Someone tell me this is right and I'm just crazy - XTi 2000

[bzb]

Does this look right to you guys? Seems like there's a significant hole in the chart right at the crossover section. Should I only do 24dB/oct?

Running a single T39 3012LF on CH1 and two OT12 2512 on CH2.



xti2000 crossover by bzbatl, on Flickr

[Benj Ross]

Hey Bzb,

As I understand it from my limited experience with my Xti, if you sum the signals, say routing both inputs to both outputs ( I forget what that option is called) it boosts the output by 6Db so what you're seeing there is where the crossover freqencies overlap you will be getting a 6db boost, thus they are cutting that freq by 6db. You will essentially have multiple speakers emitting the same attenuated 100Hz signal and they will sum to a flat response.

I would not take my word as law, but I am pretty sure that is what is happening. Maybe Leland can chime in here as our in house expert.

Benj Ross

[LelandCrooks]

At the summation point Ben is right. When you take into account the rising response of tubas/titans at 100hz there has to be a cut. What you want to see is that hole flat when the two are combined. 6db down is not an unreasonable amount, 3db from the speakers combining, another 3 or 4 db from the rising response from 80-105.

[Ron K]

The charting cannot take into account what the two sets of speakers will do when summed.It's only a reference as to where your crossover points are and how steep of a filter you are using. Summation can only be factored in after analyzing the system in different environments as all that changes with deployment and with the components chosen within the system. Add something as simple as an analog cap or a resistor and the whole thing will change yet again. There's no way the software can determine that!

Just a basic reference.

[Sydney]

Ron K established a very important distinction...
The difference between electrical and acoustic summation.
"Factors affecting include relative filer slope, relative filter corner frequency, relative filter topology, relative drive levels, relative speaker position, relative speaker efficiency and/or individual driver parameters"

Syd

[bzb]

Thanks everyone. Just when I think I'm getting it, I run into something that makes me realize I still have a lot more to learn

I don't know if anyone remembers my issue around microphones and running it through my Yamaha board, but I'm now running everything in mono with the subs on Aux1. This is done to eliminate the mics from even getting to the Titans.

As a result, I'm running the XTi in stereo mode. Should I be changing around my mix to run the XTi summed? From Leland's response it seems like what I'll be experiencing should be relatively flat even in stereo mode.

Thinking I should show up about 4 hours early to my gig today to test everything out again

[SeisTres]

Going to a lower slope will not alleviate the problem as with the L-R it automatically "summed flat". However, you will just get more frequencies that overlap at the crossover point which is something I like to keep to a minimum due to placement issues and the nulls and hotspots of different frequencies.

So, I'd keep it at 48 go from there.

[Ron K]

Best to simply analyze the rig properly after setting the DSP. What seams to work well on paper doesn't always work well in practical use. Get the rig in an open field if you can manage that and analyze it as best you can using SMAART or REQ etc. That will give you a baseline DSP setting.

When you approach each job site if possible run some noise and see how true the original settings remain. Environment means a whole lot. Sometimes you can hear the differences and sometimes not depending on where your listening local happens to be.Don't sweat small differences but do try and correct the big ones. If you manage to keep the rig tidy in the time domain then usually it stays fairly true from venue to venue as long as you dont splash the walls and ceilings with a bunch of junk that will cause the reverberant field to become cluttered. At that point basic EQ should do the trick.