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Old 3rd December 2004, 04:31 AM   #1
rs1026 is offline rs1026  India
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Default Advantages of stereo sub?

Can anyone please let me know the advantages of a stereo sub woofer over a single sub woofer? Is stereo sub recomended over single sub?

I think using a stereo sub is problematic since both of the subs have to be matched and also there may be some phase problems.Is this true?
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Old 3rd December 2004, 01:03 PM   #2
Nuuk is offline Nuuk  United Kingdom
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It depends where you cross over the sub(s) to the main speakers.

If it is under 100 Hz you may not be able to tell if you have one sub or two, or where they are placed.

However, I prefer two as it keeps both channels 'apart' as I believe they are meant to be.

Why should building two identical subs be any more difficult than building two identical loudspeakers?

But this thread may be better off in the Subwoofers section!
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Old 3rd December 2004, 01:23 PM   #3
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Quote:
If it is under 100 Hz
....it will still make a lot of sound over 100hz......

two subs are optimal.
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Old 3rd December 2004, 01:45 PM   #4
AGGEMAM is offline AGGEMAM  Denmark
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Quote:
Originally posted by tbla
two subs are optimal.
When going into the matter of optimability multible smaller subs are preferably say six to eight. Each must function as a sub, ie produce no sound over 92 Hz*, and each must be placed carefully to ensure even triggering of the room resosnances.

For simplicity use two subs one near the left (or right) speaker against the back wall distanced approximately 3/8 of the total length of back wall to the side wall, and the other placed against the side wall distanced approximately 1/4 of the total length of the side wall to the back wall.

*note: no sound in the bass registrer means a signal that is 18 dB lower than the primary signal.
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Old 3rd December 2004, 02:27 PM   #5
tiroth is offline tiroth  United States
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http://www.harman.com/wp/index.jsp?articleId=1003
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Old 3rd December 2004, 06:41 PM   #6
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with stereo subs, you can create Acoustic intereference beats in the bass region. I dont know that acoustic interference beats sound any different than electronic ones however. I dont see any advantage in having two seperate subs other than possibly a better control over room modes, although I'm not even sure if you get any advantage there. Bottom line is, you cant localize anything below ~100hz. Your ears mostly use inter aural intensity differences to localize sound. The best analogy I've heard to describe how bass waves "wrap" around objects goes back to ripples in a lake. If you are standing on a bridge that has large pillars going into the water and you pay close attention to how the waves in the water are effected by the pillar you will notice the small ripples(which have small wavelengths) are reflected when they hit the pillar, but the large waves(with long wavelengths) travel around the pillar and continue on the other side. The same thing happens with sound, high frequencys are reflected by things that low frequencys pass around. When you relate this to your head, the high frequencys will have intensity differences between your ears due to the non uniformity of the wave passing by your head. Bass frequencys with long wavelengths will wrap right around your head giving the same intensity at both ears. Subwoofers can not be localized by the sound they emit in their frequency range, BUT some subwoofers emit enough sound out of their frequency range to be localized. This can be caused by rattles in the enclosure, air leaks(whistling), or use of a low order crossover. A properly designed and built subwoofer will not have those problems.
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Old 3rd December 2004, 07:15 PM   #7
Variac is offline Variac  United States
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Quote:
BUT some subwoofers emit enough sound out of their frequency range to be localized
I suspect that some driver cones resonate at multiples of the actual frequency.
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Old 3rd December 2004, 07:45 PM   #8
AGGEMAM is offline AGGEMAM  Denmark
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While the Harman white paper is interesting and correct in it's conclusions it premises the use of symetrically placed subwoofers. And while this is natural from a logical point of view symetrically placement only enhanced variations achieved when useing multible subwoofers. Hence I dismiss it as inaccurate.

If you place two subs as described by me above and fiddle around with the optimum placement, I assure you that you will get a better result than any number of symetrically placed subs.
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Old 3rd December 2004, 11:21 PM   #9
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Aggeman I dont think what you describe is "stereo" subs, its merely two subs. Stereo subs would have discrete channels and play differnt things, just like full range stereo consists of two discrete channels. Those channels play different things. The problem with non-symetrical placement there becomes that ideally you want both speakers to have identical response in stereo. When you position the subs in different positions you will excite room modes more or less depending on position. If they are not placed symetrically, they will not have the same response. BUT if you use two subs playing the same thing in different positions, perhaps it would cancel room modes to some degree.
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Old 4th December 2004, 04:48 AM   #10
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I have just set up my subs in stereo last night. I have now implemented an active crossover 4LR which crosses to stereo subs at 80 Hz. My subs are placed either side of the couch like coffee tables. There is the slightest hint of localisation still. I maybe be able to remove this by optimising and calibrating better when I get ultracurve DEQ. However, it's not objectionable. I may also try a lower xo point.

When I first listened last night something was "not quite right." Something very strange with happening with the stereo image! I played with the balance control and found that the subs were switched. Left sub with right channel, and vice versa. The effect was quite disorienting! Switched them and the sound stage improved quite noticeably.

Two points:
* below 80 Hz even with a steep slope you can still localise a little (although I believe you can eliminate this if the subs aren't so close and they are very well calibrated regarding modes, phase, etc)
* they have a profound effect on the soundstage

Further, when placed in this location, they get the smoothest in room bass you can get without eq, irrespective of room dimensions due to the increase in the proportion of the direct field to the reverberant field, the latter normally dominates. Most don't seem to try this method, but I find it models and sounds best in my room, which is a fairly typical medium sized living room.

Try also moving around your rood and see what happens to the bass. Stand inbetween the speakers. Stand in a corner. Stand in the middle, at the back of the room. Try also modelling with FRDC room response calculator and see if what you hear doesn't match what you simulate. I have found there seems to be reasonable correlation, and I will attempt to confirm this when I get set up to measure.
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