[Duke]

Thanks for your input.  I am beginning to understand about multiple woofers or "Swarming" subs. That's a great term BTW. 

Thanks!  The idea of spreading multiple subs asymmetrically around the room came from Earl Geddes, and I use it in my Swarm system with his permission.   Independent of Earl, Todd Welti of Harmon International also investigated multiple subs, and he focused on symmetrical placement configurations.  The word "swarm" in this context is my contribution to the advancement of the art (ha!).

If I were to start a swarm, what is the best way to determine how many subs and where to put them?

The short answer is, the more the merrier.

As a general rule of thumb, two subs spread apart will have twice the in-room smoothness (half the frequency response variation) of one sub, and four subs will have twice the in-room smoothness of two subs.   I use four subs, all driven by one amplifier, and have customers who have measured plus or minus 3 dB across the bass region in their untreated listening rooms, which is arguably pretty good.   I'm not saying you need four subs, just giving you a data point. 

In addition to the acoustic smoothing that we get from multiple subs, we also get the benefit of psychoacoustic smoothing:   The ear/brain system will "average" (perceptually smooth out) peaks and dips that are within about 1/3 octave of each other in the bass region.  With a multisub system, the net in-room peak and dip pattern not only has smaller peaks and dips, but they are more numerous, and therefore closer together.   Because they are closer together, the ear/brain system's 1/3 octave averaging characteristic can kick in.  With just a single ubersub, the peaks and dips are large and usually spaced too far apart for this effect to kick in.

As for positioning, get 'em spread out, and put no more than one in a corner.  Eyeball your room and pick four locations where you can place a small sub, and as long as they aren't bunched up together, that should be a good starting point.  Some of my customers reverse the polarity of one of the four subs in a Swarm; you can experiment with that or anything else you want. 

Sometimes it makes sense to re-tune your main speakers to a much lower than optimum tuning frequency, and then to use them as additional sources of low-frequency energy.  The idea isn't to have overly massive bass - it's to have smooth in-room bass, and tuning your main speakers so that they contribute (albeit at reduced SPL) can help.

[JLM]

As I indicated in reply #1 of this thread, read Floyd E. Toole's "Sound Reproduction" to get a foundational understanding of room acoustics and documents with diagrams and charts the need/use for multiple subs (swarm).  He worked for years at the Canadian National Research Council (that independently tests speakers) before moving to Harmon International, so he's very qualified.

Looks like you've already got plenty of drivers to build a swarm.   

[musiclear]

Went to Harmon's "White Paper" tab and there is a lot of really great info there.  It's surprises me that they would actually publish that kind of data for general use.  Thanks Harmon.  I've got a lot of reading to do.  And it looks like I have at least a couple subs to build.

Reading briefly I think I saw a sentence that suggested that I place additional subs in room nulls.  Is that correct?  Could I walk around with a mike and choose locations based on where I find nulls?

[WGH]

A Sticky in the Acoustic Circle has more articles about subs and bass reproduction by Toole and Welti not included in the Harman White Paper page.

http://www.audiocircle.com/index.php?topic=58304.0

Wayne

[Jim Griffin]

While reducing room reflections for the bass region of the frequency band is important, designing a speaker that reduces additional room reflections is achievable.  It is not just adaptation for bass frequencies.   As mentioned earlier, in his review Robert Greene praised the McIntosh XRT28's ability to minimize the effects of ceiling, floor, and sidewall effects within the speaker design approach.  AJ raised some critical issues in his earlier reply and mentioned the viability of a multimodal approach.     

[Quiet Earth]

This is the room I am dealing with. It's 18' wide and 12' to the sloped ceiling.  12.5' to the couch and behind the couch is the kitchen with an additional 15' and then a family room off to the side.  It is a really big open area.

I can't tell from the picture if there is a symmetrical side wall on the right, but if there is a side wall then maybe you have another option. It seems like your speakers are way too close together for such a large room.  Have you tried placing them much closer to the side walls and toed in more toward the center? It seems like you have plenty of woofers woofing,,, I'm not sure why you would need anymore. Maybe if the speakers were much further apart they would load the room differently.

You will need longer speaker wire to test it out, but it's worth a try. You can always put them back if you don't like it.


A general laymen's thought on those "white papers" : It seems like they are suggesting the point of multiple subs is to get an even response for multiple listeners throughout the room. Or for one listener wondering around the room. Toole mentioned this over and over in his papers anyway. So if you are the only one in the room that really cares about an even response (of amplitude vs. frequency) and you don't mind sitting in the same chair, it might be a lot of trouble for nothin'.

I would love to hear a multi-sub set up like this at the next show. I guess it's too hard/too much trouble to do it at a show because I have never seen it done yet.

[Quiet Earth]

Actually, even if there is not a side wall on the right but just more wall room to spread out, you should try moving your speakers further apart.

[Duke]

A general laymen's thought on those "white papers" : It seems like they are suggesting the point of multiple subs is to get an even response for multiple listeners throughout the room. Or for one listener wondering around the room. Toole mentioned this over and over in his papers anyway. So if you are the only one in the room that really cares about an even response (of amplitude vs. frequency) and you don't mind sitting in the same chair, it might be a lot of trouble for nothin'.

One alternative to multiple small subs would be a single large sub equalized for the primary listening position.   This can yield very good results at that location, but may well degrade the results at other locations because the room-induced peaks and dips will change considerably from one location to another within the room when you only have one sub.   So that 6 dB dip you boosted to smooth out the sweet spot may have been a 6 dB peak somewhere else in the room, and now in that location it's a 12 dB peak.   Often a more conservative approach to EQ makes more sense, notching out peaks but being very gentle about boosting dips.

A multisub system may also benefit from EQ, but in this case, any residual significant peaks and dips are likely to be global (room-wide) rather than local (confined to a small area), so fixing them is likely to be fixing a global problem.   The amplifier I include with my four-piece Swarm system has a single band of parametric EQ, but I've only heard of one customer using it, and he was using it to improve the transition in the crossover region rather than to equalize residual peaks or dips. 

An single equalized sub is probably a more cost-effective solution than four small unequalized subs if your priorities are pretty much confined to the sweet spot.   If I had access to serious economies of scale I might be able to change that, but I don't. 

I would love to hear a multi-sub set up like this at the next show. I guess it's too hard/too much trouble to do it at a show because I have never seen it done yet. 

I showed a system at RMAF 2008 that included four small subwoofers, so it's been done at least once!  Might happen again, who knows. 

[JLM]

With possible bass responses of +/- 20 dB in room from a single bass source, EQ would be extremely hard to do (equivalent wattage would vary by a factor of 1 to 10,000). 

Yes, much emphasis for more uniform output (at all frequencies) around the room (isn't that what constant directivity is all about?).  I believe this was done to avoid listening alone (one advantage that A/V has over audio in that it seems to be enjoyed more as a group) and to avoid 'head in vice' limitations.

Still can't understand why the speakers are against the wall (no depth of soundstage).  Was it done to eliminate baffle step losses?

[musiclear]

I originally set up the speakers closer to the wall for better WAF.  She has since let me do my thing and they are now further out into the room and set wider apart.  That did help the depth of the sound field a bit.  These speakers are 24" deep so the drivers were set about 30" from the wall originally.  The listening couch is close enough to the speakers that if I set them any closer than they are now, it feels like they are right on top of you. 

I have also reworked the crossover to accommodate the 100hz bump and it has made a difference. This way seems smoother than just E/Qing the bump out.  Don't know why, but that seems to be the case.

And the conclusions that I have come to thanks to your generous support, is that with this system, unless I am willing to start from scratch, I am best off treating the room and adding subs until I get the flattest sound field with as little reflections and delay as possible.

I've gotten some OC703 and some Rock Board and will start treating for real next week.  I'll go at least 12" in the corners, 1" behind the screen, 2" on the back wall and 2" on the reflective surfaces on the side walls. 

I also, in frenzied probably mad purchase, got 5 of those Peerless/Vifa 10" woofers Parts Express had on sale.  VIFA NE265W-08 10" SUBWOOFER SPEAKER

I thought, why not try them and see how they sound.  I don't imagine they will be much different the Dayton RSS265HF-4 I am using now as I believe they have similar distortion specs. It should be an intersting experiment anyway.

I would like to move the crossover back up a little for a little better mid bass hit, and I am hoping that after the room treatment, I'll add a sub or two to finish smoothing out the room artifacts. 

I'll take some distortion measurements as I go along and see what I find.

Thanks for all the help so far.

[JLM]

What would a total lack of room reflections even sound like?  (Playing inside an anechoic chamber)  I've been in a couple and it's weird, feels like your ears are plugged.  We're all more conditioned to being in rooms than large halls, or outside, so embrace the room (as long as it's not a long tube, sphere, or cube) or way over/under treated (normal furnishings/windows are what we westerners are used to).

You mentioned trying your speakers closer to your listening position.  Embrace near field listening.  I follow the Cardas formula for room shape/listening set up so me and my speakers are in a 68 inch equilateral triangle while I face the front of a 13 ft x 21 ft x 8 ft room.  Near field removes much of the room effects and the imaging snaps into place as I sit in the designated place.

Recommend you first learn (research and experience) more about room effects (unless you really enjoy making sawdust).  A good alternate (if you don't care about proper imaging) would be headphones.

[Quiet Earth]

What would a total lack of room reflections even sound like?  We're all more conditioned to being in rooms than large halls, or outside, so embrace the room ....

Yes indeed. Let's take advantage of the room instead of fight against it.

Embrace near field listening.  I follow the Cardas formula for room shape/listening.....

Whoa,, wait. Did you just say.... Huh?  What happened to embracing the room?  Cardas eliminates the room, or tries to. Oh yes, the stereo imaging.....  That 3d holographic bliss,,, Walt Disney style. Yum, yum!. It is delicious, I agree.

But where did the music go? No meat on the bone, no substance. Just the hypnotic trick. Well, you can't have your cake and eat it too. Gotta pick one or the other.

[JLM]

QE:

Regarding "embracing" guess I was in a romantic mode (or just in a hurry this morning).  But without a giant room, there is bound to be some room gain of bass.

Don't know about your "where's the music/meat?" comments.  With F3 = 28 Hz and nice AlNiCo based drivers the music/meat is still there.  Yes, pulling speakers away from wall reinforcement would cause loss of bass output.

The real challenge for near field listening is driver integration (for those of you with "silly" multiple driver speakers).   

[RDavidson]

Went to Harmon's "White Paper" tab and there is a lot of really great info there.  It's surprises me that they would actually publish that kind of data for general use.  Thanks Harmon.

Publishing research is what basically validates / solidifies the work done. In the world of research, if you don't publish anything, then you're kind of just another Joe Schmoe. Yes, definitely, "Thanks Harmon."

[Quiet Earth]

Here is one example of a speaker that uses the room to achieve it's intended sound goal : http://www.stereophile.com/content/larsen-intrigues

I listened to these speakers last January in that very same room and I really enjoyed the overall sound. I found that particular room much, much easier to stay in for a long time, compared to the other rooms I heard which were typically set up for the near field "wow" experience. Of course I am already used to that sort of mid/far field non-Cardas presentation at home, so that has a little bit of influence on me.

I just wanted to share these particular speakers as one example of an idea that works without using room treatments and without placing the speakers in your lap. I don't know how many other speaker companies are working in this direction, but it doesn't seem to be very popular in the regular audiophile circles. I think if you can get over the everything should be in surround sound mentality, then it can be a very enjoyable way to listen to recorded music at home.

[Duke]

...I don't know how many other speaker companies are working in this direction...

*raises hand and waves it wildly, leans forward, eyes bugging out*

[JLM]

QE:

That's the 3rd Swedish speaker that uses the room I've heard/read about.

Then there is Klipschorns, Allisons, and of course Bose 901's.

[AJinFLA]

I don't know how many other speaker companies are working in this direction, but it doesn't seem to be very popular in the regular audiophile circles.

They're out there. 
But hopelessly outmatched by the "treatment" business folks and unshakable preconceptions. Despite all the evidence to the contrary. IOW, perfect for the intended market.
A few to choose from if you want to utilize the room beneficially, less if you want to ignore it (the benchmark imo: http://www.stereophile.com/content/gradient-revolution-loudspeaker-john-atkinson-march-1997 http://www.regonaudio.com/Gradient%20Revolution%20Loudspeaker.html ).
Preferences and exposure to live acoustic music has the largest impact.

cheers,

AJ

[ltr317]

They're out there. 
But hopelessly outmatched by the "treatment" business folks and unshakable preconceptions. Despite all the evidence to the contrary. IOW, perfect for the intended market.
A few to choose from if you want to utilize the room beneficially, less if you want to ignore it (the benchmark imo: http://www.stereophile.com/content/gradient-revolution-loudspeaker-john-atkinson-march-1997 http://www.regonaudio.com/Gradient%20Revolution%20Loudspeaker.html ).
Preferences and exposure to live acoustic music has the largest impact.

cheers,

AJ

Hi AJ,

In absolute agreement on the Gradients.

Cheers,
Paul

[musiclear]

What initially sold me on the idea of room treatments was that I happened to have some OC 703 left over from the box build and a few pieces or other glass board laying around and just threw it up in the back of the speakers and on the first reflection spots and the sound really smoothed out for me. 

I had heard what sounded like an echo phasy sound with a bit of hash or hard edge.  I thought it was the speakers until the glass went up.

That phasy sound went away and the hash went away.  I under stand that I don't want to cover everything, but reducing the reflections that I did, improved my listening pleasure quite a bit.

Now it seems like I am listening to the music from the speakers rather than the echo reflected off the walls.