In room speaker measurements and correction

[brk]

Hello,

I have been playing with REW for a few weeks. Have these measurements of my speakers in 19 x 13 room with high ceilings - the speakers have to be set up on long axis. There is a thick rug in front of them.

The measurements seem to show three "problems" - spikes at 45 and 65 hz (room nodes?), ugly bite-shaped dips in 100-300 hz area (the whole region is low), and then this peak around 1k. I tried moving the speakers all over the place without much change. I used the moving mic method - twirled the mic around my ear, sat up, leaned back, and took a long average.

In EQ, I chopped a few db off the 65 hz peak and followed strict orders from here (and elsewhere) to not even think about touching the 100-300 hz area. But could not help trying to smooth the midrange using two filters. It LOOKS better and I think sound better. Any advice as to where to go next is much appreciated.

Bryan

 

[alex-z]

That drop in treble after 5000Hz is correctable if you are willing to sacrifice 3-4dB of headroom.

Your 100-300Hz region is messed up because of wall boundary reflections. 1/4 wavelength placement causes a 1/2 wavelength cancellation. For example, if your speaker is 50cm from the front wall, there will be a null at 171.5Hz.

There are two good options. The first is pull the speakers far out, so the boundary reflections are below the subwoofer crossover point. Or push them right up against the walls, so that the reflection frequency goes up, into a range where acoustic treatment works well. If the front of the speaker is 30cm from the front wall, the null is 286Hz, easily treatable with 3.5" absorption.

SBIR calculator

SBIR calculator

tripp.com.au

All the problems below 100Hz are your axial room modes. To deal with this you need multiple subwoofers, ideally with some form of EQ.

 

[Hipper]

Hello Bryan - my brother's name was Bryan with a 'y'!

It would be useful to know the following:

• where you positioned your speaker and listening chair and whether you can move these about anywhere
• what are your speakers
• if you listen on your own or with others
• what you use for EQ

 

[brk]

Thanks!! The speakers are positioned on the long wall 6'2" apart, 2'2" from the back wall, and 5'8" from the side walls. I sit about 9 feet away (near field). I took multiple measurements moving the left speaker forward and backward from nearly against the back wall wall to about 4 feet out (as far they could realistically go) but could not get much meaningful change in that big 80-300 dip.

Despite the numerous warnings to not touch anything above 200 hz, I did try two "gentle" lowish Q filters to smooth out the midrange from 500-2500. It sounds great (to me) and measures better (in attached graph). But I have probably angered the EQ gods in some way.

 

[Hipper]

Don't worry about ignoring rules if there's a reason. The object is for you to get the best sound you can.

6'2" plus two times 5'8" equals 17'6". You said your room was 19' x 13'? Just thought I'd show off my maths!

You could try 'The Thirds'. This is the version I used:

http://www.barrydiamentaudio.com/monitoring.htm

In a 19' x 13' room that means the speakers (centre of the drivers) would be 4'4" from the back wall and 6'4" from the side walls, with your seat (more exactly your ears) 6'4" from the back wall. You would be about 7' from your speakers.

That's a starting point. I then measured to try and find the best place for the left speaker for bass response, moving it both backwards and forwards and side ways, first with big movements, say 6", then when I found the best of those positions, I would use 1" movements in that area. Make a drawing of a grid and mark and name the positions as you measure them. I used only one position of the mic (not MMM) to measure and one sweep from 0-300Hz, always using no smoothing on the SPL graph.

Once I'd found the best position for the left speaker I'd place the right in it's respective position and measure - hopefully it would be more or less the same. If your room has a symmetrical layout it should be. If it isn't the same measurement, move that around a bit to see if there is a better one and compare that to the equivalent left speaker measurements and find the best compromise.

Moving your chair backwards and forwards a little bit and measuring may also offer improvements.

For me I found almost exactly The Thirds worked best.

From there this is what I did - post 60:

https://www.audiosciencereview.com/...in-room-measurements.13540/page-3#post-411614

You can see from this link that I ignored the rules on not filling a large dip with EQ and it worked for me for some unknown reason.

 

[brk]

Thank you! Unfortunately, 4'4" out into this narrow room would just not be feasible. I will try it today just to measure and post the data. What about the poor man's rule of thirds - the rule of fifths? This would put the speakers out at 31" Am pretty sure I measured there and did not see much difference.

 

[Hipper]

Fifths worked for me once. Although The Thirds looks silly it works. My room is 14' x 13' with speakers on the 14' wall.