Phase Alignment versus Time Alignment

[Dan Twomey]

I just recently watched a video that covered REWs alignment tool and they used it to align the phases of the
subwoofer and speaker woofer at the crossover point. I found this quite interesting but it made me also think of
driver time alignment where you use (I have a two-way active system) the acoustic timing reference to
time align the drivers.

Thoughts anyone?

Regards,
Dan

 

[Keith_W]

Please read Bob McCarthy's article on phase and time alignment.

In a nutshell, the goal of phase/time alignment is to (1) get rid of egregious delays, and (2) remove nulls at the XO point as much as possible. So you have to do both - time align first, then phase align.

Look at it this way: Take two identical sine waves. If one is 180deg out of phase with the other, it will perfectly cancel. It will be the same at 540deg (180 + 360). The only difference is that the second sine wave is delayed by 1 period. If all you did was to shift the phase by 180deg, you would still be left with a delay of 1 period. At 80Hz, one period is 12.5ms. It's probably marginally audible but it's still better not to have that delay in the first place. So you have to time align first to bring the two speakers roughly into alignment, then use the alignment tool's fine delay adjustment to remove the nulls as much as possible.

 

[Dan Twomey]

I have a basic understanding of phase misalignment.

Many thanks for the link to the article.

Regards,
Dan

 

[Rolledmyown]

Hi folks, I have a slightly different variation of the phasing/delay question, which I am also struggling with at the moment. I'm currently changing my 3-way kit speakers from passive to active and integrating my SVS PB1000 sub with the speakers. I have been doing this in stages. First I did my RH speaker and sub using a multichannel amp miniDSP (both of which I've borrowed from a friend) and now I'm satisfied that going active is an improvement I've shelled-out for 2 Hypex FA123 plate amps. I've fully installed one in my LH speaker and am using delays etc arrived at using the miniDSP and lots of testing. Things are sounding nice, I have to say, but these are early days and I THINK testing has shown I have more work to do.
So, first question, I'm using a laptop/MediaCentre to send digital signals to a Wadia di122, the analogue signal from which is then split to the sub and the plate amp. So I suspect my phase/delay considerations have to include the difference in latency between the sub and its digital filters and the plate amp and its digital filters. Fortunately it seems that the plate amp is pretty quick with its analogue input (350 uS) and the sub is slower, at about 6 mS. Which is good I suspect, because if the plate amp were slower, I'd need to buy a gadget to delay the sub. Am I correct in thinking that?
Second question, because I'm doing a staged upgrade involving single speakers, whenever I've been running my sweeps I'm not able to use the other speaker for the reference chirp as it isn't connected. I have been getting rather whacky delay recommendations from REW alignment tool and also impulse response measurements. Is it OK to have the timing reference coming from the speaker that is also being swept or is that the source of whacky answers (I can't see why)? I've been trying measurements with both the mic close/on axis and also at the listening position.
Regards
PK

 

[fedele]

On my Blog and YT channel you can thind a serie of videos and articles on the topic:

The serie of all my lasts videos (in italian and English) on the recent topics of:
- Time Domain vs Frequency Domain
- Top and Sub Alignments in Time Domain
- Top and Sub Alignments with LINEAR BROADBAND IR
- IR vs Phase
I can't post the links, but you can search my Name for YT channel "Fedele de marco" and look at the blog IL LATO OSCURO DELLA FASE
in our marker (live concert industry) it was alway a misconceptin the difference between what Arrival Time and Phase Shift are.

 

[John Mulcahy]

Fedele De Marco Acoustical Education

Ricerca e Divulgazione in Acustica Applicata al Sound Reinforcement

illatooscurodellafase.wordpress.com

Fedele De Marco Acoustical Education

Fedele De MArco Acoustical Education. Pagina di Divulgazione in Acustica e Sound Reinforcement

www.youtube.com