Audibility of group delay?

[Rullknufs]

Originally Posted by tuxedocivic

Yes



Yes, up to 7.5ms iirc.

Would 7.5ms be enough to make a big improvement? On a scale from 1 to 10, how difficult is it to time adjust?

[tuxedocivic]

It should be enough in a normal room.

1 being easy. 0.25. You just type it in with all the other settings. In 0.02ms intervals. All the work will be the measuring to determine the amount. If you leave it hooked up to your computer, do what Waltersys was saying by reversing the phase on the woofer. Adjust the delay (start with 1ms intervals and iterate) until the null is deep. That's the delay you should use. Save it to the minidsp and flip the polarity back. You can even reverse the phase on the mini I think...? Not sure about that though.

[Rullknufs]

That's cool...
But regarding cabinet options, what do you suggest I use? I'm not sure if I will be able to use the boosted bottom response that the ported box gives compared to a closed one. I mean, my room is about 16sqm. Should I go with a sealed box and maybe use some LT EQ (can miniDSP do that?) and boost bottom end if I feel the need?

[tuxedocivic]

The minidsp can do LT EQ. If you have the amplifier power.

[Rullknufs]

I can adapt.
So, do you think a smaller sealed box would be a better option than a larger vented box?

[PeteMcK]

I'm almost scared to ask, but what does a 'Gaussian aperature' look like????

[Boscoe]

Originally Posted by toenail

I'm working on a ported sub enclosure that has a group delay peak of 32.4ms @ 20.1 hz. Is this considered excessive? Transfer function phase peaks at 179.2* @ 22.0 hz.

I've been reading some interesting articles that suggest the phase and the dalay graphs are simply two different ways to show the same characteristic of output. How audidble is this?

If I understand phase correctly, being close to 180* out of phase at 22 hz means that waveform of frequencies in that range will arrive at a later time than those at say 30* out of phase. This would mean that my perception of those frequencies would be that they were played at a lower db level, though in reality they're not. I'm wondering, could I could actually hear the difference, and what the threshold is for acceptibility of group delay/phase? Bass would sound sloppy/slow due to different frequencies arriving at different times?

Any thoughts appreciated.

The low the frequency the more GD you can get away with. The sound of the bass won't change just the time it gets to you and your ears aren't very sensitive to changes in bass distortion wise. Personally I'm a bit of a perfectionist I don't like to see GD rise above 50ms at 20hz. Slopes bass generally means poor quality drivers with low power amps and poorly tuned ported enclosures. If you use a passive crossover it doesn't matter how good you kit is you've already lost any hope what so ever of good bass reproduction. The passive crossover is the worst thing in hifi that has ever existed, along with tubes...

[weltersys]

Originally Posted by Rullknufs

I can adapt.
So, do you think a smaller sealed box would be a better option than a larger vented box?

Cabinet decisions should be made with the sound pressure level level desired, BR,TH,and BP type boxes all have a big level advantage over sealed subs.

Since you are limited to around 7.5ms of time correction, cabinet designs showing more group delay at the crossover point would not be a good choice.

The TH 200 sq shown below, a long path tapped horn, requires a bit more than 7.5ms to align a sealed top cabinet.

The Sammi is a ported cabinet using a pair of $5 speakers, it would require little or no delay to align with a sealed top cabinet.

The 7506 is a Sony 7506 headphone, used worldwide in studios and soundstages. It has fairly flat response, where it is flat the phase response is also flat. Unfortunately for the screen shot below, most of its response happens to fall at about -180 degrees, so much of the trace ends up not being visible, it would be right at the top or bottom of the display.

Phase and frequency response are reciprocal, if DSP is applied to flatten the frequency response, it also flattens the phase response. If a PEQ setting were applied to correct the 7506 broad boost centered at 60 Hz, and the dip at 250, it’s phase response would also flatten out.
Same with the Sammi problem at 475 Hz.

The TH response above 250 would require far too many filters to correct, but sounds quite good in it’s intended pass band of 30 to 100 Hz. It would require sealed top cabinets to be delayed by around 9ms optimally.

The difference between 7.5ms and 9 is within 1/4 wavelength at 100 Hz, so your DSP would still work fine for that large tapped horn, but many home theater type TH designet to work down to 16 Hz would require twice that delay time to be integrated perfectly.

That said, there are many proponents using several subs all around the room without any time alignment to even out room response, things can subjectively sound good even though that type of set up is terrible when phase or group delay is considered.

In a small room, getting too picky about phase/group delay is akin to complaining about a kid with a squirtgun shooting at you in a rainstorm.

Art

[Ron E]

Originally Posted by PeteMcK

I'm almost scared to ask, but what does a 'Gaussian aperature' look like????

Transmission curve (cross section) is a gaussian curve,
It holds for optics as well, but I don't think it is all that practical for acoustics in air except in limited frequency ranges - like Keele's CBT arrays.

[Soundminded]

Group delay by itself is inaudible. A recording is a group delay. The issue becomes important when the group delay of two drivers operating at the same frequency at the same time have different group delays. Their differences will cause an interference pattern in space where at some point at some frequencies they will add in phase to combine for a 3db gain in amplitude and at others will cancel completely causing a net amplitude of zero. This is the theory behind the so called "time aligned" speaker system, matching group delays between drivers. However, unless the drivers also happen to be coaxial there will be similar cancellation and reinforcements at various points in space. This is a direct consequence of classical wave mechanics analysis. If you want a speaker system to be phase coherent it must be time aligned at the crossover region and coaxial. Generally the tweeter has a shorter group delay than a midrange, a midrange shorter than a woofer. This is due to differences in inertial mass. If the drivers are coaxial, one way to align them in time is to apply the correct digital time delays to each driver using active crossovers and multiamplification and then sit on the coincident axis of the speakers. This will not cancel out effects due to room reflections however. The good news is that it's all probably very unimportant. There are far more serious issues related to accurate sound reproduction. In the 1970s it was one of the fads du jour, today it's been replaced by newer more lucrative fads in this industry.