Why are my XTZ plots so much different

[Brad225]

I have been working with XTZ II Pro for a few days now. Puzzled at best and drinking more wine.

Two plot: 1 Full Range 2 Room Analyzer.

Both measured with the same settings on all equipment. Why the big dip on FR at about 160Hz and not on RA.

At this point I am not concerned with the bump at about 28Hz I can bring that down with EQ if needed.

 

[RUR]

Hmmmm, try re-running the bottom measurement (RA?) at 12PPO, vs. the 3PPO (1/3 octave) shown. Narrow peaks and dips often disappear when measuring at 1/3 octave - 1/12th octave is much more useful in the LF region.

 

[sleepysurf]

Brad, RUR nailed it! That one null should show up with 12 PPO resolution. Further tweaks in sub placement should help minimize that.

BTW, you're overall trace looks pretty darn good, and the RT-60 values are what you'd expect given your degree of absorptive room acoustic treatments.

As for the 28Hz bump, I would think the Depth i 25 Hz control can easily tame that (if it persists after further sub positioning).

 

[RUR]

Brad, RUR nailed it! That one null should show up with 12 PPO resolution. Further tweaks in sub placement should help minimize that.

Hey Alan, that 160Hz ain't in the sub region, so moving subs won't help. I often make this same mistake and then catch myself, usually later rather than sooner.

Probably a boundary null due to mains placement. Move the offending main or live with it - it's narrow enough to be somewhat inaudible.

Ken

 

[Brad225]

Here is the Room Analyzer plot again same settings 12 PPO. That still doesn't look as you would expect from the Full Range plot.

I have the 25Hz at -10db on both Depth I's and it really doesn't do as much as I would have thought in the 28Hz bump area.

Probably a bit of EQ and enjoy the wine.

Thanks

 

[sleepysurf]

DOH! RUR is correct again re the 160 Hz dip.

As for measurement consistency, you can occasionally get spurious results with XTZ (and other tools). I always try to measure a few times (using the triple measurement option from either a single or multiple seating location). Also, if your seating location is reflective (e.g. leather upholstery), cover it with a heavy blanket to eliminate reflections which your body would normally absorb.

 

[RUR]

Here is the Room Analyzer plot again same settings 12 PPO. That still doesn't look as you would expect from the Full Range plot.

I have the 25Hz at -10db on both Depth I's and it really doesn't do as much as I would have thought in the 28Hz bump area.

Probably a bit of EQ and enjoy the wine.

Thanks

Hey Brad,

As Alan has said, consistent measurement, particularly in the bass region, can be a pain in the you-know-what. You never get the mic in the same exact position, etc. etc. etc.

Better than nothing, but those gross adjustments on the subs are a blunt instrument. I'd roll in a couple of PEQ filters for the big peak @ ~30Hz, and another for the peaks @ ~180Hz. Should make a big difference, including improving the long decays seen in the itty bitty decay graph, top right.

Have fun!

Ken

 

[Brad225]

Moved my subs around more and played with the adjustments and this is what I came up with.

Still crossed over at 65Hz. Phase at 270 both subs. Interestingly enough I was able to back down the 25Hz adjustment to -6db.

Definitely helped the 30Hz area but still have issues with either 150Hz and 230Hz or 160Hz depending on which plot is correct.

If these are boundary nulls how do I go about trying to decide what direction to move the mains. I would prefer to move speakers to improve the curve to a point I can live with rather than introduce another piece of equipment that may or may not change the sound.

If moving is not possible what PEQ would you suggest?

 

[RUR]

Looks a heckuva lot better, Brad, including the decay at the two earlier problematic frequencies. Boundary nulls can be a bear to eliminate, but if the center of that first null is 150Hz, look for a reflective path 1/2 the wavelength (3.75 ft.) which will cause the reflected wave to reach the LP 180deg out of phase.

OTOH, a null that narrow may not be particularly audible. If XTZ will measure @ 24ppo, try that as it may be even narrower than what we see @ 12ppo.

 

[Brad225]

The XTZ only goes to 12PPO so that is all I will get.

So are you saying I need to look for dimensions in a multiple of 3.75'? Right off the mains are 3' 9" from the front of the acoustic panel behind them to the back of the panel. Approx. 3' 9" from the center of the panel to the side wall acoustical panels. Does that mean anything?

If it were you would you bother with it? If I move the mains to eliminate this null am I apt to create a new one and need to reposition the subs all over? What information would be missing in that frequency range. If I don't notice anything missing I may live with it and enjoy the music until the next wave of obsession washes over me and have the need to fine tune something else.

 

[RUR]

Brad, you're looking for a reflective path length which is 3.75' longer than the direct path from speaker to your LP. Odd multiples of 3.75 count, but the SPL of the reflection will diminish and become increasingly less problematic. Even multiples will be in phase with the direct wave, so you can ignore those.

Yes, if you move the mains, you'll simply shorten or lengthen the distance, lowering or raising the frequency at which it occurs. If you're not noticing anything missing, just sit back and enjoy. You've already mitigated a bunch of nasty bass boom and ringing with the improvements you've already made.

 

[Brad225]

I'll get the tape measure out and see how things layout. Thanks for the help I'm out of my element with this stuff.

 

[sleepysurf]

Brad, what happens if you move the listening position/mic a bit more forward or backward relative to the speakers? Does that main null change? You might also try experimenting with speaker toe-in, and see what happens. As a last resort, move the speakers 2-3" at a time forwards and backwards (a la Jim Smith's Get Better Sound) and see what happens.

I do agree with Ken, however, that the relatively narrow width of that null is probably barely audible, and might not be worth stressing over!

 

[Brad225]

Funny you should mention Jim Smith, Alan. I pulled his book off the shelf about 3 weeks ago and reread everything specifically related to main speaker, sub and listening position.
Based on Jim's recommendation for panel speakers I moved my listening position forward about 2 1/2'. This is still a bit further from the mains relative to their spacing apart than he suggests but it's as close as I want to be.

With that I needed to reposition my mains to have more toe-in and they needed to lean forward a bit more to keep my ears centered on the panels. This distance creates a much more intense sound stage than I have ever been comfortable with but I am going to live with it for a while and see.

I did try my LP/mic at different distances and the current one gave me the best ability to blend the subs to get the current plots shown.

With more room behind my LP than behind the mains I am going to move the CLSs 2' further into the room and move my chair back the same. That will give me at least 5 1/2' behind them to the front wall. I would think it will extend the image/sound stage but we'll see. Going to give it a few days to get used to the current sound before making another change. I hope the subs can stay mid wall and I don't have to start over.

As a mentioned in another thread moving my subs to the middle of the side walls has made a huge difference in the sound. Not just being able to blend and strengthen the bass to the mains but the new found clarity through out the middle frequencies. Never realized how much being between and behind the CLSs negatively affected the sound.