Bass trap placement - high or low? Does it matter? - Page 6 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #51 of 110 Old 02-20-14, 05:26 PM
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Re: Bass trap placement - high or low? Does it matter?

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ajinfla wrote: View Post
Perhaps Sanjay can explain how a 4" thick pillow surgically "traps" 20-50+ foot wavelengths, much less having no effect on spatial perception and timbre? I don't see how that's possible.
Where did I tell liteglow to use 4" thick pillows for his dip between 20-50 Hz? I explained why bass traps are placed at boundries (or where boundries meet). For his low frequency dip, I asked if he could move his sub.

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post #52 of 110 Old 02-20-14, 06:09 PM
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Re: Bass trap placement - high or low? Does it matter?

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Where did I tell liteglow to use 4" thick pillows for his dip between 20-50 Hz? I explained why bass traps are placed at boundries (or where boundries meet). For his low frequency dip, I asked if he could move his sub.
Hi Sanjay, well here, you may not specifically mention "4inch ", but you say:

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liteglow wrote: View Post
But why make a smooth bass on the corners when I only listen i the middle og room.
It is reflections from the walls that are causing the cancellation (drop in level) in the middle of the room where you sit. Placing absorption/traps on the walls reduces those reflections, thereby reducing the cancellation at your listening position. To make more efficient use of absorption, you can place the traps where walls meet (corners).

Also, is it possible to move your subwoofer to the middle of the room where the dip is occuring?
So what thickness "bass traps" does he need to place on his walls to mitigate the LP 20-50hz dip? And where on which walls exactly?

AJ

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post #53 of 110 Old 02-20-14, 06:55 PM
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Re: Bass trap placement - high or low? Does it matter?

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DanTheMan wrote: View Post
Everything makes a difference. In general, you want to absorb the whole front wall with something thick like 4" thick or so. Bass trapping the front corners with broadband absorption like John has. The next absorption point would be your first ipsilateral reflection and then the middle of the rear wall. Some people will also recommend absorbing the first reflection from the ceiling.

Dan
Sorry to hijack a thread but its related...
I can't place a trap or panel centred on the rear wall but I can place it +/-30" from the rear wall. Would this be worth the effort and cost?

Edit, I missed that there are 55 posts thus far in this tread, just checked the new post section and I ended up on page 1. The question relates to post #9.

Last edited by brwsaw; 02-20-14 at 07:00 PM.
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post #54 of 110 Old 02-20-14, 10:16 PM
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Re: Bass trap placement - high or low? Does it matter?

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ajinfla wrote: View Post
Hi Sanjay, well here, you may not specifically mention "4inch "
They why start a post with "Perhaps Sanjay can explain how a 4" thick pillow surgically "traps" 20-50+ foot wavelengths"?
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ajinfla wrote: View Post
So what thickness "bass traps" does he need to place on his walls to mitigate the LP 20-50hz dip?
Depends on the type of trap used. Membrane traps can be placed on the wall, where pressure is greatest. With fluffy fiberglass, it would take a couple feet thick, which would be better placed in corners.
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And where on which walls exactly?
In which room, exactly? Can you post a floor plan and some pics of the walls?

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post #55 of 110 Old 02-20-14, 11:50 PM
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Re: Bass trap placement - high or low? Does it matter?

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JohnJSmith wrote: View Post
I got a set of 4 Acoustimac 48x24x4" corner traps, and I'm wondering where to put them. Should they go up near the ceiling or down by the floor or in the middle? Or does it make any difference? I don't want them right on the ground because I don't want my cats mistaking them for scratching posts, but I don't have to put them right up against the ceiling to keep them out of claw range.
If truly bass traps, then best practice is 1st location placement, at the tri-corners near the ceiling and at the tri-corners near the floor. everyone needs bass traps and plenty of them, for proper mode reduction. Bass modes pile up in the corners. Their are some great room mode calculators out there that can graphically indicate the modes in your room based on dimensions and give you relative placement of the traps and the required trapping frequencies.
Ultimately, it would depend on the type of trap construction as to placement. then measure measure measure.
Bottom line is, no matter where you put them, it will help the room. The question is how many do you have room for, and are you willing to incur the associated cost of treating the room. It is my opinion, that it is one the best investments you can make for your theater or listening room.
JMO.
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post #56 of 110 Old 02-21-14, 05:43 AM
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Re: Bass trap placement - high or low? Does it matter?

Hi AJ

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ajinfla wrote: View Post
What about nearfield placement or adding a 2nd or 3rd sub to spatially average out the dips and eq'ing down any peaks?
Do you mean nearfield placement of the subwoofer or nearfield placement of absorbers.

If it is the placement of subwoofers I doubt that simply putting them closer to the listening position helps with room modes.
Because the subs excite the room modes depending their position in the room and not relative to the listening position.

That's why I put thelink to a very good paper on this:
Quote:
Babak wrote: View Post
Regarding modes and bass traps...
The link that I posted (the White Papers from Harman) leads to papers regarding good low frequency performance, including the optimal number and placement of subwoofers.

The paper " Part Three: Getting the Bass Right"
( http://www.harman.com/EN-US/OurCompa...ndRoomsPt3.pdf)
summarises everything in a very good way.

How to avoid exciting room modes is an important point.
You don't need bass traps for room modes that are not excited.
I would recommend putting the subwoofer on a null of a room mode and the listening position on another.

As you proposed, using 2 subwoofers would also help to get a better bass response.
Position: in the middle of the front wall and the rear wall, respectively.

Or try to put them further away from the wall, so you get a position where 2 nulls meet.

Cheers
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post #57 of 110 Old 02-23-14, 08:34 AM
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Re: Bass trap placement - high or low? Does it matter?

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liteglow wrote: View Post
Sounds like there is some testing that can be done.
I think I will start a new thread about my problem, and add pictures of the room including schematic etc..
as soon I got time...
Good idea. And perhaps answer how the subs and measurement in middle of room was done.


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sdurani wrote: View Post
Good info, but doesn't apply to the low frequencies being discussed in a thread about bass traps.
Again Sanjay, can you explain how in room "bass traps" can be spatial perception transparent? Thus making babaks concerns not applicable. Thanks.

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sdurani wrote: View Post
They why start a post with "Perhaps Sanjay can explain how a 4" thick pillow surgically "traps" 20-50+ foot wavelengths"?
Because the thread (starting at post #1) is about:
Quote:
Bass trap placement - high or low? Does it matter?
I got a set of 4 Acoustimac 48x24x4" corner traps..
Your quoted response was to niteglow, in this thread, who is asking where to place traps for his 20-50hz dip. Perhaps I misunderstood your response in the context of the thread.

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sdurani wrote: View Post
Depends on the type of trap used. Membrane traps can be placed on the wall, where pressure is greatest. With fluffy fiberglass, it would take a couple feet thick, which would be better placed in corners.
Ok, you believe is is feasible and perhaps even advisable to remove the peaks around a mid room 20-50hz dip with the right "trap"? Or are other methods not involving traps more prudent?

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sdurani wrote: View Post
In which room, exactly? Can you post a floor plan and some pics of the walls?
Niteglows room that you are discussing.
I'll be interested in seeing how you do your bass trap analysis based on his pics.
Always trying to learn here, thanks.

cheers

AJ

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post #58 of 110 Old 02-23-14, 08:50 AM
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Re: Bass trap placement - high or low? Does it matter?

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Babak wrote: View Post
Hi AJ
Do you mean nearfield placement of the subwoofer or nearfield placement of absorbers.
The sub.

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Babak wrote: View Post
If it is the placement of subwoofers I doubt that simply putting them closer to the listening position helps with room modes.
I disagree, it will change things significantly. Nearer than 1m should practically eliminate all (sub) modal effects.

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Babak wrote: View Post
Because the subs excite the room modes depending their position in the room and not relative to the listening position. That's why I put thelink to a very good paper on this:
I would recommend putting the subwoofer on a null of a room mode and the listening position on another.
I know that paper well . It's specific for "listening area", as in a multi seating HT. I think niteglow is only interested in his seat/sofa.

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Babak wrote: View Post
As you proposed, using 2 subwoofers would also help to get a better bass response.
Yes.
My position is that EQ and multiple subs is a superior LF smoothing solution, for most HT people, than anything related to "traps". Without affecting spatial perception. Or making your room smaller.
YMMV.

cheers

AJ

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post #59 of 110 Old 02-23-14, 01:52 PM
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Re: Bass trap placement - high or low? Does it matter?

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ajinfla wrote: View Post
Again Sanjay, can you explain how in room "bass traps" can be spatial perception transparent?
By placing them in locations that contribute the least to spaciousness (corners or front & back walls).
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ajinfla wrote: View Post
Because the thread (starting at post #1) is about:
But my two replies were to niteglow (starting at post #20), not the OP, so the 4" traps were never part of the discussion I was having with niteglow (I don't even know if he has traps yet). Hence my asking why you were linking me to 4" pillows.
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Your quoted response was to niteglow, in this thread, who is asking where to place traps for his 20-50hz dip. Perhaps I misunderstood your response in the context of the thread.
You did. If you read both my replies to niteglow, you'll see that I was explaining how bass traps work. Not once did I ask him to use bass traps, let alone 4" pillows. Instead, I asked if he could move his sub. It's in my posts, none have been edited.
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ajinfla wrote: View Post
Ok, you believe is is feasible and perhaps even advisable to remove the peaks around a mid room 20-50hz dip with the right "trap"? Or are other methods not involving traps more prudent?
I believe it should first be addressed via subwoofer placement, hence my question to nightglow. If that fails, then do what is possible using traps.
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ajinfla wrote: View Post
Niteglows room that you are discussing.
In that case, I'll repeat my question: Can you post a floor plan and some pics of the walls?
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ajinfla wrote: View Post
Always trying to learn here, thanks.
LOL

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post #60 of 110 Old 02-23-14, 03:17 PM
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Re: Bass trap placement - high or low? Does it matter?

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sdurani wrote: View Post
By placing them in locations that contribute the least to spaciousness (corners or front & back walls).
So now you state they will contribute to/affect spatial reproduction. Then Babaks spatial reproduction aspect posts were indeed relevant.
I agree. Any "trap" (aka huge absorber) that would remotely affect niteglows 20-50hz wavelengths, will certainly affect spatial reproduction. Corner or not.
I'll use the term affect rather than say, "harm", since many like those sighted effects.

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sdurani wrote: View Post
Not once did I ask him to use bass traps, let alone 4" pillows. Instead, I asked if he could move his sub.
Well, my reading of this:
Quote:
It is reflections from the walls that are causing the cancellation (drop in level) in the middle of the room where you sit. Placing absorption/traps on the walls reduces those reflections, thereby reducing the cancellation at your listening position. To make more efficient use of absorption, you can place the traps where walls meet (corners).
Also, is it possible to move your subwoofer to the middle of the room where the dip is occuring?
Suggested he use traps and also consider moving his sub.
My suggestion is more subs and less "traps".
We'll have agree to disagree on effective/spending suggestions for 20-50hz issues.

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sdurani wrote: View Post
I believe it should first be addressed via subwoofer placement, hence my question to nightglow. If that fails, then do what is possible using traps.
As above, agree with the relocation/placement, disagree with the use of traps instead of subs.

Quote:
sdurani wrote: View Post
In that case, I'll repeat my question: Can you post a floor plan and some pics of the walls?
If niteglow sends me one I'll post it for you. I'm fascinated so see where 20-50hz traps are placed in 8 (or more) room corners.
Or are they usually full floor to ceiling height?

cheers

AJ

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