Wall reflections

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Danny Richie

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Wall reflections
« on: 29 Jun 2018, 11:03 pm »
Last week I set something up to show wall reflections. I drug in a 4' by 8' sheet of paneling and stood it up vertically in my measuring area. I then set up a N1 Mini monitor on a rolling platform with a lift that I use for measuring large speakers. I was also able to set a gated time window to allow only the wall reflection to be part of the on axis response and no floor or ceiling reflections. So you will be able to see the effects of the wall only.

Here is the response on axis with no wall reflections. It is better than +/-2db from end to end.



For this set of measurements I left the mic in place and turned it to face the speaker as the speaker was rolled closer to the wall. Here it is at 3 feet from the wall and including the wall reflection.



Here it is at 30" from the wall.



And 2 feet from the wall.



18 inches from the wall.



12 inches from the wall. Now it is really starting to look rough.



And 6 inches from the wall.



And 1 inch from the wall. These measurements are from the outside edge of the cabinet to the wall.



For this next set of measurements I moved the mic so that it was in front of the speaker the whole time. So both speaker and mic moved together. And this one is at three feet again.



30 inches from the wall.



2 feet from the wall.



18 inches from the wall.



1 foot from the wall.



6 inches from the wall.



And 1 inch from the wall.



Interesting huh?

SoCalWJS

Re: Wall reflections
« Reply #1 on: 30 Jun 2018, 01:46 am »
Very interesting. I find this stuff amazing.

Raises more questions in my tiny brain though. Would love to play around with measurements of my speakers in relation to side and and "front" walls, but it's such a PITA to move everything around - everything is kind of shoe-horned in.

My current experimentation arose about 2 weeks ago when I invited a couple of very knowledgeable "new friends" from the local Audio group over for dinner and having them listen to my setup in the hopes of receiving some constructive criticism/input on my setup. They did so, and had one overriding recommendation - and it flew in the face of my beliefs.

I always thought that you should pull the speakers as far away from the front wall (the wall behind the speakers as viewed from the main listening position)(i.e., as far in as SWMBO would allow), so that's what I did. The LS6's are over 50" from the front wall. I know that most of the high end dealers I go to have the Speakers in their big rooms well away (sometimes 6-8' !!) from the Front wall.

These guys said I needed to move the speakers closer to the front wall!  :o

Their reasoning was that a rear ported speaker needs to have some of that energy that is sent to the rear, return to the listener in a resonable amount of time in order to better create the sense of depth when listening .

Now I've been trying to research information on speaker/wall distance interaction. I would love to move the speakers a bit closer to the front wall, but it will take my wife and I the better part of the day to move everything around in order to give it a shot.

Danny, anything you have on this speaker/wall interaction I really enjoy seeing. I would love to sit down and pick your brain at some point..... :green:

mlundy57

Re: Wall reflections
« Reply #2 on: 30 Jun 2018, 02:51 am »
Are these front or side wall reflections?

Danny Richie

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Re: Wall reflections
« Reply #3 on: 30 Jun 2018, 03:35 pm »
Are these front or side wall reflections?

The effect seen is the side wall reflection only. All other reflections are gated out of the measurement.

mlundy57

Re: Wall reflections
« Reply #4 on: 30 Jun 2018, 04:46 pm »
Just to clarify, you would not expect to see the sidewall reflection issues with an open baffle speaker due to the fact that they have nulls to the side, correct?

Danny Richie

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Re: Wall reflections
« Reply #5 on: 30 Jun 2018, 04:52 pm »
Just to clarify, you would not expect to see the sidewall reflection issues with an open baffle speaker due to the fact that they have nulls to the side, correct?

It depends on frequency and distance. There can still be issues.

gab

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Re: Wall reflections
« Reply #6 on: 30 Jun 2018, 06:17 pm »
It would be interesting to see the results if you re-measured with a 2' x 4' RealTrap or equiv on the plywood next to the speaker