| rs1026 |
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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| Nuuk |
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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| tbla |
| 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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| AGGEMAM |
| 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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| BassAwdyO |
| 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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| Variac |
| 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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| AGGEMAM |
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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| BassAwdyO |
| 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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| paulspencer |
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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| paulspencer |
| Another few things I plan to try ... with ultracurve. You can widen the stereo image for the bass only, and I have heard this is worthwhile for the bass. You can also assign a delay to the subs (not sure if this is needed or helpful, but will try). At the moment I haven't done anything with phase or eq and it already sounds quite good. There is the hint of hearing a little from the subs, but a casual listener might not notice. I will have to try and ask family if they think I have the sub on or not .... |
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| AGGEMAM |
BassAwdyO, while it's correct that I'm describing a dual sub system rather a stereo sub system, the difference between the two is mostly theoretical in that most studios record bass and especially the lower bass range in mono.
PaulSpencer, have you tried moving the subs away from the near field area. Usually bass sounds best when it's acoustically coupled to the room before reaching your ears. |
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| BassAwdyO |
| You are correct that most studios mix the bass as mono, just like main vocals, but I've heard stereo bass recordings before. The only reason it was apparent that the bass was in stereo was because the left and the right were constantly playing different frequencys causing a bunch of intereference beats. When you faded left-right the beats would dissapear. I'll agree, I dont see any advantage in stereo subs, but maybe there is something I dont know about it. |
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| AGGEMAM |
| quote: | Originally posted by BassAwdyO
You are correct that most studios mix the bass as mono, just like main vocals, but I've heard stereo bass recordings before. The only reason it was apparent that the bass was in stereo was because the left and the right were constantly playing different frequencys causing a bunch of intereference beats. |
I agree, and have heard such recording myself, but non-symetrical place of the subs doesn't negate that effect, it actually augments it in that each subs is slightly differently acoustically loaded to the listening room. And since you can't localize a sub (outside in the near field area) it doesn't really matter where you place them as long as both are approximately the same distance from the listening position. |
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| tbla |
| quote: | | And since you can't localize a sub |
well, you can - in the real world......it will always make some sounds higher than 80-100hz.
18" sub at 20-30 hz and under.......:) |
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| AGGEMAM |
| quote: | Originally posted by tbla
well, you can - in the real world......it will always make some sounds higher than 80-100hz.
18" sub at 20-30 hz and under.......:) |
That really depends on how carefully you construct it. Nor does it matter with the placement I proposed earlier in this thread since they would still be relatively near their respective speaker to not make a difference whether or not they do emit small quantities of sound above 92 Hz.
And 18" woofers are simply too slow in my opinion though I've heard some quite good 15" and 18" woofers I really prefer 10" or lower due to dynamic perfomance. You just need more drivers. |
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| tbla |
| quote: | | And 18" woofers are simply too slow |
....20hz is actually slow - and we assume that the motor is ok.
nothing can beat cone area.....i use a 3-way speaker with a 12" but i can assure you that the 15" version is a lot more potent.
:) |
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| leadbelly |
I think you guys are missing out on "the big one" when it comes to the issue of sub localization: distortion. Even using the best subwoofer driver available you will wind up with enough higher freq distortion content to make it localizable if you listen critically. There's some good threads on this but it has been so long I have forgotten what keywords to search on.
EDIT: Oops, sorry Variac, I didn't see your post the 1st time :) |
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| AGGEMAM |
| quote: | Originally posted by leadbelly
I think you guys are missing out on "the big one" when it comes to the issue of sub localization: distortion. Even using the best subwoofer driver available you will wind up with enough higher freq distortion content to make it localizable if you listen critically. |
Actually, I think we did take that into account if you've read the previous posts.
You cannot localize sound under 92 Hz. A carefully constructed sub will have very little sound above that. And careful placement will make that rest localizable correctly.
That's the recap of the previous posts here, I believe. |
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| paulspencer |
Now this thread is delving into some hot territory ... woofer speed etc! Do I dare get into this one?
| quote: | | BassAwdyO, while it's correct that I'm describing a dual sub system rather a stereo sub system, the difference between the two is mostly theoretical in that most studios record bass and especially the lower bass range in mono. |
This has not been my experience. My subs are crossed at 80 Hz and there was enough stereo information below that point for the subs when channels were swithced by mistake to do very strange things to the soundstage. I could not figure out what was wrong until I swithed the subs back. Of course ... if I were to experiment with this a little more with a view to actually testing out if stereo bass does really do anything more than dual mono, I might change my mind ...
I have heard conflicting information on this matter of how bass is mixed - mono or stereo. In the past I believe it was mixed mono due to the limitations of vinyl. I have heard via a recording artist and audio enthusiast that bass is now commonly mixed in stereo. What is actually standard practice (if there is one) I don't know. Perhaps someone can shed some light on this. But please keep in mind, another person who says "bass is normally mixed mono" won't really help without a little more elaboration. We don't know who you are or your basis for saying this, whether you are a recording engineer who has worked in the biggest recording studios or if you are someone who heard it from Jack who heard it from Jill who heard it from Bruce who sounded like he knew what he was talking about!
Another issue is how movies are mixed. I have had the impression so far that even movies are mixed with stereo LFE bass. I will have to observe this more carefully, but so far it has been apparent.
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PaulSpencer, have you tried moving the subs away from the near field area. Usually bass sounds best when it's acoustically coupled to the room before reaching your ears. |
I have tried my subs corner loaded, also as a H frame dipole in the middle, and right next to the main speakers. I tried this before direct field placement, which was clearly superior. The only disadvantage of the latter is the xo point becomes more critical. The response was much smoother. My room has a fairly typical midbass hole around 50 Hz. This all but disapears with direct field placement.
Some may consider this hair splitting but it's not strictly speaking correct to call it near field placement. Near field would be with your ear right up to the driver like when nearfield measurements are done. The distance at which I'm talking is outside the nearfield region. It is instead in the direct field, which is different. A room has both a direct field and a reverberant field. The latter is where room acoustics has a more dominant impact on the sound. In the direct field, the output of the subwoofer itself dominates what you hear. This is not quite the same thing as near field, and it sounds better than the reverberant field unless the room modes make a contribution that actually happens to appeal to your preferences more than a flatter response.
I prefer direct field as it's as smooth as I can get, potentially smoother than a dipole, and very easy to eq flat, and then tailor the response to suit preferences.
Later on when I get ultracurve to calibrate, I will try different sub locations. That will be the real test - what sounds best in different locations when all of them are eq'd flat.
| quote: | | You are correct that most studios mix the bass as mono, just like main vocals |
Where does this info come from? When I take notice, I often find the main vocals are off centre.
| quote: |
And 18" woofers are simply too slow in my opinion though I've heard some quite good 15" and 18" woofers I really prefer 10" or lower due to dynamic perfomance. You just need more drivers. |
Now, there's a biggie! It's hard to discuss woofer speed as there is much debate on what it actually means. It could mean transient response, it could mean "subjective tightness" which some would equate to group delay. It could relate the to bass rolloff. It could relate to the integration of the lower midrange to the bass. It could also relate to a lower F3 which excites an ugly room mode that a smaller driver with a higher F3 might not excite. It could be related to LeVC and transient response, as suggested by Adire. Bigger drivers with long voice coils often have a higher inductance, which might reflect this notion of bigger woofers being slower. However, with good design, a larger woofer can have a lower inductance. Many of these things relate to design more than the actual driver.
I would tend to disagree with blanket statements like '18" woofers are slow.' An 18" woofer might need much less excursion than a 12" working much harder to do the same job. The larger driver would be more linear when doing the same job, and may in fact have far better transient performance while also having lower distortion. Now if you are talking about RE audio's 18" subs based on XBL technology, then you are talking about big subs done right. In a suitable alignment integrated properly I'd be very surprised if anyone could characterise the sound as "slow." Unless of course the driver is reproducing sounds that the recording engineers didn't pay much attention to as their speakers had rolled off too much at that point.
| quote: | | I think you guys are missing out on "the big one" when it comes to the issue of sub localization: distortion. |
I had considered this when I tried direct field placement. Adire recommend placement near the mains for this reason. However, subjectively speaking, this hasn't appeared to be very significant in my case.
The best sub setup I have heard so far actually has 5 subs. One at the back of the room, the others at the front. They were all calibrated with both Ultradrive and Ultracurve DEQ. UD to set the phase and delay (and probably crossover), and UC to eq them all flat in room. The result is perfect integration. You can't localise them until you put your ear right up to the cone. Even sitting abnormally close to them, you can't tell they are doing anything. I went to the rear sub, it was an M&K which I though he would not be using since he had the Tumult. I listened up close and thought it was not running. "Do you have this sub going as well?" His comment was that localisation also relates to room modes. The subs were crossed at 80 Hz. As I have not achieved the same "subwoofer dissapearing act" yet, I assume it is a matter of calibration and setup. |
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| paulspencer |
| quote: | | Actually, I think we did take that into account if you've read the previous posts. |
Leadbelly is talking about distortion products which will be above the passpand of the sub. Variac mentioned this but much of what has been discussed as reasons why subs can't be localised has ommited to mention this factor, which may in fact undo all attempts to get it right.
The argument used is that bass can't be localised and subs don't need "time alignment." However, it may be that phase and time alignement correction digitally will in fact prevent out of band distortion from the driver from messing things up. |
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| gmphadte |
Human ear does not have sense of direction below 200Hz.
Gajanan Phadte |
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| paulspencer |
| quote: | | Human ear does not have sense of direction below 200Hz. |
100 Hz tones are easily located. Try playing some through your system and it will be quite obvious. |
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| BassAwdyO |
200hz is aweful high, I'd say you might be wrong there.
Paul, perhaps the music you listen to has some funky balance on the vocals, but of what I've heard only a very few tracks have the main vocals in stereo. There are programs available for free from sites such as download.com that use that fact to "erase" vocals from the music. If you simply invert the polarity on one channel, then add it to the other, you will get only the signal that is not shared by both. Everything that is the exact same on both channels will be canceled out due to the signals being of opposite polarity(just like when you wire up DVC subs wrong and they dont play anything). If you have a DVC speaker you can experience this easily by wiring up one coil to the left and one to the right out of phase. On most recordings, the bass wont exist and the vocals will be barely audible. There is a phaseyness to the sound which reminds me of being underwater or something. |
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