JBL MRX Help, New with Driverack PA+
michaelcinter
Posts: 0
Hey everyone,
Im new to using a DBX Driverack Plus. I've always been a man with traditional eq, gates and crossovers and this is definately new to me.
Im getting back into sound, and i've recently purchased the following equipment.
2- MRX 525 Full Range Loudspeakers
1- MRX 528s Subwoofer
1- QSC RMX 2450HD (Bridged to run sub, mono)
1- QSC RMX 4050 (Stereo Mains)
1- DBX Driverack Plus w/ RTA Mic
I read the manual and followed the setup wizard. Used the RTA Mic, and ran the auto eq.
The Mains hit very well, But i could never could get sub to do much. The dbx driverack kept turning down the sub, and turning up the mains during Auto EQ. I noticed it moreso in the crossover.
I "experimented' with it for about 2 hours yesterday, and i even took the sub back to guitar center today to check and make sure it was working correctly. I had to do alot of manual eqing to get the sub to sound... "ok". But felt like i was missing something. And it certainly didn't hit like it did at the store.
Bottom line, the overall output level for the mains was significantly higher than the subs, physically seen on the driverack front panel meters, and noticed throughout the eq/crossover.
Im very confused at this point. Isn't the point of the RTA to auto adjust the levels so that the sound is perfect? Why would i have to go back into the crossover and adjust the db gain? What was i doing wrong with the sub?
Any help will be much appreciated! Thanks
Im new to using a DBX Driverack Plus. I've always been a man with traditional eq, gates and crossovers and this is definately new to me.
Im getting back into sound, and i've recently purchased the following equipment.
2- MRX 525 Full Range Loudspeakers
1- MRX 528s Subwoofer
1- QSC RMX 2450HD (Bridged to run sub, mono)
1- QSC RMX 4050 (Stereo Mains)
1- DBX Driverack Plus w/ RTA Mic
I read the manual and followed the setup wizard. Used the RTA Mic, and ran the auto eq.
The Mains hit very well, But i could never could get sub to do much. The dbx driverack kept turning down the sub, and turning up the mains during Auto EQ. I noticed it moreso in the crossover.
I "experimented' with it for about 2 hours yesterday, and i even took the sub back to guitar center today to check and make sure it was working correctly. I had to do alot of manual eqing to get the sub to sound... "ok". But felt like i was missing something. And it certainly didn't hit like it did at the store.
Bottom line, the overall output level for the mains was significantly higher than the subs, physically seen on the driverack front panel meters, and noticed throughout the eq/crossover.
Im very confused at this point. Isn't the point of the RTA to auto adjust the levels so that the sound is perfect? Why would i have to go back into the crossover and adjust the db gain? What was i doing wrong with the sub?
Any help will be much appreciated! Thanks
0
Comments
Had you spent an extra second looking at the opening screen you might have noticed it says:
READ ME FIRST BEFORE POSTING
and while that would have actually led you to the answers you seek ... it would have also made you aware of the fact that you have a LONG WAY TO GO!
I'm betting that you measured the system indoors...
I'm betting that you were in a small space....
I'm betting that you had the measurement mic on a stand...
I'm betting that you had both sides running...
I'm betting that the one sub isn't nearly enough to match those tops...
Know why? We do, and the answers are all here, but your going to have to do some of the work yourself...
so, START HERE:
viewtopic.php?f=61&t=959
the links and suggestions there will lead you to the answers... but if you skipped some of it.. I suspect most do... because it is a LOT to take in.. then you need to go here:
viewforum.php?f=60
and read read read... and find out what the rest of us already know....that "The more you learn... the less you know!"
So, your either intrigued.. or pissed because you didn't "just get the answers you seek"...
Let me give you a hint...
Standing waves...
Now press the [EQ] button on DRPA until the geq shows up...look for ANY fully boosted or cut bands...(especially those above 100hz)
Those are reflected cancellations... (covered in the reading proscribed)
the ones below 170 hz (mostly below 100hz) are (indoors) from standing waves...
see what you come up with and formulate your questions ... were always here...
Gadget
While i should have read the FAQ, the forums been down all weekend (especially when i needed it saturday.) and i threw up a rhetorical question. Shame on me!
Now, with that being said. Let me answer your questions!
(yes I know that sub...er...woofer 3dB down at 40hz...) The MRX series..one step up from the terrible JRX series...
with a statement like this in your post forgive me if I didn't "assume" you weren't "new to this digital world :?
Now that we have the barbs out of the way, we'll answer your questions... for the umpteen thousandth time, (I realize this is your first time here but I have been answering these same questions here for ni-on to a decade now) with constructive discussion...
Perhaps dbx included a clip for this maneuver:
The fact is...if you place the mic on a stand at WHATEVER height indoors, you will have direct, and reflected energy hitting the mic correct? What do you think happens when the direct and reflected energy comes together out of phase by just 1/4 wavelength... they cancel completely... move the mic a few inches and that problem is gone but another crops up...
Try placing the mic on a towel or other soft material, about 25 feet strait out instead. BUT...only one side at a time. Why only one? Because you are again introducing multiple paths to the measurement mic. remember the reverb time you complained about...THAT will raise hell with the measurement process...
Several things will cause the LF measurements to be skewed... especially indoors.
1. The inexpensive mics are LEAST linear in the extremes, LF AND HF...
2. The frequency centers (ISO) are farthest apart in the LF region
3. Standing waves, super bass modes that set up as bass waves combine indoors.
The RTA based measurement platform is NOT very accurate, and mostly looked down upon by much of the pro audio community.. in fact they consider it pretty much useless! What we have found here is that it can help...but there are major limitations to it's usefulness. The things proposed here are time tested and have helped thousands of others.
Try setting up outdoors away from all reflective surfaces and get a baseline flat response on the system... THEN take it indoors and try the mic in various locations and compare that to the saved flat preset.
Your best bet in a huge space like that is to get as much energy on the water bags, and off the reflective surfaces as possible.
Gadget
site moderator...
If you had 500 bucks to spend on one subwoofer, and you'd been researching for several weeks on what to get. yes, yes you'd buy the same thing. I wish i could buy array systems and ground shaking equipment to fuel my rock concerts with, but its 2010, and giant cash flow and big loans are both virtually non-existent in this day and age. We work with what we can afford.
Moving on...
I appreciate the hilarious picture, but i have to be honest. One of two things worry me. Its obvious that dbx envisioned this microphone to be mounted on a stand. However, i question DBX's abilities to create a piece of technology such as the RTA w/ the Driverack, since their envisioned goal and device is flawed from the beginning. ESPECIALLY after i hear a comment from you saying..."The RTA based measurement platform is NOT very accurate, and mostly looked down upon by much of the pro audio community."
Yes, i agree, the room does have a lot to do with it (RTA or Not). However heres the part i dont understand... Why wouldn't and shouldn't the Driverack over compensate for the Low frequencies? OR at the very least, keep them at same level?
Question: Is this RTA problem localized to the "entry level PA Driveracks" or this problem plagued through the product line (4800 included)?
Now, i have a better question.
When you set the driverack pa + within the setup wizard to read stereo mains, and a bridged mono amp sub. Does the driverack believe that there are two bridge amps and two mono subs? Or just one? If it thinks theres two subs and identical amps, this all makes a lot more sense.
I set the microphone up about 25 feet away from the speaker cabinets, pointed directly at them at approximately 5.5ft height. I now realize that perhaps some of the lower frequences were being cut out (due to physical mic level height. ) But still, brings me back to my original question, in theroy the driverack should have over compensated rather than reduce. Simply because, it should have heard less lower frequencies then more.
I think its a great piece of technology, dont get me wrong. And it will save me overall time during setup. I think it was premature of me to honestly believe i could throw a mic up in the middle of the room and believe the driverack would be smart enough to make the room sound awesome, without the use of a sound engineering ear.
I appreciate the heads up and lessons, Inspector Gadget, please keep them coming. But you gotta watch those panties sometimes, they keep wadding up on you and turning into emotioncons. :roll:
Cheers mate!
-Mike @ Virginia
All kidding aside, the driverack doesn't "think" at all.. it has an algorithm that tells the system how to behave. The 4800 has NO auto eq system.. but does have an RTA input. The thing is, the folks @ dbx weren't trying to provide a truly "professional" measurement and auto eq device and they know the limitations, but were trying to help out the newbie, that has little or no experience or knowledge of sound, or equalization. The older DRPA was FAR worse at over doing the LF and the mid and HF as well...I speak often with the designer of the DRPA platform (well one of them anyway) and we have had protracted discussions about the auto eq pro's and cons, and he we have ruminated on the shortcomings and we are in agreement about the mic position and NOT putting it on a stand.. that is ASKING for trouble...BUT the ultra conservative element of dbx doesn't have the same view of this and the dissension fosters some ill advised rhetoric that actually ends up in the manual.. and especially in some of the speaker "tunings"...
That said, we are here to set the record strait...and to make sure that a this technology, be it flawed, or not "totally plug and play" like it's advertised, and disseminate the information to make it work for you.
That picture is no joke actually.. it incorporates PZM (pressure zone microphone) technology and it was used in a bar to monitor the sound using the DR260 as FOH controller. It gets the mic off the floor... where it wouldn't last long...
As for the LF and standing waves, that portion of the spectrum is almost exactly the opposite of the higher frequency cancellations so it CUTS them.. as I said, due to coupling of the waves to create ADDED volume at low frequencies.. this rolls off after about 100-170 hz and thus we recommend that you do those frequencies (below 170 hz) by ear... If you were to put the measurement mic in a corner of the room you would be able to eliminate most of this effect, but that HF portion would be skewed immeasurably
remember that LF sound is omnidirectional up to a point, and gets more and more directional as the frequencies get higher top a point where it is bullet like and bounces around like a bullet in a metal room... Check this out:
http://webphysics.davidson.edu/Applets/ ... fault.html
Move the red dots around and see what happens when you place them far apart.. and close together in a corner...note the shading, indicating acoustic power, and the finger like comb filtering of cancellations.. then imagine (that is one frequency) multiple frequencies and the all the potential paths and interactions when dealing with 20-20000 hz worth of frequencies. :shock:
Well that's all for now.. "panties" included...otherwise how can you really impart ANY emotion into the writing without voluminous writing?
G
One other question, if anyone knows...
"When you set the driverack pa + within the setup wizard to read stereo mains, and a bridged mono amp sub. Does the driverack believe that there are two bridge amps and two mono subs? Or just one?"
OR... A different way to ask. Does mono (in relation to output) mean one speaker/amp or does it refer to actual signal (meaning two mono outputs)?
Thanks!
Bring it on...
The ONLY, and I mean ONLY thing that does is provide a "voltage" gain setting "knob" location... When you choose a mono sub and bridged the DRPA ASSUMES you have set the amp like the suggested.. it has NO idea if you have or not...
I say, it doesn't matter.. unless you simply cannot set the gain structure properly.. even then if you auto eq you WILL end up at the same point through equalization/amps setting, and DRPA setting.. and it matters NOT if you add the gain in the DPRA, or the amp...
If you don't have the EXACT models listed in the menu.. (and even if you do) it makes no difference if you add or subtract the gain @ the amp or crossover... I DON"T CARE WHAT THE MANUAL SAYS!!!!
The driverack doesn't know (or care) if there is ONE sub, or 2000
G
Just for the record I'm running two Behringer B115D speakers for the mains and two Behringer B1800D-Pro for the subs.
Comment: I don't know why the heck the PX mismatched my output levels by 10db but it did. This leads me to assume this is a common problem so I wanted to post a simple answer. My first gig with this new system and my 2000w RMS total of subs were nothing more than silent stands for the mains. I could've got more bass out of an old 8 inch bazooka tube. If I can save someone from that embarassment and dissapointment I am happy to. I realize your initial post is four years ago but I was sent here when I searched my problem so I want this answer to be available for the next guy.
Gadget: I've been doing high end tech support for over a decade as well. Most often the simple answer is the best. You never even asked him to check the output levels. You just dove headfirst into overly complicated and unnecessary details. Nobody should be told to read for hours about standing waves when the real answer is to simply turn up the output volume. Please take this as constructive criticism. Sometimes having a ton of knowledge and experience can actually be a handicap. I've made similar mistakes myself. Nobody's perfect all the time.