# Boundry effect



## geopango (Jun 24, 2012)

Just found this very well laid out page on boundary effect, phase cancellation and speaker placement.

http://arqen.com/acoustics-101/speaker-placement-boundary-interference/

I have always been a strong advocate of room treatment and speaker placement as the most effective methods of addressing in room frequency anomalies.
I have never been satisfied with equalizing a signal source, however broad and gentle high pass shelves can be effective. That said i have found that axis positioning can also be equally effective and more satisfying than this kind of eq. I would recommend equalizing a speaker in a proper anechoic chamber or wide outdoor location . Control the in room effect with placement and room treatment.


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## Wayne A. Pflughaupt (Apr 13, 2006)

geopango said:


> I have never been satisfied with equalizing a signal source...


Out of curiosity, what equalizer makes and models have you experimented with in the past?

Regards, 
Wayne


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## geopango (Jun 24, 2012)

I have used digital and analogue equalizers. My current system employs a DCX2496. In my work in recording studios and live sound I have regularly used a variety of parametric and graphic equalizers mainly for filtering out unwanted frequencies or controlling feedback. For instruments my favorite eq is a simple 6 or 12db shelving filter providing a tilt of the overall tone.
During the recording and mastering stage eq and compression are often added to enhance the apparent liveness and loudness of the master.


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## Peter Loeser (Aug 11, 2012)

Interesting that he suggests in-wall or on-wall positioning for mains, unless you have a big enough room to space them out more like 7ft (depending on the speaker) into the room.


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## geopango (Jun 24, 2012)

Yes unless you're dealing with small bookshelf speaker with a high fs, positioned about a meter and a half from the rear wall you're going to have to either position your speakers somewhere in the middle of a long room or right up against the back wall to avoid cancellation in key bass frequencies.
I have a pair of largish 12" 3way speakers positioned only a few cm from the back wall. The bass is great but i'm aware of standing waves at the listening position where the sofa is positioned against the opposing wall. In my measurements there is null in the upper bass at around 170hz. 
The three images below represent measurements fro 30cm, 100cm and 3 meters.

At 30cm the unfiltered driver displays a very linear response only slightly affected by close to wall positioning by a gradual rise in low end bass response.








At 1meter, filtered of at 315hz you can see a node developing at 170hz and peak at 120hz, with a difference of 8db between these two points.








At 3 meters which 1 meter from the opposing wall, the null and standing waves become more pronounced.








As you can see from these measurements correcting the response via equalisation from one distance will not translate into consistent results from other locations. It is clear that serious room dampening is required.


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## Wayne A. Pflughaupt (Apr 13, 2006)

geopango said:


> I have always been a strong advocate of room treatment and speaker placement as the most effective methods of addressing in room frequency anomalies.
> I have never been satisfied with equalizing a signal source...





geopango said:


> I have used digital and analogue equalizers. My current system employs a DCX2496. In my work in recording studios and live sound I have regularly used a variety of parametric and graphic equalizers mainly for filtering out unwanted frequencies or controlling feedback. For instruments my favorite eq is a simple 6 or 12db shelving filter providing a tilt of the overall tone.


Between your two posts I can’t tell for certain if by “equalizing a signal source” you mean playback speakers or an actual signal source like a guitar or trombone. However, considering that the link you posted in your first post relates to speaker placement, I’m going with the former.

Treatments primarily address reflections in the room to reduce comb filtering. That can certainly be a great benefit, but if a speaker has aberrations in frequency response (_and most do_, if you’ve ever seen the lab data from professional speaker reviews that include quasi-anechoic measurements), treatments aren’t going to help that.

If your equalizing experiences are limited to filtering unwanted frequencies, controlling feedback and enhancing the sound of live instruments, I can understand why you haven’t been satisfied equalizing playback speakers. 

The two have nothing in common. Equalizing playback speakers is a lot more complicated. It requires being able to generate a viable frequency response graph and being able to look at it and recognize what problems will make an audible improvement when corrected with precise parametric equalization. And conversely, what problems won’t be audible, or can’t be realistically corrected, and therefore should be ignored. 

It also requires knowing which part of the frequency range where independent filters can be applied to a stereo pair of speakers without affecting imaging, and which part requires matching filters. 

In addition, it requires knowing how to recognize if the equalizer on hand is of sufficient quality for use in a hi-fi system.

A breakdown anywhere down the line is sufficient to deliver poor results, which inevitably leads the user to “determine” (and proclaim all over the internet) that equalization add noise, destroys imaging, doesn’t sound good, etc.

Regards, 
Wayne


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## Wayne A. Pflughaupt (Apr 13, 2006)

geopango said:


> At 30cm the unfiltered driver displays a very linear response only slightly affected by close to wall positioning by a gradual rise in low end bass response.
> View attachment 85242


The graphs would be a lot more meaningful if they were properly scaled – see here:

Getting Graphs Ready to Post




> As you can see from these measurements correcting the response via equalisation from one distance will not translate into consistent results from other locations.


Well sure, that’s not news. However, most of us concern ourselves primarily with the main listening position, as people typically don’t hop around from one seat to another when listening to music. With movies (this is a home theater forum after all), dead-on accuracy for every seat in the room isn’t important, as movie bass content is mainly just boom and explosions.

In addition it’s not entirely accurate to universally claim that “correcting response vial equalization from one distance will not translate to consistent results from another location.” No two residential rooms are the same, and what’s true for one won’t be true for all. For instance, in my room response is fairly uniform for any seat on the sofa, which are the main listening positions.

Regards,
Wayne


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## Wayne A. Pflughaupt (Apr 13, 2006)

Peter Loeser said:


> Interesting that he suggests in-wall or on-wall positioning for mains...


I found that curious as well. I thought it was pretty much universally recognized that in-wall placement was detrimental to imaging. :huh:

Regards, 
Wayne


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