Stacking subs?

[jacksonbart]

Is stacking two subwoofers the proper way to place two subs in a room? I have never done it and always wondered placement of more than one should work, never thought about doing stacking until spending time on this site. (BTW Thank you, this site is much more educational than spending time at Barnes and Noble reading the typical Audio Mags, too cheap to buy in most cases.)

I know two of the same subs would increase the volume by 3 decibels and can smooth out the response in the room. Please correct me if I am wrong. Basically I would have thought, based on no scientific knowledge to place the second one in the opposite corner, for corner placement or one the side of the front wall for subs placed along the front wall. At least that is were I would start moving it around until I thought it sounded best. Mine currently is along the front wall, right corner. Found that works best for me, just wondering where to start for adding a second sub?

[tommyboy]

I dont know about stacking them, but definitely put them in a corner if you do.

[IAmtnbikr]

I believe stacking them is the way to keep the low frequency waves from interfering with each other and causing muddy and poor bass sound. Sort of why subs have the phase switches on them; so they do not clash with the low frequencies from the other speakers if running the system so bass below say 100 hz or so is fed to anything other than the sub...

[Professor.Ham.Slap]

I have my subs stacked and I really like the way it sounds... Basically you're looking at having a narrower soundstage in the bass region (although generally speaking you can't hear where the bass is coming from, but there is a slightly noticable difference) but easier placement with maximum decibel increase. Placing them across the front in two different places will open things up a little but more, but it takes a lot of trial and error to get the system to sound smooth across all frequencies at that point.

[gcoker]

What I have read is that for movies place the two subs in the

same corner. For Music place the subs in opposite corners. I have

mine in opposite corners due to placement issues. If you want the

two subs for increase bass then place them next or on top of each

other.

[colterphoto1]

I like what gcoker says. If you're more into 2-channel music and IF your receiver outputs to subs in stereo modes, keep them near your main stacks to keep the stereo image straight (yes even in the lower ranges it's important). If you're into HT more, keep em together. However, I LIKE FLOOR SHOCK, the feeling you get from moving the room, you'd get more of this in a side by side arrangement rather than a stacked group, and you'd be keeping the woofer in the same sound space, so there seems like there would be less chance of phase differences.

Michael

[jacksonbart]

Thanks for the replys. Anyone has two RSW-15s stacked on top of each other?

[InnovaZero]

I dunno, but I know theEar's has a RSW tower. It Consists of a RSW-10,12, and 15 stacked.

[TheEAR]

Yes I have an RSW tower,thr4ee RSW subs stacked.In one corner,and a PolkAudio PSW404 and 505 stacked.Plus A couple of Sunfire subs along side the wall(since these micro brutes have so much electromotive force they cannot be stacked safely).Subs I did not stack are the HGS18,Servo Signature,SW12 and B15.AsI like to stack the same make(from big to small,pyramid stacks).

As long as all subs are working as ONEand not fighting each other its A ok.PHASE is the key word here.All working as one.

[shoe11]

I had my 15's stacked for a while, but after moving them around in my room I decided I liked them better seperated. Basically you need to play around with them in your room and find the response that pleases you best.

~shoe

[Colin]

This is a subject for which the industry giant harmon/kardon has published a lot of research:

Subwoofers: Optimum Number and Locations

By Todd Welti

Research Acoustician

Harman International Industries, Inc.

Intuition tells us that putting a large number of subwoofers at different locations in a room is likely to excite room modes in a more "balanced" manner, as compared to a single subwoofer. This idea has potential where there is not a single listening location, but rather a listening area. In this case we look for consistency of acoustical response with in this area. One way to approach this problem is to excite all modes evenly. Another approach is to excite as few modes as possible. Using simulations and measurements we have made an investigation to determine if using a large number of subwoofers is advantageous, and in particular what configurations give the best results. Several interesting and surprising results were uncovered along the way.

http://www.harman.com/wp/index.jsp?articleId=1003

[Sanman023]

like shoe...in my room i get a better sound at different spots...very low WAF....

[Olorin]

Try one dead center in front of you, and one dead center behind you. As Colin mentioned, the Harman white papers offer some really good information on this topic. http://www.harman.com/wp/index.jsp?articleId=1003, especially pages 13-18 might interest you.

[Mjaudio]

I was told once that stacking 2 subs gives you an increase of 6db. I have never tried it but I really do like using 2 subs in different locations. My last house was a bass graveyard. I actually used 3 subs to achieve the same effect that one sub produced in my prior house.

The best thing to do with subs is experiment but I definately recommend using at least 2. It is not so much louder just more powerful, if that makes any sense. I read somewhere that bass frequencys have longer cycles so if your listening chair is in the wrong position you could be in a null and get no bass. In my old house the sweet spot sounded great but the other couch was like the beach at Normandy, you would have thought there were 6 bass shakers in that sucker.

In my last set-up I used only one sub (Velodyne HGS-18 at the time) when listening to music, this was located between the main speakers about 6 feet from the side wall and 3 feet from the back wall. For home theater I fired up a pair of HSU TN-1225 driven by a Parasound HCA-1200 which is custom built for subwoofer use and has a subsonic filter along with the Velo 18.

This was a great combo as you can have too much bass for music and not enough for HT. Beats changing the levels when you switch from music to HT.

Just get your self 2 or more subs and enjoy!

[jacksonbart]

Colin / Olorin

Thank you for the white paper. Much appreciated.

[DrWho]

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On 2/21/2005 3:00:45 AM Mjaudio wrote:

I was told once that stacking 2 subs gives you an increase of 6db.

I read somewhere that bass frequencys have longer cycles so if your listening chair is in the wrong position you could be in a null and get no bass. In my old house the sweet spot sounded great but the other couch was like the beach at Normandy, you would have thought there were 6 bass shakers in that sucker.

----------------

Stacking gives an increase of 6dB because the acoustic output of the two woofers couples and work in tandem. Seperating the subs brings you back down to a 3dB increase (you lose the coupling effect).

What you read, or your interpretation of it is partially true and I wanted to comment on it because it's a cool concept. It is a common misconception that your room's longest wavelength determines the lowest note that can be produced in that room. What really is happening is that the sound reaching your ears isn't just the direct sound, but a bunch of reflected sound as well. At lower frequencies, the wavelengths are long enough that standing waves are forming. Sitting in the null of a standing wave means you won't be hearing anything (whereas sitting in the peak means you'll be hearing a good boost).

Apart from the standing waves (which are the biggest issue), you also have the reflections in the room interacting with the direct sound which is also causing some shifts in the frequency response (and in the time domain). It becomes more of an issue with lower frequencies because they are less directional to our ears and thus we just hear the effect of the interaction and don't percieve it as natural reverb (unless of course we're in a huge auditorium).

[Mjaudio]

Thanks for clearing that up for me DrWho.

Since you seem to know what your talking about could I ask you about adding a Parametric Eq to the sub or subs. I was thinking about adding a couple of Art 351 or a BEHRINGER DSP1124P since they are now only $99 new at parts express.

Is this a complicated process and are the benefits worth the expense and time?

I know I would need to measure first since I could be lucky and already have a flat response. In this case an EQ would seem to be useless if there are no dips or peaks to correct.

Do you know if there are any resources online that could explain the process in the easiest possible manner? I already have a Radio Shack SPL meter and a copy of Avia like a respectable HT nut should have.

Any comments would be greatly appreciated.

[DrWho]

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On 2/21/2005 4:03:15 PM Mjaudio wrote:

Thanks for clearing that up for me DrWho.

Since you seem to know what your talking about could I ask you about adding a Parametric Eq to the sub or subs. I was thinking about adding a couple of Art 351 or a BEHRINGER DSP1124P since they are now only $99 new at parts express.

Is this a complicated process and are the benefits worth the expense and time?

I know I would need to measure first since I could be lucky and already have a flat response. In this case an EQ would seem to be useless if there are no dips or peaks to correct.

Do you know if there are any resources online that could explain the process in the easiest possible manner? I already have a Radio Shack SPL meter and a copy of Avia like a respectable HT nut should have.

Any comments would be greatly appreciated.

----------------

Yikes, the first thing that should be pointed out is that EQ doesn't work with room related dips in your frequency response...boosting those frequencies just increases the level at which the cancellations are happening.

For a parametric EQ to be most effective, you really should get an RTA and measure pink noise on your system. I think a good RTA + Mic combo costs about a $1000 (someone correct me if I'm off the wall here). If you have a frequency generator (a pc will work), then you could just measure a bunch of tones on your system and draw yourself a graph and see what kind of issues you might be having. Solid tones can be a bit decieving and they don't tell you anything about the frequencies between the tones. There is a $20 or so mod for the radio shack spl meter that gives it a flat frequency response (and faster response time), otherwise you'll have to use the correction charts on the web.

In all honesty, I would sooner look to room treatments before any form of EQ. There are a bunch of psychoacoustic issues regarding EQ and the natural sound of your room. A pair of bass traps in the corners behind your speakers will probably have more natural results than that of any EQ. There is a lot of interesting reading (i don't necesarily agree with all of it) from the anstendig institute regarding these issues: http://www.anstendig.org. EQ should be used to attenuate the program source material, not undo the influences of your room.

Generally with EQ, it is far easier to destroy the sound than it is to make it sound better. Also, it usually always sounds better initially, but when you come back the next day it will sound very akward. EQ is more of an art in that there are no strict rules to follow, but rather guiding concepts.

Nevertheless, if you're still interested in EQ then don't let me stop you. I personally use EQ all the time, but I do so understanding the limitations. There are many people on the forum who claim great results after adding an EQ (even when trying to correct room related dips in the response too, which can be attributed to the fact that nothing is perfect or completely effecient).

[dodger]

In order to get the full 6 db of extra bass, one would need 4 subs, thus two stacks.

Placement wouls be in the center of the wall approximately 1 -3" away from each wall.

The pistons would then have move at the same rate and you would wind up eliminating a standing wave or a noticable POS of bass. Another point would be to make sure that the subs are radiating within one wavelength of each other in order to achieve the full effect.

Phase would also be sure to be correct - matching.

Think of a chess board. Yor seat in one place, stationary. Now figure the patterns that would seem to be noticable.

[dodger]

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On 2/2/2005 10:08:22 AM colterphoto1 wrote:

I like what gcoker says. If you're more into 2-channel music and IF your receiver outputs to subs in stereo modes, keep them near your main stacks to keep the stereo image straight (yes even in the lower ranges it's important). If you're into HT more, keep em together. However, I LIKE FLOOR SHOCK, the feeling you get from moving the room, you'd get more of this in a side by side arrangement rather than a stacked group, and you'd be keeping the woofer in the same sound space, so there seems like there would be less chance of phase differences.

Michael

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As long as the internal wirings are the same (volt/ohm meter) and the leads going to the terminals, plus your actual amp to sub wires are correct you should have all in phase.

Where most people fail is the examination of the internal sub +, - vs the mains +, -. You do have to open them to determine, but that's a small matter when it comes to some of the tweaks.