60hz is dead in my room. Help - AVS Forum
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post #1 of 38 Old 02-11-2014, 06:39 PM - Thread Starter
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I've been fighting a terrible dead spot all the way down the center of my room length wise. Its from the ground to about 3 1/2 feet high from one end if the room to the other right down the center and it's about 3 feet wide. There is literally no sound at 60hz. It could be 100db and you move your head 2 feet and it's completely gone.

My room is 24 x 13 with 8 foot ceilings.

What are my options to try and cure this. There really is no way I can set the room up that doesn't put me in this dead zone one way or another without me sitting also right against the wall.

Treatments? Spots to put it first?

Any help would be great. Ask any questions you like and I'll try and answer in as much detail as I can.
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post #2 of 38 Old 02-11-2014, 06:50 PM
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I suggest doing the sub crawl and finding a better location in your room for your sub placement. That may very well solve your problems. After trying that you may want to consider buying a 2nd sub for more even bass response throughout the room across more listening positions. Finally, there is downloading REW and getting a mic so you can take measurements and then getting a minidsp so you EQ. 

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post #3 of 38 Old 02-11-2014, 06:51 PM
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My case might not have been as bad as yours, but I solved it by a combination of doing the subwoofer crawl & dual subs.
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post #4 of 38 Old 02-11-2014, 06:57 PM - Thread Starter
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I've tried every spot on the room I can put a sub by doing the crawl. Where it is is the best spot everywhere else. Every spot I've tried 60 hz is dead right down the middle. I use to have a velodyne SMS-1 I think it's called but nothing helped it at 60. I'm using multeq xt32 and it's got it sounding great but nothing can fix the 60 hz with EQ or placement. I think I need to go treatment but I have no idea how or where to place it. It's very confusing.

It's bad enough I was playing a 60hz tone and it was at 95db and I would move the meter 2 feet to the spot and it dropped to 68. I muted the sound and the Meter didn't change it stayed at 68. It's like witchcraft.

I'm also not sure a second sub would help since placement doesn't effect it. Plus I can't afford another svs pb 13 ultra. I was hoping one of them would be enough.

Is there a way to test where treatment would help the most to get rid of a problem like this?
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post #5 of 38 Old 02-11-2014, 07:14 PM
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^ that's something I have no idea about. Hopefully somebody will chime in with some help though. 

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post #6 of 38 Old 02-11-2014, 07:17 PM
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Quote:
Originally Posted by bevofrancis View Post

I've been fighting a terrible dead spot all the way down the center of my room length wise. Its from the ground to about 3 1/2 feet high from one end if the room to the other right down the center and it's about 3 feet wide. There is literally no sound at 60hz. It could be 100db and you move your head 2 feet and it's completely gone.

My room is 24 x 13 with 8 foot ceilings.

What are my options to try and cure this. There really is no way I can set the room up that doesn't put me in this dead zone one way or another without me sitting also right against the wall.

Treatments? Spots to put it first?

Any help would be great. Ask any questions you like and I'll try and answer in as much detail as I can.



It is normal for the center of the room to behave badly. It is recommended that you never place your seating at the 1/2 way points in a room.

What do you have for programs to measure the FR of the speakers in the room?
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post #7 of 38 Old 02-11-2014, 07:18 PM
 
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Reads like you badly need a second sub on the opposite wall.

My understanding, when two waves of the same frequency run into each other (reflections) they cancel each other out, creating a null in the process.

This can be cured by adding an equal second sub and placing it on the opposite wall.
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post #8 of 38 Old 02-11-2014, 07:37 PM - Thread Starter
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Quote:
Originally Posted by J_Palmer_Cass View Post

It is normal for the center of the room to behave badly. It is recommended that you never place your seating at the 1/2 way points in a room.

What do you have for programs to measure the FR of the speakers in the room?
I'm sitting in the middle of the width but in the front 1/4 of the room. All I have to measure with is my ears and a radio shack spl meter.
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post #9 of 38 Old 02-12-2014, 03:31 AM
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Quote:
Originally Posted by bevofrancis View Post

Quote:
Originally Posted by J_Palmer_Cass View Post

It is normal for the center of the room to behave badly. It is recommended that you never place your seating at the 1/2 way points in a room.

What do you have for programs to measure the FR of the speakers in the room?
I'm sitting in the middle of the width but in the front 1/4 of the room. All I have to measure with is my ears and a radio shack spl meter.



SPL meters and single frequency test tones can be a bit deceptive. Yes, you may have a narrow band null in your room with the use of test tones. However, with real world wide band content you may not even notice.

I sit about 2/3 of the way back in my room and my problem frequencies are a bot higher in frequency. I may measure about 1/4 of the way from the front just to see how that measures.

Measurement software is required so you can see what is going on.

REW is a free measurement program.

True RTA is available for a one time charge. The basic limited function program is free. I purhased the 1/24 octave version.

Download the free version and use your SPL meter for the microphone. Connect the SPL meter audio output into line in on your PC / laptop.

http://trueaudio.com/
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post #10 of 38 Old 02-12-2014, 05:17 AM
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Depending on how badly that null bothers you, you could just get another sub which covers that frequency. You don't have to buy another PB13 just to take care of 60 Hz null, you might look at a Hsu MBM-12 which was designed to tackle issues exactly like this. The Premiere Acoustics PA-150 also has huge 60 Hz output, but it may not be quite as tight, plus it has quite a bit more distortion for the same loudness levels as the PB13, so it doesn't match up as well.
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post #11 of 38 Old 02-12-2014, 05:30 AM
 
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Another way to look at it, does anybody sit in the null while watching movies? Just saying, if not, who cares? The point, sound management is about the listening positions and not the part of the room where nobody cares.

(trying to be encouraging here)
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post #12 of 38 Old 02-12-2014, 06:05 AM
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Quote:
Originally Posted by bevofrancis View Post

All I have to measure with is my ears and a radio shack spl meter.
You'll never get it right without measurement software, and you'll never get it right with just one sub. The reason is that what gives you the best result broadband results in that 60Hz null, so you need a second sub placed to that its maximum output at the LP is at 60Hz to fill the hole. Finding the right spot is a hit or miss proposition without measuring gear.

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post #13 of 38 Old 02-12-2014, 07:12 AM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

You'll never get it right without measurement software, and you'll never get it right with just one sub. The reason is that what gives you the best result broadband results in that 60Hz null, so you need a second sub placed to that its maximum output at the LP is at 60Hz to fill the hole. Finding the right spot is a hit or miss proposition without measuring gear.
I'll try and use the software this weekend. I've got a friend that had a pb 12 plus sub. Maybe I can talk him into upgrading and selling me his.
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post #14 of 38 Old 02-12-2014, 07:41 AM
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Quote:
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I'll try and use the software this weekend. I've got a friend that had a pb 12 plus sub. Maybe I can talk him into upgrading and selling me his.

LOL, I like that approach. Tell him how much happier he would be with an Ultra and then offer to help him out by buying his old sub. :)

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post #15 of 38 Old 02-12-2014, 09:59 PM
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Dual subs, a microphone, and software .... It is the only sane way to deal with this problem. Personally I had a great deal of benefit simply moving my seating position back about 6". The other comments are right... the middle of the room sucks (literally).

Room treatments are unlikely to kill a null of the magnitude you are talking about. I have plenty of room treatment and still have certain nulls.

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post #16 of 38 Old 02-13-2014, 05:10 AM
 
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And unless sitting and viewing from the middle of the room, the null it moot.

All us experienced listeners care about, is what comes to our ears where we sit.......okay, and where our guests sit but that's because our mothers told us to play nice with guests or she'd steal our ears and not give them back.

...tongue.gif
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post #17 of 38 Old 02-13-2014, 07:10 PM
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I would bet at least 95% of guests in home theaters could care less about the exact acoustics of the room and would not even notice or listen critically.

This is certainly the case with my crowd who might plop themselves on the side or corner of the room or whatever...

I would suggest optimizing the owner's position above all other considerations since that is likely who will be using the home theater for any "critical" listening.

If the rest of you guys have a group of audiophile buddies then you are either really lucky to have a group of friends that share your interests... Or you and your friends are all nerds... Or both!

Blazar!
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post #18 of 38 Old 02-13-2014, 07:24 PM
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Originally Posted by blazar View Post

Room treatments are unlikely to kill a null of the magnitude you are talking about.
+1. Damping out a 60Hz reflection isn't practical, unless you don't mind having your room look like this:


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post #19 of 38 Old 02-13-2014, 11:29 PM
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Originally Posted by bevofrancis View Post

Spots to put it first?
Can you try putting the sub in the null (midpoint of room width)?

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post #20 of 38 Old 02-13-2014, 11:59 PM
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Can you try putting the sub in the null (midpoint of room width)?

Wont this just lead to another null elsewhere? I would guess you still need another sub at least

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post #21 of 38 Old 02-14-2014, 12:13 AM
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Wont this just lead to another null elsewhere?
You mean create/add a null that wasn't there previously? Doubt it. Might exacerbate a peak at the midpoint of room width, but peaks can be brought down with EQ. No such luck with nulls, hence the suggestion to move his sub there. Besides, trying it doesn't cost anything and is reversable (if it doesn't help with his problem, he can move the sub back where it was).

Sanjay
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post #22 of 38 Old 02-14-2014, 05:03 AM
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Anthem's ARC does both mode and antimode so it can help with nulls, but finding better placement is the best strategy.
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post #23 of 38 Old 02-14-2014, 05:18 AM
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Quote:
Originally Posted by blazar View Post

Quote:
Originally Posted by sdurani View Post

Can you try putting the sub in the null (midpoint of room width)?

Wont this just lead to another null elsewhere? I would guess you still need another sub at least

Sometimes moving the null to a place where nobody ever sits is sufficient.

Trying to equalize deep nulls can be like playing with fire because they can absorb a lot of power.
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post #24 of 38 Old 02-14-2014, 05:26 AM
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Yeah agreed, eq'ing nulls leads to a mess.

How much does adjustment of the phase on one or both subs affect nulls and their magnitude? I have played with phase settings on both my subs and havent solved null problems in my room.

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post #25 of 38 Old 02-14-2014, 06:28 AM
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Quote:
Originally Posted by blazar View Post

Yeah agreed, eq'ing nulls leads to a mess.
How much does adjustment of the phase on one or both subs affect nulls and their magnitude? I have played with phase settings on both my subs and havent solved null problems in my room.
Nulls are caused by the distance from the sub to the room boundaries, the distance from the sub the LP, and the distance from the LP to the room boundaries. You can't change the position of the boundaries, so that leaves changing the position of the sub and the position of the LP. EQ can be used to fill a null, but for every place in the room where the null gets filled at least one more ends up with a peak. That leaves using additional subs as the only real cure, as that will put a completely different set of sub to boundary to LP distances into the equation, and if you do it right where one sub creates a null at the LP the other creates a peak and the combined result will be flat enough that EQ can finish the job. Adjusting phase controls may help, but only in fine tuning.
Subs are like real estate. What matters is location, location, location. The source of any null can be identified by comparing the frequency of the null and the distance between the sub and/or LP to a boundary that would cause it. This can help in that regard:
http://www.padrick.net/LiveSound/CancellationMode.htm

BTW, fans of 'nearfield' sub placement can be making matters worse rather than better, due to ceiling and wall bounce. If the sub is next to the LP there will be a null where the sub is 1/4 wavelength from the ceiling. If that distance is six feet, for instance, there will be a null at 48Hz. By the same token if the distance from the sub to a sidewall is, say, eight feet, there will be a null at 35Hz. With respect to subs and LPs a simple rule is that they both should be very close to or very far from boundaries.

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post #26 of 38 Old 02-14-2014, 06:47 AM
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I have a room with almost identical dimensions. I have that null at 63 hz. Used a umik 1 to derermine. I have 2 fv15hps upfront. Havnt tried moving one sub to the rear but i might try it. really hard to find a place anywhere other then the current loacations.
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post #27 of 38 Old 02-14-2014, 07:08 AM
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Quote:
Originally Posted by Axxion View Post

I have a room with almost identical dimensions. I have that null at 63 hz. Used a umik 1 to derermine. I have 2 fv15hps upfront. Havnt tried moving one sub to the rear but i might try it. really hard to find a place anywhere other then the current loacations.
With both subs in the front of the room they'll both excite the same peaks and nulls off the wall in the back of the room, and the same for the distance to the LP. Where below 100hz is concerned symmetry looks good, sounds bad.
Don't overlook ceiling bounce as a major contributor to poor response. Not only will you get better results with the subs on opposite ends of the room, you'll also get a better result with them on the opposite vertical plane. One on the floor and one elevated will work better than both on the floor. You seldom see subs on stands, but that doesn't mean they shouldn't be, just that it's not as easy as floor placement.

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post #28 of 38 Old 02-14-2014, 07:23 AM
 
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Quote:
Originally Posted by Axxion View Post

I have a room with almost identical dimensions. I have that null at 63 hz. Used a umik 1 to derermine. I have 2 fv15hps upfront. Havnt tried moving one sub to the rear but i might try it. really hard to find a place anywhere other then the current loacations.

The only way I found to get rid of these problems was to place a sub nearfield on the opposite wall of the main equipment/flat screen wall. Fortunately, the wife cooperated. Problem solved. biggrin.gif
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post #29 of 38 Old 02-14-2014, 08:53 AM
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The subwoofer game is so much fun isnt it! Our own little zen garden. Imagine how happy we are made when we have found our perfrct flat response! Then we have to make something else better...

It is fun to see what the universe is capable of. And then there is that big black hole at the center of our galaxy.... Big vacuum cleaner waiting to destroy all existence as we know/knew it.

Enjoy the experience, as everyone on avs is a type of hedonist essentially...

Sorry, had to get those dark thoughts out of my system. Back to calibrating subwoofers!

Blazar!
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Enjoy the experience, as everyone on avs is a type of hedonist essentially...

...biggrin.gif
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