# Time alignment for subwoofer



## Lightninghoof (Aug 6, 2006)

I asked this question in another thread but thought maybe I should create my own thread about it.

I understand the importance of time alignment (among other factors) for tuning SQ systems and optimizing the sound stage, but my question is, how important is it to time align the subwoofer? Let's say the subwoofer is mounted in the trunk and not physically up front with the 2-way/3-way speakers.

What sort of impact would it have to overall sound, performance, and staging?


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## MarkZ (Dec 5, 2005)

In my opinion (and this probably goes against the grain a bit), it's more important than any of the other speakers. Even simple phase reversal usually results in a very noticable difference, moreso with subs than elsewhere. If you have the ability to introduce time delay or even some sort of phase shifting to your sub setup, do it.


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## Lightninghoof (Aug 6, 2006)

spacemonkey on caraudioforum posted this:

"Time alignment is not important for woofers because of the length of the wave.

here are some examples:

what is the difference between your sub being up front playing 50Hz and in back playing 50 Hz

50Hz = 50 cycles per second = 20ms per wavelength

say the diffference between having the sub up front and in the back is 5 feet, and sound travels at 1100 fps so it takes an extra 4.5ms for the sound to reach your ears if the sub is in the back than if it is in the front. This is less that 1/4 of a wavelength. For most peoples ears, you need more than a wavelength to hear any difference, and your ears are less sensitive at lower frequencies.


Now lets look at front speakers. Say you have 1 tweet 2 feet from your head on the left A-pillar, and another 4 feet from your head on the other A-pillar. These tweets are playing at 10,000Hz

10kHz = 10,000 cycles per second = 0.1ms per wavelength

the pathlength difference between the two tweeters is 2 feet or 1.8ms at the speed of sound. So at 10kHz there is a difference of 18 wavelengths between those tweets. This is a pretty big difference.


Now, add into the fact that relative phase has been altered (the left tweet may not be at the excact same place in the wave as the right) which will cause constructive and destructive interferance, and will actually affect the frequency response of the system. This isnt an issue with subs because they are generally much closer to each other than the length of a wave, so their relative phase to each other should be pretty close."


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## Rbsarve (Aug 26, 2005)

I´D say it´s the difference between having a coherent, dynamic sound and not having it. It is also damn hard to do. 

I usually time align my sub to my right side midbass, then the left side midbass to the right side one, then the right side midrange to my left side midbass, and so on. This helps a lot.


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## MarkZ (Dec 5, 2005)

Lightninghoof said:


> say the diffference between having the sub up front and in the back is 5 feet, and sound travels at 1100 fps so it takes an extra 4.5ms for the sound to reach your ears if the sub is in the back than if it is in the front. This is less that 1/4 of a wavelength. For most peoples ears, you need more than a wavelength to hear any difference, and your ears are less sensitive at lower frequencies.


Keep in mind that time alignment can also be used to adjust the phase (delay less than one period). From that standpoint, it becomes very useful. As I said in my other post, an all-pass filter capable of shifting the phase can also yield dramatic effects. Admittedly, that's not "time-alignment" per se, but it's worth pointing out that time alignment processors can achieve those goals.


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## Exalted512 (Jul 23, 2006)

whats the formula to find how many ms/wavelength on a certain frequency? Or is that just something youd have to look up?
-Cody


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## Ocelaris (Jun 23, 2005)

I think it's a listen and tell what you like... Calculating all the bouncing off the trunk, ceiling, doors etc... to get to your brain, some areas have a better sound than others.

The best subs for home do extensive phase, time, and eq manipulation, and I had customers swear by them... if my brain wasn't in such a funk, I could remember the higher end subs which have even self testing time alignment, phase and a parametric eq.. the microphone testing thingy... some had even a serial port interface for mapping the room... maybe a tad much, but since the waves ARE so long, it's even more important to balance really where they all crash into each other, because you can have the sub 2 feet from your head and have a dead spot... but another foot to the side it's all collecting together... 

I know that wasn't very convincing, but my brain is shot, and you'll just have to look at some of the crazy expensive subs and the features they have... just my .02$


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## chad (Jun 30, 2005)

Regardless, phase and delay are 2 completely different things, you can correct for phase interference between passbands KINDA with delay but not the other way around. In an anechoic environment they can act much like each other, in the real world... there is no way in hell. Because music contains more than one note, delay affects the spectrum, delay conveyed as phase changes infinitely.

I feel in a car the ONLY way to line things up is a delay AND a phase control, with the phase completely adjustable, this combination in MY car is un beatable, I built an adjusatable phase box for my PA not too long ago to match the front loaded subs to the horn loaded bass bins. The difference is AMAZING! Delay would never (never did) work in that situation due to wave compression in the Horn (hence compression horn).

So you should have both. Make sure both drivers have the first pulse hit at the same time time then move the adjustable pulse to match the reference (midbass).

There are countless engineering papers on this, I'll see if i have any in my stash.

There will be huge spelling erros and typos in this reply, I'm not a crack-head, I'm on my wifes REALLY slow computer on one of them split keyboard thinga ma bobbers. Please excuse. Fish out of water here!

Chad


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## MarkZ (Dec 5, 2005)

chad said:


> Regardless, phase and delay are 2 completely different things, you can correct for phase interference between passbands KINDA with delay but not the other way around. In an anechoic environment they can act much like each other, in the real world... there is no way in hell. Because music contains more than one note, delay affects the spectrum, delay conveyed as phase changes infinitely.


Yeah, a set delay period is going to have different implications in terms of phase for different frequencies. But time delay can achieve many of the same results, particularly at and around the crossover point where the problem often lies. And with such a (relatively) narrow bandwidth, you're not talking about a difference of several periods.


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## chad (Jun 30, 2005)

agreed as long as people realize they are different then they can play the same roles in certain instances. went from a ****ty computer to a pocket pc, sorry for no cap$

chad


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## Andy Jones (May 12, 2006)

Try this. Leave your time alignment for the subwoofer set at zero and then start delaying your entire front stage (all speakers the same amount). You will hear the subwoofer start to migrate to the front. Someone recently told me to do this---it works. I don't understand how or why completely--but it works.


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## goodstuff (Jan 9, 2008)

*back up in that ass with the resurrection*










Hmm...I never could hear a change with t/a on the sub. Delaying all the front speakers at once, seems like there would be no change or it would be a wash. Interesting.


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## 6262ms3 (Feb 27, 2008)

I followed the Alpine manual, where you measure the distance to the furthest speaker (usually sub), then subtract the distance to the speaker you are delaying (btw this is all in metres). Divide that by 343 (speed of sound) then multiply by 1000 to get your delay time for that speaker in milliseconds. ie: 2.25m (sub) - 0.5m (fl mid) / 343 x 1000 = 5.1 ms.
So each speaker is delayed in relation the furthest speaker (which you leave at zero). I noticed an improvement in bass clarity, plus the bass moved forward. There was a slight improvement in the front stage imaging (great considering I'm using fail stock speaker locations). I've been happy enough with it that I never tried any other technique.


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## goodstuff (Jan 9, 2008)

6262ms3 said:


> I followed the Alpine manual, where you measure the distance to the furthest speaker (usually sub), then subtract the distance to the speaker you are delaying (btw this is all in metres). Divide that by 343 (speed of sound) then multiply by 1000 to get your delay time for that speaker in milliseconds. ie: 2.25m (sub) - 0.5m (fl mid) / 343 x 1000 = 5.1 ms.
> So each speaker is delayed in relation the furthest speaker (which you leave at zero). I noticed an improvement in bass clarity, plus the bass moved forward. There was a slight improvement in the front stage imaging (great considering I'm using fail stock speaker locations). I've been happy enough with it that I never tried any other technique.


I tried using a tape measure once. Then I threw it out the window and just used my ears.


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## 000zero (Mar 12, 2011)

Rbsarve said:


> I usually time align my sub to my right side midbass, then the left side midbass to the right side one, then the right side midrange to my left side midbass, and so on. This helps a lot.


x2 I just did this in my car and I have more impact coming from my dash. I used a song by Crystal Castles to do it, they usually have very good bass beats.


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## dvcrogers (May 31, 2007)

Delaying everything but the sub moves the sub forward in the same manner as the explanation (bear with me).

Imagine you are standing in an open field with a person 10 feet in front of you and another person 50 feet in front of you. The person 10 feet away is holding your front stage and the person at 50 feet is holding your sub. The sound from your front stage will get to your ears first and the sub later due to the distance. 
Now delay(have the person at 10 feet step back to the 50 foot mark) the front stage and now your ears think the sub has moved forward or up to the front sound stage.

The front is delayed but you do not have a reference mark on the notes to tell you when they SHOULD have arrived. (you kinda only notice when they are late)

Does that make sense?


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## ZAKOH (Nov 26, 2010)

No this does not make sense to me. Based on what I have heard so far, according to psycholinguistics research, humans localize the source of the sound based on the location of the closest source. Based on this view, I should conclude that it seems like a subwoofer in a typical car install, with box in the trunk, does not need any TA for the purpose of obtaining upfront bass feel. For the overlapping bass notes, the sound emanated from your front mids will arrive first, and therefore the source of bass note will be localized to the front.. TA may perhaps be useful for shifting phase of sub bass. Can someone else comment on this thinking? Thanks.


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## ecbmxer (Dec 1, 2010)

Are there any car-specific processors (not a carpc) that can allow separate phase and time delay adjustment of each speaker?


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## chad (Jun 30, 2005)

ZAKOH said:


> No this does not make sense to me. Based on what I have heard so far, according to psycholinguistics research, humans localize the source of the sound based on the location of the closest source. Based on this view, I should conclude that it seems like a subwoofer in a typical car install, with box in the trunk, does not need any TA for the purpose of obtaining upfront bass feel. For the overlapping bass notes, the sound emanated from your front mids will arrive first, and therefore the source of bass note will be localized to the front.. TA may perhaps be useful for shifting phase of sub bass. Can someone else comment on this thinking? Thanks.


It goes even deeper than that my brother.

We all know that cars have a transfer function, which is an instance from where the mode goes from wave-front to pressurisation and you get an incredible amount of gain down low.

What will floor you is using impulse based or transform based time measurement. In the area where the transfer fucntion of the vehicle gets rolling there is an inherent delay, this delay corresponds to the development of said mode change, What I refer to as "the car lighting up"

If I look at the distance measurements with the sub running full range and the hatch open, it's dead nuts on, close the hatch and engage the crossover and that sucker is 35mS away  and I drive a Civic, not a school bus


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## 14642 (May 19, 2008)

Chad, all of this depends on how you're determining the arrival time based on the measurement. The slope of the line is determined by the amount of high frequency info in the signal. It's relatively simple to determine the arrival time of a tweeter. Ths initial peak is very tall and very narrow. The initial impulse is NOT the peak, it's where the line STARTS to rise. We just pick the peak because it's easier and so long as there's plenty of high frequency, the error is so small that it doesn't matter. 

If we measure the impulse response of the subwoofer, especially with a low pass filter, then slope of the line is more gradual. Picking the top of the hump is a big error, because the peak is NOT the arrival time of the initial impulse. It works the same way with a midbass driver. Cross the thing over at 200Hz and you'll measure enough error to throw your TA settings pretty far off. 

If you're making measurements to determine TA, it's best to shut off any low pass filters and then pick the peak. Another trick that works pretty well is to normalize the measurememts (most impulse response measurement tools do this anyway) and then back up from the peak to a point that's about 12dB lower. This minimizes the effect of the slope on your estimation of arival time and minimizes the error.

Despite all of this, there is merit in the arguement that bass waves are so long that TA for the sub doesn't matter. What does matter is the phase of the sub and the phase of the midbass drivers in the band of frequencies they both play. Steep slopes minimize the need for any sub TA and I find that TA on the sub is really not necessary, so long as plenty of attention is paid to proper EQ in the crossover region-in CARS. In a PA, that's not true, since the listeners are MUCH farther away and the arrival time error is much larger when compared to the wavelengths in the crossover region.


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## dvcrogers (May 31, 2007)

ZAKOH said:


> No this does not make sense to me. Based on what I have heard so far, according to psycholinguistics research, humans localize the source of the sound based on the location of the closest source. Based on this view, I should conclude that it seems like a subwoofer in a typical car install, with box in the trunk, does not need any TA for the purpose of obtaining upfront bass feel. For the overlapping bass notes, the sound emanated from your front mids will arrive first, and therefore the source of bass note will be localized to the front.. TA may perhaps be useful for shifting phase of sub bass. Can someone else comment on this thinking? Thanks.


You kinda agreed with everything I posted.


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## chad (Jun 30, 2005)

Andy Wehmeyer said:


> Chad, all of this depends on how you're determining the arrival time based on the measurement. The slope of the line is determined by the amount of high frequency info in the signal. It's relatively simple to determine the arrival time of a tweeter. Ths initial peak is very tall and very narrow. The initial impulse is NOT the peak, it's where the line STARTS to rise.


That's what I do but unfortunately when the software is correcting for amplitude as many do in an "auto mode" even full range, the real impulse gets trumped by cabin gain and things start looking silly quick. Even with the LPF engaged, opening the hatch and windows gives me a real number that's accurate.

Like you, I still prefer to just shut the crossover off on drivers that are not damaged easily... AKA, not tweets.


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## minbari (Mar 3, 2011)

Exalted512 said:


> whats the formula to find how many ms/wavelength on a certain frequency? Or is that just something youd have to look up?
> -Cody


dont think anybody answered this yet.

ms =miliseconds and that is the inverse of freq.

so 1khz = 1/1000 = 1mS
3.3khz = 1/3300 = 0.3mS
100 hz = 1/100 = 10mS


your wavelength is how far that sound travels.

since 1khz is 1mS in time, it will travel 1.1264 ft in 1 mS, that is the wavelength

3.3khz would be .341 ft
100 hz is 11.2 ft

now for the big one 20 hz, 56.2 ft. (this is why bass travels so far and can be heard so far away, very large wavelength!)


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## minbari (Mar 3, 2011)

ecbmxer said:


> Are there any car-specific processors (not a carpc) that can allow separate phase and time delay adjustment of each speaker?


phase and timedelay are kinda the same thing. phase is simply an ac waveform that is leading or lagging in time from a referance point. ALL TA systems use a reference point (usually the subwoofers) and then start introducing time delays from there.

so any of the DSPs that allow independent TA for each channel will do it. I beelive the H700/701, bitone, ms8, etc all do it.


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## SouthSyde (Dec 25, 2006)

Andy Jones said:


> Try this. Leave your time alignment for the subwoofer set at zero and then start delaying your entire front stage (all speakers the same amount). You will hear the subwoofer start to migrate to the front. Someone recently told me to do this---it works. I don't understand how or why completely--but it works.


Maybe in most competition cars the seats are moved wayy back to the point where the subs are closer to the person than the front stage. Therefore delaying the entire front stage allows the arrival time of both the front stage and the sub to be identical.


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## ZAKOH (Nov 26, 2010)

Last week I tried to play with time alignment between the front components and the subwoofer on my head unit. It seems like delaying the front stage by about "3 feet" (I assume approximately 3ms) does seem to improve midbass clarity and impact. Not a night and day difference you get from applying TA to left/right front stage speakers, but still noticeable on a right recording.


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## MinnesotaStateUniversity (Sep 12, 2012)

Gotta love threads like this.

Everyone has their own theory, but yet no verdict

lmfao, on to the next


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## subwoofery (Nov 9, 2008)

MinnesotaStateUniversity said:


> Gotta love threads like this.
> 
> Everyone has their own theory, but yet no verdict
> 
> lmfao, on to the next


What verdict? Did you try to have perfect phase between your subwoofer and your midbass with T/A? Did you try without? 
Interested in hearing your results 

Kelvin


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## MinnesotaStateUniversity (Sep 12, 2012)

subwoofery said:


> What verdict? Did you try to have perfect phase between your subwoofer and your midbass with T/A? Did you try without?
> Interested in hearing your results
> 
> Kelvin


Lulz Kelvin!

No, I didn't try anything. I have an extra Mini DSP I could utilize for my subwoofer, but meh I could sell it for some extra cash. I'm searching the best I can in hopes that I won't need it lol.


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## subwoofery (Nov 9, 2008)

MinnesotaStateUniversity said:


> Lulz Kelvin!
> 
> No, I didn't try anything. I have an extra Mini DSP I could utilize for my subwoofer, but meh I could sell it for some extra cash. I'm searching the best I can in hopes that I won't need it lol.


There's no verdict coz both method works with and without T/A... I find it easier to adjust sub to midbass transition by delaying the sub than just EQing back what is missing (Andy Wehmeyer and the MS-8's method). 
So really that's the reason there's no verdict - whatever is easier... 

Kelvin


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