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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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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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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 :rolleyesno:
 

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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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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 :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.
 

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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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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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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?
 

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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/OurCompany/Innovation/Pages/WhitePapers.aspx?CategoryID=White papers

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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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.
 

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Good info, but doesn't apply to the low frequencies being discussed in a thread about bass traps.
The same for post #24.

Also your post could be understood in terms of comb filters:
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).
This is a description of comb filters due to reflections canceling out certain frequencies i.e. causing dips.

Also dips in low frequencies are not heard very well by listeners. Lo

The main effect of low frequencies in small rooms are standing waves leading to room modes.
Dips through comb filtering is not such an issue.

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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.

Cheers
Babak
 

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Also your post could be understood in terms of comb filters:
Not when taken in context (i.e., in a discussion about bass traps, where liteglow was asking about a drop in the 20Hz to 50Hz region).

I don't want to dissuade you from introducing other concepts (comb filter effects, how our hearing works, spaciousness, perceived soundstage, Precedence Effect, first reflections, diffusors, etc.) into this discussion, but I hope you understand that they aren't related to this particular discussion (using bass traps to address a drop in the 20-50Hz region).

Like I said, it is good information but is applicable to frequencies outside the bass range.
 

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Not when taken in context (i.e., in a discussion about bass traps, where liteglow was asking about a drop in the 20Hz to 50Hz region).

I don't want to dissuade you from introducing other concepts (comb filter effects, how our hearing works, spaciousness, perceived soundstage, Precedence Effect, first reflections, diffusors, etc.) into this discussion, but I hope you understand that they aren't related to this particular discussion (using bass traps to address a drop in the 20-50Hz region).

Like I said, it is good information but is applicable to frequencies outside the bass range.
I appreciate your input.

Again, the topic of reflections was not introduced by me. I just responded to an earlier post.

Also taken in the context of low frequencies, your sentence
It is reflections from the walls that are causing the cancellation (drop in level) in the middle of the room where you sit.
describes reflections that cause cancellations leading to a decrease in sound pressure level.

That's the same thing that leads to comb filtering and something different than standing waves leading to room modes and nulls.

It doesn't matter where the dips in the frequency response come from - comb filter effects, cancellations through reflections, narrow band filters or EQ's.

Listeners don't hear dips in the frequency response very well - if at all.
That is the case no matter whether it is in the high or in the low frequency region.

The reason for this lies in the way the hearing works.
Microphones work in a different way, and that's why these dips can be measured but hardly be heard.

I hope you understand that the topic whether dips can be heard is relevant for this discussion, as liteglow wrote about dips.

However, as long as we don't know how liteglow made his measurements and how the results look like, all of this discussion is only speculation.


Cheers
Babak
 

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I hope you understand that the topic whether dips can be heard is relevant for this discussion, as liteglow wrote about dips.
Again, if you want to obfuscate a discussion about low frequencies and bass traps with concepts (comb filter effects, spaciousness, perceived soundstage, Precedence Effect, first reflections, diffusors) that apply to frequencies outside that range, then that's up to you. However, if you could offer something (anything) that could help liteglow with his 10dB dip between 20-50Hz (besides telling him "listeners don't hear dips"), then that would be even better.
 

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Again, if you want to obfuscate a discussion about low frequencies and bass traps with concepts (comb filter effects, spaciousness, perceived soundstage, Precedence Effect, first reflections, diffusors) that apply to frequencies outside that range, then that's up to you. However, if you could offer something (anything) that could help liteglow with his 10dB dip between 20-50Hz (besides telling him "listeners don't hear dips"), then that would be even better.
There's no need to get offensive.
Nobody wants to obfuscate anything, so please take it easy.

Maybe I was not clear.

As I wrote before, the topic about reflections was not introduced by me but I only responded to that.
So you should place your complaint about that somewhee else.

Obviously you have overread my other comments to liteglow's bass dip issue.
I also understand that some points appear obfuscating if the connections are not clear.
So I'll try to explain it in another simpler way.

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The first question is, whether the dip is a problem at all-
It would help to see the measurement

There are tolerance limits for variations the room response curve.
Is the dip going below the lower limit of that tolerance range?

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The second question is what causes the dip.
It would be good to know how the measurements were made.

The dip could be a measurement artefact.
Or - if it was a measurement of the room response curve - the dip can be a cancellation between direct and reflected sound.

If it is a cancellation issue it doesn't matter because the ear does not perceive those cancellations that are measured by the microphone.
Ears and microphones work differently and hence response differently to that.

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The third question is whether the dip can be heard at all.

Experiments were made using dips with a certain center frequency, a certain width and a certain amplitude with peaks that have the same parameters.
Listeners perceived the peaks pretty clearly whereas they did only weakly respond to the dips, in many cases they did not perceive them at all.

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So I think that this is an issue that could possibly not be relevant.

It can be a measurement artefact or a dip that is not perceivable (but measurable) or both.


As long as we don't have more details about the measurements, nothing can be added to the discussion.
There is no point in making speculations.

And there is also no point in picking words and starting a dispute about them.


Cheers
Babak
 

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Hi

regarding the question, whether the dip is too big one can refer to the recommendations of the ITU (International Telecommunication Union)

Recommendation ITU-R .1116-1
Methods for the Subjective Assessment of Small Impairments in Audio Systems Including Mulstichannel Sound Systems

http://www.itu.int/dms_pubrec/itu-r/rec//R-REC-.1116-1-199710-I!!PDF-E.pdf

Especially interesting for this topic:
8.3.4.1 Operational room response curve
It reads as follows:
The operational room response curves are defined as the one-third octave frequency responses of the sound pressure levels produced by each monitor loudspeaker at the reference listening position, using pink noise over the frequency range 50 Hz-16 kHz. The measured operational room response curves shall fall within the tolerance limits given in Fig. 2.

The differences between the operational room response curves produced by each of the (stereo or multichannel) front loudspeakers at the reference listening point should not exceed the value of 2 dB within the whole frequency range.
This is why I asked about details, how the measurement was made.
Was it measured with pink noise?
Was is measured in one-third octave bands?
How does it compare with the tolerance limits for operational room response curve on page 13?

It would also be helpful to see the RT60 measurements of the room


Cheers
Babak
 

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As I wrote before, the topic about reflections was not introduced by me but I only responded to that.
Are you able to separate low frequency reflections in the modal range vs reflections above the transition frequency that result in comb filtering, spaciousness, perceived soundstage, precedence effect, first reflections, diffusors? I only ask because the post you responded to was about the former but the information you posted is about the latter, giving the impression you can't separate the two concepts.
 

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Sanjay,

Are you able to separate low frequency reflections in the modal range vs reflections above the transition frequency that result in comb filtering, spaciousness, perceived soundstage, precedence effect, first reflections, diffusors? I only ask because the post you responded to was about the former but the information you posted is about the latter, giving the impression you can't separate the two concepts.
I don't have clue why you try to provoke me by using this offensive style.

In my point of view there is a difference between reflections that lead to cancellations (comb filtering) and room resonances blow the Schroeder Frequency causing standing waves that lead to exaggerated response and booming bass at certain frequencies (modes).

So if you really want to go down the route to be picky on terms and definitions:
When looking at low frequency standing waves (room modes) we are talking about resonances and not about reflections.

What is written here about reduction of sound pressure due to reflections has nothing to do with resonances/standing waves/room modes but is a comb filter effect taking place also at other frequencies.

In my understanding those are the two concepts that need to be seperated but are mixed up here.

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Regarding spaciousness, reflections precedence effect etc.:

My answer in post #29 was a reply to the posts #24.

Post #24 stated
A typical room has many areas of cancellation and reinforcement that vary by frequency.
That's describing comb filtering, similar to other posts that deal with reflections that cause cancellations.

The best compromise is finding listening and loudspeaker locations that yield the least variation and yet provide good imaging.
Good imaging is dependent on reflections and includes spaciousness. Precedence Effect plays a major role here.

Try moving the seat closer to the rear wall [...]
This would increas early reflections, probably also those earlier than 5 ms. That reduces imaging, soundstage. The Precedence Effect plays a major role here as well.
So I would reccomend not to move the seat too close to any wall.

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My other posts #31, #34, #36 and #37 did not deal with those topics at all.
Can it be that you did not read them because you are still stickig to my post #29?

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Room acoustics deals with a whole bunch of topics at the same time.
One cannot really look at optimal positioning of the loudspeakers and the seat in regards to room modes without looking at the consequences in regards to the wall reflections at the same time.
The optimization of one parameter can lead to a worse situation with a different parameter.

Maybe that is also one thing that seems to obfuscate things.
One simply cannot look at one parameter in isolation.

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So, again my three main points from those posts:

It would be interesting to see the data and the graph from the measurement.
Then we could see what the observed dip really looks like and wheather it is beyond the tolerance levels.

It would also be good to know how the measurements were conducted.
Maybe the dip is more a measurement artefact.

The human ear does not really perceive dips very well. Often it does not perceive them at all.
It is more sensitive to peaks.
So maybe the observed dip is just a detail that only looks ugly in a measurement but is not relevant for the listening experience.

Cheers
Babak
 

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In my point of view there is a difference between reflections that lead to cancellations (comb filtering) and room resonances blow the Schroeder Frequency causing standing waves that lead to exaggerated response and booming bass at certain frequencies (modes).
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.
 
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