Need advice about REW and house curve

[Zedly]

I am trying to improve my bass management using REW. I have dual SVS SB12-NSD subwoofers. These subwoofers go down to about 20 Hz or so. When I run them, I get a lot of increasing gain to 45-50 Hz and then it decreases to 120 Hz. To get a flatter response while keeping the lower frequencies, I've EQ'd so that 20-40 Hz is flat at 93 dB. However, to do this, the upper frequencies are being brought down by 15-20 dB. I've read that it is not advisable to adjust by this much, and REW gave me a warning message. My thought was that I could EQ to 93-95 dB and then increase the gain on my subs or amplifier to bring up the volume if necessary. Is this approach ok or are there downsides that I am not aware of?

 

[Wayne A. Pflughaupt]

Try it and see, but don't be surprised if it clips like crazy. You've essentially boosted 20 Hz more than 18 dB.

I'm going to hazard a guess that you have the subs at the worst possible location in the room. Put them in a corner with uninterrupted walls in both directions and you'll be amazed what a difference it will make.

Rewards,
Wayne A. Pflughaupt

 

[Zedly]

I don't understand. I'm not boosting anything at all. I'm decreasing dBs at all frequencies. At 20 Hz, it's only been decreased by 1 dB. The top curve is my unequalized response, and the bottom is REW's predicted response.

 

[Wayne A. Pflughaupt]

See here, starting below the graphs where it says “Another no-boosting myth...

https://www.hometheatershack.com/threads/my-first-rew-attempt.28325/page-2#post-262132

Regards,
Wayne A. Pflughaupt

 

[Zedly]

Thanks. I think I am beginning to see the issues here. Unfortunately, one side of my room has no wall at all, and the other side has a stairwell, so the subwoofers are in the only place they can realistically be. Since the room is not ideal, I am trying to make the best I can out of it. Given the response I have, do you have any suggestions about how to improve it?

 

[Wayne A. Pflughaupt]

Don't try to EQ anything below ~30Hz - below that point it's a lost cause.

Regards,
Wayne A. Pflughaupt

 

[Wayne A. Pflughaupt]

Just for grins, does the version of REW you’re using have the ability to turn off the measured response and just show the “action” of filters you’ve employed? You’d be shocked by that visual.

Regards,
Wayne A. Pflughaupt

 

[dasdoing]

Try it and see, but don't be surprised if it clips like crazy. You've essentially boosted 20 Hz more than 18 dB.

well, the point here is to use the headroom. If he put's the volume knob 19dB louder he has the 20Hz where he wants them. the rest is attenuated. there is no boost in terms of fullscale

 

[zermak]

Don't the subs have their own active/passive crossover? It usually let's you cut high frequencies from 80Hz. EDIT: I've seen the backplate on them and it can actually go as low as 30Hz so you can use it to cut off and rew measurements to equalize the peaks.
And what about your mains? I see you cut off at 35Hz with a 6dB/oct slope. Your mains should follow the same slope ideally.

And as long as you don't add you can be safe, adding too much it is risky only because it can cause clips of the input signal.

 

[Wayne A. Pflughaupt]

well, the point here is to use the headroom. If he put's the volume knob 19dB louder he has the 20Hz where he wants them. the rest is attenuated. there is no boost in terms of fullscale

That's functionally the same thing as merely boosting at 20 Hz. It doesn't matter which way you do it - boost @ 20 Hz, or cut everything else down to its level. The result is the same as far as the amplifier is concerned: It's going to see a huge boost at the low end.

Regards,
Wayne A. Pflughaupt

 

[dasdoing]

That's functionally the same thing as merely boosting at 20 Hz. It doesn't matter which way you do it - boost @ 20 Hz, or cut everything else down to its level. The result is the same as far as the amplifier is concerned: It's going to see a huge boost at the low end.

Regards,
Wayne A. Pflughaupt

it is the same, and not the same. If the system has the headroom, ok. if not then you have a (pontential dangerous) problem with the boosting method. with the reducing method you will just find out that now the volume is too low.
there is no problem with boosting at all if all stays in range (digitaly and analog). if the system is capable of producing 83dB at 20Hz, it is capable of producing 83dB at 20Hz.

 

[Wayne A. Pflughaupt]

with the reducing method you will just find out that now the volume is too low.

That's correct. And that "volume too low" issue will be compensated for by boosting the signal somewhere else to make up for what was lost to bad equalizing technique. So, you're right back to where you started - there's no free lunch. On top of that, using the equalizer as a volume control to reduce everything virtually across the board, like you're proposing, is really poor form.

there is no problem with boosting at all if all stays in range (digitaly and analog). if the system is capable of producing 83dB at 20Hz, it is capable of producing 83dB at 20Hz.

I think you're talking headroom in the signal path, and I don't disagree. However, I'm talking amplifier headroom. It's audio 101 that any equalizing places demands on amplifier headroom, as well as the subwoofer driver, and extreme equalizing chews up both pretty fast.

But certainly, at the end of the day all that matters is if one has sufficient amplifier power and a subwoofer system to accommodate it. If someone has 10 18" high-excursion subwoofers pushed by 9,000 watts in a 14' x 14' room, they can probably boost to their hearts content. But try what you're recommending on a 8" sub with a 150 watt amp - well, no one wants to listen to that even if the sub survives it.

Regards,
Wayne A. Pflughaupt

 

[Zedly]

I will be doing some more tests in a couple weeks (I am having a new A/V stand made, and the positioning of things will be changing). One thing I have learned in the meantime is that my measurements may be running into the limits of long-term output compression. Based on an image from Audioholics, I found that, at the SPLs I was measuring at (>100 dB), the output compression is keeping the response from being flat until almost 50 Hz. Since I never listen that loud, when I remeasure, I'm going to try take measurements at a 85 dB level to see how it looks.

 

[Wayne A. Pflughaupt]

Seventy-five dB is perfectly fine for measurements. A measurement simply gets you information on your system's frequency response. You don't get better "information" by measuring at high SPL.

Regards,
Wayne A. Pflughaupt

 

[dasdoing]

that "volume too low" issue will be compensated for by boosting the signal

well, that is not possible without clipping.
unless you are talking about boosting the filter signal back to near fullrange, which is necessary. after creating a filter the digital peak level should be tested anyways.
the whole idea of reducing is that you find the limits without risks (and yes, I am talking about the analog limits).
(also in REW with auto eq it is the only way to extend LFs, as REW want do that with boosting (probably because of the risks I mentioned))

now @Zedly is right that you also have to stay out of the limiters range. the resulting filter should always be remeassuered in REW at reference level.
the sub in the example has no problems being EQd flat down to 20Hz @83dB.

 

[dasdoing]

Seventy-five dB is perfectly fine for measurements. A measurement simply gets you information on your system's frequency response. You don't get better "information" by measuring at high SPL.

Regards,
Wayne A. Pflughaupt

he is trying to find out if the limiter kicks in at that level

 

[dasdoing]

I don't think meassuring very high is a good idea. meassure with the filter you created. if it rolls off, after you adjusted volume it is the limiter

 

[Wayne A. Pflughaupt]

well, that is not possible without clipping.

Exactly. That's why the cutting scheme ultimately works no better than the boosting scheme: You end up at the same place in the end.

Regards,
Wayne A. Pflughaupt

 

[daftcombo]

I don't understand the replies you gave to the OP.

The solution is simply to mess with REW setting to get a flat blue curve (target) and then apply EQ calculation. Then you'll have the EQ settings you need. That's the whole point of room EQ.

Edit: the advice not to touch anything below 30 Hz and aim at a flat curve only above is wise though.

 

[dasdoing]

the advice not to touch anything below 30 Hz and aim at a flat curve only above is wise though.

look at the blue curve and trace a flat line at 85dB. if you reduce all what is above you have a flat response down to 19HZish. and by looking at it this way it should be totaly understandable that doing so is totaly in the range of capatilibies of the sub, and more so, not doing it is a waste imho.