# Dual subs positioning and phase question



## ovillegas

I have a couple of subwoofers, Infinity SW-12 and Klipsch RW-12D. I had been running only the infinity for a while and it sounded ok, I felt like it needed a little more power for the low tones, so I bought the klipsch. 

I have tried both in the front (letf and right corners), and also on diagonally opposite corners of the room. It seems that the bass was lost as I added the 2nd sub as if they were on opposite phases, but changing the phase does not help either. I know I will have to play around until I get it right.

Long story short, here is my main question:

If I have the subs on diagonally opposite corners (front-left and rear-right), do they need to be on opposite phases? (one at 0 and the other at 180)

I guess the question goes if the subs are oriented so they are facing each other.


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## Wayne A. Pflughaupt

Hey oville,

One of the most important issues in implementing multiple subwoofers is time-aligning their distance to the primary listening position. A “either or,” 0-180° phase switch isn’t going to cut it if your subs have mismatched distances. You need continuously-variable phase controls for each sub, or an external digital delay processor.

Typically people go with multiple subs for one of two reasons. One is to achieve smoother bass response around the room (i.e. eliminating or minimizing “hot zones” or “dead zones” where bass levels are severely different from one listening location to the next), or to increase output. The best way to achieve the latter is to co-locate both subs in the location that gets the best performance. If that location is a corner, you can realize a 6 dB gain in total output.

Regards,
Wayne


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## Vader

Hi oville,

I also run duals, but mainly for the first reason Wayne mentioned. My HT room is rectangular, but not entirely symmetrical (acoustically speaking): different wall coverings, a small opening into a hallway on one side, etc. I found that a single sub in each of the available positions would not work for me, so I went with duals flanking the front channel. While they are not collocated, I still get about 4dB gain in headroom. The overall response is greatly smoothed, and all nulls previously observed are now pretty much gone. As for phase, since they are both equidistant from the seating position, they are in phase across the spectrum (both are set to 0 deg). Just remember that it is the relative distances from the seating/measuring position that determines the phase differential (translation: if they are the same distance, they should be at the same phase setting). If the distances are not the same, that's a whole different ball game. That's were the continuously variable phase control Wayne alluded to is needed. Bottom line: the sound must arrive at the measuring position in phase, and if the distances are different, that becomes frequency dependent. Good luck!


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## PT800

When using two subs, it is generally best to have them up front. And the corners my not be the best placement. If you have a Radio Shack spl meter, then place one sub at the main seat location. Run pink noise through it, while you go around the room checking spl. Note the locations that produced the highest output. Those are the locations where your subs should go. Then you may or may not need to change one of the phases.
Usually, when the subs are located up front, near the mains, their phase should be 0.


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## ovillegas

When you say:



PT800 said:


> When using two subs, it is generally best to have them up front. And the corners my not be the best placement.


Does that mean to have both in the front but not on the corners (front corners)? or are you just referring to "corners" as "diagonal corners"?


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## PT800

ovillegas said:


> When you say:
> 
> 
> 
> Does that mean to have both in the front but not on the corners (front corners)? or are you just referring to "corners" as "diagonal corners"?


Having subs along the front, other than the front corners. Corner positions will provide more boundary reinforcement, but may very well provide too much boomy bass output. Very room is different. 
If using 4 subs in a very large room, placing them at the midpoints of all four walls will provide good bass throughout the entire room.
The best thing is to find where the bass hotspots are, besides the corners, best done with a RS spl meter and the crawl.


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## fschris

This is good information for me. I am going to build another sub for the HT and I am a bit of novice when it comes to room placement etc. I think the next item I purchase will be a SPL meter.


I am going to position my subs in the front of the room flanking the plasma. Does that sound like a bad idea? The center channel will be in between the two.

Chris


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## PT800

It should work quite well. I co-located my subs with my mains in my last house. As those were the hotspots.


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## dazzdax

Hi Wayne, I'm using an odd order high pass filter for my main speakers (18dB). Main speakers are Soundlab electrostatics. Subwoofers have a 24dB filter. Do you recommend inverting the high pass filter because of the odd order slope?

Best Regards,
Chris Hie (Netherlands)


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## tesseract

Varying the distance of the sub(s) and/or the mains to the listening position can help time the subs and the mains irrespective of the crossover slope and phase.

Try experimenting with placement. Personally, I like to find where the mains are happy first, place the sub where it likes to be, then move the sub around in small increments until I get a nice blend. I've never had to invert polarity of the mains or the sub, but with a 3rd order high pass you could invert the mains and get a nice blend, if need be. 

Welcome to HTS, would love to hear your Soundlabs, Chris.


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## sdurani

fschris said:


> I am going to position my subs in the front of the room flanking the plasma. Does that sound like a bad idea?


There might be some better choices, depending on your room. 

If you've got a closed and symmetrical room, try placing your subs 1/4 of room width in from the side walls to cancel some of your room's resonances (standing waves). 

If you're in an irregularly shaped room, try placing the subs right behind your seating. Nearfield placment means you hear more of your subs and less of the room, giving you tighter/smoother bass. 

Experimenting with placement doesn't cost money, so it is one tweak I really encourage.


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## dazzdax

Thank you for your reply Tesseract. My subs are located at different locations (asymmetrical placement).
Unfortunately I'm not allowed to post links to images.
I like 18dB of slope for the high pass better than 24dB: it sounds better to me. Inverting the phase of the main speakers give a more "dimensional", less flat soundstage.
Because of the room characteristics (the room is entirely made of concrete with tiles covering the floor) I will never get a satisfactorily room response. The RT60 for frequencies below 200Hz for example varies between 0.8 and 1.1 seconds!
I suppose I need lots of bass traps!

Chris


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## tesseract

dazzdax said:


> Thank you for your reply Tesseract. My subs are located at different locations (asymmetrical placement).
> Unfortunately I'm not allowed to post links to images.
> I like 18dB of slope for the high pass better than 24dB: it sounds better to me. Inverting the phase of the main speakers give a more "dimensional", less flat soundstage.
> Because of the room characteristics (the room is entirely made of concrete with tiles covering the floor) I will never get a satisfactorily room response. The RT60 for frequencies below 200Hz for example varies between 0.8 and 1.1 seconds!
> I suppose I need lots of bass traps!
> 
> Chris


You need five posts for images, those can be knocked out in the Post Padding Thread. I would love to see your system. We also have a 2 Channel Picture Gallery.

You can address bass ringing with additional subs, too. While bass traps can help in the mid bass frequencies, it would take prohibitively large traps to reach 40 Hz and below, so multiples really help here.


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## dazzdax

http://s96.photobucket.com/user/dazzdax/media/IMG_0244_zpsd5359d20.jpg.html

http://s96.photobucket.com/user/dazzdax/media/IMG_0242_zps5f52b6c1.jpg.html

http://s96.photobucket.com/user/dazzdax/media/relocatedsubwoofers_zps49b3c38b.jpg.html?sort=3&o=7

Last pic was taken prior to relocation of the subwoofers Rythmik Audio F15's.

I give you also a link to a pic of the best audio system in existence (at least I think). It consists of huge horns with Goto drivers. Even Goto himself was mightily impressed by what he has heard. The system is located in Germany.

http://s96.photobucket.com/user/dazzdax/media/Hoorns-van-Klaus_zpse007b864.jpg.html?sort=3&o=0

Chris


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## tesseract

Wow, that is such a great system, dazzdax. Please post that in the 2 channel pic thread.

I've seen that Goto horn system or another one like it, the bass horns extend far outside the home's walls if I am correct? Crazy stuff!


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## leenorm1

Hi i have dual subs placed symetrically from the main listening position, i am contemplating more subs which will be behind me and closer than the front pair.After looking into this i decided that an external digital delay unit (i believe behringer manufacture something quite small and relatively cheap) is what would be needed. You can then calibrate the sub furthest away from you with the rest of the system then using REW and the digital delay unit calibrate the other sub to the rest of the system by increasing the delay until it is in phase.


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