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Discussion Starter · #1 ·
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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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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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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Discussion Starter · #4 ·
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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Discussion Starter · #5 ·
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 o_O?
 

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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,
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:


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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Discussion Starter · #8 ·
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
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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Discussion Starter · #9 ·
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!


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.

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

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Discussion Starter · #11 ·
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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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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Discussion Starter · #15 ·
...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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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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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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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}
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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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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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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