How does my subwoofer REW graph look?

[Matthew J Poes]

I haven't finalised the sub level yet I've just been trying to get a flat response so far. They might come down in volume.

How do I know what headroom I have and how do I know if i'm clipping the sub or minidsp?
My process was to EQ using the miniDSP before Audyssey then tweak it after. These are the filters I used to get the final results.

Band 1 = Frequency 22, Gain -3.6, Q 2. Band 2 = Frequency 32, Gain -16, Q 2.4. Band 3 = Frequency 38, Gain -3, Q 18.9. Band 4 = Frequency 20, Gain -0.2, Q 9.2. Band 5 = Frequency 30, Gain 4.7, Q 4.6. Band 6 = Frequency 45, Gain 8, Q 7. Band 7 = Frequency 59, Gain 4, Q 6. Band 8 = Frequency 59, Gain 4, Q 6. Band 9 = Frequency 50, Gain 2, Q 6. Band 10 = Frequency 60, Gain 1, Q 7.

I don’t know of a way to know based solely on gain values like this. I normally would watch the level meters in the software if available or measure the output of the DsP and look for distortion. You can usually hear it too.

Normally if you avoid much gain things are ok. In your case you have a couple that are a little strong. Like the bands at 45hz and above are all gain, and at 45hz its 8dB which is a lot. I would tend to avoid that.

All that sub gain in the upper band is likely causes you to lose about half of your subwoofers peak output abilities in the sense that you are applying so much gain there. But that is not really an accurate characterization. You applied gain across the middle range of the subs operation and it’s broad, so really it acted more like a level control. Again, this is a scenario where you would have to go by your ear. Does it sound good?

You could measure the actual dynamic limits but that is tricky to do, and If you don’t know what you are doing, can lead to damage to your sub.

 

[Bone9]

When watching the level meters do I do that when playing a sweep or when watching a film or listening to music?

If I avoid those gains i'd have a dip in the response though. How am I supposed to fix that?

Haven't really demo'd much yet as I wanted to check I was safe to do so music sounds good at moderate volume.

 

[Matthew J Poes]

When watching the level meters do I do that when playing a sweep or when watching a film or listening to music?

If I avoid those gains i'd have a dip in the response though. How am I supposed to fix that?

Haven't really demo'd much yet as I wanted to check I was safe to do so music sounds good at moderate volume.

I set the gains based on test tones. I run pink noise and look at the level meters to see roughly where it is. I also listen carefully with just the subs on while playing pink noise and actual music and movie scenes. If o hear obvious distortion that appears to be due to input clipping, I turn the gain down.

As for the gain/dip problem. A few thing: first is that the dips tend to be less obvious than peaks. So they may not be that audible, or at all. Second, it is better to reduce the levels around the dips rather than boost the dips. This avoids running into internal headroom problems as some dsp systems don’t adequately compensate for the boost. If the dips are high Q I would ignore them completely. I would have to go back and look at your boosts again, but basically anything over 5 is probably too narrow to eq. There aren’t hard and fast rules, especially since this kind of PEQ interacts across bands, but in general it is too narrow to EQ.

What I sometimes do if there is an audible dip that needs a boost is apply boost but less than is called for. I might add 3-4 dB and that’s it.

Also, look at the response with no smoothing at all and make sure those dips aren’t cancelation dips that are actually infinitely deep. If they are, then any boost is fruitless. Having said that, you seek to be getting benefit so that seems unlikely. It’s still a good general rule to follow.

 

[Bone9]

All of my graphs always have no smoothing applied to them.

I did massive cuts in the low frequencies and some gains in the higher ones. If the higher gains don't clip the sub what's the problem? Why give me the adjustment if I can't use it?

 

[Matthew J Poes]

All of my graphs always have no smoothing applied to them.

I did massive cuts in the low frequencies and some gains in the higher ones. If the higher gains don't clip the sub what's the problem? Why give me the adjustment if I can't use it?

Eq can be used for lots of things, so you wouldn’t want to restrict certain capabilities just because it can be a bad idea in certain applications.

The primary risk of applying a lot of boost is clipping the amp. If you never clip the amp then it probably isn’t a major concern.

But think of it like this, if you apply an 8dB boost over a narrow bandwidth, as you do with eq, then you automatically reduce the peak output of the sub, when faced with a wider bandwidth signal, by 8dB.

 

[Bone9]

So if my sub has alot of headroom i'll be fine boosting by 8 as long as it doesn't clip at my listening volume?

 

[John Mulcahy]

You could run into problems with material that has high level content around your boost frequency, clipping the source rather than in the sub or its amp. An issue with filling dips is they can be quite localised, so it creates peaks at other positions. Worth checking the result at a few locations around your listening position.

 

[Bone9]

So clipping the miniDSP which is inline between the avr and sub?

I have checked the 3 main listening positions and one position has a boost at that frequency, one is flat and one dips. I do have a graph that I can post when I get home to show you.

 

[John Mulcahy]

Yes, depending on the headroom available - I think you can set an input attenuation to create headroom for boost if necessary, though if you open the miniDSP app and watch the typical input levels you'll see whether there could be any risk of clipping. It isn't a big worry with the settings you have.

 

[Bone9]

I've watched both the input and output while playing a 10 - 200hz sweep at 0 on the avr and -12dbf in the rew settings and the input and output went to about -20 on the clip meters.

 

[Bone9]

Here's the graph of just the sub response in the main 3 seats.

 

[Bone9]

Had a play and now this is my latest graph...

Sub only.

 

[Bone9]

Hi! So I've purchased another subwoofer! I want to use multi sub optimizer to eq the subs and set the delays etc

What Measurements Do I Need to Take?
For each listening position you wish to measure, you need to measure the frequency response of each sub individually at that position. If you are using MSO to integrate the mains and subs, you must also measure the main speaker(s) at each listening position. When using Room EQ Wizard (REW) with an HDMI interface and a USB microphone, you must use the REW acoustic timing reference to obtain time-synchronized measuremnts. The description on the measurements page gives suggestions for measuring both left and right main speakers and subs or just a center speaker and subs. You'll need to keep track of which measurement is which for later reference. When using MSO to optimize both the subs and their integration with the main speakers, HDMI channel 4 must not be used when energizing the subs for the measurements. When using MSO to optimize subs only, using HDMI channel 4 to energize the subs for the measurements is okay.

Namely the acoustic timing reference. Am I ok to use my spl meter for this? What settings do you recommend for my set up?

Spl to motherboard of htpc then HDMI to avr.

Thank you