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Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How... - Page 237

post #7081 of 9539
Quote:
Originally Posted by LastButNotLeast View Post
 

I will experiment this week. Thanks for the suggestions.

Michael

 

And, as long as I'm still here, does anyone still have a link to the "limp membrane traps" that were talked about a few pages (eons?) back? The search function here is useless and Google takes me everywhere but anywhere productive.

Thanks.

 

Did you mean this:

 

http://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/743040-tims-limp-mass-bass-absorbers.html

 

Oh yes, you did :)

 

[/readahead]


Edited by kbarnes701 - 11/18/13 at 3:38am

Gear mentioned in this thread:

post #7082 of 9539
Quote:
Originally Posted by jlpowell84 View Post

What is the simple answer?

The simpel answer is: it doesn't correlate with how we hear.
post #7083 of 9539
Quote:
Originally Posted by kbarnes701 View Post
 

 

Did you mean this:

 

http://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/743040-tims-limp-mass-bass-absorbers.html

 

Oh yes, you did :)

 

[/readahead]

I did, thank you, and I've already ordered this:

http://www.homedepot.com/p/Unbranded-dB-3-4-ft-x-8-ft-Acoustical-Barrier-DB348X96BX/100663624#.UooOjSiWXGk

Stay tuned.

post #7084 of 9539
Thanks Jerry.
Quote:
Originally Posted by AustinJerry View Post

First of all, your sub seems to have a very good low end--that is a nice, flat response all the way to below 20Hz. The response in the 60-90Hz range indicates that there may be phase issues at the crossover point.  Have you tried adjusting the sub delay to see if it has any effect on the FR flatness?
yes I have, there is v good phase tracking throughout the XO region. The chart below shows the R vs SW, the L vs the SW is a bit more uneven because the L has 1-2 sharp nulls in this region but it's as well aligned as it can be.


There is more detail (inc the mdat) in this thread on HTS if you're interested.
Quote:
Originally Posted by AustinJerry View Post

The waterfall looks quite good, although I would have preferred seeing a 450ms window.  There is a bit of ringing shown by the "mountain" at approximately 90Hz.  the smaller time window might add some perspective.
do you mean the "time range" (the z axis) or the "window" control? I don't see a difference in the view around that frequency by changing the window control. Here's a view with the time range reduced to 300ms anyway.


Quote:
Originally Posted by AustinJerry View Post

At a minimum, I would recommend that you conduct some of the exercises described in this thread to at least isolate what might be causing the reflections.  This way you might find an easy way to improve the reflections without a lot of effort.  Those reflections must be coming from something quite close to the speakers or your listening point.  The font in the graph is quite small, but it seems as if the reflections colored in blue might be slightly worse.  Consider the "blocking technique" to identify where these are coming from.  Taming the reflections has the potential of significantly improving your listening experience, in my opinion.
I will look into doing that, at least if I know where it comes from then I decide whether it is treatable or not given the room constraints whereas at the moment it's just guesswork.
post #7085 of 9539
Quote:
Originally Posted by markus767 View Post

Phase alignment is meaningless at such low frequencies in acoustically small rooms. If two frequency responses with the same dip and phase response are combined, the result will be an even deeper dip. Frequency response smoothness is more important than phase alignment.
Why is phase completely meaningless at these frequencies? I thought phase difference is how we perceive direction at such wavelengths (down to about 80Hz) & having 2 things out of phase is going to cause a cancellation (which seems likely to be a bad thing). In my, non expert, experience getting the phase tracking right between the speakers consistently produces good results over the XO frequency range. The actual method used was to compare the impulses & the phase of the SW and R speaker around the XO frequency, adjust delays and/or polarity to match & then verify by comparing the frequency response (using REW's calculation feature).
post #7086 of 9539
^
The dip in your graph is <80.
The speaker/room interaction distorts directional information.
post #7087 of 9539
Quote:
Originally Posted by markus767 View Post

^
The dip in your graph is <80.
The speaker/room interaction distorts directional information.
assuming you mean the dip at about 70Hz, I believe that dip is a room mode as the R and SW both see about the same dip (the SW and R are quick close to each other) & the rew room sim suggests there is a tangential width/height mode at that frequency.
post #7088 of 9539
^
I've deleted one of my earlier posts, content wasn't correct.

Did you measure your speakers with a timing reference (loopback channel)?
post #7089 of 9539
Quote:
Originally Posted by jlpowell84 View Post

I'm sorry if this question has been answered. I have mostly kept up with the thread but working 7 days a week as of recent I may have missed. I will post a clip from J's recent comment that I have yet to find a satisfying answer for. Again I have been keeping up mostly with the measurement technique discussion but didn't hear a direct answer.

If you decide to view a full range measurement with L+R+Sub(s) you will most likely be disappointed above about 1khz or so (most of the time and unless you are VERY careful and have very exact speaker and mic placement between the speakers) as the wavelengths start to become so small the slightest movement of the mic will cause phase interactions, comb filtering, and a very poor and inaccurate measurement in the higher frequencies. There really isn't any reason for this. Again, the only measurement necessary for L+R+Sub(s) - combined - should be to look at the overall bass response, below 300hz, unsmoothed.

I did accidentally do this the other day. On my Mac I have to switch audio output to sound flower 64ch as per JPA's wonderful guide to only get one speaker plus LFE channels at a time. I had switch back to my Denon, which allows for both LR to play, to listen to a song for differences during tuning and forgot to change it back. I did notice some not so good looking graph up in the top end.

Why don't we do this? It seems this would be the most important since we listen with both of these speakers (plus a center usually) during a movie or multichannel music. What is the simple answer?

 

Here is an example of the interaction between left and right signals at the upper frequencies:

 

 

Note the significant dip in the combined (green) response curve.  Clearly, the individual speaker response curves do not suggest such a severe roll-off in the high end.

 

BTW, as mentioned previously, all you have to do is adjust the mic position an inch or two to the left or right, re-measure, and you will see the interaction diminished significantly.  I always try to place the REW mic in the same spot as the Audyssey mic (Audyssey shows identical left and right speaker distances), but the graph shows how hard exact placement can be.

post #7090 of 9539
Quote:
Originally Posted by AustinJerry View Post

Here is an example of the interaction between left and right signals at the upper frequencies:




Note the significant dip in the combined (green) response curve.  Clearly, the individual speaker response curves do not suggest such a severe roll-off in the high end.

BTW, as mentioned previously, all you have to do is adjust the mic position an inch or two to the left or right, re-measure, and you will see the interaction diminished significantly.  I always try to place the REW mic in the same spot as the Audyssey mic (Audyssey shows identical left and right speaker distances), but the graph shows how hard exact placement can be.

That's where mic stands and exact tape measures come in handy...and OCD biggrin.gif
post #7091 of 9539
Quote:
Originally Posted by AustinJerry View Post

but the graph shows how hard exact placement can be.

I had a very similar experience this weekend and was going to comment on how much of a heartbreaker REW can be. I have a few dips in my FR above 2k that I was thinking might be due to SBIR. (pending front wall treatments.)

By moving my speakers a cm at a time I did manage to get my right speaker (but only the right one) to give a flat response in that region. But then I moved something and the dip was back frown.gif

After a few hours I settled.
post #7092 of 9539
Quote:
Originally Posted by markus767 View Post

^
I've deleted one of my earlier posts, content wasn't correct.

Did you measure your speakers with a timing reference (loopback channel)?
yes I do
post #7093 of 9539
Quote:
Originally Posted by markus767 View Post

The simpel answer is: it doesn't correlate with how we hear.

Ok. I don't see it in my mind still but I certainly believe all you guys smile.gif. It just seems as both speakers or all front three is how we would hear since we listen with all speakers on at the same time and not just my left with subs or right with subs. Please forgive my inability to see this yet smile.gif. So I just keep thinking that the interaction is what we would be most concerned about
Quote:
Originally Posted by AustinJerry View Post

Here is an example of the interaction between left and right signals at the upper frequencies:




Note the significant dip in the combined (green) response curve.  Clearly, the individual speaker response curves do not suggest such a severe roll-off in the high end.

BTW, as mentioned previously, all you have to do is adjust the mic position an inch or two to the left or right, re-measure, and you will see the interaction diminished significantly.  I always try to place the REW mic in the same spot as the Audyssey mic (Audyssey shows identical left and right speaker distances), but the graph shows how hard exact placement can be.

I do measure my mic and have found 94 inches from the sidewall to be center. I have been eyeballing away from the back of the couch. I could measure both ways I guess
post #7094 of 9539
Quote:
Originally Posted by 3ll3d00d View Post

yes I do

That's good. How much does the dip change with mic location? You could try and equalize it. It seems to be minimum phase.
post #7095 of 9539
Quote:
Originally Posted by artur9 View Post

I have a few dips in my FR above 2k that I was thinking might be due to SBIR. (pending front wall treatments.)
For the cancellation to be SBIR caused by the front wall, the driver would have to be within a couple of inches of that wall. Might be something else.
post #7096 of 9539
Quote:
Originally Posted by jlpowell84 View Post

Ok. I don't see it in my mind still but I certainly believe all you guys smile.gif. It just seems as both speakers or all front three is how we would hear since we listen with all speakers on at the same time and not just my left with subs or right with subs. Please forgive my inability to see this yet smile.gif. So I just keep thinking that the interaction is what we would be most concerned about
I do measure my mic and have found 94 inches from the sidewall to be center. I have been eyeballing away from the back of the couch. I could measure both ways I guess

We have two ears. So the first mistake is to use only one single mic at a single location. There's also a head. That head causes shadowing effects. Our measurements don't incorporate those effects. There's also a brain in that head which processes the signals received by the left and the right ear. It doesn't apply a fixed window time on an impulse response like our measurements do.
post #7097 of 9539
Quote:
Originally Posted by markus767 View Post

We have two ears. So the first mistake is to use only one single mic at a single location. There's also a head. That head causes shadowing effects. Our measurements don't incorporate those effects. There's also a brain in that head which processes the signals received by the left and the right ear. It doesn't apply a fixed window time on an impulse response like our measurements do.

I have heard of measurement systems that employ a dummy head and two mics.
post #7098 of 9539
Quote:
Originally Posted by markus767 View Post

We have two ears. So the first mistake is to use only one single mic at a single location. There's also a head. That head causes shadowing effects. Our measurements don't incorporate those effects. There's also a brain in that head which processes the signals received by the left and the right ear. It doesn't apply a fixed window time on an impulse response like our measurements do.

Ok, I see. With LR we get the higher frequency tiny wave interference right at the tip of the mic. We don't have that with our head there. A dummy head and two mic measurement system would be interesting Jim.

So as we listen, we get essentially the EQ line that we measure with just L or R or C plus subs correct? It would be somewhat different correct with multiple sources radiating sound?(LCR). Or is it basically what we measure?
post #7099 of 9539
Quote:
Originally Posted by jlpowell84 View Post

Ok, I see. With LR we get the higher frequency tiny wave interference right at the tip of the mic. We don't have that with our head there.

We do, just not the same way a mic picks it up and there's the processing of our brain that gets information from the left and the right ear at the same time.
Quote:
Originally Posted by jlpowell84 View Post

So as we listen, we get essentially the EQ line that we measure with just L or R or C plus subs correct? It would be somewhat different correct with multiple sources radiating sound?(LCR). Or is it basically what we measure?

The idea is simply to make the single speakers to behave as similar as possible. So measuring them together doesn't give us the information we're interested in. It's nearly the opposite for lower frequencies.
post #7100 of 9539
Quote:
Originally Posted by markus767 View Post

That's good. How much does the dip change with mic location? You could try and equalize it. It seems to be minimum phase.
it varies quite a bit across the 2 main listening positions so I think I either need to really seriously prioritise one seat only or leave as is.



It is also quite different across the L and R as well so I suspect I'd need per channel control (which I won't have until I switch to the PC as the only source) over correction to deal with it. Mind you I may well be doing that (heavily prioritising one seat) already based on the L+R+SW in the 2 positions.

post #7101 of 9539
Quote:
Originally Posted by sdurani View Post

For the cancellation to be SBIR caused by the front wall, the driver would have to be within a couple of inches of that wall. Might be something else.

The back of the speaker was about an inch from the wall and the depth of the speaker is 10 in. Would that do it?

thanks!
post #7102 of 9539
Quote:
Originally Posted by artur9 View Post

The back of the speaker was about an inch from the wall and the depth of the speaker is 10 in. Would that do it?
Have you tried moving the speaker away from the wall to see if the dip moves to a different frequency?
post #7103 of 9539
my latest sub response (hope im doin it right with new guidelines)
]

IM wondering what that null is around 88hz
post #7104 of 9539
Quote:
Originally Posted by Brian Fineberg View Post

my latest sub response (hope im doin it right with new guidelines)

IM wondering what that null is around 88hz

Close, and not bad.

It doesn't make any sense to go down to 5Hz. Start at 15.

The null is probably because of the size of your room. One of the experts will no doubt chip in and guess one of the dimensions of your room to within 6 inches.

;)

post #7105 of 9539
Quote:
Originally Posted by Brian Fineberg View Post

IM wondering what that null is around 88hz
Might not be the sub, since it is only happening with the right speaker and not the left. Can you post a sub response that's only a sub response (no speakers)?

BTW, is your room 24 feet 6 inches tall by any chance?
post #7106 of 9539
Quote:
Originally Posted by sdurani View Post

Might not be the sub, since it is only happening with the right speaker and not the left. Can you post a sub response that's only a sub response (no speakers)?

BTW, is your room 24 feet 6 inches tall by any chance?

will do tonight
post #7107 of 9539
Quote:
Originally Posted by sdurani View Post



BTW, is your room 24 feet 6 inches tall by any chance?

biggrin.gif
post #7108 of 9539
Quote:
Originally Posted by sdurani View Post

Have you tried moving the speaker away from the wall to see if the dip moves to a different frequency?

Yes. On the left speaker moving it back and forth changes the dip from 3k to 8k. Unfortunately, nothing I've done so far gets rid of the dip completely on the left side.

On the right side all the dips are gone if the speaker is placed 15.5 cm or so from the back wall. At least, I did manage that once smile.gif Dip came back after I toed in the right a little.

I think the true recourse here is 2" acoustic panels behind the speakers?
post #7109 of 9539
Quote:
Originally Posted by artur9 View Post

I think the true recourse here is 2" acoustic panels behind the speakers?

Or maybe just to stop measuring:

http://www.avsforum.com/t/1478854/the-science-of-the-room-with-paul-hales

;)

post #7110 of 9539
Quote:
Originally Posted by AustinJerry View Post
 

Sorry, that is not correct.  A mono signal is routed exclusively to the center channel.

And therein lies the rub.

Using the generator function, I am, indeed, getting output only from the center channel.

However, running the sweeps, the left and right are also participating.

Oh, well.

Michael

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