Help with understanding the "Alignment Tool" and what to look out for.

[Exponential]

Hello from Manchester, England!

I hope you're all well and not suffering anything unfortunate through these crazy times!

I've been using REW for a couple of years now and am quite competent in it's use but only at a basic level. I absolutely love taking measurements and find it to be a very relaxing and enjoyable experience but it's the "alignment tool" I'm struggling with!
Basically, I don't understand the influence of phase at all, especially at the crossover frequency. I have been focussing on SPL throughout my years using REW and, after speaking to a fellow audio obsessed friend, I quickly learn that phase is even more important than pure SPL!
I typically use an 80hz crossover and always have done but I don't know if this is the most optimal crossover required?

Being a typical English home which is small in comparison to an equivalent American home, I suffer with a nasty room mode at 40hz and, as you'll see, a couple of suck outs at both 200 & 400hz which upsets me but I think that is down to speaker placement.
Before anybody asks, I cannot move my speakers at all and same goes for my subs.

I have a 2.2 set up with the following components:

Spendor A7 loudspeakers
BK Electronics XXLS400DF subwoofers (x2)
Purifi P451 monoblocs
Anthem STR Preamp
Minidsp 2x4HD
OPPO UDP 203 for HT duties including LFE channel (not measured)
Other components that aren't relevant to this thread.

I use the Asynchronous USB input when measuring, a windows 10 laptop and a Minidsp Umik1 mic set at the MLP.

There is no EQ or filters applied with these measurements.

I have my distances set in the STR at:

L & R - 3 metres
Subs (mono) - 2.5 metres

Subs are gain matched at 75dB.

For the subs, I added the combined distances and halved it to come to 2.5 metres.

Minidsp 2x4HD is set to minus 4 on the input level to allow for some adjustment if needed on the output levels.

Attached are my most recent measurements and I would be grateful if someone with the relevant knowledge could take a look and point me in the right direction.

 

[Exponential]

After reading through a good portion of similar threads in this section which ask a similar question to myself then using the info learned, I'm quickly coming to the conclusion that there's not much that will help me as far as getting good integration between my subs and mains. Unless I'm being a bit thick, which is possible...….

I need to learn more I think.

 

[Exponential]

@jtalden I don't suppose you have the time to have a quick look at my MDAT file please? You seem to be the "dude" when it comes to deciphering the information. If so, I would be very grateful.

 

[jtalden]

Oops, I intended to comment, but forgot about this thread.
SPL is much more important than phase. Phase just helps us understand why the SPL is sometimes difficult to manage. The SW XO timing is normally targeted initially on close phase tracking of the direct sound. Often due to room effects the room disrupts the direct sound phase at the LP and it is thus helpful to adjust the timing somewhat to obtain a more favorable SPL of the overall sound arriving at the LP. The XO timing we select will not impact the SPL outside of the XO range.

I just now took a quick look at the mdat. The combined SW SPL response is very favorable for SPL (and phase tracking) so there is no need to change the current SW1 vs SW2 timing. The choice of 80 Hz for the XO also looks to be a favorable one. The phase response is relatively quiet across the 80 Hz XO frequency range for both the SWs and the mains.

For analysis of XO timing using the alignment tool, these are not the correct measurements. Acoustic timing was properly used for the measurements and the 2 SWs were correctly measured using the L channel, but it appears the XO was not active. It is necessary to measure again using these settings.

Setup:

• Mic at LP
• XO active (main speakers set to small)
• SWs set to work as mono
• Acoustic timing active
• Sweep full-range for all 4 measurements (10-20k Hz in this case)

Measurements:

1. FL (alone)
2. FR (alone)
3. SW1 (alone)
4. SW2 (alone)

We can easily combine the SWs and main speakers in REW for the combined results so this just reduces the number of measurements needed.

 

[Exponential]

Hi. Thanks so much for responding! I really appreciate it!

After watching various YouTube videos, I thought the same as you, SPL is king but, after talking to a close friend who is big into 2 channel and Home Theatre, He convinced me that phase alignment is much more important.
That's where things started to go wrong for me as I was chasing my tail looking for the perfect phase alignment but the problem is, I have no idea how to find it!

Please forgive my ignorance but how do you tell if the phase looks good? What do you look for? I understand SPL as that is just a line you can follow which you can tweak to achieve the response you like but I just don't understand the phase in the Alignment Tool.

I have a multitude of measurements so I'll dig out the crossover one's for you to take a look at.

I must warn you I have a nasty peak at 40hz which even the crossover can't get rid of!

Using ARC Genesis cures it though,

I'll post back shortly with some MDATs.

Thanks,

Mike.

 

[Exponential]

Ok, I was being optimistic.

It seems I don't have the necessary files. I'll run some measurements first thing in the morning and post them for you.

In regards to my nasty 40hz peak, do you think stuffing the port could help with that or am I risking damaging the drivers?
The ports are not designed to be stuffed at all (they are a large rectangular port at the bottom rear) but I have cut some foam out anyway to see the effect.

 

[jtalden]

how do you tell if the phase looks good? What do you look for? I understand SPL as that is just a line you can follow which you can tweak to achieve the response you like but I just don't understand the phase in the Alignment Tool.

Phase is confusing for a lot of us. It usually takes some solid science background to really understand it. The alignment tool helps us to use it, but does not help really understanding it. I will try to point what I looked for when I analyze your data. There are many other ways to get favorable SW XO timing that are easier to understand. I like this method because it provides a better understanding of which of the favorable timing options we have chosen.

 

[jtalden]

In regards to my nasty 40hz peak, do you think stuffing the port could help with that or am I risking damaging the drivers?
The ports are not designed to be stuffed at all (they are a large rectangular port at the bottom rear) but I have cut some foam out anyway to see the effect.

If ARC mitigates the peak anyway then it is probable not necessary to worry about it. No problem trying it though. It will not hurt the drivers. It is not likely to help the 40 Hz peak very much if the SW port is tuned near 20 Hz. It will have more impact if the port is tuned significantly higher. plugging the port will normally drop the SPL about 6 dB at the tuning frequency but will have no effect an octave above that.

Please check it out if you like and make the decision on which setup to use before posting the new measurements. Changing the port output will change the timing to some extent so we want be using the correct measurements for the XO timing analysis.

 

[Exponential]

If ARC mitigates the peak anyway then it is probable not necessary to worry about it. No problem trying it though. It will not hurt the drivers. It is not likely to help the 40 Hz peak very much if the SW port is tuned near 20 Hz. It will have more impact if the port is tuned significantly higher. plugging the port will normally drop the SPL about 6 dB at the tuning frequency but will have no effect an octave above that.

Please check it out if you like and make the decision on which setup to use before posting the new measurements. Changing the port output will change the timing to some extent so we want be using the correct measurements for the XO timing analysis.

Sorry for the confusion but I was referring to my mains with regards to the 40hz issue. My subs are sealed.

Regardless, I'll do a few before/after measurements and settle on what I'm happy with then post it here.

 

[jtalden]

The mains SPL should be rolled off pretty well by 40 Hz using an 80 Hz XO. If not, then moving moving the XO up to 90 or 100 should help.

 

[Exponential]

The mains SPL should be rolled off pretty well by 40 Hz using an 80 Hz XO. If not, then moving moving the XO up to 90 or 100 should help.

You'd think so wouldn't you but not in my case. If I set an 80hz xover in the Anthem STR, it DOES a form of an xover but not quite.
I have a measurement of my left speaker with an 80hz xover in place but, as you'll see, it doen't quite work out that way...

 

[Exponential]

The above is just a sample as I've moved my subs since then but you get the idea about the mains continuing to output beyond/below the xover.

 

[jtalden]

Yep, not much rolloff there. Blocking the ports may help a little and will cause no problem for the mains. It may be particularly helpful if they are tuned to 40 Hz. Some processors have a choice of the high pass filter slope applied in the XO. The standard is 12 dB/octave for sealed bookshelf speakers the optional setting is 24 dB/octave for large mains that have strong output well below a 80 Hz XO. Most processors don't have this option. They only provide the standard 12 dB/octave HPF.

 

[Exponential]

Yep, not much rolloff there. Blocking the ports may help a little and will cause no problem for the mains. It may be particularly helpful if they are tuned to 40 Hz. Some processors have a choice of the high pass filter slope applied in the XO. The standard is 12 dB/octave for sealed bookshelf speakers the optional setting is 24 dB/octave for large mains that have strong output well below a 80 Hz XO. Most processors don't have this option. They only provide the standard 12 dB/octave HPF.

Completely agree with you there. Like I said, I'll do a few measurements first thing in the morning for you. Funny thing is though, when Anthem Room Correction is engaged, the roll off at the xover is definitely in play with no bleed-off.

Anyway, I'll post back in the morning (you'll be asleep).

Mike.

 

[Exponential]

Just a quick post with the measurements of my Left speaker without the port plugged and with....

 

[Exponential]

@jtalden

Ok. So I ran a series of measurements this morning with various xovers engaged and these are the results.
As you suggested yesterday, you can't really call them xovers as it doesn't really apply one in a strict sense.

 

[Exponential]

I also plugged my speakers to see what the result would be and it was interesting. Plugging the ports managed to tame the 40hz room mode by around 7dB but didn't eliminate it.

Plugging the ports also affects the xover region but my inexperience doesn't allow me to decide if that's a positive thing or not?

These are the mains plugged at various xovers.

 

[Conrad.]

What happens if you enforce the crossovers in either the minidsp or on the subs themselves?
It might not be ideal for long term (unless you want to cascade your crossovers, I'm doing that, works well), but it should show you whether you're capable of bringing that response down.

 

[jtalden]

Mike,
I looked at all files. I judged the plugged ports on the mains to be the better option. I also judged the 100 Hz XO might work okay for EQ so I did the analysis using those 2 options.

100 Hz XO using plugged mains:
The best phase tracking with a heavy (2 cycle FDW) applied results in a -3ms delay change of the SWs. This setting provides poor SPL support in the XO range at the LP with the FDW remove. This would not be a favorable delay setting, but gives use insight as to the correct delay setting if the room effects were not present.

1. A favorable delay setting was found at -6.62 ms from the current setting after removing the FDW. This timing is shown in measurement 7 and 8 in the attached mdat. It provides strong SPL support in the XO range. The resulting overall SPL appears to be okay for EQ. I tested that judgement using the REW EQ feature and REW found resonable EQ settings to match a typical house curve. It used a little more total gain range than I normally like to employ. It is still within the range that many setups employ so this appears to be a good setup. The attached charts show the SPL, phase tracking and the relationship of the Mains to SWs impulse timing for the original SWs timing vs the new timing.
2. There is another delay setting that I suggest you also test for sound quality. Set SWs delay -16 ms from current setting. There will be a little less SPL support across the XO range. The advantage is in the overall group delay. The setup of #1 is the closer to the conventional setup, but the room effects results in most of the SWs energy to arrive well delayed from the SWs direct sound. As a result the group delay appears to be much larger than normally expected in the bass range. This is not an unusual situation for many setups. This -16ms delay change better accounts for that condition and thus appears much better on the spectrogram chart. Phase tracking and step response charts will not look as good, but many find a significant difference in sound quality. It is worth testing this yourself with a simple change to the SWs delay to see which setting you prefer. I did not post charts for this setting, but this timing is shown in measurement 9 and 10 in the attached mdat.

Other options may work as well so I you want me to analysis 1 additional combination of XO frequency and/or plugged ports I can do that. There are too many options here to analyze them all. I did look at timings with the SWs inverted but did not find any more favorable than the 2 options above.

 

[Exponential]

What happens if you enforce the crossovers in either the minidsp or on the subs themselves?
It might not be ideal for long term (unless you want to cascade your crossovers, I'm doing that, works well), but it should show you whether you're capable of bringing that response down.

Hi Conrad.

To be honest, the crossover application that the minidsp applies is super solid! It does exactly what you ask it to do which puzzles me somewhat as I current own a £250 minidsp 2X4HD which is able to do a better job at a crossover than my preamp which cost more than 10 times its price!

It is only when you apply Anthem Room Correction that a true crossover is applied with no "bleed out" to speak of.
Makes me consider selling my Anthem preamp and putting the RME ADI-2 DAC back in its place.
If it wasn't for the room correction, I would probably do just that!

 

[Exponential]

Mike,
I looked at all files. I judged the plugged ports on the mains to be the better option. I also judged the 100 Hz XO might work okay for EQ so I did the analysis using those 2 options.

100 Hz XO using plugged mains:
The best phase tracking with a heavy (2 cycle FDW) applied results in a -3ms delay change of the SWs. This setting provides poor SPL support in the XO range at the LP with the FDW remove. This would not be a favorable delay setting, but gives use insight as to the correct delay setting if the room effects were not present.

1. A favorable delay setting was found at -6.62 ms from the current setting after removing the FDW. This timing is shown in measurement 7 and 8 in the attached mdat. It provides strong SPL support in the XO range. The resulting overall SPL appears to be okay for EQ. I tested that judgement using the REW EQ feature and REW found resonable EQ settings to match a typical house curve. It used a little more total gain range than I normally like to employ. It is still within the range that many setups employ so this appears to be a good setup. The attached charts show the SPL, phase tracking and the relationship of the Mains to SWs impulse timing for the original SWs timing vs the new timing.
2. There is another delay setting that I suggest you also test for sound quality. Set SWs delay -16 ms from current setting. There will be a little less SPL support across the XO range. The advantage is in the overall group delay. The setup of #1 is the closer to the conventional setup, but the room effects results in most of the SWs energy to arrive well delayed from the SWs direct sound. As a result the group delay appears to be much larger than normally expected in the bass range. This is not an unusual situation for many setups. This -16ms delay change better accounts for that condition and thus appears much better on the spectrogram chart. Phase tracking and step response charts will not look as good, but many find a significant difference in sound quality. It is worth testing this yourself with a simple change to the SWs delay to see which setting you prefer. I did not post charts for this setting, but this timing is shown in measurement 9 and 10 in the attached mdat.

Other options may work as well so I you want me to analysis 1 additional combination of XO frequency and/or plugged ports I can do that. There are too many options here to analyze them all. I did look at timings with the SWs inverted but did not find any more favorable than the 2 options above.

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Hi.

Wow! I honestly can't tell you how much I appreciate your efforts! You're a legend you really are.
You're lucky I live in a different country because I would be round at yours regularly trying to learn from you!

I'm about to go out for the night but I'll look over your findings very soon and get back to you with how I feel about it.

I've kept the foam plugs in my mains and I'll be keeping them there but I think there's a lesson to be learned here.
Always always get a home demo of any speaker before you buy it! Looking at my room and it's problems, especially in the 40hz range, I should've bought a set of sealed bookshelves that roll off around 60hz.
You live and learn I guess (or not in my case as I keep spending money on audio gear).

I'll be in touch over the weekend with my thoughts on your efforts.

Thanks so much!

Mike.

 

[jtalden]

I should've bought a set of sealed bookshelves that roll off around 60hz.

Yes, the XO common for most AVRs and AV pre/pros is to target an acoustic LR-24 XO. They assume sealed bookshelf mains will be used and thus the 12 dB/octave rolloff of the speaker along with the But-12 HPF filter in the AVR ideally results in the target 24 dB HPF response. I commonly see the mains rolloff too shallow even when using sealed bookshelf mains due to room effects. This isn't a fatal problem it just makes the XO range wider and more of an issue to EQ in some cases.

It's now more common to see the newer automated setups effective at creating a favorable SPL response no matter the speakers and room situation. Many room acoustics issues can't be solve with EQ, but creating a smooth SPL is still a major help to any setup.

I hope you will measure the L+SWs and R+SWs for these 2 options prior to EQ to confirm the predicted SPL response. Sometimes mistakes are made. I would also like to see the same 2 measurements after EQ and delay settings are made. Hopefully the resulting SPL will be smooth and very similar for both of them.

If we hit our target I will be interested in your overall impression and if you have a preference for one of the options.

 

[Exponential]

Yes, the XO common for most AVRs and AV pre/pros is to target an acoustic LR-24 XO. They assume sealed bookshelf mains will be used and thus the 12 dB/octave rolloff of the speaker along with the But-12 HPF filter in the AVR ideally results in the target 24 dB HPF response. I commonly see the mains rolloff too shallow even when using sealed bookshelf mains due to room effects. This isn't a fatal problem it just makes the XO range wider and more of an issue to EQ in some cases.

It's now more common to see the newer automated setups effective at creating a favorable SPL response no matter the speakers and room situation. Many room acoustics issues can't be solve with EQ, but creating a smooth SPL is still a major help to any setup.

I hope you will measure the L+SWs and R+SWs for these 2 options prior to EQ to confirm the predicted SPL response. Sometimes mistakes are made. I would also like to see the same 2 measurements after EQ and delay settings are made. Hopefully the resulting SPL will be smooth and very similar for both of them.

If we hit our target I will be interested in your overall impression and if you have a preference for one of the options.

Hi.

Of course I'll re-measure to confirm your estimates! I'm certain that they will track extremely close to what you suggest they will.
I'm not going to let you go to all this effort for nothing mate!

As far as AVR's are concerned, you're correct in that they "assume" bookshelf speakers are being used and that the xover is not exactly a "strict" xover.
I've had Rotel, Anthem MRX series and more recently, Arcam and they all exhibit the same poor xover properties.
The amount of times I've measured my equipment only to be massively disappointed with the xover applied before room correction is applied is ridiculous.

The reason I mention this is because I don't like to listen to music that has room correction applied so I like to apply my own xover but it's pointless as the xover is never truly applied in a meaningful way.

I don't know what your personal opinion is on this but it's infuriating sometimes!

 

[Exponential]

What's your honest opinion of my (in room)
speaker (not subs) response. I find it awful really.
Up to 600hz is particularly terrible.

 

[jtalden]

Well, it's in need of EQ to a good house curve. It is difficult to say if this response is worse than average as I have no way to judge that. There are many more bad rooms than good ones.

Your mic calibration is unusual above 5 kHz for most measurement mics. What mic is this and are you orienting the mic so it that matches the calibration orientation?