what are the advantages of stereo subs? - Page 3

This is the crux of the matter. One would want point sources, where possible. And outdoors, it's almost trivially easy to get point source radiation from woofers. Only when there is a large array of woofers do you have a problem, but a single woofer acts as a point source.

Indoors, that's not the case. Even a single woofer acts like multiple sources because of the reflections from boundaries. At low frequencies, multiple subs are used to provide dense interference. Dense interference isn't as good as coherence, but it is better than course interference. At least with dense interference, you can smooth the sound field, make it act a little more like the reverberent field.

At low frequencies, it is again almost trivially easy to get a smooth sound field indoors because you just put a bunch of subs in the room. They aren't localizable, so you can pretty much use a "more is merrier" approach. If you have four subs or more, it almost doesn't even matter where you put them as long as they aren't clustered together.

Where it's hard is in the midbass and lower midrange. Sound is starting to localize in this range, yet it is still modal. So the traditional multisub configuration is best modified with a slightly different approach, which is to flank the mains with corresponding helper woofers. As I said in my last post, what you want is to have them just a few feet away, a little bit below, behind and beside the mains. They should be blended up to about 150Hz, to smooth the self-interference from the wall behind the mains and the higher frequency modes, just below the Schroeder frequency.

This 100Hz-200Hz transition region is what flanking subs are used for. It's low enough that you are still dealing with discrete modes, but high enough that sound begins to become localizable. Even if there were just one woofer, it is still effectively acting like "multiple midbass modules" because there are multiple midbass modes, due to the reflections from the boundaries. So just like the multisubs are there to provide dense interference at low frequencies, we use flanking subs to mitigate problems from boundary reflections in the midbass and lower midrange frequencies.
Edited by Wayne Parham - 10/21/12 at 11:45am

If you use an AVR / pre-processor, the LFE channel is never turned off when you set the subwoofer output in the AVR to OFF / NONE. That fact is common knowledge. More detail in the link below.


http://www.avsforum.com/t/1434726/which-subwoofer-connection-is-better-lfe-coax-or-high-frequency-speaker-cables#post_22511665



Your statement shows a bit of confusion on your part. "My guess, what's creating the confusion is, for entertainment purposes, people are messing with the whole space time continuum thingy by dumbing 5.1 signals down to stereo and trying to pump stereo up by adding subs to the stereo chain".

Stereo is not limited to 2 channels of bass information.

I experimented with 2 channel music years ago (2.0 and 2.1, no PL). I set my AVR to small mains, and I adjusted the crossover frequency in my AVR via my remote control while listening to music. The crossover adjustment range was from 40 to 200 Hz in 10 Hz increments. The 40 to 50 Hz crossover area always sounded the best no matter what connection method I used.

I have 4 subwoofers available, so I did a lot of experimenting. Subwoofers stacked in a single corner location worked best, crossed over near 50 Hz. The vertical stacking of subwoofers helps out with vertical modes / coupling.

I must also note that modern movie tracks do not sum the L/R low frequency content. An AVR does that via bass mangement, but the movie mixers do not use bass amangement.



Here is a sample of music with stereo bass. Taken from a Blur CD. Sounds like guitars are placed on the left channel and drums are placed on the right channel. Note that a crossover near 50 Hz will keep the stereo bass on the correct channel speaker, while a crossover at 80 Hz will spit the bass between the mono subwoofer and the main speakers.



Edited by J_Palmer_Cass - 10/21/12 at 7:13pm

Alright, between some googling and that link, I think things are making more sense. So the bottom line is
#1) If you have a sub (or subs), hook them up via the LFE/sub out and the AVR will work the magic.
#2) Doing the stereo bass can be beneficial for mid-bass, but not the stuff below ~80 hz
#3) LFE and other tracks may be dropped by a "source device" such as a dvd player, but will be retained by an AVR/sound processing unit which can compensate despite your speaker layout (missing speakers, etc.)

Am I any closer to the Golden Nugget of Bass Wisdom?

So then it would be a good idea to pick up two Polk Audio PSW10 and just run it inline with your left and right speaker so like AVR to PSW10 to Front Channel speaker in the manner described to enhance those channels audio while still having say a nice size 12" sub or two on the sub out (.1) somewhere else in the room.

Would it be worth wild to do the same to all the other channels?
Edited by Daniel Chaves - 10/21/12 at 3:08pm

That is the standard / typical way to bass manage your speakers.





More like down to the nominal 50 Hz area. Mid-bass is 50 to 100 Hz.





Only the LFE (.1) channel (if available on the source material) is dropped when you use the 2 channel analog outputs on a DVD player (and similar source devices). No other channels are dropped.

If you want to experiment, set the subwoofer output in your AVR menu to OFF / None and set the R & L mains to Large. Remove the speaker grills on your L and R main speakers. Play an action DVD at your usual volume level. If your main L & R speakers are stressed in that bass management mode, then you can easily see that simply by watching your main speakers. If your main speakers can not handle the program material, then you stop right there.

Too many subwoofers is a waste of resources, so you have to know what you are doing before you buy anything.

I have Polk Audio Monitors 40 series II for my front channels and I didnt have a sub for awhile and they seemed to handle everything alright.

Multiple subs are not worth the extra setup IMO. Subs cancel each other out at certain parts of the room whenever they are split. As already stated for mid bass its great but below 80hz is no good.
A properly tuned 5.1 system will leave the listener puzzled as to wear exactly the sub is located in the room if it's not in sight.

You are entitled to your opinion, however your opinion in wrong. First, the term "multiple subs" and "stereo subs" are not the same. These are two different topics. Whether stereo subs are worth the effort is debatable. Multiple subs nearly always will have an audible advantage when set up properly. The primary benefit is a smoother overall frequency response as well as a more consistent response throught the room at different seats. This does not even take into account the benefits of higher output and greater headroom of two or more subs versus just one sub. As far as multiple subs being "worth the extra setup," most of us here are audio hobbiests. To most of us it is well worth the extra setup effort if it brings much improved results. I've yet to hear from any of the regulars around here that they did not have a significant improvement going from just one sub to multiple subs.

By the way, in my system I have both a pair of stereo subs as well as two LFE subs. The audible payoff was well worth the effort.

That's true only in very large rooms, where the shortest room dimension is at least one wavelength within the pass band. In rooms that large low frequency response is dominated by the distance between the sources relative to the listening position. In typical home listening rooms the exact opposite is the case, with low frequency response dominated by the distance relationships between room boundaries and the listening position.

Interesting sample.

After about 21:30:12 the music is almost mono.

Prior to 21:30:12 the music is almost mono below 60 Hz.

It appears that if one had stereo subwoofers crossed over at 60 Hz or less, you could mix the inputs to the speakers into mono or not, and you'd probably hear no difference.

Well that's the controversy. ;-)

What I conclude from the available information is that positioning the 2 subwoofers along the side walls per the Harman recommendation when it fits, seems like a win-win situation. If the sub-bass is mono (which it apparently will be much of the time if you play a random selection of recordings from the standpoint of stereo bass) you get the most uniform distribution of the bass. As the recordings morph/if they morph into true stereo, the sub bass is at least no worse than it would be if you had the subwoofers located elsewhere.

I have a Quin set up.

Most music has mono bass. I just checked one CD at random, and only 3 out of 12 songs had stereo bass. I have no idea how common stereo bass is in music.


Below is a link to a paper on stereo bass. Note that the paper mentions that there is no need to run subwoofers in stereo below 50 Hz. I run mono single location corner stacked subwoofers, and run stereo bass above 50 Hz nominal for the mains and for the surrounds speakers.


http://www.filmaker.com/papers/RM-2SW_AES119NYC.pdf

There s a difference between 'stereo' bass and bass that envelops you as though it is 'stereo'.

I used to have a Lexicon prepro lie Wayne mentioned above and used the side subs. It works very well whether the bass is stereo or not. I currently have a single sub below 60 hz and it isn't localizable. But you can tell it isn't 'everywhere'.

Fortunately my mains are flat to 20hz. I overlap them with the sub and get flatter response and envelopment. If I had the space and no sense of aesthetics I'd add side subs too.

Side subs, and front and back subs, create that feeling of immersion.

If you want to do that then don't waste your money on PSW10's. they are about the worst POS subs out there.