Uneven subwoofer performance through room - AVS Forum
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post #1 of 16 Old 07-27-2013, 09:03 AM - Thread Starter
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I currently have a dedicated theater room in my home that seats two rows. My Denon X4000 has been calibrated for the main listening position in the front left seat. However last night I was forced to sit in the backrow due to having guests. The bass frequencies in the front row sound a bit weak and I kicked everything up from the Audyssey settings initially. They are still not amazing but they seem to be more even in the front row. Last night sitting in the backrow I was smothered with bass frequencies. It was overbearing and for the most part distracted from the viewing experience. Bass frequencies were very heavy, booming, and easily twice if not more, the volume of the bass frequencies in the front row. I am hoping to have the bass frequencies be haflway between what they are in each row for both rows.

I have stared to treat my room acoustically with 6 total 2'x4' 2" panels along the side walls and the backwall. I have not done much else yet. I am still learning this process of treating the room. I am looking for some suggestions to get more even sound in the back and front row. I will eventually build a riser for the backrow and thinking of setting it up in some way that will absorb some of the intense bass frequencies of the back row.

I hope I am posting this is the correct place. Let me know if I need to move it. Here is a bit of information about my room.

16x19 dedicated home theater room (screen on 16' wall)
Denon X4000 (no external amp yet)
Polk RTiA7 front
Polk CSiA6 center
Polk FXiA6 side surrounds
Polk RTiA1 back surrounds
2 x Polk PSW505 on the front wall about 4 feet from either side wall
Front row is about 12 feet from from sound stage
Back row is about 17 feet from front sound stage is is flush with the back wall

Let me know what additional information is needed and thanks in advance.
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post #2 of 16 Old 07-27-2013, 09:57 AM
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Bass is always strongest around room boundaries and weakest in the room center. EQing can't really remove bass from the back while strengthening it in the front row. The best thing for that is to find new placements for the subwoofers. Bass traps won't do much to affect the subwoofer band. You might try near-field placement for the subs for the front row.
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post #3 of 16 Old 07-27-2013, 11:14 AM
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Placement and multiple subs is the way to start the project to correct the bass. Sub EQ can only fix a few things and is at the end of the fix it line for the most part. The panel mentioned by the OP are fine for higher bass frequencies but, it is the stuff under 80 Hz that require 1 ft or thicker traps that most of us don't want in our HT rooms. Pioneer Elite avr's have a nice standing wave correction feature that is very good IMHO.

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post #4 of 16 Old 07-27-2013, 11:45 AM
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I would try nearfield placement as suggested by shady. you mightneed 3-4 subs to even out the bass response as well.
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post #5 of 16 Old 07-27-2013, 12:52 PM
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How far is your 2nd row of seats from the rear wall? If you have 4-5 feet space available behind the 2nd row, try putting one sub behind it in one corner and the second one diagonally on the front wall. That will effectively disperse bass energy across all seats. You can also try putting subs along the side walls; one on each opposing wall along half length.

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post #6 of 16 Old 07-27-2013, 01:21 PM
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Quote:
Originally Posted by Isantus View Post

The bass frequencies in the front row sound a bit weak and I kicked everything up from the Audyssey settings initially. They are still not amazing but they seem to be more even in the front row. Last night sitting in the backrow I was smothered with bass frequencies. It was overbearing and for the most part distracted from the viewing experience. Bass frequencies were very heavy, booming, and easily twice if not more, the volume of the bass frequencies in the front row.
Seems your front row is around 5 feet from the back wall, which is near the location of a 60Hz null in your room length. By comparison, your back row is flush with the back wall, which is the location where that same bass frequency is peaking. Might be why you're experiencing such a big difference in bass.

Would you be willing to move your front row about 16 inches forward so you are no longer sitting in a bass null?

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post #7 of 16 Old 07-27-2013, 01:31 PM - Thread Starter
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Quote:
Originally Posted by sdurani View Post

Seems your front row is around 5 feet from the back wall, which is near the location of a 60Hz null in your room length. By comparison, your back row is flush with the back wall, which is the location where that same bass frequency is peaking. Might be why you're experiencing such a big difference in bass.

Would you be willing to move your front row about 16 inches forward so you are no longer sitting in a bass null?

My measurements for actual rows is a bit rough so I would have to actually measuring everything to give exact details. I do appreciate everyone's help thus far. It is a bit disappointing with this room but I don't sit in the back row often. I have thought about moving one of the two subwoofers to the back right corner and leaving one in the front left corner to help even things out. I was also thinking about moving the back row out about a foot. In addition I was thinking that with the riser I would fill it will insulation of some kind and put vents in behind the couch to hopefully absorb some of the frequencies. Even if I did decide to put in bass traps they certainly wouldn't be 1 foot thick as I don't have the room. I have also thoughts about moving the subwoofers to the side walls. ON one wall it wouldn't be a big deal but on the other it would be right in the entry pathway and would be a problem.

With a third subwoofer on the back right corner, do you think that would help the overall frequencies? I kind of feel that as of this point with the problem being in the front row away from the wall that a third subwoofer is only going to make the problem worse. Would it be beneficial to turn the subwoofers out toward the walls or in toward the MLP, or perhaps move them closer to the side walls?

Thanks again everyone! Love this hobby but the small things are killing me.
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post #8 of 16 Old 07-27-2013, 01:33 PM - Thread Starter
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Originally Posted by basshead81 View Post

I would try nearfield placement as suggested by shady. you mightneed 3-4 subs to even out the bass response as well.

Sorry but I am not sure what you mean by near field placement. I'm still kind of new at this whole thing.
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post #9 of 16 Old 07-27-2013, 02:12 PM
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Near-field placement is when the sub is very close to the listening position, like an end table or right behind the seat. Doing this to your front seats may bring the loudness at those positions up disproportionately more than the back row, so it would be easier to EQ down and even everything out better. Adding more subs might exacerbate the problem until you can tame the current response.
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post #10 of 16 Old 07-27-2013, 02:26 PM - Thread Starter
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Ok. That makes sense and also what I was thinking. I am going to look at trying to move them to the side walls which would get them closer, but not sure if close enough. I am sure this is something many people have to deal with. I will continue my research.
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post #11 of 16 Old 07-27-2013, 02:29 PM
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Quote:
Originally Posted by sdurani View Post

Would you be willing to move your front row about 16 inches forward so you are no longer sitting in a bass null?
It would still be in a null zone, albeit one with a lower frequency. Having both subs in the front of the room is the problem, they both will excite the same reflection cancellation frequency reflection off the rear wall.

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post #12 of 16 Old 07-27-2013, 02:38 PM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

It would still be in a null zone, albeit one with a lower frequency. Having both subs in the front of the room is the problem, they both will excite the same reflection cancellation frequency reflection off the rear wall.

So the only way to get rid of this would be two have two subs different distances from the MLP, correct? In other words I would have to put one on the back wall (assuming the distance from back to MLP and front to MLP are different), or place them on the side walls?
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post #13 of 16 Old 07-27-2013, 02:38 PM
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Quote:
Originally Posted by Isantus View Post

I have thought about moving one of the two subwoofers to the back right corner and leaving one in the front left corner to help even things out. I was also thinking about moving the back row out about a foot. In addition I was thinking that with the riser I would fill it will insulation of some kind and put vents in behind the couch to hopefully absorb some of the frequencies. Even if I did decide to put in bass traps they certainly wouldn't be 1 foot thick as I don't have the room. I have also thoughts about moving the subwoofers to the side walls.
You're not willing to move your front row so that it is no longer sitting near a bass null? You don't have to do it, just curious why that isn't an option.

Sanjay
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post #14 of 16 Old 07-27-2013, 02:40 PM - Thread Starter
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Originally Posted by sdurani View Post

You're not willing to move your front row so that it is no longer sitting near a bass null? You don't have to do it, just curious why that isn't an option.

No that's not the case at all. I will move the front row if it changes it and improves it but something tells me I am just moving it to a different null zone, correct?
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post #15 of 16 Old 07-27-2013, 02:41 PM
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Originally Posted by Bill Fitzmaurice View Post

It would still be in a null zone
Not for the first 4 length modes of that room.

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post #16 of 16 Old 07-27-2013, 02:47 PM
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Quote:
Originally Posted by Isantus View Post

I will move the front row if it changes it and improves it but something tells me I am just moving it to a different null zone, correct?
Not correct. If you have Microsoft Excel, you can download a free room mode calculator that will graphically display where nulls and peaks are in your room. It's the second item on this page:

http://www.harman.com/EN-US/OurCompany/Innovation/Pages/Calculators.aspx?CategoryID=Calculators
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