| | Thomasdk1405
Maybe it's not a big deal - maybe you cannot hear the difference - also tried the different tunes to get the group delay lower - and yes - I can hear changes in bass - but also loose the scary part.
First of all, don't forget that group delay is just one thing changing with a lower tune. The anechoic frequency response is changing, and subsequently the in-room frequency response. That's the primary contributor to our perception of sound below the Shroeder frequency of a given room.
Second, remember that you probably can't even hear 20hz. What's the likelyhood of you hearing group delay at 20hz?
Third, remember that while the vent introduces delayed sound, so too does the ROOM! A wavelength of 20hz might bounce around 5, 6 times before your ears properly register it.
Fourth, remember that the impact of a vent on group delay, is not dissimilar to the impact of a crossover on group delay. you're more likely to hear so-called "group delay" at an 80hz crossover, than you are at a 20hz vent. Do you hear it?
As an addenum to number four, consider the following:
From what i've read, the group delay introduced by a Linkwitz-Riley crossover, is not proven audible as far out as a 96db/oct slope - that's 16th order! Comparitively, the average vent, plus electronic filter, might have group delay equivalent of 4th to 8th order max. Now back to frequency response. All that i've read, says that our ear is mostly only sensitive to group delay below 1khz and above 6khz. That 96db/oct qualifier above, in essense, is mainly of concern between 1khz and 6khz - and i'm sure any speakers you listen to have at least 12db/octave crossover slopes leading to some group delay right between 1khz and 6khz - and more will have 18db or 24db slopes with even more group delay. Don't quote me on this, but i'm also pretty sure the audibility of group delay from 96db/oct slopes exists only in anechoic listening (IE anechoic chamber or headphones). Again, rooms impact things significantly.
80hz is already around 4 octaves below 1.2khz, and 20hz is another 2 octaves lower. That's roughly six octaves below the relative cutoff frequency for the audibility of extreme
Personally, I'm not one to deny anyone's personal experience, but I'm basically on the same page as Ed Mullen when I say that there's a lot of factors that dominate our hearing at these frequencies and group delay (and subsequently ported/vented) is far down on the docket to the point that it's just splitting hairs.
As far as tuning, I personally prefer lower tuning frequencies. What little headroom /flat response they may lose between 20hz-30hz, is often made up by the room, along with deeper extention. Most of these subs have excess headroom as it is.
In my opinion the best thing to do for best sound quality isn't to focus on output/group delay/EQ from one sub, but to spread out the response with a second, even four! Not only does it give you less dips at the listening position, but don't forget your body in a sense represents many different listening positions because we feel bass as much as we hear it. Compound that with the wider sweet spot...so go buy three more subs!!!
Generally if you've got adequate headroom below 30hz, you can even get away with lesser subs as long as they can match the large "focal point" sub above 30hz. The modal region is roughly 40hz to 300hz (though room dependant of course) so you only really need one sub below 30hz assuming it's loud enough for you. The biggest advantage of multiple subs is in the modal region so you could even get away with a less deep-extending second sub, especially thanks to the great limiting behavior on the DSP SVS subs.
Either way, have fun and don't fret about group delay! Fret about frequency response