Bass trap placement - high or low? Does it matter? - Page 5 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #41 of 110 Old 02-20-14, 11:22 AM
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Re: Bass trap placement - high or low? Does it matter?

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

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


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post #42 of 110 Old 02-20-14, 11:50 AM
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Re: Bass trap placement - high or low? Does it matter?

Quote:
sdurani wrote: View Post
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.

------------------

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.

------------------

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

In post #28 you stated the following:
Quote:
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:
Quote:
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.

------------------

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.

------------------

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

Your suggestion where to place the bass traps is not very concrete:
Quote:
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 ...

------------------

And again.

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

So what are you arguing about?

Cheers
Babak

Last edited by Babak; 02-20-14 at 01:36 PM.
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post #43 of 110 Old 02-20-14, 03:07 PM
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Re: Bass trap placement - high or low? Does it matter?

Quote:
Babak wrote: View Post
I replied to post #24 by rkeman, especially beause he mentioned moving the seat closer to the wall.
You replied to post #28 by me, which can be seen quoted in your reply (post # 29).

Sanjay
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post #44 of 110 Old 02-20-14, 03:55 PM
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Re: Bass trap placement - high or low? Does it matter?

Is 100mm thick enough for bass traps?
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post #45 of 110 Old 02-20-14, 03:58 PM
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Re: Bass trap placement - high or low? Does it matter?

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
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post #46 of 110 Old 02-20-14, 04:33 PM
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Re: Bass trap placement - high or low? Does it matter?

Babak, I'm ecstatic to see someone here paying attention.
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

AJ

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post #47 of 110 Old 02-20-14, 04:35 PM
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Re: Bass trap placement - high or low? Does it matter?

Quote:
HDMan wrote: View Post
Is 100mm thick enough for bass traps?
You mean absorbers? For what frequency range? What material?

AJ

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post #48 of 110 Old 02-20-14, 05:19 PM
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Re: Bass trap placement - high or low? Does it matter?

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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post #49 of 110 Old 02-20-14, 05:21 PM
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Re: Bass trap placement - high or low? Does it matter?

Quote:
liteglow wrote: View Post
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

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?

AJ

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post #50 of 110 Old 02-20-14, 05:25 PM
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Re: Bass trap placement - high or low? Does it matter?

Quote:
Babak wrote: View Post
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?

AJ

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