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post #4231 of 9577
The mode calculator shows a 2nd order mode associated with the width at 71Hz. The 2nd order mode has a null at the 1/4 and 3/4 marks which, like jkasanic says, are 4' from the left and right walls. To address the dip in your frequency response, you need to place the subs in the nulls. The only way to get rid of a null is to excite it by placing a speaker in the null.

Unfortunately, it looks like the cylinder subs are too tall and would obstruct the screen. What kind of subs are those, and how attached to them are you?

How about having two subs on the back wall, and one sub up front? Perhaps the rear subs could be at the 1/4 and 3/4 marks.
Edited by AustinJerry - 7/19/13 at 7:27pm

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post #4232 of 9577
Quote:
Originally Posted by cuzed2 View Post

Although my current sub positions are pretty much locked in, I can certainly move them around for test purposes. I will keep this on the "test-to-try" list in order to understand what's happening.
A subwoofer in the corner of a room should theoretically excite all room modes. Without moving any of your subs, can you do a sweep through your right front sub only (the one in the corner)? Make sure there is no crossover in the signal path.

If there is a noticeable pattern of peaks & dips, then the dip around 70Hz might be modal. If there is no discernable pattern, then it might be a cancelation caused by one of your other subs and/or speakers being out of phase with the corner sub at that frequency. Speakers still output sound below the crossover point.

If the problem turns out to be modal, and since the subs positions are locked in, would you be willing to move your seating to minimize the dip? If the problem turns out to be a phase cancelation with another sub, you might have to put the other front sub on your receiver's Sub 2 output so that you delay it relative to the corner sub (i.e., move it virtually rather than moving it physically). Hopefully that won't cause the dip to simply move elsewhere in the subwoofer range so we end up playing the acoustic equivalent of whack-a-mole (look, it's at 55Hz!).
Quote:
Originally Posted by cuzed2 View Post

This is the first example of the room node calculator that brings it home and makes sense for me.
As handy as it is, it is only as useful as the dimensions entered. For example: if there is no left wall to your theatre room, then do the low frequency sound waves behave asthough the theatre is 16 feet wide or 30 feet wide?
post #4233 of 9577
Quote:
Originally Posted by cuzed2 View Post

Here you go. The 70 Hz is still there ....

Have to say this is one of the oddest FR curves ive ever seen. That huge + 12db peak at around 600hz must have multiple in phase reflective bounces in the room contributing to this frequency range. The +6db peaks at 7K and 120hz also need attention.

Is this being Eq'd in any way?

I would also measure each channel separately.
post #4234 of 9577
Quote:
Originally Posted by jim19611961 View Post

Have to say this is one of the oddest FR curves ive ever seen. That huge + 12db peak at around 600hz must have multiple in phase reflective bounces in the room contributing to this frequency range. The +6db peaks at 7K and 120hz also need attention.

Is this being Eq'd in any way?

I would also measure each channel separately.

I agree. However; That particular graph is my worst case , No eq (it was taken in pure direct). I hope to continue my efforts this weekend, including single channel, and single sub measurements ...
post #4235 of 9577
Quote:
Originally Posted by AustinJerry View Post

The mode calculator shows a 2nd order mode associated with the width at 71Hz. The 2nd order mode has a null at the 1/4 and 3/4 marks which, like jkasanic says, are 4' from the left and right walls. To address the dip in your frequency response, you need to place the subs in the nulls. The only way to get rid of a null is to excite it by placing a speaker in the null.

Unfortunately, it looks like the cylinder subs are too tall and would obstruct the screen. What kind of subs are those, and how attached to them are you?
**They are SVS 16-46s up front and the rear is an SVS 20-39 also tuned to 16Hz.

How about having two subs on the back wall, and one sub up front? Perhaps the rear subs could be at the 1/4 and 3/4 marks.
**My entry doorway and built-in equipment rack really do not allow for many placement options on the back wall
post #4236 of 9577
Quote:
Originally Posted by sdurani View Post

A subwoofer in the corner of a room should theoretically excite all room modes. Without moving any of your subs, can you do a sweep through your right front sub only (the one in the corner)? Make sure there is no crossover in the signal path.

If there is a noticeable pattern of peaks & dips, then the dip around 70Hz might be modal. If there is no discernable pattern, then it might be a cancelation caused by one of your other subs and/or speakers being out of phase with the corner sub at that frequency. Speakers still output sound below the crossover point.

If the problem turns out to be modal, and since the subs positions are locked in, would you be willing to move your seating to minimize the dip? If the problem turns out to be a phase cancelation with another sub, you might have to put the other front sub on your receiver's Sub 2 output so that you delay it relative to the corner sub (i.e., move it virtually rather than moving it physically). Hopefully that won't cause the dip to simply move elsewhere in the subwoofer range so we end up playing the acoustic equivalent of whack-a-mole (look, it's at 55Hz!).
As handy as it is, it is only as useful as the dimensions entered. For example: if there is no left wall to your theatre room, then do the low frequency sound waves behave asthough the theatre is 16 feet wide or 30 feet wide?

sdurani,
Thanks! Some great troubleshooting suggestions. In another conversation with a very knowledable friend; the need to elimiate the possibility of phase cancellations was also empahasized! I hope to pursue these suggestions during the weekend.
post #4237 of 9577
Quote:
Originally Posted by cuzed2 View Post

Quote:
Originally Posted by AustinJerry View Post

How about having two subs on the back wall, and one sub up front? Perhaps the rear subs could be at the 1/4 and 3/4 marks.
**My entry doorway and built-in equipment rack really do not allow for many placement options on the back wall
I've already gone through your HT build thread (some funny stuff in there), but for those that haven't, you should post a pic of the back of your room so that folks can see what we're working with when making suggestions.
post #4238 of 9577
Quote:
Originally Posted by AustinJerry View Post

What does the Preferences/Mic-Meter screen look like?




For my UMM-6, the calibration button is available.  I don't now why yours would be disabled.  I have never seen that in REW before.  Even with the UMIK-1, which has REW integration coded in, the Calibrate button is still active.  Perhaps this is a question for Dayton.




By the way, the calibration file you download from Dayton is a zero-degree calibration file, which is not quite as accurate as the custom files you would have received, had you ordered the mic from Cross Spectrum Labs.  The 90-degree calibration file is recommended for REW use (at least for the type of room measurements we are doing here).  Did you get a better price directly from Dayton Audio or Parts Express?

Jerry

Thanks for you looking at this. I could not have gotten back to you sooner as I was struggling my failing HT system. The 12 year old amp went out on me. Got a replacement in on Friday and then my prepro gave up on audio (the infamous Integra/Onkyo HDMI board issue). I will certainly re-engage again after I get the system up and running again.

I bought the UMM-6 from Parts Express. Sounds like that was a mistake as the difference in price is $10 but I did not know there was a difference between the correction files (the guide did not mention about this explicitly). Anyway, all of these need to wait now. I am listening through the TV speakers now. frown.gif
post #4239 of 9577
Hi all

Here's the new measurement, now done with STEREO, L+R+Subs
Plus L+Subs and R+Subs for the 1st reflection.

The above pattern is done for each of the three rows.
Labelled, Back, Mid and Front.

Since I don't have a centre seat (due to four seats in a row), I created a fake seat in the middle of each row, so the reflections of the mic are similar to a seat.
This fake seat was also done prior with XT32 for the 1st mic position in the middle. I used towels to block off the open back so the seat back looks similar to the rest of the seats, prior to this the back was open.

All the REW measurements are done with XT32 on and DEQ off.

https://dl.dropboxusercontent.com/u/8646227/21%20July%20measurements/21%20July%20all%20measurements.mdat

Let me know your thoughts.
post #4240 of 9577
Quote:
Originally Posted by SHadoWFoX View Post

I bought the UMM-6 from Parts Express. Sounds like that was a mistake as the difference in price is $10 but I did not know there was a difference between the correction files (the guide did not mention about this explicitly).
It definitely is not a mistake to buy the standard one from PE. That is the one I own. For the purposes of measuring a room response, such calibration differences are not material. You are not trying to set absolute levels or absolute frequency response. Nor designing gear where such accuracy may matter. All you are doing is measuring, making changes, and measuring again to see the effect. The relative differences readily show up there nicely with stock UMM-6.

Any difference will show up at higher frequencies anyway where measurements hugely deviate from what we actually hear. So accuracy differences there are also moot.

At some point, we have to stop being slaves to these numbers and precisions. They have little value in room acoustics. Dr. Toole says it best in his book:

"In some ways, our problems with rooms, especially small rooms, began when we started to make measurements. Our eyes were offended by things seen in the measurements, but our ears and brain heard nothing wrong with the audible reality. As we will see, some of the resolution of the dilemma is in the ability of humans to adapt to, and make considerable sense of, a wide variety of acoustical circumstances. Separating sound sources from the spaces they are in is something humans do routinely."

The actual frequency response curve should be set by ear. And expected performance at higher frequencies achieved through purchasing of well-designed speakers.

If Jerry wants to present evidence that we get worse sounding rooms by buying the standard mic, I am all ears, pun intended smile.gif. Otherwise, we should not make people feel bad about buying the stock unit.
post #4241 of 9577
Quote:
Originally Posted by RapalloAV View Post

Let me know your thoughts.

Something's wrong. The sub level is at least 10dB too hot.

I've asked this now a couple of times, why don't you first measure the response within your room without XT32 to get a feeling for how your room behaves? I'd measure the response of the sub(s) at multiple locations. Don't waste your time on measurements that don't have any value at this stage in the process.
First you want to get the bass response as similar as possible across the listening area. Did you miss my earlier post http://www.avsforum.com/t/1449924/simplified-rew-setup-and-use-usb-mic-hdmi-connection-including-measurement-techniques-and-how-to-interpret-graphs/4050#post_23529024
post #4242 of 9577
Quote:
Originally Posted by markus767 View Post

Something's wrong. The sub level is at least 10dB too hot.

I've asked this now a couple of times, why don't you first measure the response within your room without XT32 to get a feeling for how your room behaves? I'd measure the response of the sub(s) at multiple locations. Don't waste your time on measurements that don't have any value at this stage in the process.
First you want to get the bass response as similar as possible across the listening area. Did you miss my earlier post http://www.avsforum.com/t/1449924/simplified-rew-setup-and-use-usb-mic-hdmi-connection-including-measurement-techniques-and-how-to-interpret-graphs/4050#post_23529024

I did many measurements without XT32. I moved subs all over the place, 3" to the left, right. 6" to the left, right etc etc etc.... I came up with the "best" sub position I could find, without placing subs on stairs, seats, aisles, ceiling, etc etc......
The position I now have is the best I could find.....
post #4243 of 9577
Quote:
Originally Posted by sdurani View Post

I've already gone through your HT build thread (some funny stuff in there), but for those that haven't, you should post a pic of the back of your room so that folks can see what we're working with when making suggestions.

sdurani,
I'm impressed (and honored) that you took the time to check-out my thread - Thanks! You are correct; a picture is worth a thousand words, I should have shared these originally.
My back wall situation is as follows. The modified SVS sub is hiding in plain site as pub table (a 20-39, one port plugged 16 Hz tune, 12.3 driver driven by QSC RMX 850 amp). Not a lot of space back there for placement options.
(P.S> my rear surrounds are Klipsch imn-ceilngs just outboard of the overhead lights)


The Left Front
powered SVS16-46PC+


Right Front,
I read somewhere during my build that with multiple subs raising one might have benefits. So this one is on a shelf above my water meter, The cavity underneath is filled with bagged pink insulation batts. The short wall to the front is framed only , covered with GOM fabric


I spent several hours yesterday following some of your suggestions. I will have some promising results to share here just as soon as I sort out the many REW photos I captured smile.gif
post #4244 of 9577
Here are the results of last nights testing, per sdurani's suggestions. I started out by characterizing how the subs in their current location are behaving: This was done with no crossovers and running REW sweeps of each Sub individually (Mic is fixed at the MLP).

Green is the LF = worst behaved with dips at 48 and 75 Hz
Red is the rear = dips at 72Hz and 90 Hz
Blue is the RF = best behaved perhaps because it's position is not tight into the corner and is further out along the sidewall?




Next up; was the combined response of all 3, YIKES!
(sorry I just realized I captured that snapshot with X graph limit set full range)
post #4245 of 9577
With the combined response showing that extremely sharp dip at 120Hz, I decided to investigate phase issues (per advice from drewmc, and sdurani):
My front subs have variable adjustment on the built-in BASH amps (these are together on sub channel 1)
The rear sub is on channel 2 and is powered by an out board amp. I thought I would start out by looking at the combined group response with the rear sub's polarity switched 180 degrees.

Here is what happened. The violet line is the original 0 degree polarity, the green shows how ugly it can get with the phase being severely mis-adjusted.

Switched back to the violet setting of 0 degrees, and decided to move to smaller phase tweaking up front
post #4246 of 9577
My next step was to leave the phasing on the rear SW alone, and see what could be done by fine tuning the phase of the fronts.

What I did was to take the fronts one at a time and combine them with the fixed settings on the rear.
Made many trial error measurement sweeps with varying phase settings. Below are two snapshots of varying the RF phase (combined response of RF and rear):

Sorry; seems I failed to grab a before snapshot of the RF when it was at it's original 0 degree phase setting
Trust me it was messy. The next two (of many runs) show the trial and error process of dialing the phase to a best setting of 85 degrees


I then moved to the front left and repeated the process of tweaking the LF phase while monitoring the combined response with the rear.
post #4247 of 9577
In the end my fronts were readjusted as follows (rear remained fixed at 0 degrees)
LF was 0 degrees, new setting 110 degrees
RF was o degrees, new setting 85 degrees

Here are the before after comparisons of this phasing exercize
Before:


After:
post #4248 of 9577
I then took a look at how the Subs combined response looked against the center channel (with the new front SW phase settings):


And combined (1/6 smoothing, No Audyssey):


Oh and early-on in this process; I did try one comparison of changing the placement of the rear sub. I wish my floor-plan had the flexibility to allow me to optimize the positioning. Red is the position I am stuck with, Green is when I tested with it tucked into the corner nearest my equip rack


Next up is to re-run Audyssey, and make some new REW graphs concentrating on the L/R mains.
Hopefully by then I can also figure out how to manually tweak and save post Audyssey settings on the Denon 4311 rolleyes.gif.

Thank You to Everyone here for their tutoring, wisdom and patience !!
post #4249 of 9577
Quote:
Originally Posted by RapalloAV View Post

I did many measurements without XT32. I moved subs all over the place, 3" to the left, right. 6" to the left, right etc etc etc.... I came up with the "best" sub position I could find, without placing subs on stairs, seats, aisles, ceiling, etc etc......

How many masurements at what locations did you take during each iteration? What was your criteria for "best" (flatness, point-to-point variance, level, etc.)? Could you post those measurements?
post #4250 of 9577


Looks like the loudest peak is around 82dB and the quietest dip is around 76dB, or as they say in the biz "±3dB". The "before" graph seemed flatter, if you crossed it over at 60Hz.
Edited by sdurani - 7/21/13 at 8:58am
post #4251 of 9577
Quote:
Originally Posted by cuzed2 View Post

Here are the results of last nights testing, per sdurani's suggestions. I started out by characterizing how the subs in their current location are behaving: This was done with no crossovers and running REW sweeps of each Sub individually (Mic is fixed at the MLP).

Green is the LF = worst behaved with dips at 48 and 75 Hz
Red is the rear = dips at 72Hz and 90 Hz
Blue is the RF = best behaved perhaps because it's position is not tight into the corner and is further out along the sidewall?

Hi cuzed2, for sub(s) measurement, shouldn't the graph limited be set where the verrtical graph is 45dB-105dB and horizontal graph is 15Hz-200Hz? Or does it matter?
post #4252 of 9577
Question on ETC graph. Is ETC graphing just for speakers only?
post #4253 of 9577
Quote:
Originally Posted by sdurani View Post



Looks like the loudest peak is around 82dB and the quietest dip is around 76dB, or as they say in the biz "±3dB". The "before" graph seemed flatter, if you crossed it over at 60Hz.

I agree; If I could cross at 60Hz. However; with my mains I need to cross at 80 Hz.
post #4254 of 9577
Quote:
Originally Posted by JChin View Post

Hi cuzed2, for sub(s) measurement, shouldn't the graph limited be set where the verrtical graph is 45dB-105dB and horizontal graph is 15Hz-200Hz? Or does it matter?

To make viewing and analyzing the graphs easier you are correct. I failed to reset the limits or making those "snapshots" eek.gif
post #4255 of 9577
Quote:
Originally Posted by JChin View Post

Question on ETC graph. Is ETC graphing just for speakers only?

Please define "speakers only".
post #4256 of 9577
Quote:
Originally Posted by sdurani View Post

Hopefully that won't cause the dip to simply move elsewhere in the subwoofer range so we end up playing the acoustic equivalent of whack-a-mole (look, it's at 55Hz!).

biggrin.gif

I'm sorry, but I just thought this line was worth repeating in case anyone missed it the first time. Made my day.

post #4257 of 9577
Quote:
Originally Posted by markus767 View Post

Please define "speakers only".

Hi markus767, sorry for be unclear. Meaning like L/F only, R/F only, Center only (single speaker measurement), that ETC is not meant to measure sub reflections.
post #4258 of 9577
It's not meaningful to look at low frequency behavior by using a model that is based on specular reflections. Here the wavelengths of the frequencies in question are about or much larger than the room dimensions. For example 40Hz has a wavelength of 8.6m (28 ft).
Here's a good read: http://www.aes.org/e-lib/download.cfm?ID=13686&name=harman
post #4259 of 9577
Quote:
Originally Posted by LastButNotLeast View Post

biggrin.gif

I'm sorry, but I just thought this line was worth repeating in case anyone missed it the first time. Made my day.

 

Funny, but both true, and discouraging.  As I have struggled with improving my listening room acoustics, there are countless changes that I have made that have fixed one thing, and made something else a bit worse.  Now, every change requires a microscope to analyze its effect on frequency response, bass resonance, early reflections and imaging.  Quite tedious, actually.

post #4260 of 9577
Quote:
Originally Posted by cuzed2 View Post

I agree; If I could cross at 60Hz. However; with my mains I need to cross at 80 Hz.
Have you measured your L/C/R speakers to see if they have enough output at 60Hz to move the crossover down?
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