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EQing to reduce boundary effect.

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EQing to reduce boundary effect.

Postby MGBR65 » Tue Apr 02, 2013 1:07 pm

I have my monitors set up at quite a distance from the wall to reduce the boundary effect.
They sound fine where they are now, only problem is it takes up a lot of room space that way.
Can I really just put them up to the wall and reduce the low end with eq untill I get a balanced sound again or are exact measurements needed to know which frequencies to take out?

I have PMC TB2's (passive version) and the dimensions of my room are 2.55 meters wide, 5.55 long.
Height is a bit difficult because it's a slanted roof, short walls go straight up for about 1 meter and then start sloping towards the highest point wich is more than 4 meters high.

Monitors are "of course" set up on the short wall firing down the long end.

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Re: EQing to reduce boundary effect.

Postby Hugh Robjohns » Tue Apr 02, 2013 3:53 pm

You can't put them very close because of the rear-firing port, but you could certainly move them closer and re-equalise if you have suitable facilities in your monitoring chain.

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Re: EQing to reduce boundary effect.

Postby tacitus » Tue Apr 02, 2013 5:58 pm

I'm not sure it's just the distance from the wall that makes the difference. I have occasionally asked myself where I could put speakers so as to annoy my wife the most: that's usually been where they sound best. Conversely, whenever I see speakers and can say 'my wife would like them there', I'm pretty sure they're going to sound terrible.

I should say there is no scientific evidence to support this, but I know it's true.
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Re: EQing to reduce boundary effect.

Postby Hugh Robjohns » Tue Apr 02, 2013 6:02 pm

:bouncy:
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Re: EQing to reduce boundary effect.

Postby MGBR65 » Tue Apr 02, 2013 7:47 pm

A drummer friend of mine once came home to find his speakers moved to the shed in the garden.
Turned out that his wife had rearranged the living room and the speakers didn't fit in with the new look. True story.

But back on topic, I assume that I can take out some low end on the masterchannel of my DAW and not to forget to turn it back on when I render?
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Re: EQing to reduce boundary effect.

Postby GIK Acoustics » Wed Apr 03, 2013 1:48 am

The problem is that the boundary interference is not simply like a low shelf EQ that just goes up, but a series of peaks and nulls due to the distance. Panels between a speaker and a wall can reduce SBIR effects, but otherwise, you're left to simply test and see what works best and is less damaging. In the case of many people's rooms, they might still be fine quite close to the wall. I have rear ported speakers about 4" from my front wall, albeit with absorption directly behind them. The culprit is SBIR, and an EQ would actually only bring up the level of the frequencies not associated with the nulls, and make the peaks more severe. Any null caused by SBIR cannot be brought up by EQ.

More on SBIR here: http://gikacoustics.com/speaker-boundar ... onse-sbir/
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Re: EQing to reduce boundary effect.

Postby MGBR65 » Thu Apr 04, 2013 7:09 am

Hi.

As always, the deeper I dive into it the more complicated it gets.
Guess for now I'll leave my monitors where they are,I'm used to how everything sounds now and mixes translate reasonably well.
I'm afraid that when I start eq-ing I'll do more damage than good.

Thank you for your help.

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Re: EQing to reduce boundary effect.

Postby Hugh Robjohns » Thu Apr 04, 2013 8:08 am

MGBR wrote:As always, the deeper I dive into it the more complicated it gets.


;) Always the way! ...and that's what keeps it interesting! :D

I'm afraid that when I start eq-ing I'll do more damage than good.


There is always that risk.

A handy way to think of how a speaker works in a room is to imagine duplicate speakers behind each boundary (side walls, back wall, floor, ceiling etc), at the same distance behind the boundary as the real speaker is in front. Then imagine the boundaries are acoustically transparent... so that you hear the output not only from the real speaker in the room, but also from all the imaginary ones behind the room boundaries -- at least at low frequencies.

So as you move a speaker within the room, the imaginary speakers move too, and so the phase relationships between their outputs and the real speaker change, causing peaks and nulls at different frequencies.

It's always going to be a mess unless you are preprared to work in a padded cell... although that might have a certain appeal. I've always liked those nice white jackets with the really long sleeves and buckles, too.... ;)

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Re: EQing to reduce boundary effect.

Postby GIK Acoustics » Wed Apr 10, 2013 5:05 am

That is a neat analogy Hugh, do you mind if I steal it? I always feel awkward discussing a phenomenon with the daunting name "Speaker Boundary Interference Response"
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Re: EQing to reduce boundary effect.

Postby Hugh Robjohns » Wed Apr 10, 2013 8:36 am

GIK Acoustics wrote:That is a neat analogy Hugh, do you mind if I steal it?

I don't see why not... I did! ;) It's actually quite a commonly used analogy in a lot of acoustics text books.

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