That dip in the left channel frequency response around 100 Hz was bothering me. It seemed this might result from improper adjustment of the time delay between woofer and panels. I played pink noise on left channel only and seemed to improve the situation slightly with some adjustment. Then I played stereo and the dip got worse.
At first, I believed this was an old problem I'd never solved before (but, I solved it tonight!). It turned out to be another problem I would shortly discover.
The old problem was that the woofer to panel distances are not equal for right and left. There has always been insufficient space to do that. However, over time, the direction of the difference has changed. Originally, the right panel and speaker were the closest. But when I got the 2+2's, I had to squeeze in everything more away from the door, and not it's the reverse. The right panel and speaker are now the closest.
But for many years, it has seemed that I could NOT set delay times differently for the left and right channels in the Behringer 2496 DEQ's I use for both crossover and EQ. I typically set the delay time after experimentation in the right channel, and then just accepted whatever resulted for the left channel. Sometimes I tried phase reversal of one unit or the other, and sometimes that phase reversal was required (or not) because of how I had most recently replaced a defective plate amplifier in the subwoofers. There is a LONG history here going back 5 years and more if you count the time I was using DCX units which did allow me to set the delays differently. Finding the polarity adjustments on the subwoofers to have weird results, I tended to use an XLR polarity reversal device. I was still using that by mistake until at least November. Currently I am not polarity reversing either subwoofer as I find the two subs sound out-of-phase when I do that when I play them with panels turned off, and I believe that to be an important requirement (even though it more illustrates the out-of-band performance of the subwoofer than the in-band performance).
However, it occurred to me I might have left some polarity change setting set in the left subwoofer because I have to crawl behind equipment and on top of it to read the settings, which is hard to do and I sometimes forget.
So, I did just that, bringing a mirror with me to read all the electronically displayed settings of the left channel PB13 Ultra. I find that once you start adjusting or reading a setting, the only way to get back to the menu is to just let go of the knob, let the display time out after a few seconds, and then press the knob again. Even just letting go, the adjustments you have made remain selected. If you hold the knob down, the sub turns off instead of returning to the main menu. I find this counterintuitive but finally figured this little detail out.
Well, it turned out I had set a 15 degree phase change in just the left subwoofer (it was zero degrees phase change on the right subwoofer). That was not intended, or at least I did not remember it. I readjusted the phase change back to zero. This seemed to flatten the left channel response around 100 Hz. But when playing pink noise in stereo again, it didn't seem to help the 100 Hz suckout much.
Looking at the right channel by itself (and I should keep reminding myself to only do adjustments looking at one channel at a time for the bass) I found the bass had been turned way down. It had been set to -20dB at the PB13 control panel. I flattened the bass out by raising it to -16dB. But when I do that, this channel definitely needs a 100 Hz EQ notch with at least -1.5dB to have flat response, previously I had that notch as big as -6dB.
The current situation at 100 Hz is this: the response in either channel and with uncorrelated pink noise in both channels in flat. But when playing correlated pink noise (centered) there is still a notch. This is still a puzzle. I usually adjust bass using the uncorrelated pink noise finding the correlated pink noise is always tricky. But in some ways, and especially the bass, the correlated pink noise is more like real music.
Despite not fully fixing the 100 Hz dip (it does seem a bit better) actually many other aspects of the bass are now fixed and obviously better. (For example, the right channel was very lean in the bass, and the left channel had a notch and other issues caused by unintended delay.)
Actually, maybe I dialed in the 15 degree delay at some time in the past to try to fix the 100 Hz dip in stereo. But it doesn't.
Future adjustments may be more productive because I've now figured out how to adjust the delay separately in each channel of the Behringer 2496 DEQ. The trick is you have to hold down the "B" button next to the Left/Right switch on the delay page to get it to shift from Left+Right Together to Left or Right Independently. Then you can tap it to adjust only the left or right channel. Not being able to do channel independent adjustments has been a huge problem for 5 years since I replaced the DCX's with DEQ's. It took a careful re-reading of the manual to figure this out, it would have been more intuitive if the independent adjustment were the default but it appears not to be. Behringer considers it a feature you can adjust delays independent regardless of stereo-link or dual-mono modes which normally control how the Left/Right switch works on other pages. But that also means you have to toggle the Right/Left switch between together and independent modes, just for the delay page.
I also adjusted the 45 Hz notches separately for right and left subs. They very much need to be adjusted separately, the left channel requires notching at 45 Hz but strangely the right channel doesn't seem to need it anymore, and I wonder if my Etrap in the far right corner of the hallway helps that. Notching 45Hz when a notch isn't needed adds to undesired depression at 56 Hz.
By the afternoon of January 14, I had gotten impressively flat uncorrelated stereo response (btw, it's flatter than the scale on the right suggests, divide those numbers by about 6 because they're not the kinds of numbers we are used to, they are sixth-octave-bin-weighted dB's, I know this now as I can "move" the graph by an apparent 3-6dB or so with only a 1dB adjustment on my EQ).
This is also showing my new EQ's in the highs I worked out this morning. I've progressed from one "Gundry-Linkwitz" dip to two tailored dips also helping with Acoustat resonance around 6kHz, to now 3 tailored dips in the 2-9kHz region, yielding very smooth and flat response. As I added a new upper notch, I found I had to strengthen the other notches or else they seemed to bulge up. In the end, these are the notches (as of Jan 14 at 1:41 CST):
9037 Hz, 1 octave, -2.5dB
5200 Hz, 1/2 octave, -4.5dB
2729 Hz, 1/3 octave, -2.0dB
I tuned the 9037 notch entirely by looking at pink noise on the RTA. When I set the bandwidth less an one octave, it was clear that there was bulging around the edges of the notch. Only with 1 octave bandwidth, and centered at about 9kHz, did I get essential flatness. It might even look slightly flatter at -3dB, but that made it sound dull, I thought, so I backed off to -2.5dB.
Normally I have used an log dial oscillator and ear to set notch frequencies and width along with rough level. Level is then fine tuned with RTA and music listening. That's my "basic PEQ method" and it's essential for the bass where very steep EQ's are generally required to compensate for room nodes. For upper frequency issues, and especially wide bandwidths, the oscillator isn't much use and just using RTA might even be better. It's certainly easier. I should go back and double-check these adjustments with oscillator. That's the final part of "my method." Always going back and double checking, sometimes using a different method.
Only the people I know who are far removed from science seem to think such relentless double checking is not a good idea. Cranks think you can simply take one perfect test or measurement and be done with tests and measurement. Things don't work that way. Where I've tended to fail is not in relentless repetition, but in establishing the narrative so I remember what I was most recently trying to do by what I did, and so on, so I invent false narratives sometimes and end up going around and around in circles before I get the correct narrative sorted out--if I ever do. (I believe that's not uncommon among audiophiles, only most do this differently--because they depend on highly unreliable and improper listening tests, so poor judgments are initially made, only later to be reversed--if the audiophile is sufficiently open minded to even reverse an earlier bad judgement--many simply double down.)
Establishing the narrative correctly is what I'm trying to do with this blog, and hopefully better this year than in the past. Having a notebook and using it correctly was always my weak spot in science class. I had to work very hard to make things up that I hadn't written down at the time.
Here are the latest EQ settings as of Jan 14 2PM
Here is the Stereo-correlated pink noise response, showing a notch at 112 Hz (either it changed slightly or I imagined it wrong):
Otherwise, it looks pretty good, still showing a bit of peaking at 71 Hz (which I am suppressing with a 13dB notch which doesn't seem justified by the uncorrelated response). The highs look very smooth.
I have dialed back the notches on both sides of the 112 Hz notch, and nothing seems to make much difference. It varies greatly by room position, suggesting it is a center room cancellation mode, not something caused by other EQ's.
As stated (I got something right for once) there is no "100 Hz" or nearby notch at 100 Hz in the Right Channel, in fact there is a slight peak at 100Hz (which is already being suppressed by EQ in this channel so it isn't far worse). At the same time, there isn't ANY peak at 45 Hz, the frequency that has dogged me since I first got subwoofers. The EQ for 45 Hz in the right channel is dialed back to zero. This hasn't always been true in the past, I remember it being as high as -9dB. It may be because of the ETrap in the far right corner of the hallway nearby (but I should test that idea). This channel is not contributing directly (or uncorrelatedly) to the notch at 112Hz in the correlated response.
Nor is there a notch at 112 Hz in the Left Channel, however there is a tiny dip (remember, 6dB on these scales is really like 1dB) at 100 Hz. I am not attenuating 100 Hz in this channel. Conversely, there is a slight rise at 45dB in this channel, which would be far worse if I were not already attenuating it by 4dB.
Both channels need to be heavily attenuated at 40Hz, where there is still a rise showing. But I do not attenuate below 40 Hz. I used to even have difficulty getting a solid 32 Hz for some reason. That appears not to be the case now (but the only thing I seem to have changed is the Acoustats, which aren't even playing at 32 Hz). 32 Hz is musically very important. If I were to attenuate it, I'd weaken that musically critical region, and experience important regions below. I think the bulge at 32 Hz is also position dependent also. But mainly, it's new, I haven't investigated it, and I don't even think it's a problem yet.
Many Audiophiles use Room Curves ramping up to as much as 20dB below 100 Hz. A tiny octave bulge around 32 Hz of 2dB or less is not only not a problem, it's possibly beneficial. (Divide the scale numbers shown by 6 because we are considering the whole spectrum.)
Possibly the solid 32 Hz is because of the center room position. My previous position, before the 2+2's, was about 1/3 from the front.
At first, I believed this was an old problem I'd never solved before (but, I solved it tonight!). It turned out to be another problem I would shortly discover.
The old problem was that the woofer to panel distances are not equal for right and left. There has always been insufficient space to do that. However, over time, the direction of the difference has changed. Originally, the right panel and speaker were the closest. But when I got the 2+2's, I had to squeeze in everything more away from the door, and not it's the reverse. The right panel and speaker are now the closest.
But for many years, it has seemed that I could NOT set delay times differently for the left and right channels in the Behringer 2496 DEQ's I use for both crossover and EQ. I typically set the delay time after experimentation in the right channel, and then just accepted whatever resulted for the left channel. Sometimes I tried phase reversal of one unit or the other, and sometimes that phase reversal was required (or not) because of how I had most recently replaced a defective plate amplifier in the subwoofers. There is a LONG history here going back 5 years and more if you count the time I was using DCX units which did allow me to set the delays differently. Finding the polarity adjustments on the subwoofers to have weird results, I tended to use an XLR polarity reversal device. I was still using that by mistake until at least November. Currently I am not polarity reversing either subwoofer as I find the two subs sound out-of-phase when I do that when I play them with panels turned off, and I believe that to be an important requirement (even though it more illustrates the out-of-band performance of the subwoofer than the in-band performance).
However, it occurred to me I might have left some polarity change setting set in the left subwoofer because I have to crawl behind equipment and on top of it to read the settings, which is hard to do and I sometimes forget.
So, I did just that, bringing a mirror with me to read all the electronically displayed settings of the left channel PB13 Ultra. I find that once you start adjusting or reading a setting, the only way to get back to the menu is to just let go of the knob, let the display time out after a few seconds, and then press the knob again. Even just letting go, the adjustments you have made remain selected. If you hold the knob down, the sub turns off instead of returning to the main menu. I find this counterintuitive but finally figured this little detail out.
Well, it turned out I had set a 15 degree phase change in just the left subwoofer (it was zero degrees phase change on the right subwoofer). That was not intended, or at least I did not remember it. I readjusted the phase change back to zero. This seemed to flatten the left channel response around 100 Hz. But when playing pink noise in stereo again, it didn't seem to help the 100 Hz suckout much.
Looking at the right channel by itself (and I should keep reminding myself to only do adjustments looking at one channel at a time for the bass) I found the bass had been turned way down. It had been set to -20dB at the PB13 control panel. I flattened the bass out by raising it to -16dB. But when I do that, this channel definitely needs a 100 Hz EQ notch with at least -1.5dB to have flat response, previously I had that notch as big as -6dB.
The current situation at 100 Hz is this: the response in either channel and with uncorrelated pink noise in both channels in flat. But when playing correlated pink noise (centered) there is still a notch. This is still a puzzle. I usually adjust bass using the uncorrelated pink noise finding the correlated pink noise is always tricky. But in some ways, and especially the bass, the correlated pink noise is more like real music.
Despite not fully fixing the 100 Hz dip (it does seem a bit better) actually many other aspects of the bass are now fixed and obviously better. (For example, the right channel was very lean in the bass, and the left channel had a notch and other issues caused by unintended delay.)
Actually, maybe I dialed in the 15 degree delay at some time in the past to try to fix the 100 Hz dip in stereo. But it doesn't.
Future adjustments may be more productive because I've now figured out how to adjust the delay separately in each channel of the Behringer 2496 DEQ. The trick is you have to hold down the "B" button next to the Left/Right switch on the delay page to get it to shift from Left+Right Together to Left or Right Independently. Then you can tap it to adjust only the left or right channel. Not being able to do channel independent adjustments has been a huge problem for 5 years since I replaced the DCX's with DEQ's. It took a careful re-reading of the manual to figure this out, it would have been more intuitive if the independent adjustment were the default but it appears not to be. Behringer considers it a feature you can adjust delays independent regardless of stereo-link or dual-mono modes which normally control how the Left/Right switch works on other pages. But that also means you have to toggle the Right/Left switch between together and independent modes, just for the delay page.
I also adjusted the 45 Hz notches separately for right and left subs. They very much need to be adjusted separately, the left channel requires notching at 45 Hz but strangely the right channel doesn't seem to need it anymore, and I wonder if my Etrap in the far right corner of the hallway helps that. Notching 45Hz when a notch isn't needed adds to undesired depression at 56 Hz.
By the afternoon of January 14, I had gotten impressively flat uncorrelated stereo response (btw, it's flatter than the scale on the right suggests, divide those numbers by about 6 because they're not the kinds of numbers we are used to, they are sixth-octave-bin-weighted dB's, I know this now as I can "move" the graph by an apparent 3-6dB or so with only a 1dB adjustment on my EQ).
This is also showing my new EQ's in the highs I worked out this morning. I've progressed from one "Gundry-Linkwitz" dip to two tailored dips also helping with Acoustat resonance around 6kHz, to now 3 tailored dips in the 2-9kHz region, yielding very smooth and flat response. As I added a new upper notch, I found I had to strengthen the other notches or else they seemed to bulge up. In the end, these are the notches (as of Jan 14 at 1:41 CST):
9037 Hz, 1 octave, -2.5dB
5200 Hz, 1/2 octave, -4.5dB
2729 Hz, 1/3 octave, -2.0dB
I tuned the 9037 notch entirely by looking at pink noise on the RTA. When I set the bandwidth less an one octave, it was clear that there was bulging around the edges of the notch. Only with 1 octave bandwidth, and centered at about 9kHz, did I get essential flatness. It might even look slightly flatter at -3dB, but that made it sound dull, I thought, so I backed off to -2.5dB.
Normally I have used an log dial oscillator and ear to set notch frequencies and width along with rough level. Level is then fine tuned with RTA and music listening. That's my "basic PEQ method" and it's essential for the bass where very steep EQ's are generally required to compensate for room nodes. For upper frequency issues, and especially wide bandwidths, the oscillator isn't much use and just using RTA might even be better. It's certainly easier. I should go back and double-check these adjustments with oscillator. That's the final part of "my method." Always going back and double checking, sometimes using a different method.
Only the people I know who are far removed from science seem to think such relentless double checking is not a good idea. Cranks think you can simply take one perfect test or measurement and be done with tests and measurement. Things don't work that way. Where I've tended to fail is not in relentless repetition, but in establishing the narrative so I remember what I was most recently trying to do by what I did, and so on, so I invent false narratives sometimes and end up going around and around in circles before I get the correct narrative sorted out--if I ever do. (I believe that's not uncommon among audiophiles, only most do this differently--because they depend on highly unreliable and improper listening tests, so poor judgments are initially made, only later to be reversed--if the audiophile is sufficiently open minded to even reverse an earlier bad judgement--many simply double down.)
Establishing the narrative correctly is what I'm trying to do with this blog, and hopefully better this year than in the past. Having a notebook and using it correctly was always my weak spot in science class. I had to work very hard to make things up that I hadn't written down at the time.
Here are the latest EQ settings as of Jan 14 2PM
Here is the Stereo-correlated pink noise response, showing a notch at 112 Hz (either it changed slightly or I imagined it wrong):
 |
| Stereo-Correlated Response |
Otherwise, it looks pretty good, still showing a bit of peaking at 71 Hz (which I am suppressing with a 13dB notch which doesn't seem justified by the uncorrelated response). The highs look very smooth.
I have dialed back the notches on both sides of the 112 Hz notch, and nothing seems to make much difference. It varies greatly by room position, suggesting it is a center room cancellation mode, not something caused by other EQ's.
 |
| Right Channel |
 |
| Left Channel |
Both channels need to be heavily attenuated at 40Hz, where there is still a rise showing. But I do not attenuate below 40 Hz. I used to even have difficulty getting a solid 32 Hz for some reason. That appears not to be the case now (but the only thing I seem to have changed is the Acoustats, which aren't even playing at 32 Hz). 32 Hz is musically very important. If I were to attenuate it, I'd weaken that musically critical region, and experience important regions below. I think the bulge at 32 Hz is also position dependent also. But mainly, it's new, I haven't investigated it, and I don't even think it's a problem yet.
Many Audiophiles use Room Curves ramping up to as much as 20dB below 100 Hz. A tiny octave bulge around 32 Hz of 2dB or less is not only not a problem, it's possibly beneficial. (Divide the scale numbers shown by 6 because we are considering the whole spectrum.)
Possibly the solid 32 Hz is because of the center room position. My previous position, before the 2+2's, was about 1/3 from the front.
No comments:
Post a Comment