Sub Experts, please speak up. (1 Viewer)

[Richard Burzynski]

I've posted this question, in different forms, but I haven't gotten many replies, so I'm re-wording to be very specific. Hopefully, the resident SVS sub experts will chime in.
Let's say a guy is putting together a system (usage 50% ht, 50% music). He already has more than 1 sub (let's say 2), and none of his speakers are full range. He is playing with 2 hook up options:
(a) Bass in mono. Processor crossover fixed @ 90hz. Set all speakers to small and use lfe out (split to both subs).
(b) Bass in stereo. Set main speakers to large and sub to no. Using external crossover (hooked to r&l main signals)allows for subs to receive stereo bass.
In both options above, *ALL* bass will be directed to the 2 subs. The bass includes all hz info below the crossover point *as well as* the LFE channel. There will be no other subs, just these 2.
Placement of subs may not be optimal, but due to room constraints, the subs will reside where room permits: sub1 to left of left main speaker, and sub2 to right of right main speaker.
Once hooked up, the bass will be EQ'd to flatten out room response as much as possible.
Questions:
(1) Many say that bass is "omni-directional". Meaning, below a certain frequency, you can't/shouldn't be able to detect (from your (the main) seating position) where the bass is coming from. Sounds reasonable to me so far. First, let's define this magical number. Is it 100hz, 90hz, 80hz, 63.479hz? What do you think it is?
(2) Taking into consideration the crossover frequency used in the system, is it worth the trouble to hook up the subs in stereo? Or is mono bass just as good? One would think that as the crossover gets higher and higher, the bass would become more directional?
*** Overall goal here ***
Bass (with 2 subs), keep it mono or hook it up in stereo?
Thanks guys & gals (if we have any here).
Rich B.

 

[ThomasW]

(2) Taking into consideration the crossover frequency used in the system, is it worth the trouble to hook up the subs in stereo? Or is mono bass just as good? One would think that as the crossover gets higher and higher, the bass would become more directional?

Sub placement is just as important as mono vs stereo IMHO. Bass per say doesn't become more directional as the XO frequency is increased. But it's easier to locate the sub, and if it's location is asymetrical with regard to the mains, the potential for smearing the stereo image increases with higher XO points. There have been some studies of the amount of stereo info exists in LFE. As a result some swear that it's extremely important to have stereo subs.
However since you preface your questions with info about 2 subs in fixed positions, with a fixed mono XO point; the whole thing seems to be a theoretical exercise. But as always it might might be a good idea to hook up your system in both stereo (if possible) and mono and make the desision which you like better.

 

[Roger Clark]

Given the following:
1) You can't put the subs in the same corner.
2) The subs will be right next to the mains.
3) The crossover will be fixed at 90hz.
4) The subs are of similar capability.
I'd go with stereo subs.
1) The bass begins to be directional around 80hz (some say lower, some say higher).
2) You may have phase issues with the subs so far apart with a mono signal (you may have phase issues anyway since there may be little or no difference in the bass signal between the channels).
Or... you could sell both subs and get one more capable unit.
Of course this is just what I would do.
Roger

 

[Richard Burzynski]

Thanks for the replies.
Thomas:
"with a fixed mono XO point; the whole thing seems to be a theoretical exercise."
If I tell the processor no sub and large mains, and then include a stereo crossover in the audio chain, I will be able to achieve stereo bass, not mono.
Roger:
"Given the following:
3) The crossover will be fixed at 90hz."
If I go with an external stereo crossover (for the r&l main signals), I may (depending on the crossover's features) be able to adjust the crossover to any frequency I see fit. The mains I'm using are rated down to 45hz by the mfg FWIW.
Rich B.

 

[ThomasW]

Richard
Sorry misunderstood about the mono/stereo set up. Try it both ways.
My feeling is that the mains should have strong output to one octave below the XO point to avoid a hole in the response. So if your mains have strong output to 45Hz then use 90Hz as the XO point. If they don't then go higher, 100Hz or so. You can almost always get away using a higher XO point with stereo subs if their placement is symetrical to the mains

 

[Bob McElfresh]

Richard: My understanding (which is different from expert knowledge) is that for sounds below 200-300 hz, you are hearing a lot of wall-reflections rather than direct sounds from the subs.
And the fact that the human ear is most sensitive in the upper-mid range of sound frequencies (I think this is around 12,000 hz), it's no suprise that you cannot locate a sound source below 120 hz.
So I think this is where the concept "...you should not be able to tell where the sub is located" comes from.
Dual Subs: I thought I remember the SVS guys talking about dual-subs. Putting them in the same corner is ideal. But if you have to split them apart, play with the phase control on one of them to get them to work together.
Hope this helps.