Speakers against front wall - can this be settled?

[73hadd]

Apologies if this has been summarized already on ASR but I could not find it.

Based on this image from Genelec, shouldn't all full-range speakers be near to the front wall?

I have heard the advice that for best stereo image the speakers should be away from the front wall.

Is this "away from the front wall" advice because:

-For full range speakers there is so much bass boost that it "overpowers" the image? (activating room modes, which could be fixed with eq to reduce bass)
-Bass is radiating backwards (full space, mostly below 250hz?), is reflecting off the wall, and also radiating forwards, creating a timing issue?
-Speakers next to the front wall are toed in so much that it causes an extra reflection point?
-From this Stereophile review https://www.stereophile.com/content/dutch-dutch-8c-active-loudspeaker-system "The potential downsides of positioning the speakers so close to the front wall are midrange colorations, but those are minimized by the highly controlled cardioid dispersion of the front drivers." So maybe close to the front wall is only a problem for speakers that do not have controlled directivity? (Where Dutch & Dutch and Genelec do have control, so it's ok?)

Or, perhaps "away from the front wall" is total nonsense?

I would guess that a lot of people have their speakers in the 3-6ft AVOID! range. That cancellation/comb filtering doesn't seem fixable by EQ according to this note from Genelec "Equalization of the monitor output level does not help, as the same level change applies also to the reflected sound."

Thoughts? Thank you!

 

[wwenze]

Remember that many advices on internet are also from the same people who say you need to spend money on power cables, so...
And Genelec speakers measure well and they like to use theory and graphs like the above so that doesn't sit well with some people

Plus when you consider the anechoic frequency response of bookshelf speakers there is no way they are optimal for use away from the wall without the boundary loading.

End of the day I don't think there is any problem that needs settling because the discussers fail to define a problem statement and/or fail to resolve issues using a "WHY" approach anyway.

 

[thewas]

The problem is in my experience really existent and audible as measurements at the LP also show and personally I either place them very close to the front wall, very far (unfortunately viable usually only in very large rooms) or use subwoofers.

 

[dshreter]

The advice from genelec is accurate and matches with Neumann’s advice too. In REW it’s very easy to see the SBIR effect when speakers are placed in the avoid zone.

My personal theory is that having the speakers out a few feet “looks” like the speakers would image better. There is room in the mind’s eye for that virtual sound stage to occur. So I believe many listeners find enjoyment seeing the speakers out in space and relate that to a stronger perceived central image.

But that’s not due to improved acoustics, just the mind playing tricks. If there are valid reasons speakers should be pulled out from the wall I would be interested to learn more though.

 

[Morla]

so does it also apply to the designs of Dutch&Dutch 8C or Kii Audio Three? And if so to what extend?

 

[Killingbeans]

Probably has a bit more wriggle room, but the cardioid dispersion doesn't go all the way to the roll-off.

I bet it still has an "avoid! zone", it's just more narrow.

 

[Morla]

@hardisj review of the kii three states

the Kii THREE features subwoofers on the rear of the speaker. These subwoofers depend on boundary reinforcement in order for the response to extend as low as possible in frequency

so maybe it's even more true for those speakers? In the review they were placed 0.50 feet from front wall. I wished the manufacturer had more precise instructions

 

[moonlight rainbow dream]

The vast majority of people do not use EQ in their systems... so the boundary gain is an intractable problem for them (particularly if your speakers have full BSC). I'm guessing people prefer getting rid of boomy muddy bass over SBIR FR raggedness (which our ears are less sensitive to in the bass region anyways).

 

[markus]

Apologies if this has been summarized already on ASR but I could not find it.

Based on this image from Genelec, shouldn't all full-range speakers be near to the front wall?

I have heard the advice that for best stereo image the speakers should be away from the front wall.

Is this "away from the front wall" advice because:

-For full range speakers there is so much bass boost that it "overpowers" the image? (activating room modes, which could be fixed with eq to reduce bass)
-Bass is radiating backwards (full space, mostly below 250hz?), is reflecting off the wall, and also radiating forwards, creating a timing issue?
-Speakers next to the front wall are toed in so much that it causes an extra reflection point?
-From this Stereophile review https://www.stereophile.com/content/dutch-dutch-8c-active-loudspeaker-system "The potential downsides of positioning the speakers so close to the front wall are midrange colorations, but those are minimized by the highly controlled cardioid dispersion of the front drivers." So maybe close to the front wall is only a problem for speakers that do not have controlled directivity? (Where Dutch & Dutch and Genelec do have control, so it's ok?)

Or, perhaps "away from the front wall" is total nonsense?

I would guess that a lot of people have their speakers in the 3-6ft AVOID! range. That cancellation/comb filtering doesn't seem fixable by EQ according to this note from Genelec "Equalization of the monitor output level does not help, as the same level change applies also to the reflected sound."

Thoughts? Thank you!

I find close to wall placement beneficial: The closer the speaker to the wall the higher up in frequency the first cancellation notch from the back wall occurs. The higher the frequency the more effective is absorption on the front wall (behind the speaker). Higher directivity designs will further mitigate the back wall notch. The back wall reflection increases efficiency and level at lower frequencies. You need to counteract that with equalization though.

 

[abdo123]

The optimal configuration in my opinion for medium to small rooms is to have the speakers more than a meter away from a boundary, and have Subwoofers crossed at 80Hz.

This way the null will be in the range where the subwoofer is playing and the 3rd order null can be dealt with effectively with ~15-20cm porous absorption behind the speakers.

Anything else is a compromise, I'm gonna mention all the other comprimises in order of least compromised to most compromised.

1) In-wall installation + EQ to adjust for the baffle step compensation in the speaker's crossover

This provides the most transparency in terms of audio reproduction, while keeping the cost reasonable. However, not many people will be okay with holes in their walls in their domestic spaces. Upgradability in the future is also limited

2) Getting a cardioid speaker and placing it smack down on the boundary (Almost On-wall installation)

The Dutch & Dutch 8C is completely forward firing from 200Hz on-wards. the speaker is 15 inch (37.5 cm) deep or 1/4 wavelength of 240Hz, so leave a little bit of leeway in the back for the subwoofers to function properly and you shouldn't have any significant nulls in the response caused by the wall facing the rear of the speaker.

3) Placing the speaker as close as you can to a boundary.

the on-axis null will still be there, but hopefully the higher order nulls will be in the range where the speaker is forward firing.

 

[abdo123]

Now with that out of the way, you're almost there with your assessment.

The delay between the direct sound and a reflection determines how polluting that reflection is in terms of both sound quality and imaging. The higher the delay, the less polluting it is for two reasons.

1) Higher delay means the reflection is traveling a longer distance to reach you. Reflections lose 6 dB of energy every time they travel a distance that is double than the distance the direct sound travels.

2) the lower the delay the more likely that our brains will register both the reflection and the direct sound as one instance of sound. This effect is called the precedence effect, you can read about more here: https://en.wikipedia.org/wiki/Precedence_effect. That one instance of sound will be Direct sound + (first reflection - 10 dB) + (Second reflection -20 dB) .etc

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.

However if the speaker is 30 cm away (1/4 wavelength null at 287Hz) from the wall then the 4/4 wavelength is already above 1KHz (where most speakers are forward firing) so you only have 2 nulls and 1 peak instead of like 10 nulls and 9 peaks when it was 1.5 meter away.

Genelecs think that psycho-acoustically having less overall peaks and nulls is more important than raising the delay and reducing the amplitude of the reflections themselves by putting the speakers in the center of the room. This is your choice to make.

 

[Berlin]

Genelecs think that psycho-acoustically having less overall peaks and nulls is more important than raising the delay and reducing the amplitude of the reflections themselves by putting the speakers in the center of the room. This is your choice to make.

My speakers are currently 108 cm away from the front wall. When measuring both speakers together there is a -20 dB null at approx. 76 Hz. However, I do not think that it is audible (when listening to music or a frequency sweep). More annoying to me was the boomy bass that is corrected now by EQ.

 

[abdo123]

there is a -20 dB null at approx. 76 Hz.

and that's why i think for a dedicated studio this sort of distance is better because a subwoofer can easily fill that.

 

[dshreter]

The GIK Acoustics video on this topic is quite good.

 

[KMO]

To some extent Genelec are assuming that there will be EQ, quite likely via GLM, and as such the speakers can be EQed for any wall distance, allowing you to think about minimising hard-to-EQ SBIR problems.

Many speaker manufacturers will be expecting their speakers to be used without EQ, and as such placement advice will be significantly based on bass balance, which is an overall more significant and predictable effect than the SBIR.

 

[markus]

Many speaker manufacturers will be expecting their speakers to be used without EQ

Quite an outdated line of thought.

 

[mightycicadalord]

My speakers are currently 108 cm away from the front wall. When measuring both speakers together there is a -20 dB null at approx. 76 Hz. However, I do not think that it is audible (when listening to music or a frequency sweep). More annoying to me was the boomy bass that is corrected now by EQ.

I'm working on my room atm and feel that nulls like this are very audible. It's not just a null at 76hz, that null starts sloping down at frequencies higher and lower than the deepest part of the null. In my space I have a null that starts at ~87hz and ends at ~130hz with the deepest point being like 97hz or something. You can definitely hear that.

I haven't found placement to front wall I like yet, too close just does something weird to the mid range and pulled out creates nasty nulls.

 

[youngho]

Based on this image from Genelec, shouldn't all full-range speakers be near to the front wall?

I have heard the advice that for best stereo image the speakers should be away from the front wall.

Genelec's recommendations are primarily related to frequency response, not about imaging.

Is this "away from the front wall" advice because:
-For full range speakers there is so much bass boost that it "overpowers" the image? (activating room modes, which could be fixed with eq to reduce bass)

Again, this is primarily about frequency response. Proximity to a wall tends to boost the bass below 500-1000 Hz, basically like a tilt function. You can see it in the Figure 12.9 posted by @abdo123 above (the free-standing speaker is close to flat). Genelec and many other professional monitors have a bass adjustment to compensate accordingly. See here:

-Bass is radiating backwards (full space, mostly below 250hz?), is reflecting off the wall, and also radiating forwards, creating a timing issue?

The timing issue is the SBIR referenced above.

-Speakers next to the front wall are toed in so much that it causes an extra reflection point?

Wouldn't they be toed-in less than close to the listener?

-From this Stereophile review https://www.stereophile.com/content/dutch-dutch-8c-active-loudspeaker-system "The potential downsides of positioning the speakers so close to the front wall are midrange colorations, but those are minimized by the highly controlled cardioid dispersion of the front drivers." So maybe close to the front wall is only a problem for speakers that do not have controlled directivity? (Where Dutch & Dutch and Genelec do have control, so it's ok?)

The D&D 8C is unique in having cardioid dispersion down past 100 Hz but also the rear-mounted bass drivers that are designed for boundary proximity. Genelec has the bass tilt adjustment hard-wired, plus the room equalization software.

Or, perhaps "away from the front wall" is total nonsense?

Most home speakers are designed to be used in a free-standing setup.

 

[dshreter]

Quite an outdated line of thought.

Hardly. That might be right for studio monitors but for home hifi these companies are in the business of selling speakers that customers expect to sound right connected to anything from their vintage receiver to a minimalist integrated amp to modern room compensating systems.

Unless DSP is built into the speaker, manufacturers are giving their guidance based on the lowest common denominator.

 

[bo_knows]

Hardly. That might be right for studio monitors but for home hifi these companies are in the business of selling speakers that customers expect to sound right connected to anything from their vintage receiver to a minimalist integrated amp to modern room compensating systems.

Unless DSP is built into the speaker, manufacturers are giving their guidance based on the lowest common denominator.

This is what we get from KEF: