Acoustical help with Room EQ Wizard and in room response and decay time

[etc6849]

Thanks.  I just installed it.  Both files have a similar frequency spectrum, so I'm not sure where the noise is coming from?  Maybe the projector fan wasn't fully off when I took one of the REW measurements.  It stays running for 2-3 minutes after you turn off the projector.

Edited April 10, 2015 by etc6849

[Chris A]

I recommend taking sweeps at closer to 100 dB or higher (wear ear protection) --perhaps if the noise was from the projector, that will push those 1-10 kHz spikes down on the impulse graph.  If it doesn't, then...

 

You might also still move your fronts toward the front wall by about half the distance: if that "slap" delay decreases, then you'll know what the problem is.  If if increases the delay, then you can at least rule out the front wall. 

 

If it doesn't change the delay, then you've got a nearfield reflector issue next to your listening position.

 

Chris

Edited April 10, 2015 by Chris A

[DrWho]

Spurs from a switch mode power supply can look like that too. You mentioned using a laptop. Were you running off the battery, or was it plugged into the wall? It's not uncommon to get leakage current on the ground from your laptop's power supply. It behaves just like a ground loop except the frequencies are higher. Running off the battery can make this go away....we have this problem all the time at work.

 

Btw, what are you plugging your Dayton microphone into? These spurs could also be coupled into your microphone preamp.

 

If this is an acoustically generated noise, then you should be able to hear it with your own ears...

Edited April 10, 2015 by DrWho

[etc6849]

I'm going to rearrange things next weekend when the 4 more soffit bass traps arrive.  I did some testing moving the mic forward and backwards in 1 foot increments.  The peak gets shorter when the mic is NOT under the projector.  However it didn't dissappear when I moved the mic towards the front, but did show a longer delay the closer I moved to the front wall.  I suspect it's the sloped ceiling?  I put 4" bass traps on the back wall and the peak was still there.

 

Moving things will get me closer to the screen and out from under the noisy projector regardless.

 

What bothers me about the impulse response plot is the first peak starts ~t=0.  Should t=0 be adjusted to include the direct soundpath time to the mic?

 

I also want to figure out the 120 hz dip too.  I suspect Mike is alluding to it being a crossover or sub delay issue.

 

You might also still move your fronts toward the front wall by about half the distance

Edited April 11, 2015 by etc6849

[etc6849]

It's the USB version, it plugs directly into the laptops USB port.  I tried measurements with the laptop plugged in and unplugged; both show the interference.

 

I also hook an HDMI cable to my preamp.  I suspect using an optical cable might be smarter, but I need to buy an external sound card to do that.

Btw, what are you plugging your Dayton microphone into? These spurs could also be coupled into your microphone preamp.

 

[Chris A]

I did some testing moving the mic forward and backwards in 1 foot increments. The peak gets shorter when the mic is under the projector. However it didn't disappear when I moved the mic towards the front, but did show a longer delay the closer I moved to the front wall. I suspect it's the sloped ceiling? I put 4" bass traps on the back wall and the peak was still there.

 

This says that all of the canted ceiling, and probably the side walls, too, are the problem and any portion of them not covered up is contributing to a reflection delay of the path length difference, direct path vs. up-and-down path, which is constant for the ceiling and side wall surfaces in this case.  This also explains why other rooms that have similar ceiling configurations have also reported issues with strong reflections.

 

Perhaps one way to reduce this strong reflection is to move the front loudspeakers toward or away from the side walls so that their reflected path lengths aren't the same as the ceiling delay.  Another approach is to move most of your absorption pads to cover the ceiling and side walls forward of your listening position.

Edited April 10, 2015 by Chris A

[etc6849]

I think my ceiling is my most likely issue.  Please note that I edited my post to state:  "The peak gets shorter when the mic is NOT under the projector."  I was typing on my 4" cell phone, and missed typing the word not!

 

I still could be seeing ceiling reflections as I measured this at 3 feet toward the front wall from the MLP, staying at the same height and centered just like the original measurements.  This was out from under the projector after two feet, but more into the canted ceiling area the closer I went to the front wall.

 

Going away from the MLP and away from the front wall, the mic is no longer under the canted ceiling area after two feet.

 

 

 

This also explains why other rooms that have similar ceiling configurations have also reported issues with strong reflections.

Edited April 11, 2015 by etc6849

[DrWho]

It's the USB version, it plugs directly into the laptops USB port.  I tried measurements with the laptop plugged in and unplugged; both show the interference.

 

Can you hear it in the room? 

[etc6849]

I hear a slight hiss from the tweeter, but I believe this is normal as my preamp runs hot, and my amp doesn't have adjustable inputs.

 

I did some more testing with the amp off, which means only the subs with their internal amp were running.  Still the n*(1 kHz) noise is there.

 

I also tried another laptop with it unplugged from the wall, and the n*(1 kHz) noise is there.  This leads me to believe the noise is from the mics USB preamp.

 

Can you hear it in the room? 

 

Edited April 24, 2015 by etc6849

[ninjai18]

As soon as you are able, I'd build some DIY bass traps and replace those foam pieces with acoustic panels made from Roxul Safe N' Sound. Night and day difference. The problem with foam is it is terrible at treating a room for improved bass/mid-bass response. Also, you should definitely put some sound diffusers in there. That's a small room, and adding sound diffusers will help make it sound bigger than it really is. I added Aurelex T'Fusors to my small room and it made a world of a difference.

Edited April 19, 2015 by ninjai18

[etc6849]

I'm attaching a new impulse and FR plot for pure direct mode (no EQ) after rearranging the room.  Please note that I haven't rerun Audyssey, but will post updated plots after a new Audyssey pro calibration later in the week.

 

The results still show a peak in the impulse response.  I'm going to order two monster traps to screw to the ceiling.

 

Four additional soffit bass traps (8 total now) and new location get rid of a 20dB dip I had ~40 Hz when Audyssey was turned off.

 

When reading the plots, remember that pure direct mode means the main speakers are not crossed over to the sub and Audyssey EQ is turned off.

 

 

 

New room arrangement:

 

This says that all of the canted ceiling, and probably the side walls, too, are the problem and any portion of them not covered up is contributing to a reflection delay of the path length difference, direct path vs. up-and-down path, which is constant for the ceiling and side wall surfaces in this case.  This also explains why other rooms that have similar ceiling configurations have also reported issues with strong reflections.

 

[ninjai18]

I can't press it enough, I would strongly consider putting in some diffuser panels. it's one of the most neglected things I see in people's home theater rooms. Absorber panels and bass traps are wonderful and are immensely helpful, but sound diffusion is easily as important.

[etc6849]

For multi-channel audio, I'm not sure if using diffusion panels is a good idea in a small room?  I ask this because if one uses 7.2 speakers, some of the speakers will inevitably have their first reflections diffused as opposed to absorbed.  It would seem this has great potential to affect multi-channel imaging.  I'm a big fan of multi channel audio tracks, and even upconvert 5.1 to 7.1 audio using DTS NEO X.

 

I do see the value for stereo where you'd want to make the image surround you more.  I'm not an expert though, so hopefully others will chime in.

 

but sound diffusion is easily as important

 

[Chris A]

I'd try putting a thick and fuzzy blanket over the screen in A-B sweeps, with and without covering the screen with no other changes and look at the changes in the magnitude of the reflected pulse.

 

I know that high frequency reflections around 2 kHz shouldn't be in the reflected wave if the reflections are coming from the screen, but I'm not sure what else to do other than doing a 100% absorption coverage of the tilted ceiling areas in front of the LP.  This is an interesting--and persistent--puzzle.

 

Diffusion is an interesting idea: if you can't presently locate the source of the strong 4.6 ms reflection by using absorption panels, then putting diffusion panels in there probably is like a scatter gun approach--with low probability of success.  The source of the reflection(s) that are delayed 4.6 ms has to be identified before telling the poor man that he has to go buy more (and expensive) diffusion panels.

 

Chris

Edited April 19, 2015 by Chris A

[Chris A]

Did you have your surrounds unplugged during these sweeps?

[ninjai18]

 

For multi-channel audio, I'm not sure if using diffusion panels is a good idea in a small room?  I ask this because if one uses 7.2 speakers, some of the speakers will inevitably have their first reflections diffused as opposed to absorbed.  It would seem this has great potential to affect multi-channel imaging.  I'm a big fan of multi channel audio tracks, and even upconvert 5.1 to 7.1 audio using DTS NEO X.

 

I do see the value for stereo where you'd want to make the image surround you more.  I'm not an expert though, so hopefully others will chime in.

 

 

 

but sound diffusion is easily as important

 

 

 

I'm no expert either, but adding sound diffusers to my room definitely helped. I have a small room with short angled ceilings as well.

[etc6849]

Holy moly, I only installed two of the new monster traps and placed one near the door.  

 

Note as Mike suggested, I haven't reran audyssey from my last post (to aid in the comparison).  The 4.7 ms peak is almost completely gone and the impulse response is near perfect!

Left:

 

Right:

 

It is very easy to see what the two cloud/ceiling mounted monster traps have done if you compare these impulse graphs to post 91.

 

I'm going to install the third one tomorrow.  The stereo image is so much better with just two mounted its unbelievable.  I've never heard anything like it.  The image definitely has depth and is almost entirely holographic.

 

This whole experience was very eye opening and I appreciate the help Mike and Chris!  I learned a lot.

Edited April 24, 2015 by etc6849

[etc6849]

Here's a picture with the full range monster traps circled so you can see what I added and where.  The impact fixing the impulse plot has on imaging still has me surprised.  I was not expected to hear a difference so big.  My system is jaw dropping now, and my wife immediately noticed the difference too.

 

The new monster trap near the door is not the one I'm going to mount to the ceiling.  I left the one I'm going to mount out in the hallway so I can compare plots later on if needed.

 

I'm seriously considering ordering 6 more full range monster traps (three to flank each side of the new cloud mounted monster traps).

 

 

Edited April 24, 2015 by etc6849

[Chris A]

Wow, that's good news for you...and bad news for people that live in attic rooms with canted or cathedral ceilings which have that slanted ceiling portion down to head height. 

 

I've read a lot of experiences about this phenomenon in this type of room.  It's extremely important from my point of view now that you've apparently solved the puzzle.  When you think about shoebox-shaped rooms vs. lower canted-ceiling rooms, it is clear that something should be different.  Now we know.

 

Thanks for your sharing in this exercise--it helped me a lot to understand something that I've wondered about for some time.

 

Chris

[DrWho]

You may want to start pulling out some of your other panels to see if you can liven the space back up without affecting your new found imaging...