Multi subwoofers/room acoustics question
dazzdax
Thread Starter
#1
15th July 2013
Old 15th July 2013
  #1
Gear interested
 

Thread Starter
Multi subwoofers/room acoustics question

Hi folks, I would like to hear your opinion about the following issue.
I have in my living room a pair of Soundlab A-1 electrostatic speakers and two pairs of Rythmik Audio sealed subwoofers (see picture) that are located behind the Soundlabs.
My complaint are: I have a nasty reinforcement at about 55-60Hz, which I believe is related to ceiling height (10 ft) and I hear mainly midbass (double bass) and lower mids rather than deep bass.
Can I get rid of this standing wave between floor and ceiling by raising the subwoofers about 2.5 ft off the floor (= 1/4 floor to ceiling distance) in order to cancel this mode by means of destructive interference? Or do you think the applications of proper bass traps would be more beneficial?
Do you have any idea why I don't get much deep bass (with four 15 inch sealed subwoofers!)?

Soundlabs + Subwoofers Photo by dazzdax | Photobucket
Subwoofer Output Photo by dazzdax | Photobucket
floorplan2_zpsf5c8bdf2.jpg Photo by dazzdax | Photobucket

Chris

Last edited by dazzdax; 15th July 2013 at 10:48 AM.. Reason: Links to pictures were missing
#2
15th July 2013
Old 15th July 2013
  #2
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sheggs's Avatar
 

If you measure the room using REW software (link to free software and video user guide here -

Room EQ Wizard Tutorial - GIK Acoustics

Then you can experiment by moving the subwoofers around. It allows you to overlay each position to compare
#3
15th July 2013
Old 15th July 2013
  #3
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jhbrandt's Avatar
 

Chis,

Standing waves are best treated with position. According to my calculations, you will have a double instance at 62.8Hz. This is due to your length and width having a common denominator.
Ceiling axial is 56.5Hz. It could be that you are sitting in a null.

Start with your seating position about 155" from the front wall, then try 202.5. The closest you should try is around 124" but you may have to set your head in vice to keep things smooth.

Follow the manufacturer's guide-lines for the electrostatics. You'll need to 'play' with the distance from the front wall, but I can tell you this: you will need trapping on the front and side walls to eliminate the comb-filtering.

Start with the subs Right IN The corners of the room and test with REW. You will need about -12dB power in the corner as opposed to 'in' the room. Calibrate, measure, move... The best place to combat modal boosts is to USE the corner to your advantage, but distance them from the side walls by odd fractions of the width. I will often end up with a dual sub setup along the front wall corner, with the left sub about 33 degrees from center and the right sub at about 20 degrees.. or vice-versa.
You MUST test to find THE spot.

The ceiling needs to have a good absorption cloud at reflection points. You can download my ReflectionsBoundariesMass calculator from my publications page. The first tab has a little calculator to help you with placement. This will work for side AND ceiling.

Cheers,
John
#4
15th July 2013
Old 15th July 2013
  #4
Go for REW software,it works the best.
dazzdax
Thread Starter
#5
15th July 2013
Old 15th July 2013
  #5
Gear interested
 

Thread Starter
Thank you very much for your recommendations.
John, could you clarify why I might be sitting in a null?
Do you also mean the subwoofers should be placed in the corners or just out of the corners with some distance in relation to the side walls?
Why are the angles the subwoofers towards the centre not symmetrical?
What would be your recommendation regarding raising the subwoofers off the floor?

Chris
#6
17th July 2013
Old 17th July 2013
  #6
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jhbrandt's Avatar
 

Chris,

You may be sitting where the waves are converging and 180 degrees out of phase. This will create a null. Usually mid-point in the length of the room is worst, followed by 1/4 and other 'even' multiples.

It depends on testing of YOUR room. So many factors come into play so we need hard data to make our decisions. You can't just copy a format. - Everything is Connected. Your room, equipment, speakers, treatment, furnishings, etc., comprise a 'SYSTEM'.

You can start with them in the corners for testing and them move them inward. Move them one at a time & you'll see what I mean.

Do the REW testing, move the subs, test again & again until you start to see a pattern in the changing response. - You can also do this by playing sweeps and moving the subs, but this is only for the experienced. You will be able to find and adjust more quickly with the REW software.

The reason that you don't want a symmetrical alignment of the subs to the side walls is so that they do not generate sympathetic waves. By placing them at odd fractions of the width will help smooth the response.

You MIGHT end up raising them, but I've never had to do that.

Cheers,
John
#7
17th July 2013
Old 17th July 2013
  #7
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sheggs's Avatar
 

Any questions with regards the REW software just post them up Herr but as John reiterates it will help you get the best results
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