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Discussion Starter #1
I know that if the walls are straight behind speakers like most people have, the recommended distance is 0.5m from speaker to wall. But what when the wall is like this:

i.imgur.com/2EUpTKG.png

Does it mean that because the speakers are now put differently that the reflections to the listener are gonna be much smaller and because of that the distance doesn't have to be 0.5m but something lesss(how much less)?
 

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Discussion Starter #2
I meant to say "when the wall is not straight behind speaker but diagonally"... I hope you understand what I mean.
 

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The system is place in the corner. If this is a new forum member, he may not be able to post a link yet.



How far away from the walls depends on the speakers. Bookshelf can usually be closer than floorstanding. Bass heavy speakers generally need more space. I had some JBL Stadium that were only marginally happy at 24" from the wall behind. I replaced them with some Wharfedale with the exact same size drivers in the same configuration, and they are happy at 10" to 12".

It would help to know exactly what speakers and amp you have.

Also, we are all slaves to our circumstances. No one has the ideal room. We do the best we can with what we have.

Curious, any chance there is a fireplace in this room?

Steve/bluewizard
 

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I know that if the walls are straight behind speakers like most people have, the recommended distance is 0.5m from speaker to wall.
That's not the case. A speaker should be placed either close enough or far enough from the wall behind it so that the distance from the baffle to the wall is not 1/4 wavelength within its passband, as the reflected wave will meet the original wave 180 degrees out of phase, causing a response dip at that frequency. The technical term for this is Allison Effect. That means subs should usually be placed less than a meter away, mains more than a meter away, the exact requirement depending on the crossover frequency.
 

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Discussion Starter #5
About the 0.5m distance, I read that exact number in manuals from B&W and Dynaudio floorstanding speakers so I assumed that was correct... Anyway, this isn't real system yet, I'm still just looking around what to buy, don't have anything yet.

But you guys haven't answered my main question "if the wall behind speakers doesn't look like "T" to speakers, does it mean the distance between speaker and wall can be less?" What changes in reflections when the wall behind speakers is a corner and not a straight wall? Do "bad reflections" go away?
 

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About the 0.5m distance, I read that exact number in manuals from B&W and Dynaudio floorstanding speakers so I assumed that was correct...
That placement would result in a cancellation notch centered around 170Hz. The fact that you can't place a full range floorstander where there will be no cancellation notch is one of their inherent deficiencies.
" What changes in reflections when the wall behind speakers is a corner and not a straight wall? Do "bad reflections" go away
They do not, unless the listening position is on-axis to the speaker. You can realize that if the system is mono, but not if it's stereo, with speakers in two corners.
 

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...

But you guys haven't answered my main question "if the wall behind speakers doesn't look like "T" to speakers, does it mean the distance between speaker and wall can be less?"...
The simple answer is, there is no simple answer.

I think what you might be getting at is that because the rear reflections do not strike a parallel wall but rather a diagonal wall, does that make a difference, and how much difference?

It is very detail and circumstance dependent. Is this a 5.1 system or a 2.0 system? How big is the room? How big are the speakers? How bassy are the speakers?

So, yes, striking a diagonal rather than a parallel wall will make a difference. How much is unclear. Though more details would go a long way toward helping us understand the possibilities.

Generally, we do the best we can with the circumstances we have.

Steve/bluewizard
 

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Discussion Starter #8
ok, so if I got B&W 684 S2 and if they are 25cm(10 inch) from the nearest wall like on the pic below, would I be OK? These are front ported speakers and don't have a lot of bass from what I've read about them.

i.imgur.com/MJpDk52.png



B&W 684 S2:
i.imgur.com/kdFeAFK.jpg
 

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Discussion Starter #9
BTW, I don't think 684 S2 are much stronger than some bookshelf speakers like Focal Chorus 807V for example...
 

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So, yes, striking a diagonal rather than a parallel wall will make a difference. How much is unclear.
It depends on the wavelength of the reflected wave, which depends on the distance out, and the position of the LP with respect to the wall behind the speakers. All easily calculated, if sufficient data is available.
 

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It depends on the wavelength of the reflected wave, which depends on the distance out, and the position of the LP with respect to the wall behind the speakers. All easily calculated, if sufficient data is available.
I'm pretty sure you are making the assumption that the waves bounce off the wall behind and rebound forward where they interfere with the direct waves from the speakers.

However, if the waves hit the wall behind at a 45° angle, they do not rebound forward. That's the point I'm making. In a straight forward square/rectangular placement, what you say is correct. But when the speakers are 45° relative to the wall behind, the reflection and corresponding interference is not the same.

And THAT is what the original poster is asking, what happens when the waves hit the wall at an angle, and how does that effect the required distance behind the speaker?

Steve/bluewizard
 

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Discussion Starter #12
I'm pretty sure you are making the assumption that the waves bounce off the wall behind and rebound forward where they interfere with the direct waves from the speakers.

However, if the waves hit the wall behind at a 45° angle, they do not rebound forward. That's the point I'm making. In a straight forward square/rectangular placement, what you say is correct. But when the speakers are 45° relative to the wall behind, the reflection and corresponding interference is not the same.

And THAT is what the original poster is asking, what happens when the waves hit the wall at an angle, and how does that effect the required distance behind the speaker?

Steve/bluewizard
Doesn't the sound-wave get out of the speakers in circular shape, like this:
It's stronger in the front of course. but the sides and back of the speaker are equal in that regard I think.

 

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The simple answer is, there is no simple answer.
+1
IMO, the answer is to play around with speaker placement to get the best sound. I recently bought a pair of Olympica III's, and someone from Sumiko (the North American distributor for Sonus Faber) came to my house to help optimize their placement. One at a time, he moved them an inch at a time further from the back wall, and it was very obvious how these incremental movements made huge differences in AQ (focusing on the bass the entire time). Interestingly, the bass became better and worse and better again as the speakers inched further from the wall. In the end, we achieved the goal, with bass that sounded long and deep, despite both being about 1 foot from the back wall and one being in a corner.
 

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However, if the waves hit the wall behind at a 45° angle, they do not rebound forward. That's the point I'm making.
If the wavelength is long enough it doesn't matter what angle it hits the wall at, the result will be the same. OTOH if the frequency is above the baffle step there will be no reflected wave, no matter what the angle of the wall. This is all highly predictable, to the extent that software exists that will do it for you.
 

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+1
IMO, the answer is to play around with speaker placement to get the best sound. ...moved them an inch at a time further from the back wall, and it was very obvious how these incremental movements made huge differences in AQ ...
I think Bill has offered the most practical advice, which condensed down is simply forget what is ideal, and do the best you can with what you have. Don't be afraid to experiment and try new things.

Generally, the size of the speaker matters. Bookshelf will tolerate close placement more than large floorstanding.

Bass heavy speakers need more room than more balanced speakers.

Front ported are more tolerant of placement than rear ported.

And, though don't discount ingenuity, your circumstances dictate the possibilities.

In some case, as with the JBL I had, which were very intolerant of close placement, I cleaned them up by plugging the rear ports. That tame the bass and clean up the midrange to the extent that it was possible.

Generally, you have to do what you have to do. You have to place the speakers in the only place you have to place them. Just make sure you really do have to place them there, and have not simply fallen for the obvious assumption. A good dose of common sense and ingenuity plus creative thinking will take you a long way toward optimizing your system.

So, forget about doing the ideal best, and rather, do the best you can with what you have.

Steve/bluewizard
 
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