Nearfield Subwoofer Placement Questions. - AVS Forum
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post #1 of 34 Old 12-06-2013, 01:59 PM - Thread Starter
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Hey guys, I have a question regarding the concept of nearfield subwoofer placement. I have seen different posts in the last few weeks where one person says that nearfield placement solves a lot of problems when someone is struggling to get good bass. Then someone else follows that post saying that it won't fix the problem if the LP is in a null area in the room, let's say the center of the room for instance. Then someone else will follow up that they heard that nearfield will help no matter where the location is.

 

My question is: which is it? Can nearfield cover all of a room's sins causing bad bass? Or will it just help with some problems?

 

Also, does nearfield placement help if the LP is in the middle of the room and is suffering because of it? 

 

I ask these questions because there seems to be some differing thoughts on the subject. 

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post #2 of 34 Old 12-06-2013, 02:05 PM
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The center of the room is normally the worst spot, you can turn the subwoofer all directions, place it wherever and the null will still be present. Best thing to do is move the LP. Nearfield placement is great for adding more tactile response(especially on concrete floors), or when dealing with a excessively large room that is swallowing up the sub.
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post #3 of 34 Old 12-06-2013, 03:45 PM - Thread Starter
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That's what I thought but recently I have been seeing some other thoughts on the matter and wanted to get as much feedback from everyone as possible. Thanks basshead. 

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post #4 of 34 Old 12-06-2013, 07:06 PM
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Nearfield placement isn't some magic bullet that will make ALL room problems disappear. But it does let you hear more of your sub and less of your room, which is better than the other way 'round.

If your main listening position is at the midpoint of room width, then you're at the null of several room modes (room resonances, standing waves, whatever you want to call them). Placing a subwoofer in that location will minimize the null.

So if your couch is placed symmetrically with regard to room width, then placing a subwoofer right behind the couch, at the midpoint of room width, will lessen some of the nulls AND give you cleaner bass.

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post #5 of 34 Old 12-06-2013, 07:33 PM
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Quote:
Originally Posted by Hopinater View Post


My question is: which is it? Can nearfield cover all of a room's sins causing bad bass?
Do the math, literally.
http://www.padrick.net/LiveSound/CancellationMode.htm
If putting it next to you causes you to be in a null you haven't gained anything.
The assumption is often made that having a sub close to you will cause you to hear more of the direct sound and less of the reflected. That's true of the mains, producing directionally locatable wavelengths of roughly ten feet and shorter. It's not the case with the 14 foot and longer wavelengths below 80Hz unless the room dimensions are at least two wavelengths at the frequency in question.

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post #6 of 34 Old 12-07-2013, 01:07 AM
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Quote:
My question is: which is it? Can nearfield cover all of a room's sins causing bad bass? Or will it just help with some problems?

Also, does nearfield placement help if the LP is in the middle of the room and is suffering because of it?

Near-field placement of sub works great only if your MLP itself is not in a null; where ever that null is. MLP in the middle of room (Depth/Length wise) is the weakest bass region. The near-field placement of sub in that region will result in weak or bass.

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post #7 of 34 Old 12-07-2013, 07:17 AM
 
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Quote:
Originally Posted by Hopinater View Post

That's what I thought but recently I have been seeing some other thoughts on the matter and wanted to get as much feedback from everyone as possible. Thanks basshead.

Beware of rabbit holes and dense patches of weeds.

I guess your above is why eventually, we're all "forced" to purchase multiple subwoofer systems. I see nearfield placement as more of a quick fix rather than a long term solution. If seen in this light, your stated confusion makes sense.
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post #8 of 34 Old 12-07-2013, 07:28 AM - Thread Starter
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Great stuff guys. The replays are pretty much what I had hoped to get, a somewhat definitive explanation of the uses of nearfield placement as well as the role that middle of the room nulls play in bad bass.

 

So it seems pretty safe to say that the best way to defeat the middle of the room nulls and overall weak bass is to keep your LPs away from it. Would that pretty much sum it up?  

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post #9 of 34 Old 12-07-2013, 07:46 AM
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Originally Posted by Hopinater View Post

So it seems pretty safe to say that the best way to defeat the middle of the room nulls and overall weak bass is to keep your LPs away from it. Would that pretty much sum it up?
Plenty of people sit at the middle of room width in order to have a symmetrical soundstage. Placing a sub in a null will minimize it. Here's an example from another thread:
Quote:
Originally Posted by jkasanic 
Wow, check out my sub only response (no smoothing) just by relocating it to the middle of the room as Sanjay suggested several posts ago!! No Audyssey correction either (since my Audyssey calibration was done with the sub in the right corner):

Combine that will nearfield placement; examples here: http://mehlau.net/audio/dual_nearfield_sub/

Pay particular attention to the spectrogram measurements showing the decay times reduced with nearfield placement (direct sound field dominates and detrimental contributions from the room are greatly reduced).

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post #10 of 34 Old 12-07-2013, 07:53 AM
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You would still get a better response and stronger bass if the LP was relocated. That graph above is not very good imo, but was improved drastically.
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post #11 of 34 Old 12-07-2013, 08:01 AM
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Originally Posted by basshead81 View Post

That graph above is not very good imo, but was improved drastically.
The idea was to get rid of the nulls, since EQ can't do anything about them (but can pull down peaks).

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post #12 of 34 Old 12-07-2013, 08:13 AM - Thread Starter
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Interesting graph. So if I interpret things correctly the nearfield placement was the blue, showing the improvement especially at 40 and 70 hz nulls?

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post #13 of 34 Old 12-07-2013, 08:24 AM
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Quote:
Originally Posted by Hopinater View Post

So if I interpret things correctly the nearfield placement was the blue, showing the improvement especially at 40 and 70 hz nulls?
No, that was just moving one sub to the null at the midpoint of room width (where the main listening position is).

The link below the graph shows the effects of nearfield placement, which are not limited to frequency response improvements but also help with long decay times (ringing).

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post #14 of 34 Old 12-07-2013, 08:36 AM - Thread Starter
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Oh okay, thanks. I see now.

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post #15 of 34 Old 12-07-2013, 08:56 AM
 
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Originally Posted by sdurani View Post

The idea was to get rid of the nulls, since EQ can't do anything about them (but can pull down peaks).

EQ can pull up nulls, just at the expense of headroom. My thinking, if the sub has lots of headroom, then pulling a small null up ain't such a bad thing.

(anybody is welcome to jump all over my above as I know it flies in the face of convention)
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post #16 of 34 Old 12-07-2013, 09:04 AM
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EQ can pull up nulls, just at the expense of headroom.
Dips yes, nulls no.

Plus, boosting a dip makes its ringing (decay) more audible.

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post #17 of 34 Old 12-07-2013, 09:35 AM
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Quote:
Originally Posted by sdurani View Post

Plenty of people sit at the middle of room width in order to have a symmetrical soundstage. Placing a sub in a null will minimize it. Here's an example from another thread:
Combine that will nearfield placement; examples here: http://mehlau.net/audio/dual_nearfield_sub/

Pay particular attention to the spectrogram measurements showing the decay times reduced with nearfield placement (direct sound field dominates and detrimental contributions from the room are greatly reduced).

You are discussing MLP in middle of the room width-wise. Here are the FRs of MLP in the middle of the room, both width-wise and length-wise;



Brown is the response when MLP is around 2 ft from the rear wall. Magenta is when MLP is in the middle of the room (width/length). In either case, both subs are in the middle of the room one each on the mid position along each side wall. I took these readings at a friend's house in his (26Lx15Wx9H) room.

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post #18 of 34 Old 12-07-2013, 09:42 AM
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Plus, boosting a dip makes its ringing (decay) more audible.

I don't think so. Nulls ring when boosted with eq; dips don't. A boosting a null is useless anyway and wastes amp power.

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Originally Posted by sdurani View Post

Dips yes, nulls no.

I'll give you that. Dips yes, big azz nulls, no.
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post #20 of 34 Old 12-07-2013, 01:41 PM - Thread Starter
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Hmmm…. I thought I knew this but now I'm not sure I do. What are you guys considering a dip and what's a null?

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post #21 of 34 Old 12-07-2013, 02:15 PM
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Hmmm…. I thought I knew this but now I'm not sure I do. What are you guys considering a dip and what's a null?
A response dip is a natural part of the speaker response, and will be the same irrespective of either the speaker or LP placement. A null is caused by speaker and/or LP placement, and will shift in both frequency and depth based on the speaker and/or LP placement. You can EQ out a dip because it will have the same effect everywhere in the room. You can't EQ out a null because it won't have the same effect everywhere in the room.
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post #22 of 34 Old 12-07-2013, 03:11 PM - Thread Starter
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Gotcha, thanks Bill.

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post #23 of 34 Old 12-08-2013, 01:31 AM
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Nulls ring when boosted with eq; dips don't.
When sitting in a null, you can barely (if at all) hear the frequency being cancelled, let alone its decay/ringing. And since you can't boost your way out of a cancellation, its ringing won't become significantly louder. By comparison, if a shallow dip is slow to decay (its shoulder in the first few slices of a waterfall measurement doesn't fall significantly), then boosting it will make the decay louder. Like turning up the volume, just at that frequency.

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post #24 of 34 Old 12-08-2013, 01:44 AM
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What are you guys considering a dip and what's a null?
I consider a null a cancellation (either due to room dimensions or a neaby boundry). Usually seen as sharp, narrow V-shaped depressions in the frequency response.

Dips can be caused by other things, like lack of modal support (no boost from the room at that frequency, so level drops down to how loud the direct sound is). Typically seen as shallower, smoother depressions in the frequency response.

In the measurement I posted earlier, you can see the response dip between the two peaks in the blue trace. By comparions, the red trace shows V-shaped cancellations (nulls).

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post #25 of 34 Old 12-08-2013, 07:22 AM
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When sitting in a null, you can barely (if at all) hear the frequency being cancelled, let alone its decay/ringing.

I'm with you on nulls and dips. Null cannot be boosted as every effort to try and boost it is in vain. It's like a sonic vacuum. But that is specific to MLP. Changing MLP can get rid of null at that frequency but may or may not create nulls at some other frequencies.

IMO, the best way to deal with nulls is to have multiple subs placed in different parts of the room.

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post #26 of 34 Old 12-08-2013, 09:47 AM
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But that is specific to MLP.
Sure. Outside the MLP the same mode that is causing the null will be causing a peak. At that location, boosting the problem frequency can result in more ringing (as you had said). But I was limiting my comments to a MLP at the midpoint of room width, since that was the question I was replying to:
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So it seems pretty safe to say that the best way to defeat the middle of the room nulls and overall weak bass is to keep your LPs away from it. Would that pretty much sum it up?
My point to the OP was that, rather than move the MLP and have to listen to an asymmetrical soundstage, better instead to minimize the null at the MLP with subwoofer placement.

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post #27 of 34 Old 12-08-2013, 10:06 AM
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Originally Posted by braveheart123 View Post

You are discussing MLP in middle of the room width-wise. Here are the FRs of MLP in the middle of the room, both width-wise and length-wise;



Brown is the response when MLP is around 2 ft from the rear wall. Magenta is when MLP is in the middle of the room (width/length). In either case, both subs are in the middle of the room one each on the mid position along each side wall. I took these readings at a friend's house in his (26Lx15Wx9H) room.
Are the two subs in the mid room length along the long side wall the best position for dual placement at your friend place? I believe that position is mentioned in one of the link you posted somewhere at one of the best position. In this position, does it matter if one sub driver firing at front wall while the other firing at back wall or both subs drivers firing at the back wall?
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post #28 of 34 Old 12-08-2013, 10:42 AM
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Are the two subs in the mid room length along the long side wall the best position for dual placement at your friend place?

Yes.
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I believe that position is mentioned in one of the link you posted somewhere at one of the best position.

Yes it is better position if MLP is close to the rear wall length-wise.
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In this position, does it matter if one sub driver firing at front wall while the other firing at back wall or both subs drivers firing at the back wall?

I tried in all orientations; there was hardly a difference in FR.

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post #29 of 34 Old 12-08-2013, 10:56 AM
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^^ thanks so much. I am planning to give this position a try in my seal 14'x19' room with MLP about 15' from front wall
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post #30 of 34 Old 12-08-2013, 11:00 AM
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My current room I sit in the middle, nearfield did not work so I went to the two front corner and it was the answer.
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