Bass trap placement - high or low? Does it matter? - Page 3 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #21 of 110 Old 02-18-14, 07:28 AM
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Re: Bass trap placement - high or low? Does it matter?

I understand. But why make a smooth bass on the corners when I only listen i the middle og room.

So basicly i need to reduce peak in corners, smooth out the levels and then turn up the volume on the sub?
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post #22 of 110 Old 02-18-14, 08:12 AM
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Re: Bass trap placement - high or low? Does it matter?

Corner absorbers smooth bass response evrerywhere in the room, not just in the corners! The reason for placing absorbtion panels across a corner, as illustrated in the photographs earlier in this thread, is that it increases the bandwidth of the absorption and wide-band absorption avoids a "dead" sounding room. Using thicker (e.g. 6" or 8") and denser material also allows more effective low frequency absorption without significantly increasing the size of the panels.
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post #23 of 110 Old 02-18-14, 10:24 AM
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Re: Bass trap placement - high or low? Does it matter?

ok, sorry for asking maybe some obvious question for somebody, but I try to learn as much as possible.

I start to understand what you say, and I also understand about the point of place bass traps and acoustic treatment around in the room to remove echo and reflection of sound you dont want to hear where you sit.

how do I know if my subwoofer are smooth or not?
I have REW and UMIC1, done some testing and can try to make a new thread about my problem.

But if my sub (PBS 13 ULTRA) is to big for my room, is there any solution to make the bass more loudly in the center of my room, or is there no hope for me ?
The perfect sound is when I sit all the way back in my room, I can hear and feel the bass below 16hz perfect and nicely. when I sit in my couch in the center of my room it feels like a dead spot with no sound at all (sound=subwoofer)

So my last hope is that maybe bass traps or other treatment for my room can solve my issue.
if not I feel it was a big mistake to buy a Hi End speaker if my room is to small
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post #24 of 110 Old 02-18-14, 11:31 AM
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Re: Bass trap placement - high or low? Does it matter?

A typical room has many areas of cancellation and reinforcement that vary by frequency. The best compromise is finding listening and loudspeaker locations that yield the least variation and yet provide good imaging. A central seating position is often among the worst choices, as you have discovered. Try moving the seat closer to the rear wall and/or the subwoofer to a different location. A relatively easy method for optimizing placement is to place the subwoofer at the listening position and listen at the various possible locations that the subwoofer could occupy. Remember that the subwoofer doesn't have to be in a corner, against a wall or even near the satellite speakers.
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post #25 of 110 Old 02-18-14, 01:13 PM
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Re: Bass trap placement - high or low? Does it matter?

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rkeman wrote: View Post
A typical room has many areas of cancellation and reinforcement that vary by frequency. The best compromise is finding listening and loudspeaker locations that yield the least variation and yet provide good imaging. A central seating position is often among the worst choices, as you have discovered. Try moving the seat closer to the rear wall and/or the subwoofer to a different location. A relatively easy method for optimizing placement is to place the subwoofer at the listening position and listen at the various possible locations that the subwoofer could occupy. Remember that the subwoofer doesn't have to be in a corner, against a wall or even near the satellite speakers.

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.
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post #26 of 110 Old 02-18-14, 02:27 PM
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Re: Bass trap placement - high or low? Does it matter?

It sounds as though there has been much experimentation with subwoofer position and phase without any significant improvement. Although unusual, perhaps the longitudinal and axial modes are arranged such that the center listening position has a broad null from 20-50Hz that simply cannot be addressed. The next suggestion would be to lower the crossover frequency of the satellites into the 40-50Hz range and test using the "all stereo" mode on the preamplifier/processor. Multiple bass sources tend to blend the room modes attenuating deep nulls and large peaks and with all the speakers and subwoofer operating the best possible room curve should emerge. Don't use high levels for this test if the low frequency response of the satellites is limited.
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post #27 of 110 Old 02-18-14, 02:54 PM
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Re: Bass trap placement - high or low? Does it matter?

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...
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post #28 of 110 Old 02-18-14, 11:36 PM
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Re: Bass trap placement - high or low? Does it matter?

Quote:
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?

Sanjay
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post #29 of 110 Old 02-19-14, 10:38 AM
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Quote:
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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?
Some helpful reading that addresses all those topics :

http://www.harman.com/EN-US/OurCompa...White%20papers

There are also very good chapters in Floyd Toole's book.
Some takeaways for me, that could help in this discussion :

Comb filter effects (dips through cancellations) are clearly measurable.
But several listening tests showed that listeners don't perceive them very well (that can be explained by the way how our hearing works).


Deadening all reflections is not a good thing, as reflections (mainly from 60 left and right) are crucial for spaciousness.
If one dampens all the reflections, the perceived soundstage will be flat.

It would be better to build on the Precedence Effect :
The speakers and the listening position should be positioned where the traveling distance of the first reflections are at least 1.7 metres longer than that of the direct sound (more than 5 ms time difference).

The reflecting walls then should be treated with diffusors rather than absorbers.


And as Dan already mentioned :
Bass traps work best when not placed on the corners where sound pressure is at a maximum but in between, where sound velocity is the highest.

Cheers
Babak
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post #30 of 110 Old 02-19-14, 12:37 PM
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Re: Bass trap placement - high or low? Does it matter?

Quote:
Babak wrote: View Post
Comb filter effects (dips through cancellations) are clearly measurable.
But several listening tests showed that listeners don't perceive them very well (that can be explained by the way how our hearing works).

Deadening all reflections is not a good thing, as reflections (mainly from 60 left and right) are crucial for spaciousness.
If one dampens all the reflections, the perceived soundstage will be flat.

It would be better to build on the Precedence Effect :
The speakers and the listening position should be positioned where the traveling distance of the first reflections are at least 1.7 metres longer than that of the direct sound (more than 5 ms time difference).

The reflecting walls then should be treated with diffusors rather than absorbers.
Good info, but doesn't apply to the low frequencies being discussed in a thread about bass traps.

Sanjay
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