# EQ Question



## matthijs87 (Jul 8, 2016)

It surely has bin asked before but i coudn't find it in the search options.

My question is about when and if to eq ?

i have read this nice tutorial from some years ago

http://www.hometheatershack.com/for...target-levels-hard-knee-house-curve-long.html

but its only meant for bass. I was wondering if this has to do with something ? 
is it more safely to eq the bass for a better response then to eq above it ? 

Or does it equaly creates the same benefits and concequences ? 
I have read allot of diffrent stories about it so im realy curious in 
what the facts are. Also where to draw the line between eq adjustments or treating the room?.


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## tonyvdb (Sep 5, 2007)

EQ to the lower end is much less invasive on the over all imaging of the soundtrack. Applying EQ above 400Hz has to be done with care and generally its not a great idea to boost. When applying EQ above those frequencies it must be done evenly on both channels otherwise imaging can be dramatically effected in a bad way.

Often room Acoustics play a larger role in how it sounds and should be addressed first.


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## matthijs87 (Jul 8, 2016)

Ah yes that makes totaly sense, thank you !.

When aplying EQ above the 400 would you say the stereo imaging is the only important thing to look out for ?


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## tonyvdb (Sep 5, 2007)

Yes, but keep in mind that when you change the imaging its not just the stereo image that can be affected. Phase is also changed.


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## Wayne A. Pflughaupt (Apr 13, 2006)

What Tony said down the line, and I’ll add I haven’t had any issues boosting above 400 Hz. Just use matching filters, and you have to use EQ judiciously on the main speakers. You can’t use any crazy boosting or cutting because the main-channel amplifiers have much less power than the typical subwoofer and as such can run out of headroom real fast.

Here’s a good thread on full-range EQ you might want to digest. Feel free to ignore most of the advice given by the party making the second post.

Spridle’s Experiment

Treatment mainly affects reflections in the room, and typically has minimal effect on speaker’s frequency response. Here’s a good post on the topic.

Equalization vs. Treatments

Regards, 
Wayne


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## matthijs87 (Jul 8, 2016)

Verry great stuff ! this realy helps allot . 

@ tonyvdb : isn't phase the only thing responsible for diffrent stereo imaging in this case ? and thus the same thing, or better said the source for the diffrent stereo image ? What i learned is that the stereo image can only be changed by diffrent (left and right)frequenties and or diffrent timings in a nutshell. thus the phase and stereo imaging are the same things for "this" example becouse the timing wont be affected when eqing, is that true ? or am i missing something ?

@ Wayne A.

Thank you ! I will read all of it . but when talking about crazy boosting or cutting, where would you say the danger zone starts approximately ?


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## Wayne A. Pflughaupt (Apr 13, 2006)

> where would you say the danger zone starts approximately ?


Impossible to say. It all depends on available amplifier power and the efficiency of the speakers, which is different in every system. Fortunately with main-channel speakers it’s not hard to tell when you’ve gone over the line, as you’ll hear audible distortion at the stressed frequency when you run out of headroom.

Regards,
Wayne A. Pflughaupt


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## matthijs87 (Jul 8, 2016)

Okay thanks, 

Is there an option in REW to edit both left and right speakers at the same time ? At the EQ Menu i can only get a prediction of one file. For the matching filters it would realy come in handy to look how it affects both. I have searched for it but cant figgure it out.


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## tonyvdb (Sep 5, 2007)

matthijs87 said:


> @ tonyvdb : isn't phase the only thing responsible for diffrent stereo imaging in this case ? and thus the same thing, or better said the source for the diffrent stereo image ? What i learned is that the stereo image can only be changed by diffrent (left and right)frequenties and or diffrent timings in a nutshell. thus the phase and stereo imaging are the same things for "this" example becouse the timing wont be affected when eqing, is that true ? or am i missing something ?


Yes and no, there is not hard fast answer to this question as there are so many variables at play as speaker position can also play a part in the outcome.


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## AudiocRaver (Jun 6, 2012)

matthijs87 said:


> isn't phase the only thing responsible for diffrent stereo imaging in this case ? and thus the same thing, or better said the source for the diffrent stereo image ? What i learned is that the stereo image can only be changed by diffrent (left and right)frequenties and or diffrent timings in a nutshell. thus the phase and stereo imaging are the same things for "this" example becouse the timing wont be affected when eqing, is that true ? or am i missing something ?


Although in theory what you are saying is correct, it seems more accurate to think in terms of timing than phase, to me at least. Looking at typical phase plots between two channels does not give a clear idea at all what might be happening with imaging, but looking at impulse timing plots can be very informative.


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## Wayne A. Pflughaupt (Apr 13, 2006)

> Is there an option in REW to edit both left and right speakers at the same time ? At the EQ Menu i can only get a prediction of one file. For the matching filters it would realy come in handy to look how it affects both. I have searched for it but cant figgure it out.


REW can only generate a single graph at a time. If you want to EQ both channels simultaneously, you’ll have to take a measurement of both speakers running. This may show a droop in high frequency response compared to a single-speaker measurement; if so ignore that. You’re mainly looking for issues like significant peaks or depressions that need to be corrected.

Regards, 
Wayne


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## matthijs87 (Jul 8, 2016)

@ tonyvdb
Yes you are right there are many variables but they all come down to either timing or frequencie related problems as far as i understand. The mic and speaker possition are time based and the room (acoustics) will determine how the frequencies respond to that. 
So when found the most ideal spot "which i have" the only thing left is to either change the frequentie response by doing so with room acoustics or EQ if they are not to big dips/spikes.

Im still wondering though how the imaging exactly occurs.
What i learned from you guys is that EQing above 400 Hz can change the stereo image drasticly when not doing it with matched filters. But why ? is it becouse you could amplify that which is already out of phase ? or is there another explaination ? 
The reason i ask is becouse from my point of logic doing filters individualy would get things more in time, so less phase coused by the timing when there is for example a dip on the left side at 100 hz (which you then treat) and on the right side its on spot(which you leave alone. What then would be responsible for the phasing in this case ? I like to know how it works 

@ Wayne A. 
Ah yes of course, thank you . What would be the reason it drops in the high frequency response ?


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## Wayne A. Pflughaupt (Apr 13, 2006)

> Im still wondering though how the imaging exactly occurs.
> What i learned from you guys is that EQing above 400 Hz can change the stereo image drasticly when not doing it with matched filters. But why ? is it becouse you could amplify that which is already out of phase ? or
> is there another explaination ?


IMO it’s because equalizers actually work by introducing phase shift, as shown in this article. As you know, phase is also timing, so you can imagine what happens to the imaging when it’s off in one speaker or the other at certain frequencies.




> @ Wayne A.
> Ah yes of course, thank you . What would be the reason it drops in the high frequency response ?


Not sure exactly why, but it has to do with the mic not being perfectly centered between the speakers.

Regards, 
Wayne


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## matthijs87 (Jul 8, 2016)

Great stuff!, but what about Linear phase EQ ? Linear-phase filters only change the magnitude of the audio, while leaving the phase untouched.




> As you know, phase is also timing, so you can imagine what happens to the imaging when it’s off in one speaker or the other at certain frequencies.


Yes but lets say there's a dip on the left speaker at a certain frequencie which isnt visible on the right speaker.
That would mean there's naturaly already phasing going on becouse of diffrent timings and amplitude at those frequencies. So shouldnt equalizing then compensate for that diffrence ? The only thing i can think of which will change becouse of "it" are the (early) reflections that are cousing the natural phasing becouse there will be more pressure on it. 

Im happy to be wrong but i like to know how it works ) ,im learning allot here.:hail:


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## AudiocRaver (Jun 6, 2012)

As others have said, a mismatch in frequency response between the L and R channels as measured at the LP can indicate an imaging problem.

Another thing to watch for is reflections. Early reflections that come from the wrong direction and/or at the wrong time can make or break imaging and soundstage performance.


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## AudiocRaver (Jun 6, 2012)

matthijs87 said:


> Yes but lets say there's a dip on the left speaker at a certain frequencie which isnt visible on the right speaker.
> That would mean there's naturaly already phasing going on becouse of diffrent timings and amplitude at those frequencies. So shouldnt equalizing then compensate for that diffrence ? The only thing i can think of which will change becouse of "it" are the (early) reflections that are cousing the natural phasing becouse there will be more pressure on it.


Phase itself is important to imaging between about 250 Hz and 1 kHz. Lower than 250, the wavelength is so long the ears don't detect the phase differential very well. Above 1 kH the wavelength is too short, so direction, and absolute timing become more important.


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