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wow I actually got a confusion headache reading all this :sweat: AND I had to look up "obfuscate":dontknow:

As for the original question of base trap placement, to be honest because you have an opening on one side and in the middle back I would say you would have to experiment, perhaps putting all 4 in the front on top of each other to the ceiling will sound better, perhaps none at all.

Play around with them, have a movie marathon where you change them around during a few intermissions, have a few friends over and get opinions.

Take some time and have some fun, its not work its a hobbie:bigsmile:
 

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In that case, you understand that you replied to my post discussing how bass traps could help a room resonance below Schroeder by posting a reply about comb filtering, spaciousness, perceived soundstage, precedence effect, first reflections and diffusors, all of which are discussed in the context of frequencies above Schroeder.
No, you are putting that wrong.
I replied to post #24 by rkeman, especially beause he mentioned moving the seat closer to the wall.
Maybe that could help with the room modes and the low frequency response, but it would make other acoustic parameters worse.

I am sure you understand that.

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I don't know what funny little game you want to play by sticking to this one post of mine and ignoring all others.
Please don't play the "ho-wrote-what-and-where-can-I-prove-him-wrong" game.

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I'm afraid, the concepts of interference and resonance got mixed up here.

In post #28 you stated the following:
It is reflections from the walls that are causing the cancellation (drop in level) in the middle of the room where you sit.
What you described here ist not room resonances but sound interference (between direct sound and reflected sound).
Interference is causing cancellations (rkeman also mentioned reinforcement) and is the cause for comb filtering.

You mention interference (reflections and cancellations) again:
Placing absorption/traps on the walls reduces those reflections, thereby reducing the cancellation at your listening position.
Interferences don't play a significant role below the Schroeder frequency.
Below that frequency room acoustics are dominated by resonances i.e. standing waves.

So there is a mix-up between the concepts of interference and resonance.

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Both interference and resonance happen at all frequencies, below and above the Schroeder frequency.
Below the Schroeder Frequency resonances dominate the acoustic behaviour of the room and interference is negligible.

No matter at which frequency - humans do not perceive dips in the frequency response very well.
Be it interferences and cancellations between direct and reflected or filters or EQs.

Above the Schroeder Frequency the acoustic of the room behaves in a more stochastic manner.
There it makes sense to work with stochastic measurements like RT60.

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Regarding the Placement of the traps (the original question):

Your suggestion where to place the bass traps is not very concrete:
To make more efficient use of absorption, you can place the traps where walls meet (corners).
What kind of bass traps did you think about?
Porous absorbers or resonators?

Dan put it right.
With room resonances, sound pressure is at a maximum at the walls (sound velocity is at a minimum).

Walls an corners the wrong place for porous absorbers, as that type ob absorbers works most effectively at points with high sound velocity (= low soung pressure - the nulls of the room modes).

The corners would be the right position for other types of bass traps (e.g. Helmholtz-Resonators or plate resonators)

I'll assume that you were thinking of resonators and not of (porous) absorbers ...

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And again.

We don't know, what the "dip" looks like and how it was measured.

So what are you arguing about?

Cheers
Babak
 

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You're right, my mistake.

First rekman wrote about reflections then you also wrote about reflections, cancellations and using absorbers against the reflections.

Point given.

Nevertheless the other points are still valid.

Are there any factual topics or do you prefer to write about me and what I wrote wrong?

Cheers
Babak
 

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Babak, I'm ecstatic to see someone here paying attention.:T
You're right on the money.
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. So your info is completely relevant.
Anyone here have measured effects of 4" pillows vs 20-50' waves? From a physics standpoint, I'd be fascinated to see the results.
And yes, it's much more difficult (if not impossible) to perceive dips (cancellations) of pressure if the Q is high. Despite what your eyes "see" your omni mic measuring as pressure.

cheers
 

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I recommend products by Vicoustic.

One can use the Wave Wood panels over the room corners. They then work down to about 100 to 125 Hz.

Then there are the Super Bass Extreme elements for getren frequencies below that.

And there are the Vari Bass Pro elements that can be tuned to specific frequencies to address room modes.
 

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You see this is where my problem begins...

I have with a great help from 1 of my friend, moved my 71kg heavy sub around the room in all possible locations.
Even in the middle of the room did we test the sub.
We did measure the difference each place with my DB tool to check the variations, usually 20 and 50 hz.
At every location we tried the sub, we did also adjust the phase direction in the subwoofer EQ settings.

The end result was that no matter where we did place the sub, there was always a -10 db drop on the center of the room, and in the corner\front\rear the sound was optimized ! (as we also would suspect in many years of HiFi)

So you tell me to sit somewhere else in the room?
I have a 110" screen in the front, the 1,5 meters on the rooms backside is where I have a work desk (this was a deal for the Lady in the house), and I have moved the couch as long forward as possible to not be uncomfortable on the screen.

So as you see, there is no room for moving the couch anywhere in the room :dontknow:

I see only 1 radical solution !!
And that is to set up a small tiny wall behind the couch to make the room even smaller, but then I will be sitting all the way back in the room, making sound better where I sit !
When I hang up a cover (moldon?) behind the couch the DB meter indicate some higher values.
Hi Liteglow, I'm a bit confused here. Your sofa is in middle of room. You moved the sub to the "middle"i.e., nearfield...and still had cancellation at the LP?
 

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I recommend products by Vicoustic.

One can use the Wave Wood panels over the room corners. They then work down to about 100 to 125 Hz.

Then there are the Super Bass Extreme elements for getren frequencies below that.

And there are the Vari Bass Pro elements that can be tuned to specific frequencies to address room modes.
What about nearfield placement or adding a 2nd or 3rd sub to spatially average out the dips and eq'ing down any peaks?
 

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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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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:

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?
 

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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.
 

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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"?
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.
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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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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Hi AJ

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:
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/OurCompany/Innovation/Documents/White Papers/LoudspeakersandRoomsPt3.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
Babak
 

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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.


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.

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:
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.

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?

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
 

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Hi AJ
Do you mean nearfield placement of the subwoofer or nearfield placement of absorbers.
The sub.

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.

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.

As you proposed, using 2 subwoofers would also help to get a better bass response.
Yes.:T
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
 

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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).
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.
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.
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.
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?
Always trying to learn here, thanks.
LOL
 

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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.

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:
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.

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.

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
 
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