Speakers against front wall - can this be settled?

[markus]

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.

I agree. The poll won't produce much meaningful information as this is not a mathematical problem with only one solution. Controlled listening tests would help.

 

[bo_knows]

The third bullet of that section of the document is:

"Move the loudspeakers closer to the corners or walls of the
listening room to increase bass response."

And then goes on to recommend absorbing first reflection points, among other things. I only mention it because it does not say "keep them away from the walls at all costs."

No and no real direction as far as how much to move speakers from the wall surfaces. Kind of ambiguous vs KEF where they provide a range. At least Revel is advocating for the use of treatments and giving us the location. My question is, do I need to have all the space between speakers and the side walls if I use the absorbers? Wouldn't absorbers achieve a similar thing (delayed reflections)? Same thing for the rear and front wall. I guess the ultimate goal for me (with the small listening space) would be to remove the room signature as much as posible.

 

[73hadd]

I agree. The poll won't produce much meaningful information as this is not a mathematical problem with only one solution. Controlled listening tests would help.

Closest to the wall placement has the most bass without SBIR, which is the mathematical starting point. Looking to identify measurable reasons not to do this. Agreed, controlled listening tests would be useful. Hoping that the poll provides some information. It might reinforce why many (most?) manufacturers do not recommend this, as typical users are not going to have a way to compensate for the boundary gain or be doing any acoustic treatment.

 

[73hadd]

No and no real direction as far as how much to move speakers from the wall surfaces. Kind of ambiguous vs KEF where they provide a range. At least Revel is advocating for the use of treatments and giving us the location. My question is, do I need to have all the space between speakers and the side walls if I use the absorbers? Wouldn't absorbers achieve a similar thing (delayed reflections)? Same thing for the rear and front wall. I guess the ultimate goal for me (with the small listening space) would be to remove the room signature as much as posible.

I am not the expert to answer this, but here is what I have heard. The absorbers should achieve a goal of reduced reflections, (shown in NRC measurements) from 5khz down to about 200hz (depends on thickness.) Below that we are back to the SBIR. The Genelec room acoustics guide notes a front wall bass gain of 6db, but in a corner, bass gain could be 12db.

So.... If you can compensate for the gain, you are left with the question of how well the absorbers work above 5khz, or what absorber gives you the equivalent effect of x amount of space to a reflective side wall.

 

[Thomas_A]

I prefer "me being able to choose"

Agreed as well. But reflections from the "lounge" part just needs more or less a normal living room; only the wall of the loudspeaker side should be acoustically invisible, creating an virtual opening against the event. Recreating my own lounge with surround speakers is not possible.

 

[Balle Clorin]

Speaker placement 105-210cm from front wall. Moving speaker less than 120cm from front wall collapses imaging.

"However, if the speaker is 1.5 meter away from the wall (1/4 wavelength of 57Hz) then there will be a null at 57Hz, then a peak at 115Hz (1/2 wavelength), and a null at 172Hz (3/4 wavelength). The cycle continues for 4/4, 5/4, 6/4 .etc till the speaker is forward firing."
I cannot see any null at 57Hz- but I see a peak at 117, a small dip at 167

Listening position has more effect on bass evenness

 

[bo_knows]

View attachment 176929
Speaker placement 105-210cm from front wall. Moving speaker less than 120cm from front wall collapses imaging.

"However, if the speaker is 1.5 meter away from the wall (1/4 wavelength of 57Hz) then there will be a null at 57Hz, then a peak at 115Hz (1/2 wavelength), and a null at 172Hz (3/4 wavelength). The cycle continues for 4/4, 5/4, 6/4 .etc till the speaker is forward firing."
I cannot see any null at 57Hz- but I see a peak at 117, a small dip at 167


View attachment 176937
Listening position has more effect on bass evenness

What speakers did you use and do you have any room treatments on the front, side, and back wall?

Trying to figure out how did you get to this conclusion: "Moving speaker less than 120cm from front wall collapses imaging".

 

[Balle Clorin]

Moving speaker closer to wall increases listening distance, and creates much more reflections to listening position. Phase plot confirmes this. 3D imaging suffers. Same effect regardless of speakers ( Audio Physic Virgo II, Gravesen TQWT, Revel F36.) Room is not symmetrical…bookshelf left side, fireplace front right corner. irregular bay window behind listening position.
No room treatment, just sofa, carpet,curtains.

 

[markus]

Moving speaker closer to wall increases listening distance,

You could move the listening position the same amount as the speakers so the distance would stay the same, no?

and creates much more reflections to listening position. Phase plot confirmes this.

How can a phase plot show "more reflections"?

 

[Balle Clorin]

More phase changes/revolutions with reflections

Long listening distance.Speaker close to wall Phase plot

Shorter listening distance, speaker out from wall.

 

[markus]

More phase changes/revolutions with reflections

A phase plot is totally unsuitable for showing "more reflections". Looking at something like a spectrogram is probably more useful.
In any case, is more reflections bad? Some argue it's good, if it's the "right" kind of reflections.

 

[abdo123]

You could move the listening position the same amount as the speakers so the distance would stay the same, no?

How can a phase plot show "more reflections"?

Once you move both the speakers and the listening position any sort of comparison between the two measurements is meaningless. (Unless the question is what works best at that particular room)

 

[markus]

(Unless the question is what works best at that particular room)

That's the question in any room

 

[tvrgeek]

My experience is the under two foot reflections are what destroys imaging. So if one needs to be closer, as in most rooms people actually LIVE in, 3 inches of OC 705 board does wonders. Sure, some in the top 1/2 of 1% may build listening rooms with dimensions as above, the rest of us make the best of what we have. I have been tempted to do the entire ceiling with them. Some sort of cloth covering. Can't be as ugly as the popcorn spray. I have a very bright room and unfortunately, behind my speakers is a picture window. It is a Living room.

 

[Thomas_A]

A phase plot is totally unsuitable for showing "more reflections". Looking at something like a spectrogram is probably more useful.
In any case, is more reflections bad? Some argue it's good, if it's the "right" kind of reflections.

In this case it would be looking for direct sound and reflections in the direction from the speakers/speaker wall within a few ms. Envelope time curve?

 

[markus]

In this case it would be looking for direct sound and reflections in the direction from the speakers/speaker wall within a few ms. Envelope time curve?

View attachment 177037

Problem with the ETC is that it "favors" higher frequencies, i.e. it can hide audible but spectrally altered reflections. Furthermore it can hide groups of several smaller reflections that otherwise are perceived as a single larger one.

 

[Thomas_A]

Problem with the ETC is that it "favors" higher frequencies, i.e. it can hide audible but spectrally altered reflections. Furthermore it can hide groups of several smaller reflections that otherwise are perceived as a single larger one.

Yes, I am aware of the limitations. A combination with frequency response could be good. Measurement outside with the speaker lying on the ground pointing to the sky perhaps?

 

[DJBonoBobo]

Yes, I am aware of the limitations. A combination with frequency response could be good. Measurement outside with the speaker lying on the ground pointing to the sky perhaps?

REW can produce a frequency dependent ETC graph ("filtered ir" -> controls -> 1/1 or 1/3).

 

[Thomas_A]

REW can produce a frequency dependent ETC graph ("filtered ir" -> controls -> 1/1 or 1/3).

Yes I did also that. But I guess that the periodical SIBR effect from speaker wall is still a bit complicated to see from that graph.

 

[73hadd]

My report back is only subjective and almost useless so I hestiate to post, but wanted to follow up.

Trying with LS50 Meta, 6ft from any wall (reflective walls), the imaging/depth is amazing.

Putting them 6" from the front wall, no treatment, I have lost the depth. Distance from side walls not changed.

Same setup, 6" from the front wall, adding 3" foam absorbers directly behind the speakers, maybe a foot coverage on either side, and above and below, behind each speaker, (probably not nearly physically wide enough to cover the 360 degree radiation at 400hz and down) this did not bring the imaging back.

I really wanted to ignore the subjective reports of loss of imaging, but I felt it too. Yes yes yes, not double blind etc.

It occurred to me that Genelec might be expecting more nearfield users. If the extra "imaging/depth" would not be found in a treated room anyway at distances where direct sound dominates (assuming the depth perception is due to reflections), then nothing is really lost.

If I ever get around to treating a much larger area or an entire wall I will try this again.