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Speakers against front wall - can this be settled?

Speakers within 1m of front wall

  • I tried this and had imaging issues, WITH front wall acoustic treatment

    Votes: 3 7.0%
  • I tried this and had imaging issues, without front wall acoustic treatment

    Votes: 9 20.9%
  • I tried this and had midrange tone issues, WITH front wall acoustic treatment

    Votes: 0 0.0%
  • I tried this and had midrange tone issues, without front wall acoustic treatment

    Votes: 2 4.7%
  • I tried this and had other issues (other than too much bass)

    Votes: 2 4.7%
  • I can't wait to try this

    Votes: 2 4.7%
  • It's great!

    Votes: 25 58.1%

  • Total voters
    43

Hipper

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I can respond to one of your comments about "2ft side and back," as I have heard from multiple places that you will want those two distances to vary from one another, to avoid duplicate wave/reflection from side wall and back(behind speakers) wall.
The objection to this (2' from the front and side walls), I would think, is bass problems, not so much back and side wall reflections. To understand this you need to understand that sound behaves differently in rooms at lower frequencies - below the 'Schroeder Frequency' or 'Transition Frequency'. This frequency is dependent on the room and its contents and is not an exact figure but a range.

https://www.soundandvision.com/content/schroeder-frequency-show-and-tell-part-1

In the case of the frequencies above Schroeder, if a speaker is two feet from the side and front wall the reflections may not necessarily be the same for a particular frequency when you hear it at your listening position.

For example, say you are six feet from the speaker. Both reflections will hit the walls at an angle before coming to your ears. You would need to draw a ray diagram to work out the distances - or apply some trigonometry. I suspect the front wall reflection has further to travel.

As a result the sound will reach you at different times - the direct sound followed by the side wall reflection then that of the front wall. This can have a couple of effects depending on whether the 'precedence effect' comes into play. In my experience, any reflections muddy the sound. Remove them and you get clarity, detail.

https://en.wikipedia.org/wiki/Precedence_effect
 

youngho

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The objection to this (2' from the front and side walls), I would think, is bass problems, not so much back and side wall reflections. To understand this you need to understand that sound behaves differently in rooms at lower frequencies - below the 'Schroeder Frequency' or 'Transition Frequency'. This frequency is dependent on the room and its contents and is not an exact figure but a range.
This interaction between speakers and boundaries (the three nearest ones being the floor, rear wall, and proximal side wall) at low frequencies was described by Roy Allison (http://www.troelsgravesen.dk/BOOKSHELF-1/RoyAllison.pdf), and the boundary dip has been referred to as "the Allison Effect." As seen in the first paper linked above "the most severe are those which occur when the system is placed at a distance from all room boundaries; the worst case is that in which it is remote and equidistant from them." The implication opposite that reached by Allison in the linked papers ("significant improvement is attainable if the woofer is placed very close to two intersecting boundaries") is that woofers should located at a different distance from to the nearest three boundaries, a recommendation also attributed to Roy Allison.`
 

abdo123

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Yes, this is the question I would like answered, if there are valid (measureable) reasons speakers should be away from the front wall. A greater side wall distance is easier for me to understand, because it can reduce short delay reflections of forward firing sound. (blurring image.)

For the experience of affected midrange when close to the front wall, I would like to know what is to blame, and what the mitigations might be.

I appreciate all of the contributions so far and here are my conclusions:

1. Nearest to front wall <1M:
Pro:
a. Reduce SBIR.
b. Uses less room space.

Con:
a. Too much bass (unless speakers were specifically designed to rely on boundary.)
b. Possible issue with "bass timing or imaging" due to a short delay between direct and reflected sound.
-Saying this with certainty means we need to know if we are sensitive to timing/blurring at frequencies below 250hz
c. Possible issue with "midrange" above 250hz. Needs more definition/measurement/evidence, as above 250hz we expect forward firing sound to not be affected by front wall reflection?
Mitigation:
-
EQ or crossover settings to reduce bass
-4" Absorbers on the front wall can provide NRC 1.0 somewhere between 250-315hz, which would help with some midrange reflections.
-No solution for bass timing issues?

2. Placing speakers in the "AVOID zone 1M-2.2M"
Pro:
"Improved imaging." Needs more definition/measurement/evidence.

Con:
a. Deep SBIR notches between 40-80hz
b. Uses more room space

Mitigation:
-Subwoofers.
-Really thick absorbers on front wall.
-Deep SBIR notches cannot be fixed with EQ, as Genelec says increasing output also increases cancellation.


3. Placing speakers 2.2M+ away from front wall
Pro:

Eliminate SBIR for all but 30hz notch?
Con:
Room space.

I should point out that Genelec does mention 2.2M+ as an option, it's not that they only recommend close to the front wall.




Back to the Midrange clarity conversation:
When placed close the the front wall, if the issue with midrange clarity is short delay reflections from the front wall adding to the direct sound:
-What frequency range is most critical? Low midrange 250-500hz? Assuming that we are not getting rearward sound above a certain frequency.
-What increase in ms delay is required to "improve clarity." It seems 1-30ms can be perceived as one event? This might be harder to define (but worth doing.)
-What physical distance is required to achieve the desired ms delay? (1ms=1.1ft, 3ms=1m)
-We would need to know answers to the two above, in order to prove whether or not the "about 1M improves clarity" is doing what we think it is doing, and use the distance more accurately to address specific issues.
-(I am leaning toward this midrange issue again being more about too much bass or SBIR than reflections)





Thanks to @thewas for bringing my attention to this concept in another thread!
SBIR is not just one notch, I explained that in my posts. it's several notches (higher order) with the most problematic ones being at 1/4 wavelength (infinitely deep null) and 1/2 wavelength (+6 dB boost). This behavior continues till the speaker is firing sound exclusively forward.

1641299896768.png
 

abdo123

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My DIY speakers have the mid-woofer about 30 cm from a wall with a damping panel behind. So first cancelation should occur around 285 Hz or so. Below measurement with 35 ms window about 1-1,5 meter from the monitors (excl subwoofer). Not sure how to window such a measurement to reveal SBIR.

View attachment 176502
And another one with about 13 ms window:

View attachment 176504
how will you measure the effect of a reflection if you're windowing it out? ;)
 

Thomas_A

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how will you measure the effect of a reflection if you're windowing it out? ;)

Well backwall reflection should arrive within a shorr time-window if the mid-woofer is 30 cm from wall. Problem is reflections that interfer.
 

abdo123

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Well backwall reflection should arrive within a shorr time-window if the mid-woofer is 30 cm from wall. Problem is reflections that interfer.
SBIR nulls are usually very visible with a regular in-room measurement. they're infinitely deep in amplitude so usually they show as -20 dB or more.
 

Thomas_A

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SBIR nulls are usually very visible with a regular in-room measurement. they're infinitely deep in amplitude so usually they show as -20 dB or more.

Nulls are visible,agreed, for various reasons. I was just try catching the speaker wall reflection here
 

bo_knows

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I can respond to one of your comments about "2ft side and back," as I have heard from multiple places that you will want those two distances to vary from one another, to avoid duplicate wave/reflection from side wall and back(behind speakers) wall.
Correct, the space between the front and side wall measured from the speaker should be different. I would assume more space from the front wall (1 meter) and less from the sidewall. Absorbers are placed in the back, corner(s), and to the sides trying to create the RFZ. As "thewas" mentioned, use absorbers between the speakers to help out with the imaging and focus.
Essentially, 1 meter from the front wall should allow speakers to create good soundstage depth and imaging. Using the crossover to 80Hz should prevent mains to create deep notches in the FR and the subwoofer close to the front wall could deal with the SBIR. EQ should/could be used on any peaks below 300hz.
Ultimately, a larger room allows for more optimum placement and deals better with the room modes. I don't have that luxury.

 

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73hadd

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Updated to add poll to the thread.

One thing I like about trying absolute miminum distance from the wall, is that it takes one variable out of the setup process.

It does limit options for the LP if your goal is an equilateral triangle, as there is only so much width between speakers to work with if you are trying to get further away from the speakers for the optimum LP for the room.

Fix the rest of the issues with EQ, subs, or treatment.

I should stop writing about this and do a bunch of testing. I have some acoustic panels on the way. Hopefully report back in a week or so.
 

restorer-john

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I should stop writing about this and do a bunch of testing.

All loudspeakers require experimentation in rooms to determine the optimum placement. Some loudspeakers are designed to be placed near the wall, others not.

No one size fits all concept.
 
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73hadd

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All loudspeakers require experimentation in rooms to determine the optimum placement. Some loudspeakers are designed to be placed near the wall, others not.

No one size fits all concept.
I agree with this as long as it's measurable. I have the impression that SBIR is not grossly affected by speaker design, with a few exceptions.

I am tired of articles and owner's manuals that say "see what works for you" or "try a few things" or "season to taste." This is ASR after all, right?
 

dlaloum

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It would be nice to have some science behind the planning, before you start to move heavy furniture, re-run cables, etc....
 

Tom C

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Seems to me there’s a trade off. Like almost everything else in life. Placing the speaker closer to the wall degrades the imaging and boosts bass. And vice versa. Experiment to taste.
 

markus

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Just bumping my own question, as I’d like to minimize the actual moving of my heavy speakers.
The simulator itself is accurate but it can't model your room in detail. You need to measure.
 

Hipper

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Updated to add poll to the thread.

One thing I like about trying absolute miminum distance from the wall, is that it takes one variable out of the setup process.

It does limit options for the LP if your goal is an equilateral triangle, as there is only so much width between speakers to work with if you are trying to get further away from the speakers for the optimum LP for the room.

Fix the rest of the issues with EQ, subs, or treatment.

I should stop writing about this and do a bunch of testing. I have some acoustic panels on the way. Hopefully report back in a week or so.

I would not get stuck on any set up arrangements, including equilateral triangles. An isosceles triangle perhaps!

My starting point is 'The Thirds' in a rectangular room, specifically this version of it:

http://www.barrydiamentaudio.com/monitoring.htm
 

Thomas_A

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By placing a speaker close the the front wall you're changing the temporal and spatial reflection pattern within the room. That reflection pattern can reduce or add spaciousness to the presentation which people like. The problem is that you add the same amount of playback room spaciousness to each and every recording.
My approach is different: remove the playback room acoustics from the presentation as much as possible and add spaciousness using additional speakers, aka multichannel. That way either the recording or the listener can control the presentation in a predictable way.

It depends largely on the model you prefer. Me being there or they being here.
 

holbob

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Poll misses some choices. Particularly I tried this.... and I'm happy with it, measures good, etc
 

Thomas_A

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The questions in the poll are quite difficult. To know if there is an ’issue’ you need to know if it is an issue or just a preference.
 

markus

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