# How to time align multiple subs with mini dsp



## mikesp1 (Oct 30, 2012)

I am wondering if someone can help me with procedure of time alignment of Four subs with minidsp and multichannel amp without audisey?

Two subs are in middle of frontwall and another two on middle of backwall.

Thanks!


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## RBTO (Jan 27, 2010)

mikesp1 said:


> I am wondering if someone can help me with procedure of time alignment of Four subs with minidsp and multichannel amp without audisey?
> 
> Two subs are in middle of frontwall and another two on middle of backwall.
> 
> Thanks!


I not sure if I should even be asking this since I'm not a speaker expert, by why are you worrying about time aligning subs? Even at the highest frequencies they typically handle, the wavelength is over 10 feet so time alignment would seem to accomplish little. I understand the need for time alignment in regular multi-speaker arrays since they handle higher frequencies with relatively short wavelengths, but subs tend to add together to create a space filling pressure wave with little or no directivity which would benefit from time alignment.

In any case, it would be a matter of setting one speaker as a reference, use something like an 80 Hz sinewave, and time shifting (delaying) the other feeds (one-at-a-time) by an amount that yields the highest sound pressure at the desired listening position (measured with a mic). I assume you are familiar enough with a DSP to program the delays.

Maybe I'm misunderstanding the question and you want to time align them with the main non-sub speakers??


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## jtalden (Mar 12, 2009)

mikesp1,

If they are time aligned then the direct signals will be maximally supportive of each other at all freq's. If they are mistimed by 90 deg at the XO freq the reinforcement will not be as strong there. [-6 dB compared to the lower freq's.] 

Because of room modes there will be peaks and valleys at your LP. It's possible that there will be a smoother response at the LP with the timing unaligned.

I would say that there is no requirement to time align the SWs as the primary objective is to provide a smooth enough SPL response to allow EQ without undo filter boosts and cuts.

I would suggest you start with the timing aligned and then deviate from that to smooth the response if needed.

Just measure the distance to the LP for both the further pair and the closer pair. Leave 0 ms delay on the further pair and add one ms delay to the closer SW pair for every 345 mm difference in distance. 

You can adjust from that initial setting as needed to smooth the response. I wouldn't expect it to be beneficial in most cases for a change greater than about 4 ms.


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## mikesp1 (Oct 30, 2012)

RBTO said:


> I not sure if I should even be asking this since I'm not a speaker expert, by why are you worrying about time aligning subs? Even at the highest frequencies they typically handle, the wavelength is over 10 feet so time alignment would seem to accomplish little. I understand the need for time alignment in regular multi-speaker arrays since they handle higher frequencies with relatively short wavelengths, but subs tend to add together to create a space filling pressure wave with little or no directivity which would benefit from time alignment.
> 
> In any case, it would be a matter of setting one speaker as a reference, use something like an 80 Hz sinewave, and time shifting (delaying) the other feeds (one-at-a-time) by an amount that yields the highest sound pressure at the desired listening position (measured with a mic). I assume you are familiar enough with a DSP to program the delays.
> 
> Maybe I'm misunderstanding the question and you want to time align them with the main non-sub speakers??


You are correct i want to time align THE front and back subs to THE front speakers because of a dip AT THE crossover frequency 70Hz.


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## BruceA (Feb 13, 2008)

I wonder if the issue is sub phase setting vs mains rather than timing. Is the droop there of you only use the subs ?


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## mikesp1 (Oct 30, 2012)

This Rew graph is with subwoofers time aligned.
As you can see it makes a lot off difference,compared to THE one above, the dip around the crossover point 70hz is completly smoothed out.
Even the hughe dip after THE crossover point AT 200hz is gone.
For me, time align subs does make a big difference.

Note: no equalisation in use


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## jtalden (Mar 12, 2009)

Well done!
The XO range looks great.

I am not sure why the 200 Hz appears to be improved that much as there is no reason it should be effected if the XO is below 100 Hz. It appears the chart has more smoothing and possibly the mic position was shifted or there was some other change that accounts for this. Regardless, it appears the XO range is very smooth now and the SWs are working well together.


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## mikesp1 (Oct 30, 2012)

Thanks Jtalden,

About THE 200hz dip. I can reproduce it over and over by by changing THE time delay for THE subwoofers.
Maybe it is because THE Oppo 105 is using a 12 db octave slope rather than 24 octave in most cross-overs.


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## jtalden (Mar 12, 2009)

Yes, that is probably the explanation.
You may want the measure the SWs separately and see if there is a SPL peak at 200. Possibly there is a room mode due to the SWs locations that is filling in that range in the main's response.

I wish my room setup was so cooperative!


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## mikesp1 (Oct 30, 2012)

jtalden said:


> I wish my room setup was so cooperative!


The problem with us (audiophiles) is that we are constant bussy with optimisation rather than enjoying our music...


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