seek expert advice on speaker position

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Aug 10, 2019
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I acquired a pair of B&W 802 speakers. I have a basement measures 4.3 m x 6 m. How far away should I placed it away from the wall ?

Also, should I placed the speaker slightly tilted towards the centre where I am seating?
 
A

Anonymous

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You have acquired some SWWEEEEEET speakers! I have spent many hours recording and mixing on these.

Start with your speakers pointing down the long axis of your room positioned at least a metre from the wall so that the two speakers and your head forms an equilateral triangle, and toe them in so the tweeters are pointing towards you.

To really get the best out of these speakers, you need to read up on room acoustics and figure out a plan to acoustically treat your room. The main problem will be first reflections, which bounce off the walls and then arrive at your ears - use a mirror on the wall and ceiling to see where these places are, then block off the sound path with absorptive acoustic panels (not too close to the wall), which you can make out of medium density Rock Wool slabs. As this is a porous-type absorber, they need to be very thick, or placed away from the walls to absorb down to as low a frequency as possible.

The next problem, which is harder to sort out, is 'room modes' - resonance frequencies that are most problematic at low frequencies. They have wavelengths which correspond to your room dimensions. E.g. your room is 4.3 metres wide; this will give you resonances at (340/8.6) Hz = 39Hz, (340/4.3) Hz = 78Hz, 117Hz etc. You need some serious carpentry skills and knowledge of resonaces to build some 'bass traps' that will absorb sound at your problem resonance frequencies to level out the bass response of your room, but with these speakers, it would definitely be a fun and worthwhile project.
 

shooter

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May 4, 2008
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Tonmeister said:
'room modes' - resonance frequencies that are most problematic at low frequencies. They have wavelengths which correspond to your room dimensions. E.g. your room is 4.3 metres wide; this will give you resonances at (340/8.6) Hz = 39Hz, (340/4.3) Hz = 78Hz, 117Hz etc. You need some serious carpentry skills and knowledge of resonaces to build some 'bass traps' that will absorb sound at your problem resonance frequencies to level out the bass response of your room, but with these speakers, it would definitely be a fun and worthwhile project.
Interesting, could you elaborate a bit more on the math, not sure what how too read it.

Also once i've found out the 'room mode(s)' how do i decide what trap to build, size and density wise.
 
A

Anonymous

Guest
The wikipedia article on room modes seems fairly accurate from a brief glance, and should get you started,

Here's a room mode calculator: http://www.bobgolds.com/Mode/RoomModes.htm

And here's a website of a guy who takes acoustics very seriously: http://www.ethanwiner.com/acoustics.html

Basically, standing waves set up between parallel surfaces in your room at frequencies whose wavelengths are: twice the dimension in question, equal to the dimension, 2/3 the dimension, 1/2 the dimension, etc, giving a harmonic series of resonances. More complex modes are set up by sound bouncing obliquely around the room in 2 and 3 dimensions, making the calculations pretty complex.

You only need to worry about room modes in small (ish) rooms and at low frequencies,

If your system is halfway decent, then sorting out room acoustics is the best way to fix muddy bass and imaging problems.

I hope this helps!
 

shooter

New member
May 4, 2008
210
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Tonmeister said:
The wikipedia article on room modes seems fairly accurate from a brief glance, and should get you started,

Here's a room mode calculator: http://www.bobgolds.com/Mode/RoomModes.htm

And here's a website of a guy who takes acoustics very seriously: http://www.ethanwiner.com/acoustics.html

Basically, standing waves set up between parallel surfaces in your room at frequencies whose wavelengths are: twice the dimension in question, equal to the dimension, 2/3 the dimension, 1/2 the dimension, etc, giving a harmonic series of resonances. More complex modes are set up by sound bouncing obliquely around the room in 2 and 3 dimensions, making the calculations pretty complex.

You only need to worry about room modes in small (ish) rooms and at low frequencies,

If your system is halfway decent, then sorting out room acoustics is the best way to fix muddy bass and imaging problems.

I hope this helps!
Thanks, looks like i have some issues in the 20-70 hz region though the walls are irregular and not flat so this could change thing's some what.

Bar the 20 -70hz dip the graph shows a nice upward trend.
 
A

Anonymous

Guest
Thank you guys, I didn't expect to get such serious and expert advice. At least I get the idea of putting the speaker at 1m away from the wall. With regard to the tilting of speaker (long axis) towards the centre along the line of equal triangle, I have never done that and I will give it a try and see (hear) the difference.

The acoustic is way beyound my knowledge, but I will give it a try after I beef up my knowledge.
 

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