# Trying to understand how to do a hard-knee house curve



## BritInVA (Feb 12, 2009)

OK so I like low end bass for movies but not all the way up to 80hz so from what I've read it sounds like a hard-knee house curve may do the trick for me.

So as I understand it the steps are 

1) Play a 80hz sine wave and take note of the SPL reading - using sub + mains but not surround
2) Play a 30hz (or lower) sine wave and increase volume on AVR so perceived loudness is the same as that at 80hz and take note of SPL
3) The difference in SPL is used to create your house curve file. 
4) Within REW, Settings, House Curve import text file.
5) Use filters to equalize your sub only measurement to the new house curve.

So I think I get all that (or do I :dunno: )

In my case SPL difference between 80hz and 30Hz was around 7-8db so that made things easy as I used the file from Ayreonaut.

So I've added the house curve and using an Average of the 6 positions I used for my Audyssey set up I get the following (without any filtering).










When I use REW to find and assign the filters between 20hz & 120hz I get.










Now my question is what do I do for the 20hz to 51.3hz range......is it OK to apply +ve gain in these areas, if yes how much (as these are not nulls)......or do I do something different?

[EDIT] My sub is a HSU STF 2 which I belive goes down to 25hz so not worth boosting anything below 25hx?

Thanks,
Mark


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## brucek (Apr 11, 2006)

> Now my question is what do I do for the 20hz to 51.3hz range


You've kinda missed the point somewhat. If you don't enjoy free room gain down low (as you do not) so you can take advantage of creating a house curve, then you have to either forget about it, or try and push your subwoofer a bit to get something for nothing.

The latter involves increasing the wholesale volume control on your sub, so the level at 20hz matches your aggressive house curve, and then use cut filters to track the target... Hopefully you have the headroom to pull it off. If not, as I said, forget about it..

brucek


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## BritInVA (Feb 12, 2009)

So if I understand what your saying I should 

a) scale back and maybe go for a 5-6db differential
b) turn the gain up on the sub (its set quite low based on my Audyssey settings) to get the 20-50hz above the target curve
c) use filters to reduce rather than increase


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

BritInVA said:


> [EDIT] My sub is a HSU STF 2 which I belive goes down to 25hz so not worth boosting anything below 25hx?


Specs aside, it’s extending down to 20 Hz in your room. :T

It looks like the sub calibrated nicely for REW’s usual 75 dB, but your house curve file has pushed the up the Target to well over 80 dB. So as brucek said, you need to readjust the sub level. Alternately, you could simply re-align the Target. You can do that under the “Target Settings” button to the left of the screen.

Regards,
Wayne


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## BritInVA (Feb 12, 2009)

Wayne, I saw in your article that you used gain on your set up. So if I bring my target down to the 81db and increase the gain on my sub first is it OK to use some gain? 

In the above example just by reducing target to 81db at the lows my gain would be max 4db to get to the line. I know you should not use +V gain to solve nulls but I don't believe thats the case here.

Thanks,
Mark


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

As you correctly note, the only reason to use a gain filter is if you have a depression in response. You don't have any. Just re-align the target to the same level you have there at 30 Hz, and EQ everything above that point down to the hard knee Target. :T

Regards,
Wayne


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## BritInVA (Feb 12, 2009)

Set target level to 71db.......how does this look?










These are the filters










[EDIT] Am I right I don't need filters 5 &6 

Cheers,
Mark


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

Yeah, 5 and 6 are above the crossover point, so they're not needed. Actually you probably didn't need all four of the others. They're all pretty narrow. A couple of broad filters probably should have been enough, with maybe a third doing a little clean-up.

Regards,
Wayne


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## BritInVA (Feb 12, 2009)

Wayne A. Pflughaupt said:


> Yeah, 5 and 6 are above the crossover point, so they're not needed. Actually you probably didn't need all four of the others. They're all pretty narrow.  A couple of broad filters probably should have been enough, with maybe a third doing a little clean-up.
> 
> Regards,
> Wayne


OK, I'll try to manually create the filters rather than going with the REW suggestions. Is there any point in boosting a little around the 20hz?

Also given I've reduced the target for measurement/equalizing should I increase the gain on the subwoofer to compensate? Based on the initial AVR Audyssey setup its set at about 40% on the subwoofer and +3db in the AVR.....I wanted to leave the AVR with a little extra gain as will be driving another amp for bitkickers (they have been disconnected during all measurements).

Cheers,
Mark


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

> OK, I'll try to manually create the filters rather than going with the REW suggestions. Is there any point in boosting a little around the 20hz?


It's generally not a good idea to boost a ported sub below the tuning frequency of the port. I can't find anything on what the port's tuning frequency is for your sub, but I doubt it's that low.

Either way, I don't see any good reason for it. There's not much music with information down that low, and action movies often deliver an artificial boost of their own, so you won't be missing anything.



> Also given I've reduced the target for measurement/equalizing should I increase the gain on the subwoofer to compensate?


There is no "compensation" needed for the equalization process. If you raise the gain and take a new reading, you'll merely have to re-adjust the Target upwards as well. The only compensation you'll have to worry about is re-blending the sub with the mains after you're finished equalizing.

Regards,
Wayne


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## BritInVA (Feb 12, 2009)

Wayne,

Thanks. 

I've now applied 4 filters on the BFD and this is the resultant average accross 6 positions.

This is what looked like without BFD EQ










And now after the BFD EQ










Going to leave things along now and just let my ears decide. Already sounds better on some limited testing.

Cheers,
Mark


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## thebuffman (Feb 4, 2009)

say brit you might want to check out my adventure producing a hard knee curve. it might help you out a bit.

linky


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