Help Analyzing My REW Measurement

[nuport]

Seeking the wisdom of those of you smarter than me. I just took my first REW measurements (9 points averaged) and am almost too embarrassed to post this response graph. There is bad flutter echo in the room, but I didn't think it was this bad. Is there something else going on here? Bad measurement technique? Is there hope without filling my living room with acoustic panels?

Thanks

 

[John Mulcahy]

Looks pretty typical. Apply some smoothing to reduce the clutter at the high end, 1/48 for example. Best applying it to the individual measurements before averaging, you can apply smoothing to all selected measurements at once with the controls on the All SPL graph.

 

[nuport]

Thanks John

 

[Sonnie Parker]

That response above 500Hz doesn't look bad at all, but I'd probably see about being able to equalize/filter the below 500Hz.

As for acoustics... I refer you to Floyd Toole's book where he did blind testing on acoustic panels. Ultimately they may not be needed in most typical living spaces sharing space with audio systems.

 

[DanDan]

Two speakers running will cause HF comb filtering at the single mic location. Measure L, R, L+R. Be sure to step away from the mic during sweeps.
Best to post the REW file so we can look into it.

Some guides to REW and acoustic measurement

AustinJerry's guide has good coverage of using USB microphones.

www.avnirvana.com

 

[nuport]

DanDan, thank you for offering your help and suggesting to measure each channel individually. I have attached fresh measurements. The left channel measures much worse than the right because the room is open on the left side. Not really sure how to deal with it except maybe a freestanding bass trap? Right now I have a carboard TV box standing up to serve that purpose and it definitely helps somewhat but still getting poor bass response.

 

[sm52]

nuport
everything is fine with you. Except for excessive midrange reverb. This usually happens with bass. But your bass decays faster than the middle frequencies. Maybe the room is big. On the left is a dip at 40-60 Hz. Try moving the speakers a little.

Can someone explain why the spectrogram of the left channel separately and the right channel separately looks good, but both together - something is wrong?
The second question is why there are two peaks in the Impuls graph of both channels?

 

[skid00]

I've looked at over a dozen mdats posted on the web, I've never seen such long decay times - 1/2 second from 500 Hz to 6kHz. I'm looking at the spectrogram screen...

 

[nuport]

I have a very troublesome room- it is semi open on the left side, and open to the kitchen behind the living room. There are a number of angled walls such as the fireplace and a sloping ceiling- 9ft at the low point, 13ft at the high point. There are also a number of cutouts such as the space above the fireplace.

The measurement I posted was taken with a TV box to the left of the left speaker in my attempt to temporarily create a boundary.

 

[sm52]

nuport
The problem is in the 40-60 Hz pit, not on the left, but on the right. There is a corner. Try to move all the elements to the left - speakers, TV by 10-20 cm. Or put a bass trap in the right corner. Long reverberations in the midrange shouldn't be in a room like yours. The reason can only be a nearby TV. Try moving the speakers away from the TV to the sofa. can be a sofa too. 20 cm. And repeat the measurements.

 

[nuport]

nuport
The problem is in the 40-60 Hz pit, not on the left, but on the right. There is a corner. Try to move all the elements to the left - speakers, TV by 10-20 cm. Or put a bass trap in the right corner. Long reverberations in the midrange shouldn't be in a room like yours. The reason can only be a nearby TV. Try moving the speakers away from the TV to the sofa. can be a sofa too. 20 cm. And repeat the measurements.

I didn't move the TV yet, but I did the following:
1) moved the right speaker 10cm to the left
2) moved the record cabinet out of the path of the right speaker
3) moved the left speaker about 10 cm to the left
4) removed the tv box that I was using as a boundary
5) recentered the couch

spl graph looks a bit better to me, but I don't know how to read the other charts heh

 

[sm52]

Got better. The right side has improved more, the left less. The long decay of the mid frequencies did not change. On the left, the dip of 40-60 Hz turned into 40-50 Hz, i.e. is also better. Do not move the right side to the right or to the left any more. Move the left one to the right, to the left to further reduce the dip of 40-50 Hz. To resolve the issue with medium frequencies, both sides must be moved away from the TV to the sofa. As far as it's possible.

 

[nuport]

Got better. The right side has improved more, the left less. The long decay of the mid frequencies did not change. On the left, the dip of 40-60 Hz turned into 40-50 Hz, i.e. is also better. Do not move the right side to the right or to the left any more. Move the left one to the right, to the left to further reduce the dip of 40-50 Hz. To resolve the issue with medium frequencies, both sides must be moved away from the TV to the sofa. As far as it's possible.

Regarding the medium frequencies, what graph should I look at and what should I be looking for?

 

[sm52]

Waterfall. You have the first picture. We must try to do as in the second picture. Attenuation no more than 250 ms.

 

[nuport]

I have been moving the tv between the speakers, couch, and speakers around but I haven't been able to get much improvement. Actually, I can't seem to replicate the responses I last posted now- the 40hz dip is now a bit lower. Each time I moved something I moved it about 6 inches- should I be trying smaller increments?

One thing that did help was placing moving blankets over the TV above the fireplace. That brought the decay down by at least 10%. I think that tells me I need to get some acoustic panels, would you agree?

 

[sm52]

I cannot think of exact reasons from afar. Try different options on your own. 6 inches of travel - better less, 2 inches. Try rotating the speakers from a position where they are looking at a point slightly in front of the listening position to a position where they are looking slightly beyond the listening position. If none of the methods gives an improvement, you will have to leave it as it is. This is the picture for many people. Over time, you will learn more information about what actions you need.