[zybar]

OK, I am getting the hang of the XTZ kit and here is a measurement of my 5A's in my dedicated listening room with plenty of room treatments from RealTraps:



As you can see from the chart above, my reverb times are generally good, but I do have some small issues at 40Hz and 80Hz.

Room details:

Dedicated space is 29'3" x 13'9"/17'6" (first 15'3 of room/second half 14')) x 8'.

Speaker placement:

37" from the side walls

80" from the front wall

90" apart (center to center)


I would love to hear some comments from our acoustics experts.

Thanks,

George

[BikeWNC]

George, where is the best place to buy the XTZ?  Did you order directly from the company website or through another site? 

[youngho]

Hi George, I am no expert, but I was wondering if you could specify the sitting location, as well.

I noticed the relative peaks at around 25 Hz, 39-40 Hz, and 78-80 Hz, with their correspondingly long decay times. The multiplicity of the 39 and 78 made me think of the possibility that you're sitting in or near the antinode of a second- and fourth-order mode whose first-order frequency is around 19 Hz, which would correspond to a room dimension of around 29 feet, which is close to the length of the room. If you're sitting near the center of the room, this could account for the issue with these two frequencies (incidentally, I also noticed a relative null at around 19-20 Hz, and of course, the center of the room would be the node for the 19-20 Hz mode). Moving the listening position either forward or backwards away from the center of the room could potentially help. Otherwise, moving the loudspeaker might be a little tricky because the closest node for the second-order mode happens to be the antinode for the fourth-order mode. But maybe I'm wrong about the 19/39/78 and the listening position, and it's just a coincidence?

I don't know about the 25 Hz, and I don't understand how to apply SBIR and non-modal "standing waves" to your case, so I'll have to defer to the experts.

[zybar]

George, where is the best place to buy the XTZ?  Did you order directly from the company website or through another site? 

I bought it through their website.

George

[zybar]

Hi George, I am no expert, but I was wondering if you could specify the sitting location, as well.

I noticed the relative peaks at around 25 Hz, 39-40 Hz, and 78-80 Hz, with their correspondingly long decay times. The multiplicity of the 39 and 78 made me think of the possibility that you're sitting in or near the antinode of a second- and fourth-order mode whose first-order frequency is around 19 Hz, which would correspond to a room dimension of around 29 feet, which is close to the length of the room. If you're sitting near the center of the room, this could account for the issue with these two frequencies (incidentally, I also noticed a relative null at around 19-20 Hz, and of course, the center of the room would be the node for the 19-20 Hz mode). Moving the listening position either forward or backwards away from the center of the room could potentially help. Otherwise, moving the loudspeaker might be a little tricky because the closest node for the second-order mode happens to be the antinode for the fourth-order mode. But maybe I'm wrong about the 19/39/78 and the listening position, and it's just a coincidence?

I don't know about the 25 Hz, and I don't understand how to apply SBIR and non-modal "standing waves" to your case, so I'll have to defer to the experts.

I'll get you my exact location when I get home tonight, but I am pretty close to around 133" from the back wall - definitely not center of the room length wise.  In terms of width, I am much closer to the center, but I thought I had moved a few inches off center.  Height wise, I am pretty darn close to the midpoint - not a heck of a lot I can do about that.

Thanks for your input.

George

[youngho]

Using dimensions can be a little deceiving because a flexible wall or fenestrations may lower the resonant frequencies and shift the nodes and antinodes from predicted positions. You might consider repeating the measurements at different listening positions.

You must have a very long torso. I thought I recalled that the average listening position was about 36-38" off the ground? I forget. If your ears were near the midpoint at 48", you might expect a null close to 70 Hz and peak close to 140, but your measurements don't demonstrate that. I suspect that you're lower than you think.

[bpape]

Generally, seated ear position (depending on the exact seating and how tall the listener is) falls somewhere around 40-43".  While it's not centered in the height dimension, it's still falling in that 40%'ish range that has some pretty extreme peaks.  I don't believe that's the problem in your room though.

Bryan

[zybar]

Generally, seated ear position (depending on the exact seating and how tall the listener is) falls somewhere around 40-43".  While it's not centered in the height dimension, it's still falling in that 40%'ish range that has some pretty extreme peaks.  I don't believe that's the problem in your room though.

Bryan

Thanks Bryan.

Feel free to be brutally honest with any thoughts or comments.

George

[bpape]

Well, the easiest way to pin things down is to simply take another set of measurements with the mic in the same position left to right and height wise but move it forward or backward 6".  We can make educated guesses all we want but an iterative process of experimentation with the mic , changing only 1 dimension at a time will narrow things very quickly.

133" from the rear wall is falling into the 38% range.  Good starting point but doesn't always work.  If it were me, I'd try moving the mic forward 6-8" and see what you get. 

Bryan

[Ethan Winer]

As you can see from the chart above, my reverb times are generally good, but I do have some small issues at 40Hz and 80Hz.

I'm more used to seeing traditional waterfall plots. But "issues" below 100 Hz are common anyway, and the only solution is more bass traps. I'm sure you knew that already.

--Ethan

[youngho]

Generally, seated ear position (depending on the exact seating and how tall the listener is) falls somewhere around 40-43".  While it's not centered in the height dimension, it's still falling in that 40%'ish range that has some pretty extreme peaks.  I don't believe that's the problem in your room though.
Bryan

That's interesting. I had read this (http://www.stereophile.com/floorloudspeakers/1208thi/index4.html) and other similar Stereophile articles a while ago, but then I also Googled http://www.audioholics.com/reviews/receivers/audyssey-multeq-xt, as well as http://digitalcontentproducer.com/mag/avinstall_real_coverage_part_3/, so clearly there is a broader range.

However, on further reflection, it's not only how tall the listener is or what the seat height is, but also the leg and torso proportions, the time of day (we're tallest in the morning), and posture (are we looking over the heads of audience members in front of us? Are we sitting back and relaxing?). I do suspect that 36" to 41" would be a realistic range to start with, but I'm no expert.

[bpape]

Agreed.  It can vary wildly.  Even within the same brand of chair but different styles, I've seen as much as 3" difference in height.

Bryan