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Author Topic: RTA shows big drop at 1.25khz  (Read 21033 times)

g'bye, Dick Rees

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Re: RTA shows big drop at 1.25khz
« Reply #20 on: July 19, 2012, 09:00:39 am »

My initial thought based on a negative result was that the OP is seeing the result of a cancellation due to mic/speaker positioning, especially since he later said he was measuring with both sides of the system on. The fact that the response does not change with eq supports that this is an interference issue. The cancellation he is seeing may be the first where the cancellation is as wide as the band measured on the RTA. The cancellations that are at higher frequencies would be narrower than the resolution of the RTA bands and would be averaged with the constructive interference before being displayed.

Or the measurement mic is broken..........
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Kevin McDonough

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Re: RTA shows big drop at 1.25khz
« Reply #21 on: July 19, 2012, 09:32:27 am »

Or the measurement mic is broken..........

haha could be.

So to sum up: 

using only one speaker at a time,  step 1 move everything; speaker, mic, laptop, etc etc into a different room or preferably outside and measure again, just to rule out the null being caused by a particular reflection or standing wave within the room your currently measuring in.

Step two, try it without the sonic maximiser connected, just to double check that it isn't a problem with that unit somehow.

if this doesn't work then step three is to reverse the polarity of the HF (i.e. unscrew it and swap the wires) and measure again see if this takes the notch away, or at least reduces it).

After this, with a passive crossover these isn't really an easy step four unfortunately, short of modifying the crossover or removing it altogether and running the box two way.

k
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Tim Weaver

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Re: RTA shows big drop at 1.25khz
« Reply #22 on: July 19, 2012, 09:35:30 am »

I'm going to say this clearly and plainly.

The BBE box does nothing more than apply a "smiley-face" EQ curve to the system that it is inserted into. If you are using a graphic EQ then you can get the same sound by boosting the lows and the highs.

Therefor, if you have the BBE on boosting both lows and highs, THEN use a graphic EQ to bring everything flat again, you have effectively defeated the BBE. Yes it will sound different if you bypass the BBE, because it will have a "reverse smiley-face" now that you've EQ'd it.

I would suggest taking the BBE out and selling it to a punch-drunk DJ on craigslist. They seem to be the only people who can truly appreciate the BBE "process". Then re-EQ your system and don't worry too much about 1 frequency that is not in spec. You bought bottom-of-the-line gear. Be ecstatic that you got something that is 90% correct. Use what you've learned here and convince the church that 2 years from now (when you are replacing this system again) it would be best to hire a professional instead of someones cousin at the music store.
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Brian Wombaugh

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Re: RTA shows big drop at 1.25khz
« Reply #23 on: July 19, 2012, 11:32:17 am »

I bypassed the BBE and ran another RTA.  The difference was not that great.  The main thing that I saw was a slight increase in the frequencies from about 1khz and up.  It definately was not a reverse smiley face.  This leads me to believe that the unit must be doing something besides being an EQ.  The 1.25khz problem was still there.  As far as bottom of the line gear is concerned - the church has invested in decent microphones (EV767). I will say that even though this is an inexpensive system, after working on speaker placement and equalization this system sounds about 90% better than a lot of sanctuaries that I have been in. I have seen it again and again where a lot of churches invested thousands and thousands of dollars on everything high end and they have a sound system that still sounds like crap because someone didn't tune it or the operator doesn't have a clue how to properly use the board and mix sound.  I am a firm believer that system optimization along with sound operater training is as just important or even more so than the equipment itself. That does not however mean that you can take a "sows ear" and make a "silk purse" out of it.  There are several very moderatly priced microphone and speaker combinations that I have found that can be made to sound very nice.  This is a good balance for some of the smaller churches  which just don't have the finacial means for all the "high end" stuff.   Thanks - Brian   
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David Sturzenbecher

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Re: RTA shows big drop at 1.25khz
« Reply #24 on: July 19, 2012, 01:16:10 pm »

I am a firm believer that system optimization along with sound operater training is as just important or even more so than the equipment itself.

Do you feel as if you are optimizing this system? 
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Jay Barracato

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Re: RTA shows big drop at 1.25khz
« Reply #25 on: July 19, 2012, 02:27:55 pm »

I bypassed the BBE and ran another RTA.  The difference was not that great.  The main thing that I saw was a slight increase in the frequencies from about 1khz and up.  It definately was not a reverse smiley face.  This leads me to believe that the unit must be doing something besides being an EQ.  The 1.25khz problem was still there.  As far as bottom of the line gear is concerned - the church has invested in decent microphones (EV767). I will say that even though this is an inexpensive system, after working on speaker placement and equalization this system sounds about 90% better than a lot of sanctuaries that I have been in. I have seen it again and again where a lot of churches invested thousands and thousands of dollars on everything high end and they have a sound system that still sounds like crap because someone didn't tune it or the operator doesn't have a clue how to properly use the board and mix sound.  I am a firm believer that system optimization along with sound operater training is as just important or even more so than the equipment itself. That does not however mean that you can take a "sows ear" and make a "silk purse" out of it.  There are several very moderatly priced microphone and speaker combinations that I have found that can be made to sound very nice.  This is a good balance for some of the smaller churches  which just don't have the finacial means for all the "high end" stuff.   Thanks - Brian

Brian,

Where are you located?

If the boxes are in factory condition and wired correctly, I find it unlikely you are going to find any benefit digging into the boxes themselves.

I would:
1. Use the RTA but confirm with your ears. Get the system sounding as good as you can without worrying about what the RTA says.

2. Get someone else with experience to come in and do the same thing.

3. Compare the results to see how you boxes are performing in your space.
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Brian Wombaugh

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Re: RTA shows big drop at 1.25khz
« Reply #26 on: July 19, 2012, 02:32:17 pm »

I feel I am  optimizing the current equipment they have.  I have worked on speaker placement to minimize sound bouncing off walls and the ceiling along with flattening out most of the room resonances to get rid of any feedback problems.  The system now sounds much better and has additional gain before feedback that it did not have before.  I have also made some slight eq adjustments on the vocal mics to increase clarity and remove any"mud" from the mics.  The system still sounds good as is.  I am just trying to tweak it even better by trying to figure out whats going on with this one problem frequency.  Thanks -  Brian
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Ivan Beaver

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Re: RTA shows big drop at 1.25khz
« Reply #27 on: July 19, 2012, 06:38:13 pm »

Or the measurement mic is broken..........
HIGHLY possible.

I have seen a number of measurement mics have notches in the response.

Measurement mics are generally not built to be rugged-but rather for accuracy.

As with any measurement-you always have to check your MEASUREMENT system-especially if you see something that looks weird.

I can't tell the number of times that I have started to jump to conclusions-only to find out it was either human error-or an issue with the test gear.

TEST THE TESTER.
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Arthur Skudra

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Re: RTA shows big drop at 1.25khz
« Reply #28 on: July 19, 2012, 07:54:51 pm »

The system still sounds good as is.  I am just trying to tweak it even better by trying to figure out whats going on with this one problem frequency.  Thanks -  Brian
There comes a point where you leave "well enough" alone, and in this case, apart from getting a higher end measurement system and being able to see things at higher resolution with the added time domain, it's hard to speculate what this cancellation is caused by.  Whether it's a crossover problem, loudspeaker problem, reflection problem, measurement mic problem, measurement system problem...you get the idea.  If this dip in the response is only 1/3 octave wide and only a few dB down, then I'd say that the human hearing mechanism is quite forgiving of problems like this.  Don't get hung up on trying to get the response curve on a RTA perfectly flat.  Often what you find sounds the best follows a shaped curve in system response.  Using dual channel FFT like Smaart or SysTune will allow you to get to the bottom of this issue.  There's only so much you can do with a RTA.
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Brian Wombaugh

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Re: RTA shows big drop at 1.25khz
« Reply #29 on: July 19, 2012, 10:17:36 pm »

Thanks to everyone for all of the good advice on this issue.  I truely appreciate it !     Brian
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Re: RTA shows big drop at 1.25khz
« Reply #29 on: July 19, 2012, 10:17:36 pm »


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