# Fun with an RTA



## theJman (Mar 3, 2012)

In an attempt to have my subwoofer reviews be more objective I decided to make time -- you know how _that_ goes -- to learn how my XTZ Room Analyzer II Pro functions. I've read the manual twice now, so I have at least a passing familiarity with all the features (which turned out to be more then I had anticipated).

My first set of measurements have been taken, so I wanted to get some feedback from those who know about measured testing to see if these numbers appear legit. I already have an opinion formulated, now I need to see if the neophytes measurements -- that would be me -- are corroborated by people who know what they're doing.

I tested two different subwoofers, the Simply Sound Audio Rumba 12 I just recently reviewed, and another sub I'm currently reviewing. The former is acoustic suspension with a front-firing 12" driver, while the latter is an 8" driver with an 8" passive radiator. That one has the driver and PR on opposite sides of the cabinet. For both subs I pointed the mic directly at the center of the driver, exactly 1 meter away. They were at least 1.5 feet from the nearest wall. The room is carpeted.

I disabled the PEQ on the Rumba, so no boost or cut was used. The PR was not mic'ed for this test. The XTZ software has a meter which denotes clipping so all tests were run up to clipping, then the gain was turned down to just below that point. You only have preconfigured tones you can send out, so the possibilities aren't endless, which is why you'll see gaps between the frequencies. I started at the lowest -- 10Hz -- and stopped at 125Hz, even though I could have gone to 250Hz. 125Hz seemed like a reasonable ceiling to me though, so I'll probably stick to that in the future as well. I haven't figured out how (if?) to save the graphs in JPG or PNG format yet, so unfortunately there are no pictures to show.

That should cover all the background info, so without further ado...

*Simply Sound Audio Rumba 12*
10Hz - 86dB
12.5Hz - 91dB
16Hz - 97dB
20Hz - 98dB
25Hz - 106dB
31.5Hz - 109dB
40Hz - 110dB
50Hz - 107dB
63Hz - 114dB
80Hz - 116dB
100Hz - 109dB
125Hz - 105dB


*The sub I won't identify just yet* :neener:
10Hz - 57dB
12.5Hz - 60dB
16Hz - 67dB
20Hz - 77dB
25Hz - 89dB
31.5Hz - 98dB
40Hz - 101dB
50Hz - 94dB
63Hz - 103dB
80Hz - 107dB
100Hz - 107dB
125Hz - 103dB


The Rumba 12's numbers look like what it sounded like to my ears, so I'm pretty content with that one. The unidentified sub looks about right too, except for that bizarre dip around 50Hz (which I tested 3 times, just to make sure I wasn't losing it), so I image it's probably pretty accurate as well.

But that's a novice talking, now I'd appreciate hearing from those who know what they're doing. Do these numbers look as though they could be legit to you? I realize without having actually heard the subs yourself you can't make a definite assessment, but in general how do they fair? I want to see if I'm doing this properly, or if I need to go back to the drawing board.


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## Phillips (Aug 12, 2011)

theJman said:


> In an attempt to have my subwoofer reviews be more objective I decided to make time -- you know how _that_ goes -- to learn how my XTZ Room Analyzer II Pro functions. I've read the manual twice now, so I have at least a passing familiarity with all the features (which turned out to be more then I had anticipated).
> 
> My first set of measurements have been taken, so I wanted to get some feedback from those who know about measured testing to see if these numbers appear legit. I already have an opinion formulated, now I need to see if the neophytes measurements -- that would be me -- are corroborated by people who know what they're doing.
> 
> ...


I think that it is best with a graph to site. Try something like save as, export.


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## robbo266317 (Sep 22, 2008)

Doing a quick graph in excel gives the following:
View attachment Sub.xls








Combined


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## theJman (Mar 3, 2012)

robbo266317 said:


> Doing a quick graph in excel gives the following:


That's pretty slick. Thanks for posting it. :T


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## robbo266317 (Sep 22, 2008)

theJman said:


> That's pretty slick. Thanks for posting it. :T


No problems.

The excel file is there if you need it.
Keep us informed of your progress.

Cheers,
Bill


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## zheka (Jun 11, 2010)

are these in room measurements?

I was told that for pure driver frequency response one has to place the mic 1 inch from the driver. At longer distance the room acoustic becomes a factor. I suspect that the 50Hz dip is due to the room and not the driver/sub designs.


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## Tonto (Jun 30, 2007)

I agree that the dip is due to the room responce because it is seen in both graphs. Take the subs outside & remeasure them without boundries (except the ground of course) and then see what you have. That will show you exactly what the subs are doing. Why don't you want to say what the second sub is? It looks less powerful, but that is just that sub, unless it is way more expensive or something.


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## theJman (Mar 3, 2012)

zheka said:


> are these in room measurements?
> 
> I was told that for pure driver frequency response one has to place the mic 1 inch from the driver. At longer distance the room acoustic becomes a factor. I suspect that the 50Hz dip is due to the room and not the driver/sub designs.


Those initial numbers were in-room, but I have since moved on to close-mic based upon results I've achieved after additional testing.

I started this thread to solicit the advice of others who are more familiar with the measuring process, because when I do my subwoofer reviews I want to add an objective component. Since posting it I have done significantly more reading and have tried myriad different mic'ing tests, all of which has lead me to the same thing it has you; the only way to mitigate room modes is to use a close-mic technique.

After having settled upon that I'm now trying to get a better feel for adjusting the input sensitivity of the mic itself, along with the gain on the sub. I still have a bit more work to do in that area, but I'm getting closer.


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