It appears to be a similar distance from the listening position as are the main speakers.
How did you determine the group delay for the sub and (since you haven’t compensated for it acoustically using the sub’s position) how did you include that delay in the feed to the main speakers?
If you haven’t done this then the sub won’t be time aligned and all high/low level arguments are moot as the sub’s crossover isn’t properly integrated anyway!
The best results I’ve had with my N-Sub were with the high level connection from the speakers. I also tried a Naim supplied long DIN to RCA lead on the low level input, and it didn’t sound quite as good, which is what Naim suggest, but the difference was quite small.
Same with my SN2 and REL T5 - connected at amp end and no issues at all.
Hi Xanthe
If you dont mind - can i push the envelope ( for me ) further
a. The Main speakers themselves are 1/5 out into the room and 1/5 from the side walls -
i saw a youtube video on such a setting and tried this for kicks… and the fonts are sounding very nice indeed…
The room is about 20 ft long by 12 ft wide ( with 1 side…right speaker side… fully open )
b. The sub is placed about 2 inches ahead of the speaker front baffle - i haven’t determined this by any scientific way - save to say its the max i can do given my constraints.
c. I am yet to determine if i can make do with the front speakers pushed back by 4 to 6 inches so that will make the subwoofer front baffle about 6 inches from the main speakers front baffle.
Question …
a. Whats the method to calculate group delay and therefore extrapolate the inches by which the sub should be ahead of the main speakers ?
Best regards
mpw
It’s difficult to calculate the group delay (it depends on the crossover filter, the amp and the mechanical properties of the speaker cone and motor), so unless you already have the figures, it’s generally better to measure it.
Typically for subs, it’ll be in the region of 2-4ms for small subs and 3 to 7ms for larger ones like yours.
The easiest way to get the time alignment right is to look for discontinuities in the minimum phase plot of a frequency sweep. It can also be done from an impulse plot, but that’s harder to interpret; it is however more accurate and can be very useful for fine tuning and/or as a final check.
is a group delay of 10 micro secs discernible to the ear - especially for freq below 60 Hz ?
In theory if i translate a group delay of 7 micro secs into wavelength…i get 2.4 mm ??
and my faitalpro 18XL1800 has 233 mm dist from the baffle to the speaker coil / magnet / cone end
The Morel MW164 midbass driver on my front speakers is 65 mm comparatively…
So the difference in cone locations = 233-65 mm = 168 mm ie 6.61 inches
So this 6.61 inches must be added to group delay in inches to get ideal subwoofer positioning relative to the fronts ?
can you cross check me please ?
Yes at higher frequency, but not at that low a frequency.
These factors are only one small element in the group delay (and so small as to be almost irrelevant).
You still need to measure it acoustically.
Thank you @Xanthe
Most helpful 
Am now using low level inputs and for my satisfaction …the sub is ahead by 6.6 niches
am flying on a biplane…no instruments…and wind in my hair… 
AAGH your top wing has broken off!
If you’ve got a parachute, bale out now!
It’s incredibly difficult to set-up a sub by ear alone.
The best way to do it is to use an instrumentation mic and something like REW to establish physical position and crossover settings. You may also wish to use a DSP to remove the room resonance peaks from the sub’s response (in your case you’ll have quite a big peak in the response at 26.4Hz - corresponding to 20ft, and may have others).
That’s the plan…once things are safer again…
I think it’s the cheapest way to further integrate what I already have…
Indeed, and it’s a solution that can work really well.
I don’t really get this. If you’ve not got enough bass end for your liking, doesn’t that just mean you’re running either an under-powered amp or your speakers aren’t up to it, or both? Or is getting a sub just a cheaper way to your required bass level than upgrading either or both of those options?
Please enlighten me… 
That’s one strong reason… 
Even if I were to get a floorstander with a powerful amp…that presents it’s challenges in terms of the lower octaves…
It’s not the bass freq in Hz alone but the Scale of the bass where I find the 18 inch sub helpful as compared to a 2.5 way common floorstander with 6 inch compromised midbass driver.
Hi @MikeD - a topical point (see the concurrent ‘Nap 500 dr speakers’ thread) which, potentially, appears to highlight this aspect, with the cure of installing subs flagged as a solution.
Intuitively, installing a sub(s) when an amp is struggling with the current demand of a speaker (in the bass domain) doesn’t seem the correct solution to me. Even if the feed for the subs is taken from (say) a Naim pre-amp (which isn’t recommended for all the reasons stated), it strikes me the speaker when delving down in to the bass isn’t going to deliver what’s expected as to timing, quality et al (flabby?), such that marrying subs to it doesn’t seem a simple exercise to perform.
To me, it’s just created something akin to an active system, with a headache around settings/configuration - which is a tad perverse. And as @Xanthe outlines, picking up a feed from the speaker terminals, when the amp is under stress from the load its facing, doesn’t seem logical.
I can understand the application of subs to boost bass output (as @anon93526344 outlines) but curing the performance limitations of a speaker (caused by the amp) which is designed to deliver out suitable bass performance in the first instance seems a tad strange to me.
Or am I mis-understanding what subs can be used for in compensating in such circumstances?
( am unable to get the large font down - so excuse me please )
Let me paste a few words from the Troelsgravesen website and maybe that will be helpful in having a view on things.
====================================================
Size matters
This may seem an odd place to start, but nevertheless: You must have an idea about what size speaker you’re aiming at. What is the size of your room and do you have a wife who thinks loudspeakers are ugly and should be stuck away on shelves in upper corners of your living room? You need to address these issues first. No point in dreaming about a 100 liter floor-standers if it means divorce.
What I have experienced from mails coming in is that people may have chosen a (small) low-efficiency speaker and “compensated” by buying a powerful amp, and they find out the speaker really can’t play that loud all the same…
*Well, it doesn’t work that way. *
*We must look at the size of the main driver, and if we’re dealing with 55-75 square centimeters of membrane area (4" drivers) it simply cannot move a lot of air.
You may have heard a speaker with a 10-12" bass driver and we’re talking 300-500 cm^2 membrane area.
Up to ten times more radiating area compared to a small mini-mini!*
Even a 6" driver, typically making some 130-155 cm^2, won’t move a lot of air in a vented or closed enclosure. A high-efficiency 6" in a huge rear-loaded horn may be another story, but few people build these things.
*Generally people have too high expectations from their diy projects and buying high-quality small drivers won’t compensate for the lack of radiating area. *
- size, efficiency and bass extension
Back to top
Efficiency is inversely proportional to the moving mass and - proportional to the square of the product of cone area and BL.
No matter what we do, we have to balance these three basic parameters, size, efficiency and low-end extension, the trade-offs in loudspeaker building.
If size is not a limiting factor , we can get really low bass and very high efficiency.
If size is restricted , we have to sacrifice efficiency - or low-end extension .
A 12" driver usually has a cone area of a little more than 500 cm^2. This is more than 3 times a ScanSpeak 18W/8531G00 driver!
All this has to be viewed in relation to your room size…
In my case
a. I have a large room
20 ft by 12 ft wide and add 8 ft more open area on the right speaker size
b
I dont think a floorstander with a 6 + 6 + 1 combo will fill my room and in someways i feel better to have a 2 way stand-mount tapering off at 55 Hz and to let the subwoofer do the bass duties…
More drivers can mean more complicated crossovers as well and that implies compromised driver efficiency in case of a 2.5 way.
A large 3 way speaker with a 12 + 6 + 1 is another matter but at this point in time i am in the 2.1 stereo journey…
An 18 inch subwoofer brings scale to the party and not just point to point bass.
Hi @anon93526344 - in your case, I can see the benefits of a sub(s) in complementing the relatively narrow bass-range stand-mounts in the overall system set-up - and the narrative you’ve cut in is interesting stuff. When it comes to bass extension, there’s no substitute for size!
What I’m trying to untangle though, is (say) you had a big pair of floor-standers, with big bass drivers but your amp couldn’t deliver 100% of what such big bass drivers demand in terms of current to optimise bass performance, would you then look to sub(s) as a potential solution?
I have been using subwoofer for a few years…
I started off with a 10 incher then replaced that with an 18 inch.
Present amp is a SN2
My other amp is a 50W Naim Nait 5i-2 …which is sleeping…sometimes I take it for a spin and the sub-woofer fills in the low end very well thru the high level connections as the Nait 5i-2 doesn’t have
Sub Out.
What you refer to in your last para is a possibility…
Of course… depending on cost and other occupants in the house etc etc…
Coming to floorstander most of the commonly used ones have either 5.25 inch or 6.5 inch or 8 inch drivers…
A subwoofer can add to the total radiating area…if you take that view.
And radiating area is sound…LF wise.
Other community members will like to share their thoughts as well…there are many experienced folks here…
I’ve just brought a Totem Storm sub to go in my media room, running of a Nova and paired with Totem Hawks, I’m mainly looking a better lower end for Blu-ray movies.
For connections, I could use the RCA sub out from the Nova to the sub. But the sub will also take a speaker cable connection from the Nova and then take speaker outputs to the individual speakers - I have a spare pair of NAC A5, so could do this and my dealer recommended it - is it the better approach?
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