• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Subwoofer Time Alignment

Ron Texas

Major Contributor
Joined
Jun 10, 2018
Messages
3,294
Likes
3,734
Location
A mysterious place with no name.
#1
Are your subwoofer(s) time aligned with your mains?

How did you do it?

How sensitive is our hearing to this? In other words can we hear a 1' or 2' delay in the subs relative to the mains. In many reviews of subwoofers I read there was no attempt made to time align them.

It is usually the mains which need to be delayed.

My single sub is midway between my mains and 1' closer. The Crown XLS 1502 powering my mains has some delay and the sub has 1 ms more delay, taken out by it's position. In some rectangular rooms this would work for two subs near opposing walls either side of the LP.
 

KozmoNaut

Active Member
Joined
Sep 28, 2019
Messages
299
Likes
553
#2
Automated room/bass EQ usually includes delay or distance adjustment, in order to control phase and time alignment. So a lot of people will have their subwoofers time aligned in this manner. How well that works depends on the system and the conditions, obviously.

In my case, I have two subs at uneven distances to the main listening position, and only a single subwoofer output, so I've tried to set up the subs as well as possible manually beforehand and let the correction do its magic. It puts my main speakers at ~3.4m and the subs at around ~2.2m, which matches up to the average of their distances to the main listening position. It seems to have coherence around the crossover frequency, no "double thumps".
 

RayDunzl

Major Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
10,845
Likes
10,332
Location
Riverview FL
#3
Are your subwoofer(s) time aligned with your mains?
Maybe not so well...

How did you do it?
Here's a way you might look at it;

Using Audacity:
Create a 30hz tone. Zoom in to see samples. Draw a "tick" at the peak of the 30Hz tone. Playback and record. Align the tick times and evaluate the result.

1572124925818.png


For extra credit try other frequencies.

---

That first cycle is hard to output
 
Last edited:
OP
Ron Texas

Ron Texas

Major Contributor
Joined
Jun 10, 2018
Messages
3,294
Likes
3,734
Location
A mysterious place with no name.
Thread Starter #4
@RayDunzl I don't understand your post. I would want to delay the mains. Is Audacity delaying certain frequencies in real time intercepting the output of your playback software?
 

RayDunzl

Major Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
10,845
Likes
10,332
Location
Riverview FL
#5
I would want to delay the mains.
Are you sure?


I don't understand your post.

Showing how I can measure what I've got going, using a contrived test signal.

Using REW I couldn't really make any determination about alignment of lows and highs. Bass "seemed" real late looking there.

Looking with this method, it doesn't. In fact, it looks 2ms early on the main system.

The tick marks the time the treble is received at the listening position relative to the bass. I just arbitrarily set the tick on the peak,

This shows the 30hz bass arrives two milliseconds earlier than the high treble, based on comparing what is heard to what was intended to be produced.

1572129981021.png


I don't see any serious problem here. Nothing more than a millisecond or three, which would mean the bass player is a foot or two closer to me than he might have been, in a live scenario. I doubt I'd notice that.

The above just puts a tick at the peak of the bass wave as a marker, to see if and or how much the bottom and top of the audible range are offset when the signal gets to the listener.

Maybe I'll throw a 2ms delay onto the 2x4HD running the subs, just to line things up that last little bit.

Or maybe I just "got lucky" and it gets goofy at other frequencies. 48Hz would be my next suspect due to room interaction.
 
Last edited:

Sal1950

Major Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
8,194
Likes
7,143
Location
Central Fl
#6
I have dual subs individually time aligned by Audyssey.
I'm not sure how sensitive we are to the issue but since my two subs are at radically different distances from the listening chair I believe it's a good thing to have compensation available. Audyssey Editor measures the distance to Sub 1 at 6.2' and Sub 2 at 16.4'
 
OP
Ron Texas

Ron Texas

Major Contributor
Joined
Jun 10, 2018
Messages
3,294
Likes
3,734
Location
A mysterious place with no name.
Thread Starter #7
I have dual subs individually time aligned by Audyssey.
I'm not sure how sensitive we are to the issue but since my two subs are at radically different distances from the listening chair I believe it's a good thing to have compensation available. Audyssey Editor measures the distance to Sub 1 at 6.2' and Sub 2 at 16.4'
What about the distance to the mains?
 

Sal1950

Major Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
8,194
Likes
7,143
Location
Central Fl
#8
What about the distance to the mains?
L/C/R 12.9/12.5/12.9
LR/RR 6.3/6.3
FHL/FHR 10.8/9.3
RHL/RHR 7.8/5.8
;)

Sub 2 is on the front wall in the left corner.
Sub 1 is in the middle of the rear wall just to the right of the listening chair.
With the Audyssey DSP I haven't noticed the closeness to the rear sub over the front.
 
Last edited:

exaudio

Member
Forum Donor
Joined
Jun 11, 2018
Messages
46
Likes
74
#9
@Ron Texas, timely question. I was just wondering about this. In the past I've always done it by playing a test tone at the cross-over frequency and then adjusting the sub's phase/delay knob to where it sounds the loudest. I'll usually use my Radio Shack SPL meter to dial it in the last little bit. Once I've got it as close as I can, then I run through the Audyssey or Dirac room correction routine.

@RayDunzl, Very clever! I thought, I gotta try that so, I pulled up Audacity and made a test tone at 25Hz and added a "chirp" at each wav peak. I played back the test tone and recorded it with Audacity and my UMIK-1, and voilà, by messing with the phase/delay on the sub, I could see the chirp move forward or backward relative to the wave peak. Cool stuff. Here's what I got:

sub_alignment.png
 

Absolute

Addicted to Fun and Learning
Forum Donor
Joined
Feb 5, 2017
Messages
581
Likes
1,021
#10
If timing in the bass was important you would clearly hear a difference in bass quality when moving closer/further away from a time aligned subwoofer relative to mains. There's no peak sensitivity in the low bass range; according to Geddes you're looking at 200-300 ms before we register low frequency bass notes.
Below 100 hz it shouldn't matter what the timing is relative to the mains. According to Toole we don't even hear the ringing (time domain) in the lower frequencies, so all that matters is even frequency response (which also means even phase response).

Because of this the multi-sub concept is working. Or so they say those people in the know :)
 

RayDunzl

Major Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
10,845
Likes
10,332
Location
Riverview FL
#11
...according to Geddes you're looking at 200-300 ms before we register low frequency bass notes.

That strikes me as unlikely, particularly when listening to someone who is skilled at playing bass...
 

KozmoNaut

Active Member
Joined
Sep 28, 2019
Messages
299
Likes
553
#12
That strikes me as unlikely, particularly when listening to someone who is skilled at playing bass...
An electric bass is mostly a mids-focused instrument.

With something like a contrabass, you're hearing a bunch of overtones.

Strip away the overtones and leave only the fundamentals in the sub-100Hz range and they'll sound indistinct and soft.
 

KSTR

Addicted to Fun and Learning
Joined
Sep 6, 2018
Messages
600
Likes
1,483
Location
Berlin, Germany
#13
When the sub-to-main XO is a true acoustic(!) LR4 at the typical frequency of 80Hz, then some offset of up to +-1m beetwen sub and mains is not overly critical, will result in a dip of a few dB.
But, almost no system really has an resulting true LR4 XO and depending how much unlinked the phase responses are already, any placement offset can have dramatic effect on frequency response and time-domain behaviour.

The only way to do that right is to measure and adjust the XO until it is textbook perfect, phases running strictly on top of each other throughout the whole XO region. The occasional execption are systems that have subs and mains made to exactly complement each other -- alas, very seldom seen in the real world.
Any "universal" sub working together with arbitrary main speakers will most likely be misaligned and is likely to underperform. Once it's aligned it also profits most from phase-unwrapping by a global FIR filter. The "lag-behind" quality of the bass with a LR4 at 80Hz is quite noticable, in other words, most people will be able to hear the difference in blind tests and will prefer the linear phase version.
 

Absolute

Addicted to Fun and Learning
Forum Donor
Joined
Feb 5, 2017
Messages
581
Likes
1,021
#14
Timing and phase are different things, so you can have phase alignment and still be off by one or more cycles in timing. According to research, phase alignment matters but timing does not. I aim for time alignment myself, but that's because I'm a little obsessive about graph perfection and not because I have decided it matters.
Some people claim it matters, but so far I've never seen evidence to support that claim.
 
Joined
May 21, 2019
Messages
71
Likes
94
Location
Columbus, Ohio
#15
Among the multitude of area covered concerning speaker performance covered on his website, Siegfried Linkwitz covered necessary time alignment for subwoofers in the section entitled "Issues in Loudspeaker Design". The URL for this discussion is http://www.linkwitzlab.com/frontiers_5.htm

In this discussion, examples are given for multiple crossover frequencies and different crossover types and slopes. It is an excellent primer on subwoofer integration and a must read.
 
Last edited:

KSTR

Addicted to Fun and Learning
Joined
Sep 6, 2018
Messages
600
Likes
1,483
Location
Berlin, Germany
#16
Timing and phase are different things, so you can have phase alignment and still be off by one or more cycles in timing. According to research, phase alignment matters but timing does not. I aim for time alignment myself, but that's because I'm a little obsessive about graph perfection and not because I have decided it matters.
Some people claim it matters, but so far I've never seen evidence to support that claim.
Well, you can have phase-alignment every 180 degrees (swapping polarity) but only one setting is the correct one for a given XO (assuming it's of the "equal phase type" and that one has matching phases with *unwrappped* phase display (which still a lot of speaker design and measurement software cannot display). Once you introduce a one cycle delay, the region where the phases overlap is much less wide than it should be, and results in signifcant frequency response wiggles. Trading time delay for phase is possible (for example, to make linear-phase higher order crossovers with aligned phases in the anlog domain) but it requieres great care to actually work well.

With today's possibilies I would think we don't need to rely on or wait until some published "scientific evidence" auf audibilty, these test can be done very easily by almost everybody at home now.
 
OP
Ron Texas

Ron Texas

Major Contributor
Joined
Jun 10, 2018
Messages
3,294
Likes
3,734
Location
A mysterious place with no name.
Thread Starter #17
I think what @RayDunzl has done is devise a very clever way to get phase dialed in. It's not timing, though.

In reviews of subwoofers there is no mention of timing. Phase is set by listening for the loudest bass. Except for some newer subs with built in EQ systems, there is no EQ. Placement is arbitrary, usually a corner. Mains are rarely rolled off. I don't know how this could yield a meaningful result, not to mention comparisons to hazy sonic memory.

For me it boils down to whether having perfect timing is more important than having even bass response throughout the room when I have even bass response at or near the LP. Output and bass localization are not an issue.
 

Matias

Major Contributor
Forum Donor
Joined
Jan 1, 2019
Messages
1,620
Likes
2,275
Location
São Paulo, Brazil
#20
How about playback a single step response and measure the arrival? Move and repeat until they match? Is what I would do.
 

Similar threads

Top Bottom