# help with measurements



## nwf477 (Feb 8, 2015)

Decided to start a new thread hopefully with correct information. I have taken 5 measurements in my room. The goal is to have 2 Marty Cubes. The first 2 files labeled 1 and 2 are where I would like one of the subs the last three 3,4,5 are the same location just facing different directions. I have noted the distance from the MLP to the sub for 1,2,3. 4 and 5 are in the same spot as 3. Hope this will help.


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

Little tip, you don’t have to save each measurement as a dedicated file. You can take multiple measurements in the same file and they will all show up as different tabs. Much easier for us to compare them and we don’t have to download a gazillion files. :T

Regards, 
Wayne


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## jtalden (Mar 12, 2009)

nwf477,
> REW properly located all the IRs at 0ms so no manual shifting was needed. This alignment is as it would be if both SW were the same distance away from the LP or if a delay was added to one SW to adjust for the difference in distance.

> I chose 3 as the smoother SPL of measurements 3,4,5 (SW rotations at the 94" location). I didn't use 4,5 for any analysis.

> 1 and 2 were each then summed with 3 to see which was best. Both are very acceptable, but 1+3 (green trace) is better than 2+3 as it has a little more SPL down low where it is needed and is a little smoother overall.










> To achieve this result a delay of 1.1ms should be set in the P-Amp channel for position 3. This will delay position 3 so sound to arrive at the same time as sound from position 1. The 1.1ms delay accounts for the 15" difference in distance.

> Since a 1.1ms difference at these low frequencies is not very large, I also summed the results without the 1.1ms delay to see the impact on SPL. Below you can see that the effect is relatively minor. If for some reason you decide not to add the delay to position 3 the results are still very favorable.









> If these positions are retained when both SWs are in place (and the room acoustics are not changed) you will measure this same result with both SW working together.


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## nwf477 (Feb 8, 2015)

Wow I was expecting complete opposite!! Thank you! Since I did not use any filters other than the HPF on the amp I turned the EQ off turned the X-over up to 200hz on the AVR should I leave it alone or do you have any other suggestions, such as using the REW EQ or smoothing? ( Maybe this sounds off but the graph you came up with is pretty flat ) 
Norman


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## nwf477 (Feb 8, 2015)

Forgot to ask, on position 3 which makes no sense to me the sub is facing the end of the sofa maybe 2-3 inches away. In my mind I would have thought there is no way this would work. Any thoughts the sofa is leather?
Thanks Again
Norman


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## jtalden (Mar 12, 2009)

I just picked the smoothest response of the 3 orientations that looked like it would blend well with 1 or 2. 4 and 5 may be okay also, but they are likely to require a little more EQ if you want it this smooth.

You may want to EQ a little to a house curve of you choice. I like to have the SPL flat in this range, but most others here seem to like to drop 2-3 dB from 20 to 100Hz. It could probably be done with just one filter in this case.


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## jtalden (Mar 12, 2009)

I should have mentioned that since the filter is likely to be active in the XO range it is better decide what filter to use after you have the SWs+main XO active so you can see what the interaction does to the response. The chosen filters may be completely different.

I prefer to optimize the XO timing/distances first and then choose EQ filters based on the SW+main measurement rather than the SW measurement alone.


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## nwf477 (Feb 8, 2015)

I hope I am not bugging you, w/o doing anything based on what you wrote it seems leaving it just the way it is would be okay? I am only asking since on SW 1 there is a dip around 44hz but I am still new to all of this so maybe as others have suggested the second sub will help with that. Truly if that is what you came up with no EQ I do not seem to think it is going to get any better. If this is all correct then leave the x-over on the AVR set at 200 and just have the HPF on for both channels on the P AMP. This went from confusing to simple.


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## jtalden (Mar 12, 2009)

The SPL traces I posted are what you will get with both SW operating. Without the 2nd SW you will have one of your original posted SPL responses.

The 2 SW made the response much smoother and eliminated the deep null. 

A single deep null is often not noticeable however. Particularly when it is at such low freq.. So, even with the one SW you can do pretty well with a little EQ. There are a lot of rooms that start out much worse than your measurements and still look pretty good after proper EQ.


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## nwf477 (Feb 8, 2015)

To make it short once I have both SW I will be good w/no eq correct?


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## jtalden (Mar 12, 2009)

'Good' is in the ear of the listener. If the SW+mains measurement looks smooth then even without any EQ the bass range should sound great. 

I also mentioned above that you could apply some EQ if you like and since you have P-Amps that include that capability you could do it there; no additional equipment needed. 

Only you can tell us which way sounds better to you.


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## Talley (Dec 8, 2010)

haha ya... good is in the ear of the listener. lol.

my coworker buddy thinks his soundbar is amazing that he just got... for 200 bucks.


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## nwf477 (Feb 8, 2015)

I agree it is only as good as what you hear. Considering what I started with to what I have now is no comparison. Lately I have been driving myself nuts trying to figure out how to get 2 subs to play together. Now that is solved all I have to do now is get the 2nd built and put it in place. Of course after I get the subs done my next upgrade will be my surround back speakers and of course that will lead to something else.


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## jtalden (Mar 12, 2009)

nwf477,
regarding your PM for more info on how the predicted SPL response for the 2 SWs can be based on 2 measurements of 1 SW in the 2 locations:
*Here* is a link to a thread that may be helpful. I think it discusses some of the process. I will try to answer and specific questions you have.

Basically REW allows you to sum measurements using 'trace arithmetic'. That allows the calculation consider the phase relationship as well as the amplitude and thus the prediction is very accurate. REW 'Help' has info on this feature. The timing of the 2 IRs must be in the correct relationship for the prediction to be valid.


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## nwf477 (Feb 8, 2015)

Thanks again !
I understand why you went with in my case SW1 and SW3, you are looking for responses that are similar but opposite ( one would have a peak and the other a dip at the same freq.) I am lost however when it comes to finding anything concerning trace arithmetic in REW. I read the link you provided but I am still unsure where you went to put in the measurements.


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## nwf477 (Feb 8, 2015)

I looked around some more and found it under controls. As long as the IR compliment each other both measurements can be summed for the predicted response.Maybe it was just pure luck but I came up with a similar response not as smooth as yours. Any thoughts on what I did not do correctly? I was convinced based on everything I have been thru so far sub placement was going to be a nightmare from what you did and the explanation behind it has been a huge help.


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## jtalden (Mar 12, 2009)

nwf477 said:


> ...As long as the IR compliment each other both measurements can be summed for the predicted response.


Just to be clear, the 2 IRs need to be aligned so they are timed properly relative to one another. If the sound from one will arrive 5ms later then its IR needs to trail the other by 5ms for the summation. Without REW 'loopback timing' activated (as you cannot do) REW just tries to align all the IRs at 0ms. The overlay shows they fall right on top of each other so the REW alignment was accurate. Since one SW is actually 15" further away from the LP this is not correct relationship unless a 1.1ms delay is set in the signal path for the closer SW. So your summation assumes this additional signal delay has been added.



> Maybe it was just pure luck but I came up with a similar response not as smooth as yours.


 Not quite right - luck or not, you got the identical result that I did. Your chart was just scaled differently than mine was. I loaded your posted file and then imported my file so I could overlay the 2 sets of results. All was identical. Each trace overlaid its twin identically. Including the 2 summations. You did it correctly. :sn:


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## nwf477 (Feb 8, 2015)

All right progress. In a different room w/ different responses and measurements w/ 2 SW's before anything else is done the IR has to be aligned for both. This is where the actual measurements come into play. The example being if SW1 is 10' and SW2 is 15' there has to be a 5ms delay added to the 10' SW. Once both IR's have been aligned then they both can be summed for the predicted response ( A + B ).
As a side note I have been told numerous ways to add a second SW some of them were simply doing a sub crawl ( to me there is lots of room for error ) to several pages of reading, and of course everybody's method is correct. For what it's worth this makes the most sense and takes the guess work out of it. 
Thank you.:T


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## jtalden (Mar 12, 2009)

Just a final thought:
Someplace I think I suggested that that REW 'loopback timing' couldn't be done with an SLM. I wasn't thinking correctly. If we have and use 2+2 analog inputs/outputs for the REW measuring setup we can install a loopback cable on the other channel. With loopback timing activated REW will properly align the actual timing relationship of the 2 IRs. I should have said that; if digital inputs or outputs are used then loopback timing is not available.


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## nwf477 (Feb 8, 2015)

Having written that would the end result still be the same?


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## jtalden (Mar 12, 2009)

Yes, It is just corrected info.


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## nwf477 (Feb 8, 2015)

Getting worried for a moment


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## Kix_N_Grins (Feb 14, 2015)

nwf477 said:


> All right progress. In a different room w/ different responses and measurements w/ 2 SW's before anything else is done the IR has to be aligned for both. This is where the actual measurements come into play. The example being if SW1 is 10' and SW2 is 15' there has to be a 5ms delay added to the 10' SW. Once both IR's have been aligned then they both can be summed for the predicted response ( A + B ).
> As a side note I have been told numerous ways to add a second SW some of them were simply doing a sub crawl ( to me there is lots of room for error ) to several pages of reading, and of course everybody's method is correct. For what it's worth this makes the most sense and takes the guess work out of it.
> Thank you.:T


Hello,

I'm just trying to follow along here, as I also have two SW's and trying to learn about everything. In your example of "_SW1 = 10' and SW2 = 15' there has to be a 5ms delay added to SW1_", are you talking about just REW or are you actually adding 5ms electronically. My AVP only has 1 sub output and I'm using a "Y" cable to connect to the 2 SW's. My AVP will allow to set SW distance for delay, but both would get the same. I guess my real question is (not knowing your system/set-up, how do you apply the extra 5ms to SW1 and not SW2? Does your AVR/P have 2 sub outputs, or are you using something else?

Thanks,
Kix


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## nwf477 (Feb 8, 2015)

My system is nothing fancy it is a Yamaha RX-V1600 ( 7.1 ). I am using a RCA to XLR adapter coming out of the AVR and then a " Y " from the XLR to the amp. Before you worry about delay it is important to get the best location for the subs. Different people will suggest different ways, I tried a few of them what I ended up doing was placing my RS SPL meter at the LP ear height hooked up to the AVR. I used REW and did the measurement at each of the locations looking for the flattest response. You can see the images on the 1st post. 1 and 3 were the best. Once you find the 2 best spots you need to open both graphs in the all SPL tab.As you can see with mine SW1 and SW2 both have peaks and nulls but they are opposite of each other where one has a peak the other has a null. If they do not align now you have to add delay. There is probably a better way to do all of this if you have the mic but I don't you have to measure the distance from where the LP is to each SW. In my ex. SW1 is 10ft. SW2 is 15ft. There is a difference of 5ft. that will be the delay it will expressed in ms.(1ms equals 1 foot ). I think there is a way you can do it on the AVR in the Distance settings but not sure? To see what the delay will do with both of your measurements on the All SPL window click controls ( it is right below the Preferences tab ) You can see where you can add the delay / measurement offset. Once that is done then you can add each image to the trace arithmetic and do an average for A and B this will finally let you see what response both of your SW's will have when playing together. 
As a side note the measuring takes the longest what I tried to explain only takes a few minutes. For me it was pretty easy I did not have to apply any smoothing no eq other than the HPF set on my amp. I hope this makes some sense.


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## Kix_N_Grins (Feb 14, 2015)

Does this mean that the delay you are adding to SW1 (in your example) is only done in REW, and that to a persons ears in the LP, there is still a 5mS difference between SW's? I'm also using a "Y" cable from my AVP to the SW's. So if I add delay via the AVP, I would be adding the same delay to both SW's. Hopefully I'm understanding right...

Thanks,
Kix


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## jtalden (Mar 12, 2009)

Kix,
The delay discussed in nwf477's example would be a 5ms IR offset for the closer SW added into REW before the (A + B) calculation to predict what the SPL would be if both SWs were measured with that 5ms delay in the physical setup. This corrects for the 5' distance difference.

nwf477 has the ability to add delay in his DSP P-Amps if he choses. Since he has only a 15" difference in his setup there is no pressing need to worry about the small delay it would take to adjust for that. He could just drive them together (without the delay) if he chooses. He will get very similar results as show above (2nd chart in Post 3).

There is no requirement that says that 2 SWs need to timed exactly alike to get good SPL results though. I like to look at that option first if the delay capability is available because that provides the highest SPL for the bass range. Small distance differences are not too problematic. If the differences get too large then the SPL is reduced in the higher bass freqs. Bigger yet, then most of the bass range starts to suffer as the SWs are working against each other. If they get far enough apart it may be better to invert one of them to keep the phase tracking as closely as possible.

In your case you will have the same delay for both SWs so there is no need to for this technique. Just measure the SWs together as evaluate the SPL. If there is several feet difference in distance to the LP then you may want to invert the polarity on one of them as well and measure them that way also.


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