# Using EQ to cure dip +7.0 dB boost - good/bad idea?



## Takechan (Oct 8, 2015)

Hi, I'm pretty satisfied with my adjustments to my setup following this thread here; however, I have a single dip at approx. 30 Hz I'm considering curing using the boost function in REW.










I know that boosting is not considered an ideal solution since it'll lower my headroom, but will it really hurt my SB-2000?  It should have plent of juice to handle a single boost of +7.0 dB considering how many peaks I've lowered?

Here are the filters and predicted FR in REW:










Let me know what you. Thanks.

Best regards,

Peter


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## AudiocRaver (Jun 6, 2012)

Take a look at it with zero smoothing so you really know what you are dealing with. Although you are already pretty close to that with the VAR smoothing.

Generally speaking, if it is not a narrow black-hole notch and if a +7 boost actually gives you a +7 change in measured output, you _might_ be able to pull it off. Remember that 7 dB of boost is equal to 5x the power level. That is a BUNCH, so be careful you don't shoot a driver core through a couple of walls (kidding, of course). Good luck!


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

Takechan said:


> It should have plenty of juice to handle a single boost of +7.0 dB *considering how many peaks I've lowered?*


There is no free lunch. Cuts penalize headroom just as much as boosts. 

To make it easy to understand, consider the case of some lucky person with great response except for a single peak that needs to be reduced. Basically the mode is “free” volume for the sub provided by the room. Since that mode is dominating the sound of the sub, it determines the level the sub is set at to properly blend with the main speakers. 

What happens when the peak is cut? The sub’s overall level is now too low compared to the mains. The obvious solution is to turn the sub up. Naturally that demands more amplifier power and as a result, reduced headroom.

Personally I prefer to keep boosts and cuts combined (i.e. the total of the worst trough and the worst peak) at no more than 12-15 dB. You’re looking at fully 20 dB. Can you relocate the sub to get a reduction on the peak-to-trough swing in response?

Whether or not you can pull off that amount of EQ naturally depends on the demands placed on the sub in your current situation. If your system is set up in a 3 m x 3 m bedroom it probably won’t be an issue. But if it’s trying to fill an “open concept” living room with vaulted ceilings, open to other areas, etc. that’s different story. 

I believe SVS typically builds in compression for their subs, so you shouldn’t be hurting anything with massive EQ – if so you’ll be able to hear it for sure. At the very least you’ll notice reduced impact on demanding passages.

Regards, 
Wayne


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## Takechan (Oct 8, 2015)

Audiocraver,
My subwoofer is next to my sofa pointing towards my tv, I'd like to avoid a situation where it blasts my TV into pieces :rofl:
How do you calculate the power required to provide a +7 dB boost? 5x is, in my mind, A LOT!

Wayne,
Will I sacrifice headroom by lowering one or two peaks using an EQ on my sub? Say I have one to two peaks at 20 hz and 40 hz and I've calibrated my sub to blend with my mains from 60 hz. Will lowering the two peaks impact my headroom? Curing a dip with EQ I understand *will* eat up headroom because I am forcing extra dBs out of it...

Here is a nearfield measurement of my subwoofer before and after EQ:










I was assuming that when my response is lower than with no EQ there won't be no sacrifice?

How do you calculate your combined boost of dips/peaks? You mentioned mine was 20 dB.

I've tried various locations for my sub and the current is providing the best response with fewest dips.

Thanks for the help guys


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## Takechan (Oct 8, 2015)

So I spent an hour or two adjusting the EQ on my subwoofer. Here are the results. 

Firstly, a comparison before/after EQ measure anechoic:










Secondly, a comparison before/after EQ measured at listening position (left, right, center averages):









Lastly, a comparison before/after EQ blended with my mains:









I've settled with a +5.0 dB gain adjustment and not 7.0 dB. It seems when looking at the nearfield measurement I'm gaining exactly that 

I hope my subwoofer won't explode ?


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## AudiocRaver (Jun 6, 2012)

When discussing power, every 3 DB is a doubling of power. 

DB gain = 10 x log(Power2 / Power1)

10 ** (7 /10) = 5.011872336273 

Trust me, it is correct, I've made that calculation about a billion times in my life.

And if you are only reducing a couple of peaks by 3dB, it will not significantly reduce headroom


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

Takechan said:


> Wayne,
> Will I sacrifice headroom by lowering one or two peaks using an EQ on my sub?


As long as the sub’s overall level stays the same (i.e. is not boosted to compensate) then headroom is “saved,” but only at the frequencies that were cut.




> How do you calculate your combined boost of dips/peaks? You mentioned mine was 20 dB.


By looking at your EQ filter table which showed one boosted 7 dB and another cut 13 dB. Didn’t look at the response curve to figure that out (should have – sorry), but doing that now I see the worst deviations at 30 and 23 Hz are only 10 dB. So I have no idea what those filter settings were all about... :huh:




Takechan said:


> Firstly, a comparison before/after EQ measure anechoic:


What do you mean, “anechoic?” You managed to take a measurement without the room influence?

Regards, 
Wayne


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## Takechan (Oct 8, 2015)

AudiocRaver said:


> When discussing power, every 3 DB is a doubling of power.
> 
> DB gain = 10 x log(Power2 / Power1)
> 
> ...


Hi again,

Where do you get the '10' from in (7 / 10) - it's nice to know how to make the calculations for future use  Thanks!


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## Takechan (Oct 8, 2015)

Wayne A. Pflughaupt said:


> As long as the sub’s overall level stays the same (i.e. is not boosted to compensate) then headroom is “saved,” but only at the frequencies that were cut.


Ok, then I *should* be ok I think!




Wayne A. Pflughaupt said:


> By looking at your EQ filter table which showed one boosted 7 dB and another cut 13 dB. Didn’t look at the response curve to figure that out (should have – sorry), but doing that now I see the worst deviations at 30 and 23 Hz are only 10 dB. So I have no idea what those filter settings were all about... :huh:


It's confusing because the filters aren't listed sorted by frequency but by 'Q'. Sorry should have sorted them by frequency instead  If you look at the response chart you'll see the numbers above referencing the filters in the table.



Wayne A. Pflughaupt said:


> What do you mean, “anechoic?” You managed to take a measurement without the room influence?


Sorry meant nearfield measurement.


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

Takechan said:


> Sorry meant nearfield measurement.


People typically measure from and equalize for the listening position, or perhaps an average of all listening positions.

Regards,
Wayne


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## Takechan (Oct 8, 2015)

Hi Wayne,

I've included both a chart showing the average of three measurements (L,C,R) from my listening positioning as well as a nearfield measurment, to show the before/after response of the subwoofer without too many room mode interferences...

Best regards,

Peter


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## AudiocRaver (Jun 6, 2012)

Takechan said:


> Hi again,
> 
> Where do you get the '10' from in (7 / 10) - it's nice to know how to make the calculations for future use  Thanks!


It comes from the algebraic reversing of the original dB formula for power ratios.

10 log (power2 / power1) = dB

log (power2 / power1) = db / 10

power2 / power1 = 10^ (db / 10}


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## chashint (Jan 12, 2011)

This may be helpful (or not)

http://www.crownaudio.com/en-US/tools/calculators.


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## jonlanghoff (Nov 25, 2015)

I've made averaged in-room measurements of my subwoofer, from which I've used REW to automatically create a set of EQ filters, which I've then implemented in my DSP.

I've then made two nearfield measurements; one with the EQ on and with the EQ off:








https://www.dropbox.com/s/ej6451l7xxxceip/submueq.jpg

As you might be able to tell, there are a number of filters subtracting energy and then one adding (quite a lot of) energy between 50 and 60 Hz. My point being, that even though there's a big boost (18 dB), the grand total is just a relatively tiny boost (2 dB) compared to the un-EQ'ed graph - and as such, it shouldn't be an issue in terms of distorted sound, overheating equiment and so on... Am I correct here??

Secondly, are there any drawbacks in having all those negative EQ filters? (as long as the resulting output is something like what I've posted here)

B.R.


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## Takechan (Oct 8, 2015)

jonlanghoff said:


> ...My point being, that even though there's a big boost (18 dB), the grand total is just a relatively tiny boost (2 dB) compared to the un-EQ'ed graph - and as such, it shouldn't be an issue in terms of distorted sound, overheating equiment and so on... Am I correct here??


I'm interested in knowing this as wel!


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

jonlanghoff said:


> As you might be able to tell, there are a number of filters subtracting energy and then one adding (quite a lot of) energy between 50 and 60 Hz. My point being, that even though there's a big boost (18 dB), the grand total is just a relatively tiny boost (2 dB) compared to the un-EQ'ed graph - and as such, it shouldn't be an issue in terms of distorted sound, overheating equiment and so on... Am I correct here??
> 
> Secondly, are there any drawbacks in having all those negative EQ filters? (as long as the resulting output is something like what I've posted here)
> 
> B.R.


Did you read any of the other posts in this thread?

Regards,
Wayne


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## ceh383 (Jan 26, 2013)

jonlanghoff said:


> As you might be able to tell, there are a number of filters subtracting energy and then one adding (quite a lot of) energy between 50 and 60 Hz. My point being, that even though there's a big boost (18 dB), the grand total is just a relatively tiny boost (2 dB) compared to the un-EQ'ed graph - and as such, it shouldn't be an issue in terms of distorted sound, overheating equiment and so on... Am I correct here??


What I'm seeing looks like everything above about 240hz has been boosted, except for a small cut at about 55hz.
I'd set my target at about 83~85db...


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## DqMcClain (Sep 16, 2015)

AudiocRaver said:


> It comes from the algebraic reversing of the original dB formula for power ratios.
> 
> 10 log (power2 / power1) = dB
> 
> ...


It's called the "deci" Bel. That's where the 10 in "(7/10)" came from. A Bel is a pretty big unit when you get down to it, so dividing the unit by 10 makes the numbers easier to wrap your head around. It would be pretty inconvenient to have to think of +1B as x10W all the time... +10dB is much more intuitive.


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## jonlanghoff (Nov 25, 2015)

ceh383 said:


> What I'm seeing looks like everything above about 240hz has been boosted, except for a small cut at about 55hz.
> I'd set my target at about 83~85db...


Sorry, I should have explained which is which to avoid this misunderstanding! 

Purple is the untreated subwoofer.

Green is the EQ'ed subwoofer.

https://www.dropbox.com/s/ej6451l7xxxceip/submueq.jpg

To reiterate: I did measurements from my *listening position*, had REW make some filters based on this, put 'em into my DSP - and then I did _these _*nearfield* measurements. So naturally, the purple line is "perfect", and the green has dips to make up for the peaks I get when measuring in-room.

My question again: I have four filters pulling the curve down and then I have ONE filter pulling up quite a bit - the one at 50-60 Hz - but since this is placed inbetween all the "negative" filters, the end result is only a small peak compared to the curve from the untreated subwoofer.

Is all good then? Or am I still putting a strain on the equipment with potential negative side effects??


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## jtalden (Mar 12, 2009)

jon,
It depends...
Assuming for example - 
> Your EQ is such that the SPL at the LP is now relatively flat.
> With EQ you have increased the level of the now flat SW by 2dB to match the mains.
> Your boost at 50-60dB is 18dB
> Your SW is capable of outputting a max of 110dB at 50-60Hz before distortion rapidly increases.

Bad case:
> You play some program that has some 50-60Hz content along with other bass notes. 
> You listen at your loudest level say 100dB in the bass range.

Then, since the signal needed at 50-60 is 18dB higher than the average needed for the other freqs to play the content, the SW will be very overloaded and highly distorted at 50-60Hz. I expect that the overload at 50-60Hz will also result in higher distortion at other SW frequencies as well. 

Good Case:
> There is no problem in the same case as above if there is no 50-60Hz content in the selected program. 

Obviously the capacity is the SW and your listening habits is very much a factor here. There is no easy answer as to whether you will have an issue in your real situation. We can only say the headroom is reduced when EQ is applied. 

In terms of SW damage it also depends on the SW. Most are designed to survive significant overload without damage. that doesn't mean it is prudent to operate them that way though.


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## ceh383 (Jan 26, 2013)

jonlanghoff said:


> Sorry, I should have explained which is which to avoid this misunderstanding!
> 
> Purple is the untreated subwoofer.
> 
> Green is the EQ'ed subwoofer.












If this is the case, why did you feel the need to EQ it?


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## willis7469 (Jan 31, 2014)

Do I follow correctly?
You measured at the LP, and EQ'd accordingly, but then took near field measurements instead of at the the LP? I wouldn't bother measuring near field unless you have multiple subs and are verifying equal output. By the time the sound gets to the LP it's unrecognizable from the near field. 


Sent from my iPhone using Tapatalk


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## jtalden (Mar 12, 2009)

It actually works well to visualize the required voltage to get a flat response at the LP. I presumed that was the intent. That makes it clear that 50-60Hz will run out of headroom well before the other freqs.


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## willis7469 (Jan 31, 2014)

Ok. That makes sense. 


Sent from my iPhone using Tapatalk


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## jonlanghoff (Nov 25, 2015)

ceh383 said:


> If this is the case, why did you feel the need to EQ it?


Because I don't care how the sub sounds from a distance of 5 cm - I'm of course more interested in how it sounds from my regular listening position, circa 3 meters away!

To achieve a smooth curve from that distance, I've had to dampen some peaks created by the room, and the end result of this is what you see with the green curve.



willis7469 said:


> Do I follow correctly?
> You measured at the LP, and EQ'd accordingly, but then took near field measurements instead of at the the LP? I wouldn't bother measuring near field unless you have multiple subs and are verifying equal output. By the time the sound gets to the LP it's unrecognizable from the near field.


Correct - and the reason for doing the nearfield measurement after EQ'ing is to illustrate which "net effect" I actually get after the equalization.

Point being that only a relatively small peak is created even though the boost is in fact 18 dB, because of all the surrounding negative filters pulling it down.



jtalden said:


> It actually works well to visualize the required voltage to get a flat response at the LP. I presumed that was the intent. That makes it clear that 50-60Hz will run out of headroom well before the other freqs.


Good point, but I guess it'll only be relevant if the sub is nearly maxed out, right? (since the 55 Hz peak is "only" like 5-6 dB higher than the next-highest peaks at 110-ish Hz and 140-ish Hz..)

Also, I only have the volume knob on the back of the sub turned halfway up, so shouldn't that "protect" me from "blowing it up"?



General question:

Are there other risks/cons related to EQ'ing a subwoofer? - Does it degrade the sound somehow?



B.R. and thanks


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## Takechan (Oct 8, 2015)

Hi guys,

Thanks for the responses! It's certainly helped me understand a lot more!

Just an update, I've managed to adjust the filters on my subwoofer and at listening positioning (L,C,R average) the response is pretty much linear within +/- 4 dB when blending with my mains.

I'm pretty happy with this and this is with a minimal amount of boost (a single +5.0dB boost) - the effective boost, is as Jon has argued, probably less given there is a "negative" filter on both sides of the boost.

Here is the FR from 10 Hz - 22 kHz:


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## jtalden (Mar 12, 2009)

jonlanghoff said:


> Good point, but I guess it'll only be relevant if the sub is nearly maxed out, right? (since the 55 Hz peak is "only" like 5-6 dB higher than the next-highest peaks at 110-ish Hz and 140-ish Hz..)


Yes, but my guess would be that the average of the rest of the response is a better baseline as to the base requirement. that would make the 50-60 Hz range about 10dB hotter. That's more than 4x the power.



> Also, I only have the volume knob on the back of the sub turned halfway up, so shouldn't that "protect" me from "blowing it up"?


I wouldn't make any assumptions on the gain level setting of the SW as I am sure they provide enough range for a wide variety of situations. We would need to know how much voltage is being provided to the SW and what the SPL impact was with that SW gain setting. Oh, we also need to know the SPL capacity of the SW. So even if we knew what your SW was, we don't have enough information, to make a rational guess as to whether there would be a problem.

In the most general terms, if you have a high quality 18" sub in a very small room there is no likelihood that the capacity will be a problem. If you have a low cost 10" SW in a large room there probably would be a sound problem with that big an EQ range. As stated, the SW is not likely to be damaged if sized reasonably, but the sound can still be distorted if overdriven. 



> General question:
> 
> Are there other risks/cons related to EQ'ing a subwoofer? - Does it degrade the sound somehow?


General advice is to size the SW for the room size and your listening habits and keep the total EQ range to 12-15dB as Wayne suggested. Do not try to EQ room nulls - try and move the SW to a better position instead. To that general advice I would add that it is best to any avoid significant EQ boost near the bottom end of the SW freq range. The SW capacity is most limited there and it is thus more easily overdrive.


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## jtalden (Mar 12, 2009)

Takechan said:


> Here is the FR from 10 Hz - 22 kHz:


Looks Great!


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## jonlanghoff (Nov 25, 2015)

jtalden said:


> Yes, but my guess would be that the average of the rest of the response is a better baseline as to the base requirement. that would make the 50-60 Hz range about 10dB hotter. That's more than 4x the power.


Good point. You're probably right.



jtalden said:


> I wouldn't make any assumptions on the gain level setting of the SW as I am sure they provide enough range for a wide variety of situations. We would need to know how much voltage is being provided to the SW and what the SPL impact was with that SW gain setting. Oh, we also need to know the SPL capacity of the SW. So even if we knew what your SW was, we don't have enough information, to make a rational guess as to whether there would be a problem.


The sub is an Audiovector Ki SUB Signature. You can look it up if you want to (cause I can't link it here since I'm new.. :nono



jtalden said:


> In the most general terms, if you have a high quality 18" sub in a very small room there is no likelihood that the capacity will be a problem. If you have a low cost 10" SW in a large room there probably would be a sound problem with that big an EQ range. As stated, the SW is not likely to be damaged if sized reasonably, but the sound can still be distorted if overdriven.


The sub has a 10 inch driver.
The room is 4.2m long, 3.8m wide and 2.7m high (13'9" long, 12'6" wide, 8'10" high).



jtalden said:


> General advice is to size the SW for the room size and your listening habits and keep the total EQ range to 12-15dB as Wayne suggested.


I guess that part's okay in my case then..?



jtalden said:


> Do not try to EQ room nulls - try and move the SW to a better position instead.


But am I right in assuming that it's also impossible to do successfully? - Meaning that you would quickly be able to see from your following listening positioned measurements that the boosting was ineffectual if it was done to treat a null, right?



jtalden said:


> To that general advice I would add that it is best to any avoid significant EQ boost near the bottom end of the SW freq range. The SW capacity is most limited there and it is thus more easily overdrive.


This sub is pretty stable from ≈35 Hz, so I guess boosting at ≈55 Hz would be okay..?


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## jtalden (Mar 12, 2009)

If you have an 18dB boost and a 6dB cut that would be a 24dB total range in our terminology. The recommendation is 12-15dB max. That's a big difference. If you listen at very modest SPL maybe it will not be a problem. Personally, I would recommend either find another location for the SW that doesn't require that much correction, or if that isn't an option, limit boost to a max of 8dB and accept the sag at 50-60Hz. 

Yes, trying to boost a null is not productive. With a large enough boost (like 18dB) some apparent progress can be made (6-8dB maybe) in the measurement at the LP, but the resulting overall room effect and SW strain is not good. If it is a sag that responds to boost 1 to 1 then it is not a null and modest EQ boost is very effective. 

Yes, if the SW is good to 35Hz then some reasonable boost at 50-60 is fine. Reasonable for me is 5-6dB or if pushing it then 8dB max.


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