems to be the Liski/Valimaki study linked to by @NTK. However, note that the study was performed with headphones and contrived test signals, with group delay simulated by DSP.

As @voodooless says:

The room has massive influence on group delay. Therefor the room and sub placement should be considered jointly with the sub. EQ for a flat or slowly sloping down in-room response, and the group delay will be good as well.

As Toole points out in Ch 4.8.2. of his book, your music has gone through multiple minimum-phase high-pass filters before it even reaches you. Nearly every part of the music recording chain has a minimum-phase high-pass filter, from the microphone to the mixing desk, and so on. Some modern consoles have linear-phase, but he still has a point. He is not aware of anybody who has attempted to calculate the cumulative phase shift, but it must be "enormous". He then asks the question - if music has already been corrupted by so much low-frequency phase shift, does it make sense to correct the last part of the chain - the loudspeaker and the listening room?

Unfortunately, Toole does not attempt to answer the question. The question is not whether group delay is audible, it is how much group delay is audible.

Furthermore, there is conjecture that the listening room itself affects the audible group delay threshold. To me, this makes sense, given that bass wavelengths are longer than most listening rooms. I would think that smaller listening rooms would have longer audible thresholds further up the frequency range. I don't think anybody has done a study on this.
 
The question is not about the overall group delay with multiple subs.

The subwoofers need to be time-aligned amongst each to perfom as one unit for best in-room frequency response. And then, this unit has to be phase-aligned with the main signal (as crossover shifts phase, mere time-alignment according to the distance is not enough).

This will normally be done by an AVR. You can do that manually by ear or using tools such as REW.

By ear, the accuracy is less than 0.5 ms at 80 Hz regarding what would be a step in group delay. It can be tested with music. The setting with the loudest and most accurate bass is the right one.

So what is audible is not the group delay itself but the cancellation of bass due comb filtering.

Comb filtering is also a problem in mixing. Many movies and also 5.1 music lack punch if the LFE channel is not shifted by up to 16 ms by the AVR to regain phase control. My Pioneer does that and the difference is significant.

Room influence on GD has already been listed by the others above.
 
So what is audible is not the group delay itself but the cancellation of bass due comb filtering.
It’s just the other side of the same coin. Any minimum-phase frequency response deviation will cause group delay. The higher the Q, the higher the group delay.
 
@just1n , the subwoofer's own group delay at the lower end is usually not a problem because the frequencies are very low and we a re not that sensitive in that range nore does it usually contain musical elements with strong timing relevance.

But the elephant in the room is the integration of the sub(s) with the main speakers. This happens in the all-important 80Hz range of frequencies. Having a high group delay there is much more critical than at 30Hz or so. Even the best-case for integration, taking only into account the group delay of the crossover, might already create a feeling of the bass lagging behind (and a timbre shift, from the altered phase relationship between fundamental and even order harmonics of an instrument).
Add in the complexity of room modes and sub-optimal placement and the group delays quickly go crazy.

You can use the test signals I'm linking to in my signature to check integration and overall balance, both for level and timing aspects.
 
@just1n , the subwoofer's own group delay at the lower end is usually not a problem because the frequencies are very low and we a re not that sensitive in that range nore does it usually contain musical elements with strong timing relevance.

But the elephant in the room is the integration of the sub(s) with the main speakers. This happens in the all-important 80Hz range of frequencies. Having a high group delay there is much more critical than at 30Hz or so. Even the best-case for integration, taking only into account the group delay of the crossover, might already create a feeling of the bass lagging behind (and a timbre shift, from the altered phase relationship between fundamental and even order harmonics of an instrument).
Add in the complexity of room modes and sub-optimal placement and the group delays quickly go crazy.

You can use the test signals I'm linking to in my signature to check integration and overall balance, both for level and timing aspects.
This is the kind of feedback that is useful. Awesome.

At and above 80hz (looking at you Dirac ART of it ever comes out for Denon AVRs). With that said, I hope Dirac and other room correction softwares address the 80hz transition point.
 
Would somebody more knowledgeable than myself be able to explain how a Dirac enabled AVR, with a limited number of IIR biquads and 1024 FIR taps, be able to address group delay at 80Hz?
 
If subs are later - simply delay mains. ?
Room-induced deviations are usually larger and more chaotic. And not always minimal phase.

The problem is that group delay is not constant in minimum-phase systems, it usually rises towards the lower frequencies. Delaying the mains would impose a constant group delay on the mains, which would do nothing to address the varying group delay issue. So this is what I do not understand - you need a heck of a lot of FIR filter taps to tackle group delay at 80Hz. How is it possible to do it with so few biquads and so few FIR taps?
 
if music has already been corrupted by so much low-frequency phase shift, does it make sense to correct the last part of the chain - the loudspeaker and the listening room?
Just for fun, the on board DAC/ADC red and over a dozen times the same blue:
1737354669775.png

1737354940923.png

I wonder what happens to the actual recordings.
 
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So this is what I do not understand - you need a heck of a lot of FIR filter taps to tackle group delay at 80Hz. How is it possible to do it with so few biquads and so few FIR taps?
If you remove the high-Q issues with sub-placement, you do not need that many taps. The taps are more about resolution, and you can go by with not that many of them for group delay because it's not that critical anyway. Ballpark is good enough.
 
Просто ради интереса, встроенный контур ЦАП\АЦП красный и более дюжины раз то же самое синее:
View attachment 422510
View attachment 422511
Интересно, что происходит с самими записями.
Hi . Please repost in English and I will delete this one . Thanks
 
Here are my 2 cents:

- from most of what I have read, ideally keep GD under 1 cycle, and definitely no more than 2 cycles in the 10-100Hz range
- most manufactured subs don't have major GD issues unless they have very unique or unusual configurations. DIY non sealed subs can be a different story
- GD in and of itself is not usually a problem, but you do want to avoid localized and rapid changes in GD
- low frequencies take some time to "ramp up" to their peak levels in a room (unless using Waveforming or Dual Bass Array techniques) which manifests itself as a delay - in a normal HT room this can be as much as 50-100ms or more as the sound needs to bounce around the room for a few cycles and resonate - so this will tend to dominate over the sub's own GD behaviour in the 50+ Hz range - you can see this clearly in GD plots in REW when you compare the as measured GD to the Excess GD plots. That said, these delays still don't seem to be all that troublesome audibly if PEQ'd appropriately and ideally with multiple subs
- IMO the most important thing to be aware of WRT GD is that each of your speakers or multi-subwoofers has similar GD performance, otherwise you will get inconsistent summation of the subwoofers or speakers when they play together
- as someone mentioned above, ideally you want your sub's GD behaviour to be similar to your Mains GD behaviour in the crossover region (typically between 40 and 160Hz)
- GD can be manipulated with All Pass filters with some expertise and the right tools, however inappropriate use of All Pass Filters using MiniDSP can also introduce audible GD issues if not done carefully - a topic that has been discussed a few times in the MSO thread. But note you cannot reduce Delay in a device, you can only add Delay
 
Humans are not very sensitive to group delays at low frequency.
The test you refer was done with headphones so if was incompetent for evaluating all effects and significance of group delay at L.F.

1737474714167.png
 
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