Room EQ, do's and dont's

[Krunok]

Ultimately that's what matters!

While there is a definite science and process to measuring - difficult rooms and attempting to average responses sometimes give wild results is my experience. Always learn something new along the way though and some of us geeks even consider it fun.

Well, I'm not an expert but here's what I would do if I were you:



I would push down that peak at 330Hz, push down for app 4dB 600-2000 Hz area and slightly raise 2200-4000 dip, and start enjoying my music!

Everything else looks fine. There's that dip at app 12000 but it probably looks worse than it would sound.

I would also check the phase as you have multiple boxes hanging from that ceiling so it may be a complex situation there.

 

[DWPress]

Well, I'm out of EQ taps for that round of measuring so I'm going to start from scratch this week and try a different measuring strategy but I've got previous attempts saved to fall back on that do better. You bet phase is way out of whack! You could rip lumber with the phase response.

Eventually these drivers will make their way into the big boxes or I will create a more seamless baffle integration with the satellites. Current incarnation has some Klipsh 4x10 horns and PRV mids but I've been auditioning these new drivers for a month now and like the flatness of the new Eminence mids and dispersion of the Fountek ribbons so it's time for a new baffle on the boxes I suspect and then the real work begins. I can switch between the old mid/tweets and new additions with a switch and a different configuration load in the miniDSP.

As is:

 

[MRC01]

Ok, I wasted a day last week doing measurements and trying to flatten out the system in different ways too. Question: Any subjective improvement in the sound? ... Sometimes I don't like with what I come up with and then it's back to measuring again....

Don't let the cure be worse than the disease! For example in my room I'm fighting bass suck-out (a deep null) between 50 and 100 Hz. If I EQ more than +6 dB, it restores the frequency response but sounds bloated, worse than I started. So instead, I'm adding new room treatments to weaken that null.
Also, don't fight the small stuff, at least not at first. Measurements can vary more than +/- 3 dB just moving the mic a few inches. One way to handle this is to measure from several different positions, compare the different measurements and fix only the deviations they all have in common. Note: this is not the same as averaging them, which obscures what portions of the different curves were same vs. different!

 

[Dogan]

Don't let the cure be worse than the disease! For example in my room I'm fighting bass suck-out (a deep null) between 50 and 100 Hz. If I EQ more than +6 dB, it restores the frequency response but sounds bloated, worse than I started. So instead, I'm adding new room treatments to weaken that null.
Also, don't fight the small stuff, at least not at first. Measurements can vary more than +/- 3 dB just moving the mic a few inches. One way to handle this is to measure from several different positions, compare the different measurements and fix only the deviations they all have in common. Note: this is not the same as averaging them, which obscures what portions of the different curves were same vs. different!

That, dear Sir, may pose a challenge.

 

[MRC01]

If it's that different from all the various locations in the room where you'll be listening, and none of the curves have anything in common, then there's no point to EQ - because whatever you improve at one location will only make it worse at others.

One alternative would be to limit the comparison to only those locations you will be using most often. See if they have anything in common.

All that said, there still is a point to room treatment. That will weaken the modes that cause many of these differences, making it sound better at most if not all of the locations.

 

[Dogan]

If it's that different from all the various locations in the room where you'll be listening, and none of the curves have anything in common, then there's no point to EQ - because whatever you improve at one location will only make it worse at others.

One alternative would be to limit the comparison to only those locations you will be using most often. See if they have anything in common.

All that said, there still is a point to room treatment. That will weaken the modes that cause many of these differences, making it sound better at most if not all of the locations.

So practically, I should take an RTA measurement around the listening position?

 

[DonH56]

Deep nulls (suck outs) from room modes or SBIR are not normally amenable to EQ and some room correction programs won't even try. For good reason -- they occur because signals are cancelling and thus it is like pouring power into a black hole. It just wastes power and makes the bass at that frequency unbearable elsewhere in the room.

 

[MRC01]

Exactly!
That's why once you've measured to learn the frequencies for these modes, use room treatment to weaken them before resorting to EQ.

Practical advice: as you measure from different locations in the room, the modes are usually the frequencies that give you the biggest swings. That's because they set up standing waves so the peaks & troughs stabilize at certain points in the room. Put differently, the standing wave between 2 walls won't always be a peak. It could be a peak or a trough, depending at what point along the distance between the walls you measure it. In the messy squiggle of graphs posted above, you can see this happening at around 70 and 140 Hz, swings of roughly 40 dB (+/- 20 dB) depending on the location!

 

[MRC01]

The MegaTraps finally arrived. Results are not what I expected - they make the problem worse! They make the 74 Hz null even deeper. Armed with that knowledge, I removed all the bass treatments (all 4 tube traps and the megatraps) from the room. Surprise! The 74 Hz null was entirely gone, bass measured relatively flat. But, spectral decay was worse, and subjectively it sounded worse.

So, the bass treatments do improve spectral decay, but they also cause this 74 Hz null. I relocated them out of the corners, which weakened the 74 Hz null they cause, yet retained most of their improvement to decay. I'm scratching my head trying to grok the fullness of what this is teaching me.

PS: another idea I will try. Test whether this null measures the same steady state, versus a freq sweep. Record 10 seconds of pink noise to the microphone, then FFT it to get the FR curve. Compare that to the curve REW builds from the freq sweep.

PPS: will also try locating them at the wall midpoints instead of the corners. Perhaps that will raise their effective freq range by an octave?

 

[MRC01]

My GIK Scopus T70s arrived yesterday. They are small (2'x2') bass membranes tuned for 70 Hz, which is where my narrow null is. Because some of the 70 Hz null was caused by LBIR to the rear wall, I installed them on the wall right behind the listener position. This was quite effective, raising the null by 6 dB. They work as advertised!

Combined with the MegaTraps in the corners, and the big tube traps I already had, the net effect was so powerful it just sucked the bass out of the room with a big dip from 40 Hz to 90 Hz. If I removed the tube traps, bass response improved in amplitude but got worse in spectral decay; it sounded slow and bloated. The challenge was, how to enjoy the benefit the tube traps give to clean fast decay and nice tight bass, without letting them suck the bass out of the room. To do that I moved them out of the corners. And this worked!

Now this room, which wasn't great to start with, is as good as I can make it. With the room treatments, frequency response from 30 Hz to 20 kHz measures within 5 dB of my target slope, a few parametric EQ bands from the Behringer DEQ2496 bring it within 2 dB of flat, decay is fast and even across full bandwidth, and distortion is quite low. Sounds pretty good. I'll post graphs soon.

 

[MRC01]

Spectral decay without the bass treatments:

The bass treatments reduce the 70 Hz ringing.

Frequency response: grey is with room treatment before EQ, red is after EQ, which is a few parametric bands:

 

[Krunok]

Spectral decay without the bass treatments:
View attachment 25038
The bass treatments reduce the 70 Hz ringing.
View attachment 25039
Frequency response: grey is with room treatment before EQ, red is after EQ, which is a few parametric bands:
View attachment 25040

Can you post Waterfall graphs? Is that FR with both speakers playing?

 

[MRC01]

Meausured from listener position with both speakers playing. I can post the waterfall; what will it show that isn't in the spectrogram?

 

[Krunok]

Meausured from listener position with both speakers playing. I can post the waterfall; what will it show that isn't in the spectrogram?

I think it will show more precisely the effect of reduced ringing at 70Hz.

 

[MRC01]

Sure, though the difference is pretty obvious in the spectrogram, and easy to hear with critical listening.

 

[daftcombo]

Does anyone know if doing room EQ, for instance by setting a room curve and correct phase, can make the THD increase?

 

[kaka89]

Should I measure both speakers individually or together?

When I measure single channel the frequency is fine, but when playing both together it produces a very different graph, there are many dips and I suspect it is because signal canceling each other. Not sure is it normal.

 

[daftcombo]

Should I measure both speakers individually or together?

When I measure single channel the frequency is fine, but when playing both together it produces a very different graph, there are many dips and I suspect it is because signal canceling each other. Not sure is it normal.

Yes, absolutely. If you move the mic a bit, it shouldn't happen.
Hopefully our ears are 20 centimeters away.

I would advise to keep a L+R measurement up to 500 Hz, to have a good idea of the bass level. Above 2 kHz though, individual measurements are to be used.

 

[MRC01]

Does anyone know if doing room EQ, for instance by setting a room curve and correct phase, can make the THD increase?

Yes, I've seen this happen when boosting frequencies. Especially when it comes to nulls, EQ boosting is just throwing energy into a black hole, increasing distortion. Try to fix with room treatment first, because that addresses the root cause. Then use EQ sparingly as a last resort.

 

[daftcombo]

Yes, I've seen this happen when boosting frequencies. Especially when it comes to nulls, EQ boosting is just throwing energy into a black hole, increasing distortion. Try to fix with room treatment first, because that addresses the root cause. Then use EQ sparingly as a last resort.

Thanks, that totally makes sense.
I don't boost dips, I only put a roll off in the highs. Can there be more distortion just because of EQing/phase correcting, but not because of an increase of SPL in an area?