Trying to understand time alignment of sub woofers

[Yelamanchili manohar]

Hi all

I've been reading up on time alignment of subwoofers, and Iam more confused now than when i started

There is one set of users, who are using subs below 80hz, and have claimed to painstakingly measure the acoustic delays between the main speakers and the sub woofer at the listener position, and have time delayed their main speakers accordingly. So that the speakers and subs are time aligned.

There is a second set, who have their sub woofers running only below 80hz, and have them placed either behind the main speakers, or placed at random in a swarm or distributed bass array with no time alignment. And claim that at frequencies below 80hz, where the bass is omni-directional and the wave lengths are longer than the distance between the speaker and sub woofer, this difference in timing is of no consequence. And one cant hear a difference in a normal sized listening room.


So was curious to hear users opinions on the same. How many have measured and time aligned their subs, and how many are just tuning by ear and happy with the results.

Coming to my use case scenario, I have bass cancellations from my main speaker outputs at approx 40, 60 & 80 hz due to my room dimensions. So I got a 10 inch sub to act as a bass fill for these frequencies. Not sure if one sub at one single location can fill all these bass nulls, in which case Iam not averse to the idea of adding a 2nd sub, though the room is really small and space is at a premium. So my doubt was do these subs also need to be time aligned .

Please feel free to post your thoughts or your experiences. And both are equally welcome. Thanks

 

[Nikhil]

Time alignment is when full spectrum sound including bass/LF emanates cleanly from your main speakers.
In reality phase changes with frequency but for subs set with crossover frequency around 80 Hz you can work with this assumption.

If your sub is right next to your main speakers (say right under the main drivers) you could start with setting your phase angle to zero. As you start moving the sub around the room you will have to play with phase settings to get the sound to what you like it to be. One way to align phase is to play your main speakers with polarity inverted and play a test tone at the crossover frequency. You will need something like the Stereophile Test CD for sample test tones. Then adjust the phase on the sub until you hit the point where you get the least bass i.e. it cancels out with your main speakers. Set your main speakers back to normal polarity and they should be in phase.

Hope this helps. Good luck!


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[Hari Iyer]

Me too never try to time- align below 100hz due to larger wavelength. The beaming effect is more pronounced in the mid frequency. Time- alignment can be easily viewed by the step response. In your main speaker tilting only the front spikes by an inch achieved perfect time alignment to me when measured

 

[efernand1]

Hi all

I've been reading up on time alignment of subwoofers, and Iam more confused now than when i started

There is one set of users, who are using subs below 80hz, and have claimed to painstakingly measure the acoustic delays between the main speakers and the sub woofer at the listener position, and have time delayed their main speakers accordingly. So that the speakers and subs are time aligned.

There is a second set, who have their sub woofers running only below 80hz, and have them placed either behind the main speakers, or placed at random in a swarm or distributed bass array with no time alignment. And claim that at frequencies below 80hz, where the bass is omni-directional and the wave lengths are longer than the distance between the speaker and sub woofer, this difference in timing is of no consequence. And one cant hear a difference in a normal sized listening room.


So was curious to hear users opinions on the same. How many have measured and time aligned their subs, and how many are just tuning by ear and happy with the results.

Coming to my use case scenario, I have bass cancellations from my main speaker outputs at approx 40, 60 & 80 hz due to my room dimensions. So I got a 10 inch sub to act as a bass fill for these frequencies. Not sure if one sub at one single location can fill all these bass nulls, in which case Iam not averse to the idea of adding a 2nd sub, though the room is really small and space is at a premium. So my doubt was do these subs also need to be time aligned .

Please feel free to post your thoughts or your experiences. And both are equally welcome. Thanks

My thoughts and experience.

I have placed a 12 inch SVS sub (SB1000) just under the Center speaker as both these are the ones who do most of the work for any movie. Sub Phase is Normal. AVR Bass Management is Main + Sub. LFE is 100hz. (I did play around with 80hz 90hz, 110hz and 120hz) Not done any time alignment but the output and performance of front speakers and sub is synched well & very good for movies & music for my place. Audyssey settings after calibration is kept as FLAT.