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Discussion in 'Sound, Music, and Intercom' started by Anonymous067, Jan 30, 2009.
Finding feedback frequencies?
RTAs have pretty much been replaced by dual-/multi-channel analyzer programs such as SMAART, Systune, and Praxis that are much more accurate than a standalone RTA. One of the big pitfalls is that an RTA is time blind.
A dual-channel analyzer type program will compare the original signal to the processed signal and, with parameters set correctly, can tell you MUCH more about the interaction with the room and the various components of the system. Also, the proper and accurate interpretation of the results you are given is CRUCIAL to achieving the desired end result.
In the end, it doesn't matter what you use or how you get it done - if it sounds good, it is good. That's the end goal, right?
Use your built-in mics. If there's too much 1kHz, knock out a few dB of it. Needs a little "body"? Maybe add something in the low mids...
Leave the tone shaping to your ears.
I'm sure some of the pros can elaborate more, but the RTA can lie to you since it is time blind and cannot take into consideration the phase of frequencies. It only says, "I sense the frequencies as higher in amplitude than these", etc.
There is no easy way around it. You'll need to take the time to get it sounding how you want to and adjust as the audience sucks up some of the frequencies.
Have fun - I'm sure you'll be fine. What's the worst that can happen? Your ears will become more well-trained than they are now? I think that's something that any of us could live with.
My only thing was for picking a crossover frequency between an active sub I'll be bringing into a venue that only has high/mid high clusters. It was designed for speech, not live music (yeah...I know thats a whole different can o worms).
I want to be able to go in and see how low the overhead clusters can accurately reproduce.
But how would I go about finding the best spot for the xover?
As long as we're discussing xovers, do they usually fall before or after the EQ.
My hope is to run EQ separate for the house and sub feed. The sub feed will come from a completely separate pre-aux send so I have complete control over it, among other site-specific reasons.
RTA's out there with options for noise criteria ,RT60 & delay propagation measurements
I use the D2 WinRTA analyzer from Acoustix LLC which is a handy 4 mic unit
If you care how it looks than thats a lighting question
But in all seriosness, twisting the knobs is how you find the "sweet spot." Every room is different, every sub-top combination is different. Many full range cabinets do the bass quite well and only need a little encouragement from the subs, while others will need much more help to get that thump many people look for.
I have my crossover after the EQ in my chain.
If you think about it, having a EQ the extends up to 16k for a sub is useless, so have a total mix EQ that is then split up (by the crossover), and distributed to the respective amps/speakers.
Just my .02
Well, if you can find out what brand and model the speakers are at the venue, the manufacturer's specs should be able to help you out with that.
Get back to us with that info and we can help you more.
You can find some good tones and sweeps on this cd. Make a cd, hook up your iPod or whatever, and play some tones at a good level through the system. Keep on moving to lower and lower ones until it just cuts out (it should be pretty apparent when that happens).
From there, it's a matter of selecting the crossover filter type (Butterworth, Linkwitz-Reiley (sp?), etc.) and changing the frequency and slope (usually in dB/Octave) until it responds the way that you want it to.
Hope that helps!
I usually put it in the rack.
It depends on how detailed you want to get. You could measure the existing system and your subs separately at very low levels, then look at the responses and see where and how they overlap and pick what you think is a good starting point. Then start there and keep playing with it. Or you could, as Wolf said, look at what the manufacturers recommend and use that as a starting point.
Two points I'll add here. First, we don't know what your crossover is or what options it has, so that somewhat limits what we can offer. You may or may not have a choice of filter type, slope, symmetrical or asymmetrical slopes, etc. Second, an RTA is only going to show the SPL at the measurement mic, it is not going to let you see what part of what you are seeing may be the room or what is happening at crossover in regards to phase. That is where something like Smaart or EASERA SysTune can be very beneficial. You can certainly setup the system without such tools but the type of information these programs can provide can be very helpful.
It depends on the physical devices and what you are trying to do. In my systems EQ is typically both before and after the crossover, before for general subjective tuning and after for objective system tuning.
One warning is to keep in mind that both the levels out of the console and the amp levels can function as part of the EQ and crossover. The EQ aspect is pretty easy to see, if you turn up the sub via the console or amp then that's like turning up all the faders for the sub frequencies.
The crossover effect is a little more indirect but if you think of the fact that a crossover is a slope, sloping down for the lower frequency element and up for the higher frequency element, then you might see how the level of each element affects where the two slopes cross. If you turn up the lower frequency element or attenuate the higher frequency component, then the frequency where the two slopes cross, the crossover point, moves up. If you turn down the low frequency component or increase the level of the high frequency component, then the resulting crossover point moves down in frequency. So remember that the relative amplitude of the signal components can affect the crossover and that any changes in those may require changes in the crossover settings. It may take several iterations of adjusting the console outputs, amps or powered speaker levels and the crossover settings to get where you want.
RTA doesn't tell you everything that's going on in a room, it only gives you amplitude by frequency. Some results could be from a room node, some could be an electrical (EQ) issue. If you know how to interpret SMAART readouts, that'd be the program I'd go with. Yet even still, those can't set your EQ for your; that is something you have to use your ears to do.
As an aside, I highly recommend Bink's test CD and the Simple Feedback Trainer. I use both quite often.
As far as the rest of the discussion regarding crossovers; it'd help to know what you're working with gear wise. Is this a little Behringer analog crossover, or an XTA? If it's a DSP, you'll get EQ before and after the crossover. I start with the manufacturer's reccomended settings for crossover, and occasionally adjust from there. You may have to contact your manufacturer for said settings, but that'd be my starting point. Spend a day in your space with a few CD's you know very well, and play around with the crossover settings and the EQ.
Beyond that, I second just about everything else said in this thread.
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