help with measurements - Page 3 - Home Theater Forum and Systems - HomeTheaterShack.com

Old 03-11-15, 02:09 PM
Elite Shackster

Join Date: Mar 2009
Location: Michigan, USA
Posts: 1,368
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Re: help with measurements

Yes, It is just corrected info.
jtalden is offline

Old 03-11-15, 03:57 PM Thread Starter
Senior Shackster

Join Date: Feb 2015
Location: Richmond Va
Posts: 129
Re: help with measurements

Getting worried for a moment
nwf477 is offline
Old 03-11-15, 07:25 PM
Shackster

Join Date: Feb 2015
Location: Cedar Rapids, Iowa
Posts: 56
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Re: help with measurements

Quote:
nwf477 wrote: View Post
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.
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
Kix_N_Grins is offline
Old 03-12-15, 01:44 AM Thread Starter
Senior Shackster

Join Date: Feb 2015
Location: Richmond Va
Posts: 129
Re: help with measurements

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.
nwf477 is offline
Old 03-13-15, 07:08 PM
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Join Date: Feb 2015
Location: Cedar Rapids, Iowa
Posts: 56
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Re: help with measurements

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
Kix_N_Grins is offline
Old 03-13-15, 09:43 PM
Elite Shackster

Join Date: Mar 2009
Location: Michigan, USA
Posts: 1,368
My System
Re: help with measurements

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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