# SVS pb 13 ultra vs group delay vs AS-EQ1



## Thomasdk1405 (Jun 23, 2008)

Hi !
Got the pb 13 ultra (old one) and the AS-EQ1. The stock tune is 20 hz and from what I read on the net - to get good tight bass you need to have the group delay low - some say 20 ms - but a lot say 50 ms for 20 hz. When I check here http://www.avtalk.co.uk/showthread.php?t=19269 it got around 75 ms in 20 hz - but here it's spot on http://www.hometheatershack.com/forums/subwoofer-tests-archived/8150-svs-pb13-ultra-20-hz-tune.html

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.

Could it be my AS-EQ that fixes the group delay so it gets in correct time with the rest of the speakers. Did follow some links to really group delay tech stuff - but that was way over my head 

Anyway - it's the stock tune - so SVS should know what they are doing - also read several tests on the net saying it was fast and tight in stock tune - even one from stereophile !!

I know a lot use the 15 hz and I've also tried that one - but there is something about that 20 hz tune - it's just so clean and sounds so untroubled for the sub.

In short - is group delay in 20 hz audible if it's above 50 ms ?

/Thomas


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## Ed Mullen (Jul 28, 2006)

Thomasdk1405 said:


> Hi !
> Got the pb 13 ultra (old one) and the AS-EQ1. The stock tune is 20 hz and from what I read on the net - to get good tight bass you need to have the group delay low - some say 20 ms - but a lot say 50 ms for 20 hz. When I check here http://www.avtalk.co.uk/showthread.php?t=19269 it got around 75 ms in 20 hz - but here it's spot on http://www.hometheatershack.com/forums/subwoofer-tests-archived/8150-svs-pb13-ultra-20-hz-tune.html
> 
> 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.
> ...


The audibility of GD is an evergreen subject, and in my personal opinion overrated. Your subjective impressions of subwoofer performance will be more affected by frequency response, power response, distortion levels, and audible overdrive artifacts. 

Regardless, it's better to look at GD in terms of cycles and not numerical values. We've been using about 1.5 cycles as a target threshold, and the PB13U in any of the three tunes is far below 1.5 cycles over the entire music bass spectrum. In fact all three tunes have almost the same level of GD down to about 27 Hz, whereupon the two vented tunes start to rise (as is the case with any bass reflex sub approaching vent resonance).

This image shows the GD of the PB13U in all three tunes, and as you can see the two vented tunes just nudge 1.5 cycles at 19 Hz and 16 Hz, respectively, which is so deep as to be a non-issue on music source material (which is predominently >35 Hz). 

http://www.audioholics.com/reviews/...pdelaycomparison800.jpg/image_view_fullscreen


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## GranteedEV (Aug 8, 2010)

Thomasdk1405 said:


> 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_ group delay. 

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


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## Ed Mullen (Jul 28, 2006)

GranteedEV said:


> Either way, have fun and don't fret about group delay! Fret about frequency response


This is really the crux of the biscuit. 

If a crossover network sums flat from an FR/phase/slope standpoint, then there is no GD associated with the final frequency response, even if each filter which comprises the crossover network has GD associated with it. 

If FR changes, then phase changes. And GD is the change in phase with respect to frequency. Anytime a subwoofer exhibits an abrupt change in FR (such as what happens at/near vent resonance and below, particularly if a HPF is also employed), then there will be an associated change in phase and GD.


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## flatfinger (Jul 27, 2011)

I appreciate the time you guys have taken in order to try and give us students here a "a ha" moment .

I have been wading through a ton of professional reviews and so many authors seem to be in the sealed or not sealed camps . The sealed camp guys have some awfully compelling arguments though , and any one who listens intently to every speaker that ever crosses there path ( a disease no doubt !) has had the experience of a bass reflex speaker that has funky overhangs and notes that are weirdly pitched or don't stop when it seems they should've been over already !!!!

Obviously it is true that it's lots easier to f-up a ported design !!!. 
( see http://en.wikipedia.org/wiki/Bass_reflex


As some one who just wants to get it right the first time and can't afford endless iterations ( plus has a wife who is on guard for the "speaker parade effect !) I am afraid of group delay !!! I'm afraid of ringing like this .












So what if the harmonic are ahead and lead the fundamental substantially ? What if the fundamental which lags is on one side of the X-over point and on the other side of a steep transition in the summation zone, the harmonics are ahead ?? 

I listen mostly in the near-field , so the far-field TR 60 room effects can bail anything out !!.


I also know that many a super cube with drivers that do high excursions and mega watt amps are steeply brick walled with a hpf at 20hz , and that this phase rotation doesn't magically go away when the next x-over zone is only a few decades away ....


I am frustrated with what is currently available commercially with subs ; either really big , unwieldy ported boxes that will make what should be soft sounds to powerful and thus are better suited to HT and are to distracting for music , or mini- me- too boxes that have broadpeaks at 40 or 50hz without real deep extension , but that don't take up too much valuable real estate and have a high WAF ..


Even more frustrating is that as a DIY'er , I can't even find SW drivers that don't have the Theil small parameters tweeked towards vented alignments and I can't do the LR transforms or other DSP tricks that could help me to build a "tween-er " that I feel I want that just isn't out there ..

I'm Stuck here:dontknow:


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## flatfinger (Jul 27, 2011)

P.S.


When can we look for the new SB13 ?? Will it still be a cube or maybe rectangular ???


A poster here http://www.hometheatershack.com/forums/svsound/48584-svsound-sb-13-plus-subwoofer-review.html 

said that it was under going a re-design ; that right ??


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## Ed Mullen (Jul 28, 2006)

flatfinger said:


> P.S.
> 
> 
> When can we look for the new SB13 ?? Will it still be a cube or maybe rectangular ???
> ...


The replacement for the SB13 will be virtually the same size. It will have a full-wrap gloss or full-wrap black oak finish vs. the previous side-panels. Front-firing with a metal grille. Will use the Ultra amp Sledge STA-1000D, and a variant of the Ultra 13.5" woofer optimized for sealed applications.


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## flatfinger (Jul 27, 2011)

Ed Mullen said:


> The replacement for the SB13 will be virtually the same size. It will have a full-wrap gloss or full-wrap black oak finish vs. the previous side-panels. Front-firing with a metal grille. Will use the Ultra amp Sledge STA-1000D, and a variant of the Ultra 13.5" woofer optimized for sealed applications.




Any ETA ?? Looking forward to seeing what you guys cook up !!:bigsmile:


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## Ed Mullen (Jul 28, 2006)

flatfinger said:


> Any ETA ?? Looking forward to seeing what you guys cook up !!:bigsmile:


This product will be shipping in the fall of 2012. Don't have the specific month yet - sorry. Watch the website for more details toward the end of the summer.


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