# RossoDiamante Theater REW Measurements



## RossoDiamante (Aug 12, 2013)

As a baseline step, now that I have 2 speakers and 2 subwoofers hooked up, I ran some REW measurements in my (very) RAW shell of a home theater. 

In the process of trying to do the level calibrations, I think I've concluded that one of my subwoofers must be defective as it seems to be bottoming out uncontrollably. The other one was a little more behaved and these initial measurements are with just one subwoofer. 

The subwoofer in question is a passive JTR Captivator (ported) being powered by a Behringer iNuke nu6000 with a built in DSP but will all the DSP settings bypassed. The AV processor was set to a crossover of 200 Hz (the highest it would go).

Please take a look and let me know what you can glean from the squiggles....


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## fusseli (May 1, 2007)

Is your mic calibrated for SPL? Your sweeps appear to be at an unbelievable SPL level. Are you sure your gains are set correctly through your AVR and the inuke? I would point towards the signal coming in, not the sub itself, for "uncontrollable bottoming out."


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## RossoDiamante (Aug 12, 2013)

Great question as I wondered about the absolute numbers as well. But my assumption was that the relative levels and waterfall chart both contain some useful information.

As far as leveling, I did two leveling steps in REW:

1) On the Soundcard Properties page, I did the level check using the subwoofers. The "reference" was -12 dB. The information box suggested a measured level between -12 dB and -24 dB. I got the subs to about -20dB and it got too loud and rumbly.

2) Using the SPL meter, I did a level calibration and the display put up a certain number and I set the input dialog box to about the same number.

Then I ran my sweep. Is there something I overlooked as far as level calibration?


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## RossoDiamante (Aug 12, 2013)

P.S. I'm using a MiniDSP UMIK-1 USB microphone which came with its own calibration file.


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## RossoDiamante (Aug 12, 2013)

My amateur attempt at an analysis of this first measurement of my RAW room:

The frequency response of the sub is pretty even from very low (15 Hz) to about 70 Hz. There it starts a pretty significant rolloff with a pronounced null at about 110 Hz.

I have a question about running the waterfall measurements, though. In this graph, I have set range of measurements from 60-150 dB. There is a peak dB measurement of around 135 dB in the range I'm measuring. So that gives me a measured range of 135-60 = 75 dB. Is that appropriate? I would think that after that much of a reduction the audibility would be questionable. I think I read somewhere that a range of 40 dB is appropriate. If this is so, my graph may look a little bit better. I can re-run the waterfall with that range and see for sure, though.

So my course of action at this point would be to set my subwoofer crossover for 80 Hz which works out well for my main speakers. And then work on bass trapping strategies and subwoofer placement options to minimize the "ringing".

From a subjective perspective, I think the sound is terrible. There is very little visceral impact from the subs. I would have expected a punch in the gut sensation with subwoofers this hefty. It's unclear to me why the bass seems so weak despite a pretty nice frequency response measurement.

I will also re-run this tonight with both front speakers and the subwoofer and see if that changes things.

Anything else I should be looking at now to help me plan the room's acoustic tuning? Another next step would be to do some full range measurements of the main speakers. Speaking of which, with a 7 channel setup, would the recommendation be to run the 3 fronts as a set separate from the sides and rears? Or all 7 together?


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## JohnM (Apr 11, 2006)

RossoDiamante said:


> 2) Using the SPL meter, I did a level calibration and the display put up a certain number and I set the input dialog box to about the same number.


For SPL calibration the number you need to enter should be read from an external handheld SPL meter, not REW's meter - REW's meter doesn't show correct figures until after it has been calibrated against some external reference.

Since you are using a UMIK-1 though you need to use REW V5.01 beta 17, the UMIK cal file (as supplied by MiniDSP) has a sensitivity figure in it that REW can use to calibrate the readings directly from the mic.


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## RossoDiamante (Aug 12, 2013)

John, thanks for the input. I was able to gather that I needed the latest beta version based on the equipment that I was using. So after downloading and installing the latest and greatest, things made a lot more sense. The ability of the software to identify the UMIK-1 and ask for its calibration file is awesome. And that was all that was needed as far as leveling and calibrating. Amazing. Thanks for the great software. I think it has really helped me already and I'm just starting this journey.


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## RossoDiamante (Aug 12, 2013)

So after getting my software updated and letting it hook up to my UMIK-1, REW showed me some very interesting things. Including why I was having such a hard time getting any reasonable sound from my subwoofers.

I took these measurements with both the subwoofers and the full range L/R speakers active.

IMAGE 1
First was a baseline with only one subwoofer and all 3 channels being driven by my Sherbourn amplifier. I wanted to take the dedicated Behringer iNuke amplifier out of the equation in case something in the DSP module was screwing up my sound. I still had the pronounced rolloff starting around 70 Hz. 

IMAGE 2
Despite changing the crossover point in the processor, I always had a big dip around the same place.

IMAGE 3
I finally found a combination of crossovers (lowering the frequency of the main L/R crossovers and raising the frequency of the subwoofer crossover) that made an improvement in that dip.


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## RossoDiamante (Aug 12, 2013)

Next, I switched the sub over to the Behringer iNuke amplifier and found essentially no difference. That was reassuring. The sound quality was quite a bit better even with this little tweak.

And then I started playing with the parametric EQ in the Behringer amplifier. At the end, the frequency response curve was quite a bit better.


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## RossoDiamante (Aug 12, 2013)

IMAGE 1
The most interesting thing happened when I added the second sub. No EQ was applied to the second sub at the start. Obviously there was a lot of cancellation going on which was especially evident around 20 Hz and between 50-90 Hz.

IMAGE 2
As a first test, I reversed the phase of the second subwoofer and things miraculously got significantly better.

IMAGE 3
A little bit of EQ tweaking and I was able to tame the new peak around 30 Hz and improve the dip around 80 Hz.

IMAGE 4
And this is what I ended up with. I raised the gain of the subwoofer amplifier a little bit and this really started giving me the visceral punch that I've come to appreciate and expect of a home theater sound system. A little exaggerated but I had a good time listening to some music sources tonight with this setup. I'm sure that when I finalize things I'll opt for a more balanced bass/treble setting, but for now the improvement in sound was dramatically improved. Plus no more bottoming out of the subs.


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## RossoDiamante (Aug 12, 2013)

I think I followed a logical progression of measurements, changes, re-measurements. As this is the first time I'm doing this, I'd appreciate suggestions on ways to do things better.

I haven't even looked at the waterfalls yet!


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## RossoDiamante (Aug 12, 2013)

Sneak preview of the before and after waterfall. I have to study a little more to figure out what this is telling me...


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## RossoDiamante (Aug 12, 2013)

Taking a quick look at the waterfall graphs, they look identical. I'm not sure if I waterfalled the wrong FR graphs or if EQing has no effect on waterfall graphs?

Also, another question. The FR graphs generated seem to have useful information up to about 100 Hz. Then they just become a jumble of squiggles. Is this typical or is it a sign of some issue I need to look into?


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## Wayne A. Pflughaupt (Apr 13, 2006)

RossoDiamante said:


> Sneak preview of the before and after waterfall. I have to study a little more to figure out what this is telling me...


Not exactly on your topic, but there should be enough info in this post to give you an idea of what waterfalls are about.




RossoDiamante said:


> Taking a quick look at the waterfall graphs, they look identical. I'm not sure if I waterfalled the wrong FR graphs or if EQing has no effect on waterfall graphs?


Yes, the two waterfalls are identical. They are more meaningful with the graph floor reduced to the ambient noise level of the room, which is typically 35-40 dB. That said, it looks like your low frequency dampening is excellent.




> Also, another question. The FR graphs generated seem to have useful information up to about 100 Hz. Then they just become a jumble of squiggles. Is this typical or is it a sign of some issue I need to look into?


The upper frequency raggedness is merely comb filtering caused by reflections. It shows up more in the upper frequencies than the low, which is why we recommend subwoofer graphs be presented unsmoothed. Fortunately, it looks worse than it sounds. You can use 1/3- or 1/6-octave smoothing for the graph to get a better representation of what you’re actually hearing.

Regards, 
Wayne


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## RossoDiamante (Aug 12, 2013)

Thanks for the great input. I'll check out the waterfall reference. I also have to read up on the ETC as I start to look at the main speakers. Now that I know that the subwoofers are not defective, I feel much better hooking everything up!


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## RossoDiamante (Aug 12, 2013)

One thought looking at the waterfall graphs above. There appears to be extended decay times at 4 frequencies in the subwoofer's range: 17 Hz, 35 Hz, 70 Hz, 100 Hz. Do I even have to worry about the 17 Hz one as it is below the audible frequency range?

I'm amazed at your "well damped" comment. Currently there are no significant dampening elements in the room. I should get a picture of the room as it stands now.


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## weverb (Aug 15, 2008)

17 and 35 Hz would require some very big absorbers or one tuned to those frequencies. Tuned absorbers don't always work correctly.

You may want to start looking at if the subs are time aligned with the mains and each other. That may impact your results.


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## RossoDiamante (Aug 12, 2013)

A great thought since the plane of the sub drivers is actually about 4-6" behind the plane of the L/R drivers. What tool do I use to assess this parameter?


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## weverb (Aug 15, 2008)

I would start researching impulse responses. There are some good threads on here about using them to help fine tune multiple subs. Here is the basic help file thread.

http://www.hometheatershack.com/roomeq/wizardhelpv5/help_en-GB/html/impulseresponse.html#top

User jtalden seems to have the most posts about this technique. Never done it myself.


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## jtalden (Mar 12, 2009)

More info would be needed for me to provide any sort of timing help.

It is surprising that inverting one the SW improved the response. I would first want to understand the reason for that. What is the measured distance of each SW to the LP (6" accuracy is good enough)? I would want to see an .mdat with a sweep of each sub individually and together (SW1, SW2, SWs) to understand the situation. [I also would need to know if the settings were are with one inverted relative to the other or if they are now the same.]

What mechanism is there to adjust delays or distance settings for the main speakers; AVR, HTPC or other? Are the current delays/distances set to measured distances for all main and SW speakers? 

Overall, it looks like the setup was coming together reasonably well so backing up and revisiting delay/distance settings in more detail may not provide any practical improvement so you may want to just continue forward using the current settings.


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## RossoDiamante (Aug 12, 2013)

Thanks for the help. I can certainly come up with those graphs. Tonight I will also have the rest of the speakers installed for a 7.2 system. I'll be interested to see how adding a bunch of speakers changes things. 

But I will do this tonight as well:

FL/FR/Sub1
FL/FR/Sub2
FL/FR/Sub1+Sub2
FL/FR/Sub1+Sub2 (change phase of one sub)

Should be interesting!


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## RossoDiamante (Aug 12, 2013)

P.S. I have the ability to adjust delays in the AVR for all channels and the amplifier for the 2 subwoofers (each individually).

The settings in the AVR are accurate to within 6-12".

Will try to get a picture of the room tonight as well.

Thanks.


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## jtalden (Mar 12, 2009)

RossoDiamante said:


> But I will do this tonight as well:
> 
> FL/FR/Sub1
> FL/FR/Sub2
> ...


I think we should first just confirm that the SWs are working together properly. After that there is normally no longer any reason to test the SWs separately. They then function as one unit and are EQ'ed together. 

The needed measurements are:
SW-1
SW-2
SWs 
> There is no need to change polarity on one of them as we can do that within the REW analysis if needed. [Advise the polarity settings actually used.]
> Measurements are best done with measured distance of the further SW entered into the AVR and no additional delay used in the INuke. [Advise the AVR distance setting and the measured distances.]
> Please use the FL (or FR) AVR channel for the signal. The XO should be set ≥80 Hz [Advise setting used and if you were intending to use lower XOs than this.]
> There is no issue if you already have some EQ settings in place for the SWs. Those can be left on as this would be the next step anyway; to achieve a reasonably smooth response through the SW range.

Also Advise:
> Information about the main speakers as make/model (or basic description if DIY).

If you intend to post just graphs it will be impossible for me to quickly confirm if the timing alignment is optimized since with a USB mic we cannot use the REW loopback timing feature. Loopback timing makes the job significantly easier. If your setup has equidistant SWs from the LP there is really little to go wrong however and the only question may be whether the polarity is correct. A simple IR chart (in %FS mode) is all that is needed. I would still prefer to get a .mdat file of the actual results however.

After the SW's alignment is confirmed and some EQ is applied then I suggest we first focus on the timing of 3 front mains as those are the primary concerns. The Surrounds and Backs can be tuned in last.

I don't think measurements of 2 or more mains at the same time adds any value as the objective is to achieve the target response for each channel separately. Measuring main channels together can be misleading as comb filtering becomes an issue at higher frequencies.


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## RossoDiamante (Aug 12, 2013)

Will do. To confirm, I'm just doing regular measurement sweeps (15 Hz - 500 Hz)?

This is what I'm starting with now before any room treatments:


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## jtalden (Mar 12, 2009)

Very Nice!
Yes 15-500 is good for SW alignment work.


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## RossoDiamante (Aug 12, 2013)

Here are the requested measurements and .mdat file. Crossover set at 80 Hz. Your thoughts are appreciated.


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## jtalden (Mar 12, 2009)

All is well with the SW timing and EQ setup! Nice job!

> Note that the mic cal file is loaded as both the mic cal and the soundcard cal. Go to "Preferences/Soundcard" and select "Clear Cal" so the soundcard cal file is reset to "none". This will correct this in future measurements.
> I removed the Soundcard cal from these measurements in the measurement tab before doing the analysis below. This corrects the measurements so there is no need to repeat them.
> The mic cal that is loaded looks very normal so there is no problem using that one.

Analysis:
> While one of the individual SW was tested with opposite polarity selected, the Impulse Response (IR) traces below show they are actually in the same polarity. This suggest something in the wiring or INuke settings is actually reversed from the other SW. This is no problem as you identified this already and I am now satisfied that you are correct. You can track this down if desired, but the setup is correct now with one of them reversed.
> Since the 2 IRs initially start down for the first small peak from 0 %FS that suggests that they are currently both set as negative polarity. To correct this you could use SWr = 180 and SWl = 0 if you like for future work. This is not critical however as it will make little difference to the end result. Neither can be said to be a better situation in my opinion. In the end it is a tradeoff.
> The IR traces shown below were manually offset to an ideal alignment. They are adjusted to overlay each other through the initial major peaks. REW tries to offset them this way automatically, but when the peaks are nearly equal size it is difficult for REW to pick the same one for alignment. The actual ms position chosen for the overlay alignment was unimportant. I just chose to set the first large positive peak to 0 ms for convenience. 








> After overlaying the IRs as above I then did an "A + B" math operation on the 2 SW traces. The provides an SPL trace that represents the ideal timing/distance settings for the 2 SWs. See the legend to identify the traces. 
> Your SWr+SWl SPL trace below shows the expected 6 dB additional SPL of the combined SWs and matches closely with the A + B calculated ideal trace. This confirms the timing is correct.
> The SPL chart also shows that the response is very flat so that is a good starting point for the initial EQ setting. You can always change this later if you decide you would like to try a different house curve.
> We no longer need to measure the 2 SWs separately as they are now proven to be a properly functioning unit now identified as "SWs". 








Whenever you ready the next steps for timing the mains would be to take the following 7 measurements 15 - 20k Hz:
[yes, measure the SWs and the mains full range for this purpose.]

- SWs 
- FL
- FR
- CC
- FL+SWs
- FR+SWs
- CC+SWs

The file size may be too large to include all in one file, but you can post these in 2 files if necessary.
Be sure the correct measured distances are entered into the AVR.


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## RossoDiamante (Aug 12, 2013)

Thanks for the analysis. This is going to take a little bit for me to understand, but from what I'm gathering, I'm basically on the right track and my ears weren't deceiving me. I was so perplexed when I had my initial burst of energy and connected up my FL/FR/SWL/SWR and put in a DVD. No bass response, very tinny. This was all before I had REW setup down there. I tried fiddling with the crossover points in the processor. I tried boosting the levels of the subs. I tried EQ'ing the subs with the iNuke. All I ended up with was a sub that was clearly bottoming out but no palpable bass response at the listening position. Very baffled. I'm so grateful for this easy to use technology that immediately identified the problem. When I measured each sub independently, I could get a reasonable amount of bass response. I also EQ'ed each one to have a fairly flat response. The Parametric EQ in the iNuke is actually quite useful in this respect. But then when I put the two together and saw that HUGE dip, the problem became clear. Something was wrong with the summation. I took a wild guess and changed the polarity of one of the subs and "voila!" I got good bass response. Then it was just a matter of twiddling with the EQ a little bit. I think I have 6 or 8 bands of EQ in the iNuke for each sub. I will go through and do a more thorough EQ once I measure all 7.2 channels together.

I finally hooked up all speakers last night and it sounds great. Unmeasured, the top end (at least the top end of my limited hearing range -- I'm old!) to my ear needs quite a bit of taming. Popped in a Blu-Ray and watched a few scenes. Wow. Lots of impact. This is going to be fun!


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## RossoDiamante (Aug 12, 2013)

P.S. For the full range responses for both the subs and the mains, you mean turn off the crossovers in the AV processor, right?


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## jtalden (Mar 12, 2009)

No, the 7 measurements should all have the chosen XOs active; 80 Hz for all 3 front speakers since they appear to be all the same design and very capable. 

We want to see the actual responses of each channel individually and then each main with the SWs to see if the timing between the mains and the SWs is correct. The objective is just to fine tune the timing a little to optimize the handoff of mains to SWs. We would expect to do this by adjusting the SW distance a little if needed to smooth the response through the XO region.

You can experiment with this yourself by changing the SW distance setting in the AVR and determine which setting provides the greatest SPL support across the XO region (from 40 to 160 Hz). The 3 fronts may all be slightly different. If so, we just pick the best compromise distance. 

I will also look to find the best setting by manually adjusting the IR locations and using "A + B" math to do the same thing with the 7 measurements you provide. When you find the SW distance setting that equals the calculated best setting I find, then the timing is optimized. 

Go ahead and play with the manual adjustments and math calculations also if you understand how to do that already. It is very complicated to explain the process without an example. I will try to provide a little explanation when I report my findings to you.


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## jtalden (Mar 12, 2009)

By the way, there is no need to test at such a loud level; 75 to 80 dB is a good target. The results for timing and for EQ will be identical.


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## RossoDiamante (Aug 12, 2013)

What did you say? I can't hear you. My ears are ringing! 

I will get these measurements tonight. I have some folks coming over to help me put up my starfield ceiling soon.


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## jtalden (Mar 12, 2009)

It must be a very high ceiling if you can place stars in there! :2stars:


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## RossoDiamante (Aug 12, 2013)

Unfortunately, too high. Couldn't get it installed with just two extra pairs of hands. I hope to try again with 4 extra pairs of hands.


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## RossoDiamante (Aug 12, 2013)

Here are the latest measurements. The subs are as previously measured with EQ. There is no EQ or any other adjustments on the main speakers. I entered speaker distances into the AV processor. All speakers had crossover frequency set at 80 Hz. Is there any need to the side or rear surrounds as well?


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## RossoDiamante (Aug 12, 2013)

Here is the REW file of the front 3 alone.


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## RossoDiamante (Aug 12, 2013)

Here is the REW file with the subs.


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## jtalden (Mar 12, 2009)

The level of the SWs is very high compared to the mains. I would suggest using a lower setting on the SWs level for the initial setup. It is unlikely that you will want it this high once all is properly adjusted. It is a matter of taste however and this level does not impact our effort in confirming the distance/timing settings.

*First let's just look at the FL to show the process:*

Below is the "All SPL" of the SWs, FL, and FL+SWs. 
> The measurements are now labeled so the legend is more helpful for the various charts.
> In the circled XO range the SPL support is not very robust. Normally we expect to see approximately a +6 dB increase in SPL at the XO frequency and tapering off throughout the range (room modes can play havoc however). It appears that there is about 0 dB of additional support through this range. This suggests that the timing has a 90° offset from the ideal timing. A 90° offset at 80 Hz is about 3 ms.









Below is the IR positions as REW adjusted them. Since REW adjusted them to the largest peak without regard to actual timing they are not in their true positions. [REW loopback Timing Reference is required to maintain the actual relative IR positions, but USB mics do not allow that feature to be used; at least not easily.] 









Below is the initial guess of the actual IR alignment. The initial rise of the 2 IRs were manually adjusted to near 0 ms. That would be the expected relative positions of the IRs with the measured distances entered into the AVR and no additional delays in the 2 channels. The INuke is a digital processing unit however so it does add some additional delay to the SW so I actually placed the initial rise of the SW to start about +1 ms rather than 0 ms. The total shift I applied to a SWsCopy to achieve this was -30 ms. 









Using these new IR locations the smoothing was removed and math A + B was applied to FL and the SWsCopy that I shifted -30 ms. Below is the resulting comparison of the SPL again smoothed to 1/24. [Note that all math operation should always be done with smoothing removed or the impact of the smoothing will distort the result. Smoothing can then be reapplied to the resulting trace to suit the need.]

The result is pretty close to the measured FL+SWs but just a little more supportive through the XO so that suggests we are only maybe 75 to 80° offset rather than the 90° that we needed to match your measured result.









Below is the comparison after making an additional adjustment the SWsCopy IR that is now adjusted at -31 ms and the SPL now matches the measured FL+SWs pretty well. This is the actual current alignment of your setup as best that we can surmise without actual Loopback Timing Reference capability.









Below the same offset technique was used to find the "ideal" or improved setting. The SWsCopy offset found was -28 ms. [Note that, the deeper null at 105 Hz should not be a concern. All these alignments will contain a deep null in this range due to a room mode. It may show up more or less deep and at a slightly different freq depending on the exact position of the mic, sample rate and possibly other factors. The apparent depth of a true null is misleading.]









*Now let's look at the FR and CC:*

Below I left the same -28 ms offset of the SWsCopy and calculated it with the FR. The FR+SWsCopy-28 looks a little improved also. This suggest that a SW distance adjustment of +3 ft (- 3 ms) from the current setting will work well for both.









The same adjustment for the CC was not as improved so in that case I adjusted the distance/timing of the CC by -2 ms to find an improved setting. The means that the distance of the CC needs to decreasd about 2 ft to provide a better handoff through the XO. The value of this is somewhat a tradeoff since it conflicts with measured distance setting used in AVR. For home theater use I would use this adjustment. For music use I probably would not. The lack of loopback timing makes this inconsistency impossible to resolve.









Overall the original settings were pretty good. The improved setting are a little better. I am unsure if you will be able to easily notice the difference in the sound. At least this way you have the assurance that the timing of the SWs to the mains is not exacerbating the dip in the XO area.

We can go through this exercise with the surround speakers as well, but that may be something that you can now address.

Sorry for long and somewhat confused post. This is not an easy process to document. 

Again the 2 adjustments we found to improve the SPL in the XO range are:
> SWs AVR distance = +3 ft
> CC AVR distance = -2 ft

I will try to address any questions you have.


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## RossoDiamante (Aug 12, 2013)

I'm certain I understand at least 2% of this! 

Starting from the end, as it were, there are two adjustments that are suggested (SWs +3 ft and CC +2 ft.).

Inputting a greater distance in the AV processor presumably serves to alter the timing of the beginning of a given waveform relative to some sort of reference. Am I assuming that putting in a distance of "0" for every channel would result in no "artificial" delay introduced into the signal? In that case every channel that I do put some value in that field will result in an amount of "artificial" delay proportional to the value input.

If I recall, the distances that were input were SW = 14', FL = 14', FC = 13.5', FR = 14'.

If I'm understanding your analysis correctly, the delay that is currently introduced appears to be 28 ms. Your analysis is also showing that a delay of 31 ms is more ideal, necessitating an increase in the value input into the AV processor of 3 ft. For the suggested SW adjustment of + 3 ft, we are in effect asking the AV processor to delay sending the SW signal by 3 more ms to get its signal to more closely align in timing to the signal coming from the FL and FR speakers.

Two questions relating to this first part: First, the need for an increase delay in the SW signal seems to run counter to your assumption that the DSP/processing in the iNuke introduces its own delay. Second, would the same net result be obtained by decreasing the distance in the FR and FL fields by 3 feet each?

For the Center, the suggested modification is to add 2 feet to the AV processor's distance. On a relative basis, I currently have the center marked as 0.5 ft. less than the FL and FR channels. This decreased distance would presumably serve to increase the delay the AV processor uses in that channel relative to the FL and FR signals. By putting in a greater distance for the center channel, it moves the relative measurement of the center channel to "behind" the FL and FR speakers (i.e. greater distance to the listening position) which would change the timing of the signal to the center from "after" the FL/FR to "before" the FL/FR. This doesn't make intuitive sense when there is presumably no additional electronic delay (i.e. iNuke) for the center relative to the FL/FR and the speaker is physically closer to the listening position. The only thing that I can think of is whether we are "measuring" and accounting for something like the length of speaker wire. 

I'll make these changes in the AV processor and remeasure. Thank you very much for your thoughtful analysis.

One thing that troubles me to a certain extent (and I'm surprised it doesn't trouble anyone else) in looking at these graphs is what appears to be a significant roll off from about 5 kHz through 20 kHz. It is consistent between the FL/C/FR graphs so I'm assuming at has to do with the actual design of the speaker or its enclosure. All 3 speakers are identical models and are mounted in nearly identical boxes. Is this something that should be EQ'd to flat? As it is, the system sounds very "bright" to me already. But that may have something to do with the lack of any sort of acoustic treatments in the room (yet). Or is my perception of "bright" a function of a relative peak from 500 Hz - 5 kHz? Perhaps it something to do with "ringing" which seems prevalent throughout the upper frequencies in the waterfall plots I've made from these latest supplied measurements.

Once this timing issue is optimized, what is the next suggested step in tuning?


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## RossoDiamante (Aug 12, 2013)

Here are the updated measurements with the SW distance +3 ft. and the Center distance +2 ft.


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## RossoDiamante (Aug 12, 2013)

Part 2


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## jtalden (Mar 12, 2009)

RossoDiamante said:


> I'm certain I understand at least 2% of this!
> 
> Starting from the end, as it were, there are two adjustments that are suggested (SWs +3 ft and CC +2 ft.).


Sorry, I got confused the CC distance should have been -2 ft not +2 ft. I edited the above post to correct this.



> Inputting a greater distance in the AV processor presumably serves to alter the timing of the beginning of a given waveform relative to some sort of reference. Am I assuming that putting in a distance of "0" for every channel would result in no "artificial" delay introduced into the signal?


Yes, all at 0 would add no extra delays. The same is true for any distances that are all equal such as all at 10 ft. The delays are added to speakers that are closer in distance than the furthest speaker. This makes the signal arrive at the LP as the same time.



> In that case every channel that I do put some value in that field will result in an amount of "artificial" delay proportional to the value input.


No, see above. The furthest speaker has no delay the closer speakers have just enough delay to compensate for difference in distance.



> If I recall, the distances that were input were SW = 14', FL = 14', FC = 13.5', FR = 14'.


So there would be no delay to any of these channels except the CC (FC). The CC would be delayed about 0.5 ms to compensate for the -0.5 ft difference.



> If I'm understanding your analysis correctly, the delay that is currently introduced appears to be 28 ms. Your analysis is also showing that a delay of 31 ms is more ideal, necessitating an increase in the value input into the AV processor of 3 ft. For the suggested SW adjustment of + 3 ft, we are in effect asking the AV processor to delay sending the SW signal by 3 more ms to get its signal to more closely align in timing to the signal coming from the FL and FR speakers.


Since we carefully entered the actual distance measurements into the AVR we can assume all the signals are arriving close to the same time except for the SW which has a little additional delay. We would expected it be delayed an additional 1-2 ms. Remember that we don't know the actual delays because we don't have loopback timing capability and REW moved the original positions of the IRs to align the largest peak near 0 ms. The peaks are not the initial arrival time. The initial rise of the IR is the initial arrival time. That is why I manually realigned them to how they would have aligned if loopback was in place. To do this I moved the SWs IR -30 MS in REW (which is actually 30 ms of additional apparent delay). It is not real delay it is just correcting for the SW IR shift that REW applied. This all gets confusing fast as:
> A manual IR shift of -30 ms in REW is increasing the delay of that channel relative to the other channels.
> If an increase in delay is needed in a channel and we intend to do that with a distance change in the AVR we need to reduce the distance setting. A +1 ms delay is obtained by reducing the distance in the AVR by about -13.5 in. or about -1.1 ft; roughly -1 ft for each +1 ms of delay needed.



> Two questions relating to this first part: First, the need for an increase delay in the SW signal seems to run counter to your assumption that the DSP/processing in the iNuke introduces its own delay. Second, would the same net result be obtained by decreasing the distance in the FR and FL fields by 3 feet each?


We found the IR alignment that we believe is the actual alignment very close to where we first estimated it to be. We guessed it would be near the -30 ms REW adjustment and a then found it was actually at an REW shift of -31 ms. We found this by matching the calculated SPL trace with the -31 ms shift to the actual SPL trace. Had we used loopback this is where we would have found the relative positions of the 2 IRs to start with on these measurements.

From that starting point we found that the REW SWs IR position needed to be shifted +3 ms to maximize the SPL. A +3 ms manual shift in REW is an -3 ms relative delay for the SW or approximately a +3 ft AVR adjustment. 

I still get confused on the directions when doing this sometimes as I did on the CC above.



> For the Center, the suggested modification is to add 2 feet to the AV processor's distance. On a relative basis, I currently have the center marked as 0.5 ft. less than the FL and FR channels. This decreased distance would presumably serve to increase the delay the AV processor uses in that channel relative to the FL and FR signals. By putting in a greater distance for the center channel, it moves the relative measurement of the center channel to "behind" the FL and FR speakers (i.e. greater distance to the listening position) which would change the timing of the signal to the center from "after" the FL/FR to "before" the FL/FR. This doesn't make intuitive sense when there is presumably no additional electronic delay (i.e. iNuke) for the center relative to the FL/FR and the speaker is physically closer to the listening position. The only thing that I can think of is whether we are "measuring" and accounting for something like the length of speaker wire.


Ignoring the direction as I confused the direction in the previous post, you are correct in the basic idea that the CC distance would logically not need adjustment relative to the FL and FR if the original measured distances were all correct. In practice however most all the SPL support distances vary a little from measured distances due to differences in room influence. Note that, the CC is not at the same distance to all boundaries as the FL and FR are. My room setup is very asymmetrical and there is a significant difference in the SPL support between the FL and FR. I chose not to compensate for this and simply try to compensate with EQ setting. I want the direct signal to arrive at same time even if the XO SPL on one side is significantly weaker and requires more EQ. In a home theater environment the CC is primarily dialog and to have the dialog arriving 1-2 ms different only shifts the persons apparent distance by that much. For music I mentioned in the previous post that I would probably not make that shift and allow the direct signal to arrive at the same time. This can be handled either way; you choose.



> I'll make these changes in the AV processor and remeasure. Thank you very much for your thoughtful analysis.


I try to look at these tomorrow. We need to compare the SPL of the new setting to the old setting an see if the expected improvement is found. The comparison should be done with the mic at the same LP.



> One thing that troubles me to a certain extent (and I'm surprised it doesn't trouble anyone else) in looking at these graphs is what appears to be a significant roll off from about 5 kHz through 20 kHz. It is consistent between the FL/C/FR graphs so I'm assuming at has to do with the actual design of the speaker or its enclosure. All 3 speakers are identical models and are mounted in nearly identical boxes. Is this something that should be EQ'd to flat? As it is, the system sounds very "bright" to me already. But that may have something to do with the lack of any sort of acoustic treatments in the room (yet). Or is my perception of "bright" a function of a relative peak from 500 Hz - 5 kHz? Perhaps it something to do with "ringing" which seems prevalent throughout the upper frequencies in the waterfall plots I've made from these latest supplied measurements.


Are you going to manually EQ the main channels? PEQ? GEQ? or maybe FIR filters? I wouldn't worry about it until the room is completed as it will all change. The house curve is very much a matter of taste and will be impacted by the speaker directivity and the room acoustics. You may want to start with the X-curve or a downward sloping curve and then decide what changes you want to try. This is a very big subject in itself. Wayne Pflughaupt is good source for threads/discussion on this subject.



> Once this timing issue is optimized, what is the next suggested step in tuning?


A glass of wine.


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## RossoDiamante (Aug 12, 2013)

Sounds like I'll have to make another measurement with the CC corrected to the -2 ft. value. Right now it should be even farther off as I made a +2 ft. adjustment in the AV processor.

But gotta go to work. Work always seems to get in the way of my fun! Thanks again for your detailed analysis and explanations.


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## jtalden (Mar 12, 2009)

RossoDiamante said:


> Sounds like I'll have to make another measurement with the CC corrected to the -2 ft. value. Right now it should be even farther off as I made a +2 ft. adjustment in the AV processor.
> 
> But gotta go to work. Work always seems to get in the way of my fun! Thanks again for your detailed analysis and explanations.


Oops, I got so involved in the explanation of the process I was using that I forgot to advise you that you do not really need to understand that math process. I use that process because I cannot take a bunch of measurements on your system and I want to see the polarity of the SWs vs the Mains and find the distance settings that I believe is appropriate so that I don't misdirect you any more than necessary.

All you really need to do is to set the measured distances in the AVR and then:
> Measure the SPL
> Adjust the AVR SW distance 2 ft and take another measurement. 
> Repeat until you have measurements covering ±8 ft for the FL+SWs
> Use the overlay SPL view to select the distance setting that provides the most SPL support in the XO area.
> Repeat for the FR+SWs and select the SW distance that best satisfies both FL and FR. They should be very similar particularly if the room setup is relatively symmetrical. Some compromise may be needed.
> Confirm that the CC+SWs is okay at the same SWs setting or adjust the CC distance a little if desired. If it is very different (like 6 ft) it may be better to invert the CC polarity and see if it is then closer. Not all speakers used for the CC are the same design as the FL and FR. If they are not specifically designed to match then the distance may be different. I don't know how common a problem this is, but mixing speaker designs can be problematic. 

Notes:
> We expect to find the best setting with the SW distance at the starting distance or adjusted maybe +2 ft from it's starting distance. It is of course not necessary to really do all the measurements; just enough to satisfy ourselves that we found the best SWs distance setting. 
> If we want to fine tune it closer, we can then move ±1 ft from that position to see if it improves a little more. 2 ft increments are adequate and there is definitely no need to go closer than 1 ft as that is a very small increment for an 80 Hz XO.
> If the distance shift is found more like 6 ft to 8 ft from the starting distance that suggests that the SWs are the reverse polarity of the midwoofers in the mains. In that case we can either inverse the polarity of the SWs and start over or just leave the setting where it was found. There is nothing really wrong with either choice. There are tradeoffs either way. Having the same relative polarity is considered the more conventional setting however. Your SWs distance was found where we expected it to be and suggests that the relative polarities of the SW to the mains is the same and also that we found the conventional setup.
> I do usually suggest that we should favor a good setting by increasing the SWs distance rather than reducing the SWs distance very far from the starting point. [The reason is beyond this scope.]
> It may be easier to drive both FL and FR together with the SWs to find the best SW distance and then confirm the CC measures okay at that setting. I don't do it that way, but I would expect the same result. I like to see what is going on channel by channel to confirm that there is no special issues with any channel; like one front being wired with the wrong polarity or a major dip at the XO of one verses the other due to room effects.

You can go through this entire process or just do the minimum to confirm to yourself the settings I suggested are actually improved compared to the starting settings. Remember it was only an educated guess on my end as to the starting point for the math because loopback alignment was not used. You also remember I sometimes get confused doing this process! 

When satisfied with the fronts, you can check the surround distance setting in a similar way. There we would only adjust the distances of the mains not the SWs as the SWs must remain properly aligned with the fronts.

I'm sure this really cleared things up for you. :gulp:


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## jtalden (Mar 12, 2009)

RossoDiamante said:


> Part 2


I just took a quick look at this new data - no surprises.

The FL+SWs and FR+SWs look exactly as we expected. A little improved from the initial settings.

The CC+SWs looks much worse and that makes sense since I had you move them the wrong way.


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## RossoDiamante (Aug 12, 2013)

This probably means your initially guesses were on target. I will correct the CC distance and remeasure.

My understanding at this point is that the surrounds would be correlated with the SWs as above and that any corrections would be implemented only on the surround distances. No changes should be made to the subs or the FL/CC/FR at this point since they should be locked together as a unit now.

It is also my understanding that these corrections have nothing to do with the frequency response characteristics of the speakers or the "ringing" that needs to be dealt with on the waterfall graphs?


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## jtalden (Mar 12, 2009)

That is correct.

This only optimizes the timing of the handoff of the mains to the SWs in regard to SPL and phase alignment. It has little to do with other concerns. It is a small portion of the overall effort. Most people do not bother with it, but the risk is the possibility of low SPL through the XO range.


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## RossoDiamante (Aug 12, 2013)

The final SWs and SWs+CC measurements with the corrected, corrected speaker distances.

I'll be able to do an audition of the speaker system tomorrow evening.

At this point, I think I will try to take a look at the surrounds next. I assume the measurement and analysis techniques are the same? Measure SWs alone and then SWs with each of the surrounds? 

Then I think it's time to take a break and actually finish this room. These seem like good "baseline" measurements of my system in a raw, untreated room. To my ear, there is quite a bit of work to be done in controlling the top end which seems overly bright and reverberant to me. 

Are there any measurements I should add to my "baseline" set before I start adding carpeting, and furniture, and acoustic treatments on the walls? What about an "all channels" test? Or just a surrounds (2 sides + 2 rears) test? What about just the 3 front mains? Would any of these be tested in the future in the final tuning phases such that a baseline measurement would be either beneficial or at least instructional?

What about adding a 3rd sub? I am thinking of adding a 3rd sub in the back of the room which is completely different in manufacturer, size, and configuration. It is an M&K sub from 20 years ago at least. I think it has a pair of 12" drivers in a push-pull configuration if I'm not mistaken. I will dig it out along with an extra 2 channel amplifier I have lying around. What would the measurement/testing process be to integrate a third sub into the system?


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## RossoDiamante (Aug 12, 2013)

jtalden said:


> That is correct.
> 
> This only optimizes the timing of the handoff of the mains to the SWs in regard to SPL and phase alignment. It has little to do with other concerns. It is a small portion of the overall effort. Most people do not bother with it, but the risk is the possibility of low SPL through the XO range.


Is the drawback of low SPL in the XO range also correctable with EQ instead of timing? On the face of it, it seems to me that it should be possible, but that compared to correcting the timing like you've done, it is more like using a sledgehammer to get the square peg through the round hole instead of just picking up a round peg instead.


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## jtalden (Mar 12, 2009)

RossoDiamante said:


> The final SWs and SWs+CC measurements with the corrected, corrected speaker distances.


I took a look at the new SWs+CC measurement and compared it to the calc SPL at this distance setting. It was pretty close but not quite as good as the calculated (possibly the mic was in a little different position). The SPL is only marginally better than your original measurement at the measured distance setting. There are 2 CC nulls in this XO area at about 80, 107 Hz, if I recall correctly. For the reason you mentioned (direct signal arrival time) and also because the room is not completed yet, it is probably best to use the measured distance setting. So that would be the corrected, corrected, corrected setting for the CC, i.e., back to where we started. 



> At this point, I think I will try to take a look at the surrounds next. I assume the measurement and analysis techniques are the same? Measure SWs alone and then SWs with each of the surrounds?


All that is needed is to set the measured distances and confirm each is okay with the SWs.
So measure the SL+SWs and see if the SPL support in the XO range looks okay. If there is a very large dip try inverting the SL polarity as see if it is better. Then move to the next speaker. 
[You could also change the SL distance setting and see if it is a significant enough improvement to make it worthwhile. Most Surrounds are not the identical designs to the FL and FR anyway so there will be compromise anyway. On the positive side it is also not as critical as the fronts so, unless there is a very large problem at the XO, I would leave them as measured.]



> Are there any measurements I should add to my "baseline" set before I start adding carpeting, and furniture, and acoustic treatments on the walls? What about an "all channels" test? Or just a surrounds (2 sides + 2 rears) test? What about just the 3 front mains? Would any of these be tested in the future in the final tuning phases such that a baseline measurement would be either beneficial or at least instructional?


Possibly the Acoustics Forum or others here have better advice on this matter. I have no real experience with before and after measurements of acoustical changes, but I would not think there is any real value beyond curiosity/learning unless you are using them to make design changes.

The SWs to mains timing setup you are doing now will not be changed unless the speakers or the LP are moved so that work was worthwhile. 



> What about adding a 3rd sub? I am thinking of adding a 3rd sub in the back of the room which is completely different in manufacturer, size, and configuration. It is an M&K sub from 20 years ago at least. I think it has a pair of 12" drivers in a push-pull configuration if I'm not mistaken. I will dig it out along with an extra 2 channel amplifier I have lying around. What would the measurement/testing process be to integrate a third sub into the system?


Your current SWs SPL response is very smooth so adding another SW is not needed in that regard. 

SPL capacity is the other consideration. This is dependent upon; capacity and freq range of the SWs, the size of the room, lost headroom due to EQ boosts, intended volume levels. I suppose it also depends upon the level of distortion you are sensitive to.

You can see SW capacity is a very personal determination.

If you do decide to add it, just go through the SW setup procedure again until they are working together well as single unit again. This may be easier or harder depending on the position of the new SW in the room and the particular design of the additional SW. In general, the more SWs in the room the easier it is to achieve a smooth SPL response without undo EQ and the more SPL headroom that be available. I would not expect it to help the lower freq limit significantly. Unless the new SW is equal or greater in capacity to the other two I would be wary about adding it.


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## jtalden (Mar 12, 2009)

RossoDiamante said:


> Is the drawback of low SPL in the XO range also correctable with EQ instead of timing? On the face of it, it seems to me that it should be possible, but that compared to correcting the timing like you've done, it is more like using a sledgehammer to get the square peg through the round hole instead of just picking up a round peg instead.


Nulls do not respond to EQ so to that extent, no. Many dips do respond to EQ so yes, they can be corrected at least to some extent by EQ. Note that even though we properly timed the SWs to front mains we still have low SPL in that range due to the room. 

Thinking generally, using some EQ is fine but it is not a good idea to use too much. I usually limit myself to ±5-6 dB and base it on average readings in the listening area. Others use a lot more EQ range and a single LP mic position. You will just have to investigate the options and decide how you want to do it.


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## RossoDiamante (Aug 12, 2013)

Many thanks for all your help and pointers. I'll measure the surrounds tonight and see what I find.

With respect to the low XO support, is it just a matter of relativity? Because the sub levels are a bit on the high side relative to the mains and because the mains seem to increase in amplitude between 500-5kHz, could the XO dip around 80-100 Hz just be relative? Assuming I'm able to either EQ out the relative peak between 500-5kHz or tune the room to absorb some of that range, could things seem more balanced or flat through the XO region?

Could more XO support also be achieved by changing the crossover frequency of the sub i.e. leave the XO for the mains at 80 Hz, but cross the subwoofers over at 100 Hz? I know at some point I measured the subs with a crossover set at something like 300 or 400 Hz, but I can't recall how much rolloff there was between 80-100 Hz naturally from the design of the subs. I would suspect that there would be at least some audible output in that range?


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## jtalden (Mar 12, 2009)

RossoDiamante said:


> With respect to the low XO support, is it just a matter of relativity? Because the sub levels are a bit on the high side relative to the mains and because the mains seem to increase in amplitude between 500-5kHz, could the XO dip around 80-100 Hz just be relative?


Well, I would have to investigate carefully again to provide any confident opinion and even then I am not skilled enough to help much. My comments, based on experience with my setup and memory your measurements, are:
> I would expect that when the SWs level is decreased the apparent XO range SPL sag may look even worse. Further changes to the timing will only make this worse. We have squeezed out the best SPL we can get this way.
> The XO range sag is primarily the result of the room dimensions, speaker location and LP location. It is very common to have nulls in the 70-120 Hz XO range and your fronts (particularly the CC) are impacted. 
> Ceiling modes are often a problem in the 70-80 Hz range. This is a problem I share with you as do many others. 
> I presume there are room design changes that could mitigate this; possibly a riser with absorbent materials filling it, possibly a coffered ceiling or suspended dome or other architectural features. 
> Possibly the other null is another mode related to width or possibly 2 dimensions that could be addressed with different architectural or acoustic changes.
> I suspect you will not be able to remove the sag (particularly in the CC XO) with EQ alone and expect that it will take significant changes to the room design to get rid of it. 
> Again though, you are not talking to an experienced person on room design or acoustical treatments. I work within a given room and with the typical room furnishings. You need to get other advice if you intend to actually make accoustical design changes.
> You can play with the REW "Room Sim" feature to get a feel as to what happens in a simple cuboid room. It gets more complicated to predict the response for other configurations.



> Assuming I'm able to either EQ out the relative peak between 500-5kHz or tune the room to absorb some of that range, could things seem more balanced or flat through the XO region?


There is no doubt that EQ can address broad SPL ranges as you show in the mid and upper freqs. Doing that will not impact the XO range however. You will not know the final extent of the dip in the XO range until you have a finalized setup to your house curve.



> Could more XO support also be achieved by changing the crossover frequency of the sub i.e. leave the XO for the mains at 80 Hz, but cross the subwoofers over at 100 Hz? I know at some point I measured the subs with a crossover set at something like 300 or 400 Hz, but I can't recall how much rolloff there was between 80-100 Hz naturally from the design of the subs. I would suspect that there would be at least some audible output in that range?


There may be some possibility here as I am doing just that currently. My impression was that your nulls were worse in the mains channels than in the SW channel. If this is correct you may be able to increase the XO and reduce the impact. I have moved to a 120 Hz XO on my latest setup (I have tried hundreds of different setups) to reduce the impact of the mains nulls. Some say they easily hear the location of the SWs when this done, but that is not a problem in my case. I use steeper LPF on the SWs than the standard 24 dB/Octave in an AVR. You could do the same by implementing another 12-24 LPF in the INuke to augment the AVR. You could also try it with just the standard AVR XO and see if "sub localization" is really a problem on program material. I suspect it will not be unless you are getting significant midrange leakage out of ports in SWs.

All this just adds up to; it may be worth trying an increase to the XO freq and see if it helps. 

You can try lowering it also, but if I recall the data correctly that is less likely to help.

Any changes in this regard also requires resetting the distances/timing of the mains to the SWs. Otherwise the sag may look worse just because the timing of the handoff is no longer correct.


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## RossoDiamante (Aug 12, 2013)

Sounds akin to poking a balloon -- pushing in one area leads to ballooning in another area!

I guess it's worth some experimentation at least. I was hoping that once the initial timing was optimized that other things could be done without affecting that optimization but it appears that everything is interrelated. 

I'll try measuring a couple of other listening positions. I'll also have to go back and re-read your post with the initial mathematically-based recommendations and see if I can follow them better. Seems more productive than taking 6-8 readings each time.


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## jtalden (Mar 12, 2009)

I overstated the final point above. There will be shift in timing due to a shift in the XO freq, but I would expect the impact to be small for a simple shift from 80 to 100, or 80 to 120. 

I should have said; you may want to confirm the timing to be sure it is still okay after the XO shift.


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## RossoDiamante (Aug 12, 2013)

As I start to move on from this initial impulse timing alignment, I'm seeing all these different measurements/graphs that REW generates from the single measurement sweeps I did above. 

In general, as I start to look at things like RT60, are these best evaluated in the context of all-channels-driven or is there still value in looking at individual channels in isolation?


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## weverb (Aug 15, 2008)

There is still a benefit to looking at individual channels in isolation. When your room is getting closer to being finished and you start adding acoustical treatments, things like the impulse graph will help show you if you have addressed things like reflections for each channel in isolation.


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## RossoDiamante (Aug 12, 2013)

I had a very enjoyable and productive evening in the basement tonight. Listened to a lot of music fiddled a bit and then spent a little bit of time putting up some Linacoustic. The results from this simple 30 minutes of work are definitely measurable, and definitely in the right direction. That being said, there is quite a ways to go. But it is gratifying to see the theory put into practice with expected results.

My baseline is in gold, post Linacoustic is in blue:


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## RossoDiamante (Aug 12, 2013)

The room has changed a little bit with the Linacoustic:


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## weverb (Aug 15, 2008)

That's going to be one nice theater! :T


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## RossoDiamante (Aug 12, 2013)

Thanks. Hopefully the star field ceiling goes up smoothly. I'll tack a few more pieces of Linacoustic up in places where some will eventually hide behind wall fabric as well and see what that does for the acoustics.


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## RossoDiamante (Aug 12, 2013)

The starfield ceiling finally got installed. If I would have known that it would be so difficult to install, I seriously might have just skipped it entirely. But now that it is up, it seems to have made some interesting acoustic changes as well as being a pretty stunning bling-bling addition to the theater.

Before measuring, my subjective impression was that the little bit of weakness I was experiencing around the XO, presumably due to a room null, was much improved. After measuring, it appears that the whole 90-200 Hz region is significantly more robust. As the level settings were the same, I can only surmise that the panels on the ceiling changed the dimensions of the room enough to mitigate that broad SPL depression. But I'm open to trying to understand another possible explanation.

The other thing that I surmised before measuring was that the reverberation or shrillness in the sounds was also somewhat improved. Measurement shows continued improvement in the RT60 graph, as predicted and expected as more "stuff" gets added into the room.

In looking at the RT60 graphs more closely, I guess I need a little more explanation as to what REW is measuring with the different plot lines: Topt, EDT, T20, T30. What has me particularly puzzled is the significant divergence of EDT in the latest measurement. In the prior two measurements, although somewhat higher in values, the different plot lines tended to track each other. In this latest measurement, all lines except for the EDT seem to have INCREASED in value, while the EDT seems to have significantly DECREASED in value in the 60-500 Hz. range.

Again, subjectively the room sounds like it is settling down quite a bit and sounds better overall to me. My question is whether the measurements are supporting my subjective impressions?


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## RossoDiamante (Aug 12, 2013)

I found this reference to describe the various parameters within the RT60 measurements:

http://www.hometheatershack.com/roomeq/wizardhelpv5/help_en-GB/html/graphpanel.html#rt60group

Very helpful.

What I still don't understand, however, is what Topt signifies in practical terms. If there really is an "optimal" decay time, why does it change so much between measurements? If this really is an "optimal" decay time, I assume that it is best to have a tight correlation between this line and some other line. But which one(s)? 

Based on the definitions of T20 and T30 given, I would have to assume that the T30 time should always be greater than the T20 time. But in my latest measurement, they are so closely spaced and tightly correlated above about 120Hz. Is this a reflection of the quality of the main speakers? Does it correspond in any way to the fact that I have my subs crossed over at 120 Hz (but my mains L/C/R are crossed over at 80 Hz)? 

I wonder if the change in room characteristic has now made my crossover settings inappropriate. I'm going to try to decrease my sub crossover to 100 Hz. or 80 Hz. next and see what that does to the crossover region.


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## RossoDiamante (Aug 12, 2013)

The starfield ceiling is a nice cosmetic addition to the theater. But it also seems to have quite an effect on the acoustics too.


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## weverb (Aug 15, 2008)

RossoDiamante said:


> The starfield ceiling is a nice cosmetic addition to the theater. But it also seems to have quite an effect on the acoustics too.


Correct, you are altering one of the reflection points that interact with the front speakers. Looks good though. :T


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## JohnM (Apr 11, 2006)

RossoDiamante said:


> What I still don't understand, however, is what Topt signifies in practical terms. If there really is an "optimal" decay time, why does it change so much between measurements?


Topt is an attempt to optimally _calculate_ the decay time, using a variable decay span that makes best use of the data rather than the fixed span used by T20 and T30. It should give a more accurate figure than T20 or T30.


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## RossoDiamante (Aug 12, 2013)

Ah, thanks. I guess I'm not supposed to match anything to anything else on that set of graphs.

It looks like I've gotten a pretty good improvement above 200 Hz, but no significant change (or maybe a little worse) below. 

What sorts of factors could explain the dramatic change in EDT from the middle to last RT 60 graphs above?


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## JohnM (Apr 11, 2006)

The odd Early Decay Time figure is because the first signal to arrive is lower in level than the signal that arrives 4 ms later, which is very unusual. One way that can happen is if a surface is focussing the sound towards the measurement position, so the direct sound is lower in level than the sound that arrives after bouncing off the focussing surface.


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## RossoDiamante (Aug 12, 2013)

I can't think of what that reflecting surface might be. I'll remeasure it again tonight as I play with the crossover points a little bit.


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## RossoDiamante (Aug 12, 2013)

Remeasurement yielded the same unusual RT60 result.

I played with crossover points of 120, 100, and 80 Hz for the subwoofer and there was no significant different in the 80 Hz dip or 100 Hz peak. Perplexing.

I settled on 80 Hz. as this is what the mains are crossed over at.

I tweaked the EQ a little bit and ended up with a SPL curve that is quite a bit flatter. The overall balance is continuing to improve.

RT60 changed marginally.


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## weverb (Aug 15, 2008)

RossoDiamante said:


> I can't think of what that reflecting surface might be. I'll remeasure it again tonight as I play with the crossover points a little bit.


Maybe the bare concrete floor or the bare wood stage? I am sure these measurements are going to change as you get the walls and floor finished. The furnishings you add will also play a part.


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## RossoDiamante (Aug 12, 2013)

I agree those two fixed items could be big contributors. But my difficulty in understanding is that those things didn't change between measurements.

Based on the latest measurements, I have been able to achieve a "flatter" SPL curve. I'm assuming that a flatter curve is the goal? When I have something like such a dramatic high-end rolloff, is it better to try to boost the high end or cut the rest? I achieved the results I got this time by boosting 20kHz, but my AVP only lets me go +3dB.


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## JohnM (Apr 11, 2006)

Another thing which can give odd looking results is testing with more than one speaker running, the time alignment between those speakers at the measurement point will determine where their individual peaks end up in the overall captured response.


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## weverb (Aug 15, 2008)

RossoDiamante said:


> I agree those two fixed items could be big contributors. But my difficulty in understanding is that those things didn't change between measurements.
> 
> Based on the latest measurements, I have been able to achieve a "flatter" SPL curve. I'm assuming that a flatter curve is the goal? When I have something like such a dramatic high-end rolloff, is it better to try to boost the high end or cut the rest? I achieved the results I got this time by boosting 20kHz, but my AVP only lets me go +3dB.


I wouldn't say a flatter curve is the goal. Keep in mind, the goal is what sounds best to you and a good looking graph second. Have you ever read Wayne's threads about house curves? This is usually the approach I take.

http://www.hometheatershack.com/forums/rew-forum/96-house-curve-what-why-you-need-how-do.html
http://www.hometheatershack.com/for...target-levels-hard-knee-house-curve-long.html

Also, I would not boost anything that high up. You could damage your tweeters. At this point in your journey, I wouldn't get too caught up in eqing until the room is done. I would just be in it for the educational aspect and seeing how each change impacts the response. If anything, I might guess that the area between 100-700Hz. might need some work based on the gold response line in post #70. :dontknow: I could be wrong though!


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## RossoDiamante (Aug 12, 2013)

The gold line in that post is the pre-change measurement. The green line is he post-change measurement. I'm current at the green line. I will take out the EQ at 20 kHZ and see what happens with the next set of changes which will be a baffle wall.


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## weverb (Aug 15, 2008)

That's what I figured. Maybe something following the "red" target might work. Again, depends on how it sounds to you. Maybe try playing the various frequencies and see what spl level get them to "sound" the same to you. Maybe the "blue" target line might sound better?


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## RossoDiamante (Aug 12, 2013)

JohnM said:


> Another thing which can give odd looking results is testing with more than one speaker running, the time alignment between those speakers at the measurement point will determine where their individual peaks end up in the overall captured response.


Interesting point. These measurements are will all 7.2 channels running. 

I have inquired about this a couple of different ways in a couple of different places. The question is whether I should be measuring and optimizing each individual speaker (or at least "bank" of speakers -- front soundstage, side surrounds, rear surrounds) separately or as a group.

Clearly the most discrete data would be with individual speakers and changes that would be needed and results that could be measured should be the most straightforward. 

But at the end of the day, the listener wants to hear a well balanced system with all channels working well together. But are REW measurements valid on groups of speakers like that? Assuming that they are, concluding what changes might be necessary and measuring the effects of these changes would definitely become more difficult.


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## weverb (Aug 15, 2008)

RossoDiamante said:


> The question is whether I should be measuring and optimizing each individual speaker (or at least "bank" of speakers -- front soundstage, side surrounds, rear surrounds) separately or as a group.


My guess is both. Subs plus the left main compared to subs plus right main as individuals. But then you want to compare (overlay results graphs) the center to the left and right main to make sure they are all trending the same which should help them sound the same and have effects not change as they pan across the front stage. Probably the same with the other four speakers. Tune individually but compare (overlay results graphs) as a group so that they all trend the same which should help them sound the same. :huh: Clear as mud?


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## RossoDiamante (Aug 12, 2013)

I was afraid of that... 

More data. More overwhelming. 

Almost done with the wood layer of the baffle wall.


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## RossoDiamante (Aug 12, 2013)

The baffle wall is constructed. Interestingly, I seem to have picked up a big null around 60 Hz. Will see if it gets better as I add more acoustic treatments to the front wall. Could it be due to a) the fact that I moved the subs up and out into the room a few inches or b) the holes along the bottom of my baffle wall?

I also am making the assumption that a bunch of Linacoustic behind the baffle wall would be of little use, so I took it all down except for down low. I'm hoping to add a bunch more fiberglass behind the baffle wall with the hope that it can act as somewhat of a bass trap via the slot at the bottom of the wall.


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## weverb (Aug 15, 2008)

Why did you choose to do a baffle wall? Just curious. Here is a picture of a friend's theater where they did a false screen wall. Not the best picture but I think you get the idea.


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## RossoDiamante (Aug 12, 2013)

I felt that a baffle wall was de rigeur because of the speakers I'm using. They are in-wall design speakers which are designed to have their front face mounted along a wall. That being said, I realize that baffle walls can be difficult to tune, especially with speakers not designed to be mounted that way.

The baffle wall is now done. 2" of Linacoustic on the front. I just have to go to Home Depot and pick up some more pink fluffy to put behind the wall.

Interestingly, I never did get the few dB augmentation nor the Change in the 2500-3500 Hz range that I expected with the wall. I'm not concerned with the dB's as the system is plenty loud. Perhaps I'll think differently once the carpet, furnishings, and wall treatments are up!

Pictures later today.


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## RossoDiamante (Aug 12, 2013)

Well, the room is essentially done. Screen is up. Carpet is in. Furniture is in. Linacoustic is on the walls. But I'm perplexed at the measurements I'm getting at this time.

The SPL has a dip in the 300 Hz range and a peak in the 10 KHz range. My parametric EQ in my preamp won't let me select 300 Hz to modify. It goes up to 200 on one band and starts at 1,100 on the next? Odd.

But what I'm really perplexed about is what seems to be a much worse waterfall picture (in the lower frequencies) compared to before I had any carpet or furniture in the room.

That being said, I'm enjoying the system immensely. Just some cosmetic stuff at this point.

Any thoughts on the measurements?


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## jtalden (Mar 12, 2009)

I suspect there are several problems related to the measuring system. 
> The Mic cal file is loaded 2 times. Once as the mic cal (okay) and once as the soundcard cal (no, delete it).
> You should be measuring the 3 channels separately instead of together. 
These 2 (above) are very minor compared to:
> That peak at near 9kHz measures 97dB when the 1/3 octave filter is removed. There are many other peaks that are equally unbelievable. 
> There is all sorts of noise in the signal before and after the measurement reaching as high as 75 dB. See the Spectrogram as the easiest place to see this.

I looks to me that you are measuring with the internal mic, but have a USB mic cal file? To confirm you could use REW RTA mode and tap the laptop and the USB mic as see which is active.

If that is the issue, just review and repeat the setup process for that mic.

It that is not the issue there are other things to try to find the source of the problem.


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## RossoDiamante (Aug 12, 2013)

jtalden said:


> I suspect there are several problems related to the measuring system.
> > The Mic cal file is loaded 2 times. Once as the mic cal (okay) and once as the soundcard cal (no, delete it).
> > You should be measuring the 3 channels separately instead of together.
> These 2 (above) are very minor compared to:
> ...



Whew. I thought it was just me having made major screwups in the finishing of my room! I am extremely anxious that I made the room sound so much worse after all the finishing stuff. Namely carpet, furniture, Linacoustic. 

Working in the basement now finishing up the tracks for the fabric wall. Will see if I can correct these issues and remeasure tonight. (Hopefully before final four!)


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## RossoDiamante (Aug 12, 2013)

jtalden,

You were right on the money with the diagnosis of faulty setup. I removed the soundcard calibration and found out that a non-functional USB port was causing the USB microphone to not be recognized, thereby using the built in microphone ( laptop mic plus wrong cal file now!).

So I ran a test using the settings the faulty setup was leading me towards and everything looked much more normal. Then I took away the sub amp EQ and then the pre-amp EQ and now am back to a baseline of straight signal. Now I see that my waterfall graph looks much better and consistent with my expectations given all the finishing.

Thanks for setting me back on the right track. Now for a little bit of tweaking!


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## RossoDiamante (Aug 12, 2013)

After some thoughtful EQ of both the sub amplifier and the pre-amplifier, I'm pretty excited about what I'm left with. Still not able to manipulate the 200-500 Hz range effectively given my electronics. 

Now for the fun part. A little ears-on auditioning of the current settings.


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## jtalden (Mar 12, 2009)

Good Job! Those final settings look like a good initial setup. 

Regarding the XO handoff from the SWs to the mains:
The phase chart suggests that the AVR distance settings may not be correct. That may subtlety impact the sound. The SPL looks okay though so there is no major impact to the sound. 
Are you still at the settings that were used earlier?
Are all the distances settings near the actual measured distance? They should be pretty close to that.
Do you have any other delays set; other than the distance setting in the AVR?

If the entered distances are close to measured then maybe it is just room mode influences that I am seeing. That could easily be the case.


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## RossoDiamante (Aug 12, 2013)

I'm sure some stuff has been changed between here and there. I really got off-track with my previous set of measurements. 

The settings in the AVR are pretty close to actual physical distances.

The one thing that I did, that I'm not sure is appropriate, is to level adjust each channel using the pre-amp prior to the other tweaks. The level adjustments were all pretty small except for a rear surround channel. Something is wrong with that channel. I haven't gone through to figure out what it is (pre-amp, amp, wires, speaker) yet and I figure the impact to the sound is pretty minimal from those rear surround speakers anyways. I was able to get the SPL level close to the others but had to turn the gain in the pre-amp to "Max".

Now that I'm pretty confident that the room sounds reasonable, I'm ready to cover the walls with fabric.

But for completeness sake, I'll go through the exercise of re-measuring the SW/Mains hand off again. If I recall correctly, that entails measuring:

SW L
SW R
SW L+R
SW L+R + Main Left
SW L+R + Main Center
SW L+R + Main Right


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## jtalden (Mar 12, 2009)

Since there is no change the mains, SWs or LP distances, there will be no change in the results. Since the distance settings are near the measured distances and the pre and post EQ results look very good I would not think it is needed. 

I was only raising the question to assure that there was not some inadvertent change to the distance settings that was overlooked.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Another tip, waterfalls are not useful beyond ~3-400 Hz, and it’s a good idea to drop the graph’s lower limit down to something approaching the room’s noise floor – maybe 35 dB. :T

Regards, 
Wayne


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