Struggling with RTA process

kents

Hi dbx'ers.

I'm struggling a bit trying to understand the procedure for RTA with my DriveRack PA. Hoping to get some help.

Here's what I think I understand.

- connect the RTA mic and enable the button
- the mixer volume is bypassed
- navigate to the level control on the dbx and turn up to performance level
- Next Page and let it do its thing

Here's whats unclear to me.

- how close should the mic be to the mains? I presume it should be at or near where the audience will hear.

- the unit seems to indicate two things ... 1) waiting for a minimally acceptable signal from the mic, and 2) \"turn up to performance level\"

The problems I had with this step were: I had to turn up the pink noise using the dbx level control to a level that clipping was reported in order to get to #1. And regarding #2, my understanding is that the mixer volume control is bypassed, so what the heck does this mean? Turn WHAT up? Perhaps I'm mistaken about the mains being locked out from the mixer?

Additional questions not addressed in the manual;
- how quiet should the room be during pinking? Its not practical to clear a venue for sound check. At times there will be Juke box and crowd sounds. Does this contaminate the process?

I tried using the function at an outdoor gig last saturday. The signal from the mic picked up a lot of extraneous noise, and the resulting EQ was horrible. I imagine similar problems with an upcoming indoor gig where I'm not going to be able to squelch the room during sound check.

Your feedback is appreciated.

kents

So.

After a couple days of dead air here I called our friends at dbx and here's the feedback (no pun intended).

- The mixer gain *is* disabled during RTA.

- The onboard compressor / limiter should be disabled as they can affect the output of the pink noise. There's a little gem that might belong in the documentation folks.

- Mic placement should be a triad between the 2 mains and the RTA mic of roughly equidistant proportion with the mic tilted toward one main speaker. Another tidbit for Version 2 of the manual imo.

- nominal amounts of ambient noise should not adversely affect the process

- don't expect to use RTA in an outside venue.

There ya have it folks.

Peace,

Kent

Gadget

Sorry zive been busy.. skip all that crap and do the new indooer method
http://www.driverack.com/drug/index.asp posted here in the tutorials section...
The problems you are facing is one of lack of knowledge of what room acoustics do to the RTA signal. readall the tutorials stuff especially the white papesr by Mike Kovach... once you understand why you cannot EQ a room you will be far ahead.. using the triad method without understanding what its doing is senseless. To many reflected paths to have any usable info, thats why it sounds terrible.. so read up and ask some pointed questions...
Gadget

cbiern

I keep asking these questions.
What is the recommended distance from speaker to microphone and microphone to the floor?
Is the reflective surface - concrete vs wood (as you show) vs earth important? A PZM has the metal body of the mic housing as its boundry, would a sheet of aluminum be a good choice?
Do you still set the output to the desired max (say 105db) for the space where you'll be performing?
Does this method work as well for setting a baseline as an open field? It is certainly easier to find an open 25sq ft area than getting alt least 50' from a reflective surface!

TIA

Gadget

Sorry, I don't always catch the questions..I'm very busy, and I am the one who has been around the longest.. so I kind of have my finger on the pulse of the DR, that doesn't mean I have all the answers...

the reason for the board was I could't get the mic close enough to the floor. The PZM would have to be as flat in response as the RTM mic for it to be used, and that is VERY FLAT.

Outdoors. 6-8 feet on axis located/aimed between the woofer, and horn of the top cabs. a concrete slab would be bad also, the farther away the louder you need to be..The DRPA will not let you get too loud.. it will tell you to turn it down if its too loud...get close to the volume you intent to run or the info is not valid...

The problem with ANY indoor RTA and 50' will still cause problems, is cancellations from reflections. every surface will cause these problems, and affect the process.. the distance off the floor will also cause problems...

Have you gone to the archive forum and read the tutorials, and user submitted white papers? if not do so there is a ton of info there..

Yes alumunium would be great...

cbiern

I think the RTA methods are being mixed here.
I understand that doing an outdoor farfield measurement you want the mic 6-8' away etc but with the new nearfield method how far away should the speaker be from the mic How close was your mic to the piece of wood ?

Gadget

The answer here depends on the speaker. A 2X15 with a horn cannot be tipped safely (without rigging) very far, so you need to tip them as far as possible)safely),then move the focus point (of the mic) but make sure the mic hears the horn directly. The resultant volume of the process would have to be louder the farther the mic is from the speaker. In the case of the co-axial monitor mains I built, the process with the DRPA was relativley quiet.

The mic is 1/8 to 1/4\" away very short wavelengths to minimise reflected cancellation...
Gadget

cbiern

Thank you. This is what I needed.
I'm also dealing with a co-axial horn top. my thought was to angle it at 45° about 6\" off the floor and put the mic on a desk stand with a boom about 2\" out in the center of the (projected) top and bottom planes of the speaker. The surface would be a 4'x4' piece of particle board. The speaker would be off the board to de-couple it.