Speaker Placement, the precedence effect and SBIR

[CK.]

Fellow members,

I am in need of your expert insight once more!

It seems that basic concepts, such as speaker placement and the optimal distance from adjacent boundaries, are often contradicted across many posts I've read.

Many enthusiasts and speaker manufacturers advise placing the speaker at least 3 feet (to be within lower limit of precedence effect? and avoid too much boundary gain?) from the nearest boundaries.
That would place the SBIR in the bass region ~90Hz.

Yet others claim that putting the speaker right against the side walls, shifts the SBIR to higher frequencies that is less audible.
In such a case wouldn't this "violate" the precedence effect lower limit (2ms?) and cause imaging distortion?

Assuming a well behaved off-axis speaker performance and EQ availability, which of the two would be most likely the best approach?
Will placing the speaker less than 3 feet from the side wall have indeed an audible detrimental effect due to the absence of the precedence effect?

Many thanks in advance!

 

[kyuu]

Maybe I need some education on this topic, but why would placing the speaker close to a boundary "violate" the precedence effect? And why is 2ms being taken as a cutoff value?

 

[CK.]

Maybe I need some education on this topic, but why would placing the speaker close to a boundary "violate" the precedence effect? And why is 2ms being taken as a cutoff value?

Hey,

That is what the research showed basically.

Regarding placement, placing the speaker less than 2 feet would mean that the early reflection from the boundary would arrive less than 2ms later and be outside the range for precedence to take effect.

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

 

[kyuu]

I'll quote that whole section for reference:

In two-click lead–lag experiments, localization effects include aspects of summing localization, localization dominance, and lag discrimination suppression. The last two are generally considered to be aspects of the precedence effect:[10]

• Summing localization: for time delays below 2 ms, listeners only perceive one sound; its direction is between the locations of the lead and lag sounds. An application for summing localization is the intensity stereophony, where two loudspeakers emit the same signal with different levels, resulting in the localized sound direction between both loudspeakers. The localized direction depends on the level difference between the loudspeakers.
• Localization dominance: for delays between 2 and 5 ms, listeners also perceive one sound; its location is determined by the location of the leading sound.
• Lag discrimination suppression: for short time delays, listeners are less capable of discriminating the location of the lagging sound.

For time delays above 50 ms (for speech) or some 100 ms (for music) the delayed sound is perceived as an echo of the first-arriving sound, and each sound direction is localized separately and correctly. The time delay for perceiving echoes depends on the signal characteristics. For signals with impulse characteristics, echoes are perceived for delays above 50 ms. For signals with a nearly constant amplitude, the threshold before perceiving an echo can be enhanced up to time differences of 1 to 2 seconds.

So I don't see why, based on this, you need the early reflection to arrive more than 2ms after the direct sound. For localization, it might make a small difference but since the reflection is off the back wall and then directly back toward the listener I don't think it would have much effect on the perceived imaging. It might actually widen the imaging a bit, I think. But it seems you believe (or you are referring to people who believe) that this research indicates that early reflections need to be in the 2-5ms window for "proper" imaging?

It would also have to be noted that this research was based on two clicks from separate loudspeakers. Its unclear to me whether it is directly applicable, particularly for the particular timing, to music or movie content played from a single loudspeaker and its reflection from the front wall. The research notes that different signals affect the perception of a delayed sound quite significantly.

 

[CK.]

I'll quote that whole section for reference:


So I don't see why, based on this, you need the early reflection to arrive more than 2ms after the direct sound. For localization, it might make a small difference but since the reflection is off the back wall and then directly back toward the listener I don't think it would have much effect on the perceived imaging. It might actually widen the imaging a bit, I think. But it seems you believe (or you are referring to people who believe) that this research indicates that early reflections need to be in the 2-5ms window for "proper" imaging?

It would also have to be noted that this research was based on two clicks from separate loudspeakers. Its unclear to me whether it is directly applicable, particularly for the particular timing, to music or movie content played from a single loudspeaker and its reflection from the front wall. The research notes that different signals affect the perception of a delayed sound quite significantly.

Thanks for the reply!

Just to clarify I am referring to side wall reflections not back with regards to imaging.

I would agree that the precedence effect is frequency depended, however, with early reflections arriving less than 1-2ms after the direct sound, does it not make sense that it will affect localization and imaging in the same sense that a mono signal playing from two speakers at the same time will place the image midway between them?

So a less than 2ms delayed reflection would act as a second source ?

What I am saying is that the limits of our brain to distinguish direct vs reflected sound is indeed the lowest limit of the precedence effect?

 

[boxerfan88]

I have my KH310 about 2ft 4in from the side wall. No issues with imaging, pretty stable imaging. On my setup, soundstage goes beyond the speaker boundary (somewhere between speaker boundary & side wall)

Do note I have a bass traps placed against the side walls where the speakers are. This is done to reduce reflected sound power, which seems to work quite well for me.

 

[CK.]

Thanks for sharing, 2ft+ (3ms delay) do not violate the precedence effect so that should be ok. Irrspective of that, reflections from the side walls will always distort the imaging somewhat but enhance the spaciousness so its personal preference really.
If your bass traps are placed on first reflections points on the side walls then you are more than ok.

Again, its personal preference for stereo music listening