Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 40 - AVS Forum
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post #1171 of 12761 Old 02-12-2013, 11:46 AM
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Originally Posted by JD in NJ View Post


+1

My listening area/living room is open along half of one side, open again to a hall at the other end of that side, and open for yet a third time for a flight of stairs. In addition, there's a section of wall that projects a few feet into the room to create a partial entry hall. I have absolutely no idea how to come up with numbers that would make a lot of sense to plug into a simple model like that.

 

We can't say for sure.  Lenght=20', this we know.  Width is either 15" or 27".   A 15' width would produce moses at 38, 75, 113, and 151.  A width of 27' would produce modes of 21, 42, 63, and 84.

 

Looking at the first respnse curve you posted, I see a peak at ~28Hz, which looks to be related to the room's lenght.  I see a dip at 42Hz, which looks to be related to the 27' width.  I see another peak in the mid-60Hz range, which could also be related to the 27' width.

 

Of course, the only value of this analysis is if you might have an opportunity of placing a speaker in the null associated with the mode. 

 

Placing a sub at the midpoint of the 20' length doesn't seem practical in your room, so that won't help the 28Hz peak.  Also, placing subs at 1/4 and 3/4 of the 27' width to address the 42Hz dip doesn't seem to be an option either.

 

Bottom line:  I don't think this model is useful in your room.

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post #1172 of 12761 Old 02-12-2013, 11:47 AM
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Quote:
Originally Posted by jkasanic View Post

Quote:
Originally Posted by kbarnes701 View Post

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Originally Posted by AustinJerry View Post

Noise Floor?

 

For those of you who have USB microphones, what are you seeing as the noise floor in your listening rooms?  I continue to see a noise floor of 50dB, which is a full 10dB higher than I was measuring using my EMM-6 microphone.  And this is after turning everything off, including the AVR, and running the laptop on battery power.  Nothing seems to affect the noise floor reading.

 

If I am alone in seeing this reading, perhaps I have a defective microphone?

 

Quote:
Originally Posted by cadett View Post

I'm seeing 54dB. That's 13 above the EMM-6 I have.

 

Quote:
Originally Posted by jkasanic View Post

Quote:

That is consistent with what I reported as well.  Mine was also close to 10dB (from 46dB to 56/57dB).

 

Isn’t this a bit worrying?  Should one ask Herb if he can shed any light on it?

 

I just sent Herb an e-mail with a link to this post.  I'll let you know if I hear anything back.

 

I am sure you will. Last time I emailed Herb he replied to me before I'd even hit 'Send' :)

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post #1173 of 12761 Old 02-12-2013, 11:48 AM
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Isn’t this a bit worrying?  Should one ask Herb if he can shed any light on it?

I just discovered the same thing recently. Basically there are a bunch of spikes at 1 kHz and its harmonics that are controlling the noise floor, without those spikes, the noise floor would be about 10 dB lower. I haven't had the chance to really dig into what's going on, other than determining that this is pretty consistent across units. I haven't been able to measure noise floor of UMIK-1s or Omnimics.

(refunds are available to anyone who finds this problematic).
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post #1174 of 12761 Old 02-12-2013, 11:56 AM
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Originally Posted by Anechoic View Post

I just discovered the same thing recently. Basically there are a bunch of spikes at 1 kHz and its harmonics that are controlling the noise floor, without those spikes, the noise floor would be about 10 dB lower. I haven't had the chance to really dig into what's going on, other than determining that this is pretty consistent across units. I haven't been able to measure noise floor of UMIK-1s or Omnimics.

(refunds are available to anyone who finds this problematic).

I don't know if I should find it problematic or not. What's the net impact of this on my attempt to measure and address room issues? Can it lead to gross errors or is it simply a matter of lower sensitivity in a certain frequency range in a room which isn't terribly quiet to begin with?

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post #1175 of 12761 Old 02-12-2013, 11:56 AM
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^ Not sure if this is an issue or not.  For Waterfall graphs, where we look for where the decay meets the noise threshold, this may be an issue.  I think someone should post this question regarding Waterfalls over on HTS to see if we can get an opinion from JohnM.

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post #1176 of 12761 Old 02-12-2013, 11:59 AM
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Originally Posted by JD in NJ View Post


I don't know if I should find it problematic or not. What's the net impact of this on my attempt to measure and address room issues? Can it lead to gross errors or is it simply a matter of lower sensitivity in a certain frequency range in a room which isn't terribly quiet to begin with?

 

I don't think it affects frequency sweeps, which is the starting point for addressing listening room issues.  As I said in my previous post, I don't know the impact on Waterfalls.  One would use a waterfall, for example, to make a decision regarding applying bass treatments, which can be quite pricey (unless you go the DIY route).

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post #1177 of 12761 Old 02-12-2013, 11:59 AM
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Originally Posted by JD in NJ View Post

I don't know if I should find it problematic or not. What's the net impact of this on my attempt to measure and address room issues? Can it lead to gross errors or is it simply a matter of lower sensitivity in a certain frequency range in a room which isn't terribly quiet to begin with?

If you're measuring levels below about 60 dB, the noise floor will contaminate the measurement and you will get errors. For room-calibration/room-mode measurements you'll probably be okay assuming your test signals are at typical listening levels (usually 75 to 100 dB).

The 1kHz & harmonic spikes may also cause issues with high-frequency distortion measurements. Low-frequency measurements will be unaffected.
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post #1178 of 12761 Old 02-12-2013, 12:03 PM
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Originally Posted by AustinJerry View Post

I don't think it affects frequency sweeps, which is the starting point for addressing listening room issues.  As I said in my previous post, I don't know the impact on Waterfalls.  One would use a waterfall, for example, to make a decision regarding applying bass treatments, which can be quite pricey (unless you go the DIY route).

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Originally Posted by Anechoic View Post

If you're measuring levels below about 60 dB, the noise floor will contaminate the measurement and you will get errors. For room-calibration/room-mode measurements you'll probably be okay assuming your test signals are at typical listening levels (usually 75 to 100 dB).

The 1kHz & harmonic spikes may also cause issues with high-frequency distortion measurements. Low-frequency measurements will be unaffected.

Thanks, guys. I think that for my purposes I'll be basically alright with this mic. That being said, I'd certainly be interested in potential workarounds or hacks to address the issue, although I suppose that anything which involved changing circuitry would probably invalidate the calibration.

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post #1179 of 12761 Old 02-12-2013, 12:06 PM
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I don't think it affects frequency sweeps, which is the starting point for addressing listening room issues. 

It could, if your sweep levels are low enough. If they are louder than around 70 dB, it shouldn't be a problem.
Quote:
As I said in my previous post, I don't know the impact on Waterfalls.  One would use a waterfall, for example, to make a decision regarding applying bass treatments, which can be quite pricey (unless you go the DIY route).

It won't be a problem for low-frequency measurements, below 1 khz, the noise floor is only a couple dB higher than an EMM-6/ECM8000
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post #1180 of 12761 Old 02-12-2013, 12:29 PM
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Originally Posted by Anechoic View Post

I just discovered the same thing recently. Basically there are a bunch of spikes at 1 kHz and its harmonics that are controlling the noise floor, without those spikes, the noise floor would be about 10 dB lower. I haven't had the chance to really dig into what's going on, other than determining that this is pretty consistent across units. I haven't been able to measure noise floor of UMIK-1s or Omnimics.

(refunds are available to anyone who finds this problematic).

Hi Herb,

I can see the spikes on REW's RTA screen - as you stated they start at 1kHz, and then repeat at multiples (2,3 4kHz).
Would you be able to contact Dayton directly - as a query from someone like you would carry a lot more weight than from us amateurs.
I have not be able to do any proper measurements - so do not know if this characteristic will cause any problems.

Regards, Mike.
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post #1181 of 12761 Old 02-12-2013, 12:35 PM
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Hi Herb,

I can see the spikes on REW's RTA screen - as you stated they start at 1kHz, and then repeat at multiples (2,3 4kHz).
Would you be able to contact Dayton directly - as a query from someone like you would carry a lot more weight than from us amateurs.
I have not be able to do any proper measurements - so do not know if this characteristic will cause any problems.

Regards, Mike.

I don't know that they will recognize me as more than an amateur as well, but I'll shoot them an email and see what they have to say. My suspicion is that this may be a consequence of a decision to optimize the mic for high SPL use (the EMM-6 and ECM8000 are really only good up to about 115-120 dB, the UMM-6 is rated up to 127 dB).
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post #1182 of 12761 Old 02-12-2013, 12:43 PM
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I don't know that they will recognize me as more than an amateur as well, but I'll shoot them an email and see what they have to say. My suspicion is that this may be a consequence of a decision to optimize the mic for high SPL use (the EMM-6 and ECM8000 are really only good up to about 115-120 dB, the UMM-6 is rated up to 127 dB).

That's pretty logical, the difference at the bottom is of similar magnitude to the difference up top.

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post #1183 of 12761 Old 02-12-2013, 01:26 PM
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Quote:
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Quote:
Originally Posted by JD in NJ View Post


I don't know if I should find it problematic or not. What's the net impact of this on my attempt to measure and address room issues? Can it lead to gross errors or is it simply a matter of lower sensitivity in a certain frequency range in a room which isn't terribly quiet to begin with?

 

I don't think it affects frequency sweeps, which is the starting point for addressing listening room issues.  As I said in my previous post, I don't know the impact on Waterfalls.  One would use a waterfall, for example, to make a decision regarding applying bass treatments, which can be quite pricey (unless you go the DIY route).

 

This is my major concern.  I switched from OM to REW for this very reason.  Going a few pages back and recalling all the discussion about taking measurements high enough above the noise floor to be meaningful is definitely concerning as we were already compromising on the high SPL measurements but now if the floor is raised then we're really bringing into question the validity of the waterfall graphs?! confused.gif

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post #1184 of 12761 Old 02-12-2013, 01:29 PM
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I am sure you will. Last time I emailed Herb he replied to me before I'd even hit 'Send' :)

 

Haha...I had to laugh when I read this because that's exactly what it felt like!  I see he even posted here shortly after!

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post #1185 of 12761 Old 02-12-2013, 01:29 PM
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Here's a drawing of my room.

Sub 1: PSA XS15
Sub 2: Velodyne F1500 circa 1995 - Just using it because it still works well and seems to smooth the response a bit.
Sub 3: PSA XS15

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Originally Posted by Alan P View Post

Makes sense except for guys with really odd shaped rooms like mine. What should guys like me do in this case??
When all else fails, try nearfield bass (the idea being to hear more of your sub and less of the room). Can't guarantee it will work, but costs nothing to try.

Move your other PSA XS15 (sub 1) to the other back corner of your room and measure the combined response of the two subs. Then try adding the Velo (sub 2) in several positions (between the two main chairs, near side of the couch, far side of the couch, along the front wall, etc) to see if it further improves the response at your main listening position. If not, then just stick with the two PSA subs.

Remember that when dealing with lateral (width) modes, moving the subs a foot left or right can make a difference in response. IF you can't move your subs much, then try the reciprocal: move your listening chair a foot left or right to see if that improves the response.

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post #1186 of 12761 Old 02-12-2013, 02:14 PM
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Haha...I had to laugh when I read this because that's exactly what it felt like!  I see he even posted here shortly after!

smile.gif

You're fortunate I'm not traveling today! My response time Wed-Fri will be much longer.
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post #1188 of 12761 Old 02-12-2013, 04:14 PM
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When all else fails, try nearfield bass (the idea being to hear more of your sub and less of the room). Can't guarantee it will work, but costs nothing to try.

Move your other PSA XS15 (sub 1) to the other back corner of your room and measure the combined response of the two subs. Then try adding the Velo (sub 2) in several positions (between the two main chairs, near side of the couch, far side of the couch, along the front wall, etc) to see if it further improves the response at your main listening position. If not, then just stick with the two PSA subs.

Remember that when dealing with lateral (width) modes, moving the subs a foot left or right can make a difference in response. IF you can't move your subs much, then try the reciprocal: move your listening chair a foot left or right to see if that improves the response.

Thanks sdurani - but I'm not really having problems with bass. It really sounds good to me, just looking for some feedback on my first graphs...do they look bad to you guys?? Do I have a lot of work to do yet??

Graphs are here.


EDIT: I'm going to try your suggestions anyways, can't hurt! smile.gif

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post #1189 of 12761 Old 02-12-2013, 04:18 PM
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Quote:
Originally Posted by Anechoic View Post

I just discovered the same thing recently. Basically there are a bunch of spikes at 1 kHz and its harmonics that are controlling the noise floor, without those spikes, the noise floor would be about 10 dB lower. I haven't had the chance to really dig into what's going on, other than determining that this is pretty consistent across units. I haven't been able to measure noise floor of UMIK-1s or Omnimics.

(refunds are available to anyone who finds this problematic).

I'm not seeing these spikes, unless I just don't know where to look. With my RatShack meter I was getting a noise floor approximately the same as with the UMM-6 - right around 50db.

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SUB: PSA XS15 x 4 (Soon to be replaced with dual T-18s!)
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post #1190 of 12761 Old 02-12-2013, 04:51 PM
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Quote:
Originally Posted by Alan P View Post

I'm not really having problems with bass. It really sounds good to me, just looking for some feedback on my first graphs...
Your measurement graph shows a pretty serious dip around 42Hz. If I divide the speed of sound by the frequency of that dip, I should end up with one of your room dimensions. 1130 ÷ 42 = 27 (the width of your room). IF the near field bass trick doesn't measure better, try running a single sub (sub 3) placed 1.5 feet closer to your main listening seat. Unfortunately, with irregularly shaped rooms, it's lots of trial and error.

Sanjay
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post #1191 of 12761 Old 02-12-2013, 05:05 PM
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Yeah, I think I need to take a week off to dedicate to sub optimization...unfortunately, that just ain't happening. I'll get there someday. biggrin.gif

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post #1192 of 12761 Old 02-12-2013, 07:16 PM
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trying to go back at now with the umm6 and java. asio just won't . . . but even more fundamental, I'd like some feedback about what to really expect in a room 10 x 11 x 8 , total 950 ft3 if you include the door opening. Ethans room mode calulator wants a room of 2500 minimum. i've poked around with others but appeal to the experience of this threads thrivers and surviviors for real possibilities/probabilities. thank you

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Revision 2.3 of the REW Guide has been posted.

 

Changes in this revision:  minor spelling and consistency fixes, thanks to the proofreading efforts of KBarnes701.

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post #1194 of 12761 Old 02-12-2013, 08:04 PM
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trying to go back at now with the umm6 and java. asio just won't . . . but even more fundamental, I'd like some feedback about what to really expect in a room 10 x 11 x 8 , total 950 ft3 if you include the door opening. Ethans room mode calulator wants a room of 2500 minimum. i've poked around with others but appeal to the experience of this threads thrivers and surviviors for real possibilities/probabilities. thank you

 

Here are your room's standing waves:

 

 

You should be able to get the UMM-6 to work with Java.  What happens with ASIO?

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post #1195 of 12761 Old 02-12-2013, 09:29 PM
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thank you for that Jerry. JPEG saved. The mike DOES work with Java as does the hdmi in 2 channel mode. Asio gets me the "computer doesn't like you" error for both UMM6 and ATI HDMI .I've noticed the mike volume slipping bewteen sessions and curently use 88% or so .Its loud! so back to work for some data to see what happens in here. Of course , any comments about room size still sought.

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post #1196 of 12761 Old 02-12-2013, 10:15 PM
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Quote:
Originally Posted by Alan P View Post

I'm not seeing these spikes, unless I just don't know where to look. With my RatShack meter I was getting a noise floor approximately the same as with the UMM-6 - right around 50db.
They are pretty visible in mine. Here is a snapshot:

i-2KNZ8Zx-L.png

The 1Khz distortion and its harmonics are clearly present as stated. Likely the cause is the USB frame sync which has a time of 1 msec or frequency of 1000 Hz. The device simply does not have proper isolation between its digital and analog sections (common problem when components are packed together this close and not enough attention is paid to such an issue.

I have email into them but I am not hopeful that they can resolve it without a redesign.

For acoustic measurements it is not a major problem but as a matter of principal, an instrumentation device needs to do better than this.

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post #1197 of 12761 Old 02-13-2013, 04:16 AM
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I don't know if I should find it problematic or not. What's the net impact of this on my attempt to measure and address room issues? Can it lead to gross errors or is it simply a matter of lower sensitivity in a certain frequency range in a room which isn't terribly quiet to begin with?

 

I don't think it affects frequency sweeps, which is the starting point for addressing listening room issues.  As I said in my previous post, I don't know the impact on Waterfalls.  One would use a waterfall, for example, to make a decision regarding applying bass treatments, which can be quite pricey (unless you go the DIY route).

 

This is my major concern.  I switched from OM to REW for this very reason.  Going a few pages back and recalling all the discussion about taking measurements high enough above the noise floor to be meaningful is definitely concerning as we were already compromising on the high SPL measurements but now if the floor is raised then we're really bringing into question the validity of the waterfall graphs?! confused.gif

 

I hope it isn't a problem with the mic. Returning a mic from the UK is expensive!  I guess we will see in the fullness of time.

 

@AJ - Jerry, your results and graphs, IIRC, from your old mic are consistent with those from the UMM-6?  If that is so, then presumably the mic is working as intended, regardless of this noise floor business?  I may measure at a higher SPL than 80dB which was my intent - maybe 90dB.

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post #1198 of 12761 Old 02-13-2013, 04:17 AM
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I am sure you will. Last time I emailed Herb he replied to me before I'd even hit 'Send' :)

 

Haha...I had to laugh when I read this because that's exactly what it felt like!  I see he even posted here shortly after!

 

Yeah - all those mics he sends out are listening to us and feeding back directly to HerbLabs HQ - LOL.

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post #1199 of 12761 Old 02-13-2013, 04:55 AM
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trying to go back at now with the umm6 and java. asio just won't . . . but even more fundamental, I'd like some feedback about what to really expect in a room 10 x 11 x 8 , total 950 ft3 if you include the door opening. Ethans room mode calulator wants a room of 2500 minimum. i've poked around with others but appeal to the experience of this threads thrivers and surviviors for real possibilities/probabilities. thank you

 

Your room is about the same size as mine. Mine is a dedicated room so I can do anything I like to it. I am using MK S150s for LCR, M&KSS150 Tripoles for surrounds and M&K LCR55s for heights. I have dual Submersive F2s (the form factor of the F2 fits this small room better than the regular SubMs. The room is fairly well treated with GIK treatments. Floor is thick carpet on concrete. The room is sealed (when the doors are shut). It is a really awkward little space.

 

The really good news for you is that my room sounds (and measures) superbly well. I was initially concerned that room was too small to get really good bass, but nothing is further from the truth. Would the bass be better in a bigger room?  Almost certainly - but it is deep and tight and focused here and I am always blown away by the overall SQ. I should say the room is used solely for movies not music.

 

The biggest single improvement came from the room treatments. Probably the SubMs were next. Imaging was substantially improved by the treatments, as was the tightness of the bass. I also run Audyssey XT32 Pro and would not be without it, ever.

 

One of the biggest challenges with such a small room is that you have very limited options for speaker placement and MLP. I have brought the two seats (fabric covered cinema recliners) as far forward from the back wall as is feasible and this puts me at a good seating distance from my 65 inch screen. One sub is in the front right corner and the other is not quite midway along the left wall. Those are really my options right now (doors get in the way of what might be better - midway along right and left walls). I may at some point experiment with moving the subs around a bit - I can use the rear corners if I get rid of my side tables, for example. 

 

I have experimented as much as possible with my OmniMic and the room treatments. I have now treated or partially treated 8 of the 12 corners. I am about to add further treatments to the back wall, but am waiting for my UMM-6 to arrive so I can use REW to help there.

 

I am not sure if this was what you were asking, but hope that it gives you som encouragement to persevere with a small room. I was similarly inspired by Mike Duke on the SubM thread whose room is similar to ours and who has also achieved a terrific result.

 

Here is a graph (OM) of the FR in the room - this is 20Hz to 20Khz, with 1/6th smoothing:

 

 

 

 

Here is a photo of the room - it looks bigger than it is because I am using an ultrawide lens (16mm) - it's the only way I can photograph it!

 

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post #1200 of 12761 Old 02-13-2013, 06:35 AM
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I think that is the first time I have seen a picture of your room, Keith.  It looks quite comfortable and well done.  I especially like that your electronics are out of the way in a different spot--it makes the room look quite clean.  Nice subs, BTW!  smile.gif  And very nice treatments as well.  Are those GIK 244's?  I suspect that door doesn't open?  And what about the picture on the side wall--is that in the first reflection point?  When you measure, you might try to see what effect a temporary treatment there might do.  This is an example of how we might use the ETC graph to see if you are getting reflections from that area.  If not, then I certainly wouldn't worry about it.

 

BTW, you have just proved Feri correct--a picture in addition to measurements is quite valuable.  Also BTW, the graph you posted looks to be only up to 200Hz...

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