Outboard Gear - What are the benefits of a graphic EQ

[achstechdirector]

The local community theatre is performing Sand Mountain soon and we are having problems with sound. Everyone is suggesting graphic EQ. I would tell you the problems but I do not want any bias answers.


To the point: The theatre board wants to know several benefits of purchasing one of these... Please help me out with your opinions THANK YOU

[avare]

Originally Posted by achstechdirector

I would tell you the problems but I do not want any bias answers.

A useful answer is impossible to give without knowing what the problem is.

A graphic equalizer provides a system to adjust the frequency response of the sound as it comes from the speakers. This can be done to:

give a more even response;
provide greater intelligibility;
reduce low end mud;
help control feedback.

The "graphic" refers to the setting of the individual sliders providing a visual clue as to what the equalizer is doing to the frequency response.

Andre

[jkowtko]

The simplest way I can sum it up --

1) help balance out the abnormal volume characteristics of the room and PA system.
2) help to minimize feedback for certain frequencies that are prone to feedback.

3) The graphic EQ will NOT deal with reflections, echo, "hollowness", or other reverberant characteristics of the room -- you will need to treat the room for this.

So, if your problem is #1 and/or #2, I would think it's worth buying an EQ.

Just a note -- I would think it beneficial to have at least one two-channel 31-band EQ around anyway. (I have 6 channels of EQ for the 5.1 speaker system in our theater ... they are always inline as the "house system" equipment). You can buy a DBX231 used for just over $100. And if that's too much for your budget, you can pick up a Behringer unit for well under $100. The quality of Behringer is highly debated, but for the price you almost can't lose by trying one out.

[DavidDaMonkey]

I often hear the benefits (or downsides) of a GEQ discussed in relation to its sibling, the parametric EQ. The biggest difference is that a graphic EQ gives you much more fine control over many specific frequencies, whereas a parametric EQ is often used for more broad adjustments.


Restating what was said above me though, its hard to tell you its benefits if we don't know what it is needed for. I think you can safely tell us the problems you are having with the knowledge that most of the people here will tell you their unbiased opinion.

[derekleffew]

Originally Posted by achstechdirector

The local community theatre is performing Sand Mountain soon and we are having problems with sound. Everyone is suggesting graphic EQ. I would tell you the problems but I do not want any bias answers.

To the point: The theatre board wants to know several benefits of purchasing one of these...

As others have said, a graphic equalizer can be a useful tool. The 31-band, 1/3 octave variety is much more useful than a 2/3 octave or 15-band. However, I can think of very few cases where a GEQ would be a panacea to solve all of one's audio issues.

Don't ask a blind question. Tell us the specific problems and we'll offer specific solutions. The answer may in fact be that you need a graphic EQ, but I suspect the problems are more deep-rooted than that. As with most audio gear; in the wrong hands, having a graphic EQ could be worse than not having one.

[MNicolai]

Don't be fooled though, because a GEQ can do just as much damage as it can good if used improperly.

[waynehoskins]

Originally Posted by DavidDaMonkey

The biggest difference is that a graphic EQ gives you much more fine control over many specific frequencies, whereas a parametric EQ is often used for more broad adjustments.

True, though I'll refine that a little bit if you don't mind.

A graph gives you N so-wide fixed-center-frequency bands of control, usually 15 at 2/3 oct or 31 at 1/3 oct, or similar numbers (as low as 27 for a 1/3). Often the graph isn't the ideal tool, because the correction you need to make is not 1/3 octave wide and centered on 630 Hz, say. Either it's more narrow, where 1/3 octave takes more out than you need, or it's wider, where you have to pull down two bands to compensate, or it falls in-between two bands. In those cases, the graph limits you more than you want; the correction doesn't necessarily fall quite right.

A parametric gives you a smaller number, typically 5, bands to adjust, but for each of those bands you can adjust the center frequency and width, as well as depth. With a parametric you have more precise control over a smaller number of bands, which often is the more correct tool. A cut that would take two or more bands (and the resulting interference) on a graph can be corrected in a single filter on a parametric.

A graph is visual; a parametric allows much more precision and a smaller number of filters to overlap and do funny things.

To the original question, I agree that a graph is a very good thing to have a few of on hand, but as to whether it will correct the problem you're experiencing, we can't say until you tell us what the problem is.

[achstechdirector]

We have are having feedback problems with some frequencies because of the way our stage is built. We are having a very muddy sound (especially on the low side of things) and several small problems. We cannot get the volume we need because of the feedback

[howlingwolf487]

A parametric EQ should only be used by those who know how to properly implement it...

A parametric EQ allows for more specific adjustments, whereas a graphic equalizer allows for broader boosts/cuts for tonal shaping or feedback fighting.

I would recommend you put the money into having a professional visit your venue and analyze the situation. Equalizers tend to treat the symptoms of the actual problem. Treat the problem (speaker placement, maybe) and you can forget the symptoms.

[museav]

Wayne did a pretty good job on clarifying some of the graphic versus parametric EQ differences, I think the primary point based on some of the comments is that a parametric EQ can have a broader filter or a narrower filter than a graphic EQ, the ability to adjust the bandwidth, depth and center frequency is the advantage of a parametric. For example, you could set a narrow notch right on a feedback frequency with one band and then use the next band to address a very broad but shallow dip in the response.

An equalizer cannot correct room related problems such as room modes and cannot correct any time related issues such as combfiltering, all it can do is adjust the amplitude response of the system itself. Many time and phase related issues do affect the resulting frequency response, however these issues cannot be identified as being time related with an RTA nor can they be fixed via EQ, although you can spend a lot of time trying.

As far as a graphic EQ helping with feedback and 'mud', it might, but as Wolf alluded to, there are a lot of other potential factors (mic and speaker locations, speaker patterns and aiming, mic selection and proper use, the room and acoustical environment, etc.) that really should be addressed before blindly applying a graphic EQ.

The comment that you have feedback as a result of the way the stage is built is interesting as it sort of begs the question as to whether the problem is truly the way the stage was built or more how the speakers and mics are implemted on that stage.