# Minimal EQ / Hard Knee House Curve Discussion Thread



## Wayne A. Pflughaupt

Please use this thread for any comments or discussion about my article Minimal EQ, Target Levels, and a Hard-Knee House Curve.

Regards,
Wayne


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## huff

Wow, just wow. :hail: Wayne, thanks for taking the time to share such a tremendous amount of experience and knowledge with REW ... and for presenting it in such an easy to follow format. Brilliant!

Having just picked up my 1124P last weekend, I'm looking forward to my first run at equalising tomorrow. This thread will be a tremendous help and I'm glad I stumbled across it tonight.

I know I've read in other threads that the BFD should be used mainly for cuts and sparingly for gains - and that gains should be kept to only 3-4 db or less. I noticed that your examples have used gains as high as 8 db. Is there a simple rule you follow for when it is OK to use a gain > 5 db?

Thanks, again. And Basia can thank you too for 1 more CD sale!

Mark


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## clubfoot

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

Very well done Wayne.

Following your train of thought it should be stressed the importance of proper sub location because without proper sub location you will be doing more equalizing than necessary as well! As an example, REW generated just two filters for my setup!!! And I can tell you honestly from day one I didn't believe I even needed those as I know with further level matching/fine tuning I can achieve a very flat response without EQ.

I'm very curious now after reading your post, what my plots will look like,...maybe today I may try your graph display suggestions.


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## terry j

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

Thanks Wayne, a lot of good stuff...will know more after I read it, I dunno, another six times! ha ha.

Yes, when we first get eq and REW, there is very much a temptation to get as perfect a graph as possible. Most people though would soon get past playing with their 'new toy' and realise that sonically the perfectly flat response doesn't sound too much different from one that is a bit rough as long as the major peaks and dips are handled.

A request please, could you post a shot of the mains you are integrating the sub with, and the completed graph??

Now, this is where perhaps my own limitations on understanding may come in, as I'm confused (?) on some of your points.

If we accept that it is better to use as few eq points as possible, then I can see setting the target curve to 'bisect' the peaks and dips as a good starting point (the line of best fit as it where), but would not the best way to go is set the sub output level to bisect the target curve rather than leave the level and offset the target curve?? The way I see it, and do it (so if I've got it wrong I'm very interested!) is that at the end of the day (for this argument let's ignore a house curve) we want the sub to blend in with the mains seamlessly. So, if our mains output is set at 75 db then of course that is the level we want the sub to be at.

If we take as an example a case where (using your method) we offset the target curve by five db -for exageration - so we get the peaks and dips bisected, then are we not then running the subs five db hot??

Out of curiousity, when you set your house curve, do you take into account the relative listening level?? ie the Fletcher-Munson curves. Setting say 20 hz the same level as 80 hz at 60 db would be different than at 90 db???

I can perfectly understand your example with the bass guitar and being able to 'notch' out rather exactly a note in the scale. But that is not how it works in our normal situation is it?? What I mean by that is that IF my room had a peak that exactly fell on one of those notes, and boosted it by 5 db say, then that is equally bad as your example where we have notched it out. However, by applying the correct filter then have we not brought the relative level of that note back down correctly??

The very interesting question you raise is whether or not changing the LHS scale may or may not be more in tune with how we actually hear and perceive music, that is certainly worth some further thought, experimentation and feedback.

I also understand what you mean regarding smoothing on the bass, I too have at times gotten perfectly reasonable and acceptable results even when smoothing (say 1/6 oct) has been applied. At times it could very well be worthwhile to switch off smoothing to make sure we have exactly the correct frequency to eq, and then switch back to a smoothed graph for the filter size.

Once again, not only an informative post Wayne, but as usual an enjoyable one.

EDIT

Your post contained so much I keep thinking of other questions!

Regarding the 'lessening' of mid bass with your method-attributed to the 'excess' energy in the standard sub rolloff vs the sharp knee-, would we not see any excess energy in the resultant FR we run full range??

If there is in actual fact less energy in some part of the spectrum, we would see that difference in the FR, yet if we have a 'flat' response, via either method, then we have a flat response no? So either there was a 'hump' in the old method, or a 'dip' in the new method, or am I missing something completely?


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## brucek

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

Good stuff Wayne.

Certainly the readjustment of the target level in REW after a measurement is something we've recommended before. The pink noise that REW uses to set the target is band limited from 30Hz to 80Hz and results in an average over that range. So, it's quite difficult for the software to find a representative target. I always manually adjust the target level after the sub measure to include the peaks that I think will work best for me.

I'm afraid we'll have to continue to agree to disagree on the smoothing of low frequency responses. I completely buy into Johns argument that he has repeated many times, that filters optimised against a smoothed response will have settings that don't accurately match the room's modes.

I can't say I agree with your recommendation for a vertical scaling use of 20dB to 130dB. Wow, a 110dB swing is being very kind to those with poor responses, and I realize that's your intent. It doesn't seem realisitic when we know 20dB is completely in the noise and that 130dB is not going to occur with a 75dB target. Our present 60dB recommendation for a vertical scale swing is fairly common. This allows +/- 30dB around our target. I agree that a lot of users get crazy and try and track too aggressively about the target, but I suppose they would do the same with a larger swing. I'd rather keep the standard we've been using and simply inform the users of REW not to be too silly about their filters. :huh:

brucek


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## Sonnie

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

This is definitely good info to have in one thread for guidance, but I do agree with brucek about the vertical scaling. I would not recommend using such a wide scale, but rather keep to the 45db-105db we've been using. Of course if anyone wants to use it to make their response look better for their own peace of mind, I see no problem, but for comparison and recommendations here in the forum, I would stick with the current recommendation.


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## Wayne A. Pflughaupt

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*


I meant to make mention that people should change the scaling back before posting – I’ll get it added.

Terry, Huff, I’ll send PMs for your questions. I’m looking at a pretty busy week, so give me a day or two.

Regards,
Wayne


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## Sonnie

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

PM's??? What, you don't want anyone else to know the answers... :dontknow:


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## Wayne A. Pflughaupt

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*


Um, I figured after scorching so many sacred cows that I’d better lie low for a while. :hide: But if you’re fine with it, I’ll go ahead and respond here.

Regards,
Wayne


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## Sonnie

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

They are legit questions... no problem here. 

I'm not aware of any sacred cows you scorched... :dontknow: Did you maybe misinterpret our recommendations?


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## terry j

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

you're kiddin aren't you Wayne??

There are a regular bunch of people who's views/comments I very much look forward to.

And you are most definitely one of them!

Keep em comin.


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## Sonnie

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

Ditto! I imagine ditto from many members!


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## huff

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

I second (3rd?, 4th?) that! Wayne, your in depth posts are very helpful and I look forward to many more! And what would these forums be without some lively discussions!?! Here's 1 more question I had. You posted these values as your hard-knee house curve:

30 0.0
35 -1.6	
40 -2.9
45 -4.0
50 -4.9
60 -6.1
70 -6.6
80 -6.5
90 -6.0


Why is the value for 70 (-6.6) and 80 (6.5) outside the range of 0 to -6.0? I thought the curve values got progressively lower from the low-end (30) down to the Xover frequency (90).


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## Wayne A. Pflughaupt

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*


Wow, thanks for the kind words, guys.

I had some time to work on the replies today, but didn’t get finished. I should have something for you tomorrow night.

Regards,
Wayne


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## Ayreonaut

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

I'm so glad that you've tried it! :bigsmile:
We definitely agree about a house curve that's flat on the logarithmic scale. 
Minimizing the EQ to fewer wider filters does sound better. 

Have you tried EQing for the average response of a few seats? 
I highly recommend it! :T

House Curve Options


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## Wayne A. Pflughaupt

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*


Wow, Naut, I’d forgotten all about that fabulous thread! I wasn’t plagiarizing your stuff, really I wasn’t!  That one should have been made a sticky.

You said there:


> As Wayne has long since pointed out, all of this is based on preference, interaction with my room, interaction with my mains, and the behavior of my subwoofer. The “rules” that I broke were self imposed. Wayne's write up has always encouraged experimentation with all of these parameters. I've proven to myself that such experimentation pays off.


Pretty embarrassing that it took me this long to take my own advice! I also said back then that I was happy with virtually flat response. That got pretty stale after a while! :dunno:

Thanks again for pointing me in the right direction! :T

Regards,
Wayne


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## Wayne A. Pflughaupt

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*




huff said:


> I know I've read in other threads that the BFD should be used mainly for cuts and sparingly for gains - and that gains should be kept to only 3-4 db or less. I noticed that your examples have used gains as high as 8 db. Is there a simple rule you follow for when it is OK to use a gain > 5 db?


 Assuming you’re not especially concerned about the prospects of increasing modal ringing with boosting filters, it’s pretty simple: Can your sub/amp handle the increased demands? It’s generally not hard to tell, as you’ll hear rude noises from the sub if it’s stressed.

What you probably didn’t pick up on those threads: Virtually _any_ equalization places additional demands on the sub. 

A basic example: Before equalizing you probably have a peaking frequency somewhere that louder than everything else, due to a room mode. That peak in response is what’s determining your subwoofer level setting in relation to the mains.

Tame that "hot spot" with a cutting filter from the equalizer and you’ll find that now your sub isn’t loud enough, so you have to turn it up. Naturally, you’re driving your sub harder than you were before, and all you did was use a single cutting filter.

So, even using cut-only filters can ultimately have increased demands on the sub/amp, just as when you boost. There’s no free lunch.



> Here's 1 more question I had. You posted these values as your hard-knee house curve:
> 
> 30 0.0
> 35 -1.6
> 40 -2.9
> 45 -4.0
> 50 -4.9
> 60 -6.1
> 70 -6.6
> 80 -6.5
> 90 -6.0
> 
> Why is the value for 70 (-6.6) and 80 (6.5) outside the range of 0 to -6.0? I thought the curve values got progressively lower from the low-end (30) down to the Xover frequency (90).


I know it seems strange, but that’s what it took to pull the line down to flat. If I used a lesser value - 6.4, 6.2, 6.0 – the line would “bulge” between 60-90 Hz. 




brucek said:


> I'm afraid we'll have to continue to agree to disagree on the smoothing of low frequency responses. I completely buy into Johns argument that he has repeated many times, that filters optimised against a smoothed response will have settings that don't accurately match the room's modes.


That doesn’t surprise me, as I know you’re new to in-room measurements. But anyone who’s spent any amount of time doing them knows modal equalizing is a problematic idea. As I discussed in Post #3, measurements changing somewhat from one session to the next, due to changes in the physical and electrical properties of the transducers (measurement mic and speakers) as a result of differences in temperature, humidity, etc., is only one of many problems with the modal equalizing method.




brucek said:


> I can't say I agree with your recommendation for a vertical scaling use of 20dB to 130dB. Wow, a 110dB swing is being very kind to those with poor responses, and I realize that's your intent. Our present 60dB recommendation for a vertical scale swing is fairly common.


Poking around on the web for speaker reviews, typically the only place to find in-room measurements like we use with REW, I can’t find any evidence of a "common" 60 dB standard.










Sound and Vision Magazine
PSB Image Series Speaker System










Secrets of Home Theater and High Fidelity
Earthquake PN-2515 Speakers










Audio Ideas Guide
Swans T200A Active Speaker System​

Regards,
Wayne


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## Wayne A. Pflughaupt

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*




terry j said:


> A request please, could you post a shot of the mains you are integrating the sub with, and the completed graph??


I’ll post them below with the hard knee vs. regular house curve frequency response discussion.



> If we accept that it is better to use as few eq points as possible, then I can see setting the target curve to 'bisect' the peaks and dips as a good starting point (the line of best fit as it where), but would not the best way to go is set the sub output level to bisect the target curve rather than leave the level and offset the target curve?? The way I see it, and do it (so if I've got it wrong I'm very interested!) is that at the end of the day (for this argument let's ignore a house curve) we want the sub to blend in with the mains seamlessly. So, if our mains output is set at 75 db then of course that is the level we want the sub to be at.


 Well, changing the sub level to bisect the peaks and dips will be a challenge, because you have to set your sub level during REW’s calibration process, before you measure and see where it’s going to fall on the target line. You _could_ re-adjust the sub level after the first reading, but it would be easier just to move the target level precisely where you need it, rather than playing "hit and miss" with the sub’s level control. Yes, at the end of the day we want the sub to blend with the mains, but that’s that a separate issue from equalizing.



> If we take as an example a case where (using your method) we offset the target curve by five db -for exageration - so we get the peaks and dips bisected, then are we not then running the subs five db hot??


Technically yes. But as mentioned, after equalizing you need to re-adjust the level – that’s generally a given, no matter what.



> Out of curiousity, when you set your house curve, do you take into account the relative listening level?? ie the Fletcher-Munson curves. Setting say 20 hz the same level as 80 hz at 60 db would be different than at 90 db???


 I haven’t found it to be a problem – I just set the house curve for an average listening level. If you happen to engage in extremely low-level listening, you could set up a separate house curve in the BFD as a separate program.



> I can perfectly understand your example with the bass guitar and being able to 'notch' out rather exactly a note in the scale. But that is not how it works in our normal situation is it?? What I mean by that is that IF my room had a peak that exactly fell on one of those notes, and boosted it by 5 db say, then that is equally bad as your example where we have notched it out. However, by applying the correct filter then have we not brought the relative level of that note back down correctly??


Theoretically, that is correct. 

My complaint as laid out in the "Useless Filters" section was that REW was applying notch filters where there really wasn’t a need for any equalization at all (this was easily apparent after switching to the "too kind" 20-130 dB window). That’s what’s screwing things up, IMO, not equalization where it’s needed.



> Regarding the 'lessening' of mid bass with your method-attributed to the 'excess' energy in the standard sub rolloff vs the sharp knee-, would we not see any excess energy in the resultant FR we run full range??
> 
> If there is in actual fact less energy in some part of the spectrum, we would see that difference in the FR, yet if we have a 'flat' response, via either method, then we have a flat response no? So either there was a 'hump' in the old method, or a 'dip' in the new method, or am I missing something completely?


A house curve, of any kind, and "flat" response are mutually exclusive.

Yes, the difference between the hard-knee and regular house curve should show up in full-range FR measurements, although it might appear to be a subtle difference.

Here’s a comparison between the two house curves’ electrical response, beyond the sub range up to 200 Hz, which I really hadn’t looked at until you posed your question. It appears that when included in the "bigger picture," the hard-knee curve looks more like a 30-60 Hz curve than a 30-90 one. I have no idea why the hard-knee curve looks like a “reverse bulge” when seen full-range.









Electrical Response
Regular House Curve w/ Extended Range








Electrical Response
Hard-Knee House Curve w/ Extended Range​

Here's my measured response up to 200 Hz with the mains added, with both regular and hard knee curves. I cropped them so they'd both show up on the same screen without scrolling, for easy comparison.









Measured Low Frequency Response w/ Mains
Regular House Curve








Measured Frequency Low Response w/ Mains
Hard-Knee House Curve​

The horizontal red lines on each graph show the sub’s highest peaking frequency (~28 Hz) in relation to the sub w/ main’s highest peak (~100 Hz). We can see in the Hard Knee graph that the red line has much more of a tilt, which means the subs are at a higher overall level compared to the mains. Also notice that the 100 Hz peak in the Hard Knee graph, and everything above that point, is several dB lower than the Regular graph. Further evidence that the subs are now at a higher level compared to the mains. 

Keep in mind this is due to the hard knee house curve’s better sonics. The regular curve’s higher mains level (resulting in flatter _measured_ response) was the result of the sub having to be reduced, because its upper reaches were overpowering when set so that the lowest frequencies sounded correct.

Furthermore, note the vertical lines at ~40 and 55 Hz, which show those frequencies in relation to the straight line. They are further from the straight line in the Hard Knee Curve graph, which shows that the frequencies between the two peaks are further down then they were before – the result of the hard-knee curve.

So yes, the differences between a hard-knee and regular house curve can be seen with measurements - at least in my case.

Regards,
Wayne


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## JohnM

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

I'll add an option in the next release for the house curve interpolation to be either linear (as it is now) or logarithmic (so that you see a straight line between points when the frequency axis is on a log scale).


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## Ayreonaut

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*



Wayne A. Pflughaupt said:


> I know it seems strange, but that’s what it took to pull the line down to flat. If I used a lesser value - 6.4, 6.2, 6.0 – the line would “bulge” between 60-90 Hz.





Wayne A. Pflughaupt said:


> I have no idea why the hard-knee curve looks like a “reverse bulge” when seen full-range.


Your house curve is getting into the crossover slope. 

In order to make the _sum_ of your house curve and crossover flat, you are making your house curve _concave._

Here's what a ruler flat house curve looks like when added to an 80 Hz crossover.

31.5 8
36 7
40 6
45 5
50 4
56 3
63 2
71 1
80 0










My house curve is lower in frequency and pretty much stays out of my 80 Hz crossover.

20 10
22 9
25 8
28 7
31.5 6
36 5
40 4
45 3
50 2
56 1
63 0


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## Wayne A. Pflughaupt

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*


Keep in mind that I was equalizing solely from a graph with a subwoofer-only target, which was pretty much a straight line down from the shelving frequency to the crossover frequency (see graphs in the article). The plain text figures I used were what was required to keep the line appearing flat for the purposes of equalizing, even if some of the values were greater than the desired 6 dB slope.

Adding the full-range data to the target, it’s apparent that different figures are needed to maintain the straight line. However, when equalizing either method should get the same results. The straight-line (i.e., non -bulging) target is the key. 

Regards,
Wayne


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## Guest

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

Hi Wayne

I'm a new REW user and notice I'm looking at this post over a year after it was written. As a new user to the forum, and the first post I've actually read, I found it really useful and written in plain language. Some great tips for me, as I'm just tuning my studio for the first time using REW. A big thanks.


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## daryn

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

I somehow missed this thread until the past weekend...

I despised a flat response, and was never really happy with a house curve but "tolerated" it because it solved my nasty resonance problems. After using Wayne's hard knee curve, I'm in heaven! I secretly re-eqed while my wife was off to an auction. I was listening to music when she returned home, and she said: "What did you do?! I can feel the bass so much better, but I don't have that dull painful throbbing in my forehead!". That's a ringing endorsement since she normally can't tell a difference even when she knows I've done something.

Thanks Wayne!


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## Chrisbee

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

Thankyou, Wayne. :hail:

Lots to think about and try on a wet Sunday afternoon. I have been adjusting REW target levels from the start to find a best fit to my response curves in REW. It seemed the obvious thing to do. 

I am increasingly of the (humble) opinion that a housecurve should follow the equal loudness curves as closely as possible. The problem is that the curves change constantly with increasing and decreasing average SPLs. I really need a perfect bass transducer and an active digital equaliser which can match the equal loudness curves to average SPLs and my own hearing.

Here's my (near) perfect bass transducer using four fairly broad BFD filters. I think you'll agree that it matches the equal loudness curves nicely at average listening levels on music. 










4 x Acoustic Elegance AEIB15s in an IB manifold. Galaxy 140 SPL meter as test microphone.
I'm hoping that adding four more drivers might give me a bit more useful extension below 12Hz. I'd hate to be missing anything. :bigsmile:


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## brucek

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*



> After using Wayne's hard knee curve, I'm in heaven!


With the new version of REW (presently in beta testing), the need to manually create this type of house curve is obviated by a new logarithmic interpolation feature.









brucek


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## Avus_M3

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

More things to do when I finish my IB

Great info!!!


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## publius

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

While not identical, JBL uses a similar house curve.



















source: http://www.jblsynthesis.com/technology/tech3.aspx?Language=ENG


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## tdamocles

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*









Wayne,

In the example above you are boosting some frequencies a large amount...I thought this was a no-no?:huh:


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## publius

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*



tdamocles said:


> Wayne,
> In the example above you are boosting some frequencies a large amount...I thought this was a no-no?:huh:


he does not seem to be using large positive EQ in order to try to fill-in any large holes (modal suckouts in the frequency response). you are correct in that trying to fill-in such holes would be a losing strategy.

what he _is_ doing is raising up the target level to the midpoint between the peaks and valley's BEFORE applying EQ. the result of this is that some frequencies require significant boost. this is okay and the whole strategy has reduced the overall number of filters. too many filters was identified as being the culprit of degraded sound quality.

the confusion stems from the complicating factor that he has also changed the target response from flat with a gentle roll-off above 60hz (aka 6db house curve) to flat to 30hz, then decreasing to 100hz, then further decreasing after that (aka 6db hard-knee house curve).

the two methods for applying filters can be contrasted in this way:
OLD WAY:
1. apply a large number of filters in order to try to bring frequency response to the old target ideal (6db house curve).

PROBLEM WITH OLD WAY: 
1. because achieving minimal variation from the target response often requires a large number of filters AND because a large number of filters degrades sound quality, the old way results in the enigma of systems that appear to measure well, while not sounding right.

NEW WAY:
1. establish the new "target response" as the midway point between the peaks and the valleys that you measure in your room. (use the 6db hard knee house curve as the target not the typical 6db house curve)
2. apply a small number of filters in order to achieve this target. do not worry about trying to get the response to match the target response perfectly. this is not required for good sound.

BENEFIT OF NEW WAY:
1. 6db hard knee house curve sounds better
2. using fewer parametric eq's sounds better


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## Wayne A. Pflughaupt

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*




Chrisbee said:


> Thankyou, Wayne. :hail:
> 
> I am increasingly of the (humble) opinion that a housecurve should follow the equal loudness curves as closely as possible. The problem is that the curves change constantly with increasing and decreasing average SPLs. I really need a perfect bass transducer and an active digital equaliser which can match the equal loudness curves to average SPLs and my own hearing.


That shouldn’t be necessary. As I discussed in the original house curve article, a house curve is a compensation for the room, not for the equal loudness curve. I’ve never felt like I needed a new curve at different volume settings, only perhaps an overall adjustment of the subwoofer level.


*_______________________________________________________________________*

Wow publius, that was a geat synopsis - simple, eloquent, and to the point! :hail:

tdamocles,

To answer your question a bit more technically, it looks like you’ve dug up the typical knee-jerk reaction to filter boosting: Someone ponders the situation, does a little math and comes up with, "Oh wow, if you boost 10 dB at 430 Hz, your 200 watt amplifier will need 2000 watts at 430 Hz to pull that off!" (Or whatever the correct figure is). 

Where did our mathematician-cum-audio-expert get the idea that an amplifier is running at maximum capacity anytime you have it turned on? Obviously, what’s not being considered is the real-world use of the HT system, which is probably never maxed out. Maxed-out systems sound bad - everyone knows it. They distort and their subs make rude noises. So people typically keep a stressed system turned down, or they upgrade to something with adequate power reserves. 

Assuming the system has adequate headroom, the next thing our mathematician overlooks is _"relative gain"_ (new term I just coined). He also has a fundamental misunderstanding about how filters work, and the way they alter electronic response.

Here’s what happens in the typical "cut only" approach to equalization, three filters in this case. The dotted line is predicted response after equalization; the lower dark green line with smooth curves is the equalizer's electronic response with those filters applied.







​

Before equalizing, the sub level was adjusted based on the 40 Hz peak, since that's where the subs output was loudest. What will happen once that peak is eliminated? As you can see in the predicted response line, overall subwoofer level after equalization is going to be greatly reduced, probably 8-10 dB in this case. Naturally, you're going to have to increase the sub's level to restore the lost gain:







​

So, did we avoided demanding undue power from the amp by not boosting? Well, I dunno. Take a closer look at the equalizer's electronic response, relative to the 75 dB target. Did we make three cuts...







​

...or did we make three boosts, one being a power-robbing shelving filter?







​

It should be plain to see that once levels are re-adjusted, downstream amplifiers and drivers will see gain-reduced filters no differently than boosted filters, because _subtracted filters leave peaks between the cuts._ Any frequency where response is peaking, more power will be demanded.

In my own installation, using the filters you inquired about, we have a somewhat reversed, yet similar situation. I know that makes no sense, but here's the electronic response of the eight filters I was initially using:







​

As you can see, even using cutting filters almost exclusively, I ended up with a honkin' boost at ~53 Hz, and another one at 20 Hz after I re-adjusted the level.

Now let's take a look at the response of the four "hard knee" filters that have mostly-boosted values:







​

Looks pretty scary, huh? I mean, boosted out the wazoo. But since this set of filters increased overall gain so much, I had to turn my sub's level down to get it back to where it was before.

Are you seeing what I mean about "relative gain?" 

Also consider, look what the severely boosted 25 Hz filter in the second graph did to response. You can plainly see that below the peak, response is forced to roll off fairly rapidly. This is ultimately going to conserve more power as opposed to the cutting approach, which left me with a de-facto boosted shelving effect that flattened response below 20 Hz.

As I've been telling folks for years, there's no free lunch when it comes to equalizing: boosting or cutting, you're usually going to end up placing increased demands on your subwoofer amps and drivers, as either method leaves peaks in electronic response. You just have to make sure you have enough headroom going in - it's as simple as that.

There are other issues with boosted filters that concern the equalizer itself, such as the potential for added noise and distortion, but we'll save those topics for another day. Fortunately, their impact on subwoofers is minimal at best.

Regarding my installation specifically, the default level setting on the Chase RLC-1 I use to remote-control my subs reduces the signal level considerably before passing it on to the sub amp. Plus, my equalizers have a 25 Hz high pass filter engaged to roll out the lowest frequencies (my throw-down subs aren't doing much below that point anyway).

Here's some more reading on the subject, from a recent thread.

Regards,
Wayne


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## Andysu

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

Wayne

Is there a formula for the BFQ2496 get this (hard knee house curve)?

Cheers


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## Wayne A. Pflughaupt

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*


Hi Andy,

There is no formula for a particular equalizer. The "formula" (house curve file) is loaded into REW. From there, any equalizer can accomplish the hard knee curve.

Regards,
Wayne


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## bevo2000

*Re: On Minimal EQ, Target Levels, and a Hard-Knee House Curve (long)*

Thank you, Wayne for the contribution.


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## ddgtr

Wayne, thank you for that article, it must be one of the best kept secrets of the forum!!! Just kidding, I am going to start reading it carefully there is a ton of great info in there.


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## Theragingwalrus

Interesting read! But I can't wrap my head around your argument against narrow filters.


> from the perspective of a bass instrument you’re essentially equalizing single notes or perhaps small groups of adjacent notes. If any of those super-tight filters happen to hit dead center on the fundamental of a bass note (there are 12 in an octave), you can literally push or pull them up or down in the mix. While 2-3 dB might not be readily audible with a broad filter, a razor-sharp adjustment hitting single notes can probably make enough of a difference to notice.


Well of course, and that's the idea. If you have a particularly high Q resonance around a frequency, then you'll want a notch filter and not a very broad one. Just because you don't like your EQ filters to be narrow doesn't mean the resonances are somehow less real. Unless you're proposing these narrow resonances are a measuring artifact.

Also:


> The objective of the "modal equalizing" method is not so much to achieve the best-sounding low frequency performance as it is to achieve the best-looking waterfall graph, which is a "3D"-like presentation that shows low frequency ringing, i.e. the time it lakes the low frequencies in your room to fully decay.


Unless you want to implement antisound with REW you can't do anything about the ringing. This is exactly the problem with room equalizing and why its inferior to room treatment: if a certain frequency is emphasized by the room, bringing it down is only a bandaid, because it's still smeared out in the time domain even though the frequency response plot looks flat. Enabling modal filters in REW makes some kind of cumultative CSD look real flat, but the reverb time will not be affected, correct?


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## JohnM

Theragingwalrus said:


> Unless you want to implement antisound with REW you can't do anything about the ringing. This is exactly the problem with room equalizing and why its inferior to room treatment: if a certain frequency is emphasized by the room, bringing it down is only a bandaid, because it's still smeared out in the time domain even though the frequency response plot looks flat. Enabling modal filters in REW makes some kind of cumultative CSD look real flat, but the reverb time will not be affected, correct?


No, not correct. See this article, for example, and there is some info in this post. This post may also be useful. Time domain behaviour can be corrected _at the locations for which the filter has been defined_ if the filter is properly configured. It is important to remember that EQ filters do not modify "the room", they modify the Transfer Function from the point where the speaker is to the point where the mic is. Between those points the room acts like a filter, that overall filtering effect is modified by the EQ applied. The main difficulty for EQ is that the room's "filter" is different for different pairs of speaker & listener positions, so any EQ that hopes to address more than a single position is of necessity a compromise based on the various room filters it is addressing for the listening positions at which it must work. There are many room filters, one for every listening position, but we can only apply one EQ solution.


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## Wayne A. Pflughaupt

Welcome to the Forum, walrus!



Theragingwalrus said:


> Interesting read! But I can't wrap my head around your argument against narrow filters.
> 
> Well of course, and that's the idea. If you have a particularly high Q resonance around a frequency, then you'll want a notch filter and not a very broad one. Just because you don't like your EQ filters to be narrow doesn't mean the resonances are somehow less real. Unless you're proposing these narrow resonances are a measuring artifact.


I’ve seen countless dozens of low-frequency response graphs during the 14 years I’ve been helping folks equalize their subwoofers, and I’ve never seen a peak so sharp and narrow that it required a notch filter (e.g. 1/12-octave or narrower). Typically room modes are readily addressed with filters 1/5- to 1/3-octave. As noted in the article, attempts to equalize every little ripple in response (about the only place you’d ever use a super-tight filter) doesn’t deliver an audible improvement, and may even be detrimental to sound quality in some cases.

Regards, 
Wayne


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## GrizzlyAK

Hi Wayne,

I just wanted to inquire if your original post is still relevant with changes/updates to REW. For example:

(1) What is the importance of the 75 dB reference you refer to. Is it required? I measure at 85 for film sound.
(2) Is the House Curve file entered in Preferences in 5.14 used ONLY in the EQ'ing process?
(3) In the EQ window in REW, the Speaker Type options are Full Range, Bass Limited, Subwoofer, and None. Does that mean you can't EQ a bass managed system where the Main and Sub are running together? Or, would you just use "Full Range" in that case?

Great information, BTW. Thanks for that.

Cheers,
Shane


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## Wayne A. Pflughaupt

GrizzlyAK said:


> (1)	What is the importance of the 75 dB reference you refer to. Is it required? I measure at 85 for film sound.


YOU can use any volume reference you want. :T




> (2) Is the House Curve file entered in Preferences in 5.14 used ONLY in the EQ'ing process?


Pretty much, yes. However, it could be used for setting levels for the drivers in something like a 3-way active system.




> (3) In the EQ window in REW, the Speaker Type options are Full Range, Bass Limited, Subwoofer, and None. Does that mean you can't EQ a bass managed system where the Main and Sub are running together? Or, would you just use "Full Range" in that case?


Yes, you can and you’d use “Full Range.” It’s easy enough to create a house curve file for full-range instead of simply the subwoofer. Naturally, the “hard knee” part is only relevant to the subwoofer itself.

Regards, 
Wayne


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## GrizzlyAK

Thanks Wayne!! :yourock:


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## Nick

Hi Wayne, how do you think about setting up house curves for 2 channel music playback without a sub? I’ve mostly been trying to replicate what you talk about in your posts, but I think they don’t show the full frequency response through, say 10000hz. My room has a big bump at 45hz and another narrower one at 89hz. I have 5 filters I can use in each channel that I play with manually. Are you trying to have a flattish response after 100hz?


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## Wayne A. Pflughaupt

If by “after” you mean “above,” response usually continues to drop, but more gradually. The slope will depend on the size of the room and how close you the listening position is to the speakers.

Regards, 
Wayne


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## Nick

Thanks, Wayne. Yes I meant 'above'. My room is 24x14.5x10. My speakers are dipoles. I have the tweeters about 30 inches from the side walls and 5 feet from the wall behind them. While my speakers are full range, I'm minus a few decibels below about 35 hz. With a resonance at 45hz my peak volume is there even after I apply filters. So, it seems I have to have a curve that slopes down from 45hz by about 5-6 decibels to 100hz. My room also also has a rise around 300hz, so I don't seem to be able to create a downward sloping curve the way I would like to. The 'psychoacoustic setting' looks good, but do people rely much on what it looks like? 

Meanwhile, I'm wondering about some of the products that offer Dirac DRC. It seems that would be a much easier way for a novice to get the room sounding its best. I'm about to search the forums to see if there are discussion about the pros and cons of using something like one of the miniDSP products.


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