# Setting Time Alignment for Rear firing sub in the trunk



## axipher (Oct 7, 2015)

I just ordered a MiniDSP C 6x8 and downloaded the software to start working on my initial tune. I haven't got impulse response measurements figured out in REW yet or how to do the loopback analysis so I'm sticking with calculated TA values for now then I can fine-tune with some listening.

I'm using this site to figure out TA values quickly: http://theguitarforum.net/ta/

I'm measuring from 3 inches in front of my head rest to simulate the middle of my head and making sure to measure to the dust cap on my woofers and to the tweeters dust cap as well.

My question is what distance would I use for my sub woofer if it's in the front of the trunk firing backwards in a sealed box?

The distance from my head to the front face of the box with the cone of the woofer is 72" while the distance to the backside of the box is only 58".

From the sub-woofers dust cap to the rear wall of the trunk is an additional 18".



So from head to closest point of box is 58"

From head to woofer cone on front of box is 72"

Adding in the reflection of the rear trunk wall would make it 108"


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## sqnut (Dec 24, 2009)

Measure left side speakers to left ear and vice versa. Measure the shortest distance from your ear to the speaker cone. For the sub use the 72".


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## axipher (Oct 7, 2015)

sqnut said:


> Measure left side speakers to left ear and vice versa. Measure the shortest distance from your ear to the speaker cone. For the sub use the 72".


Thanks sqnut, I'll give those a try next week then the DSP actually comes in. I'm going to load up few different TA settings and crossover settings on the 4 presets, should make it a little easier to find the right tune.


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## Babs (Jul 6, 2007)

Can you group drivers with the MiniDSP software, so you can adjust multiple drivers at once? If so, good.. Once you've verified your other drivers are all timed and phased in, flip phase to 180 out on the sub, adjust delay of all other drivers together, extending their delay until the sub is audibly completely out of phase at the peak of completely out of phase. Then flip back to 0 phase on the sub. Done. Your sub is now timed and phased in with your mains. Don't be alarmed if the setting you end up with thinks your sub is in the car behind you rather than the trunk .. That's caused by crossover phase shift. What you will end up with is a sub that's timed to "thump" a kick drum nicely in line with your main drivers without lag, and will be in phase with your mid-bass. Do this only after your dialed in with your crossover work and TA on mains.


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## Niick (Jun 3, 2015)

I'be come to the conclusion that distance DOES NOT WORK for in-car subwoofers. I believe this has more to do with the fact that the wavelength of low freq. is physically larger than the propagating medium (volume of air within the car), so, while you CAN think of the direct energy radiating off of a tweeter's dome, for example, you CAN think of this as literally leaving the dome.........propagating thru some distance of air(spending some measure of time)...........reaching your ears......etc., I don't think you can think of subwoofers (in a car) in this way. I tend to visualize subwoofers kinda "compressing and de-compressing" the entire volume of air at once. 


Now, if the subwoofers were those at an outdoor live music venue perhaps, then yes, the low frequencies WOULD travel from the sub..........thru the medium.......to the listener.

But in a car, only those drivers that reproduce shorter (higher freq.) wavelengths behave that way.


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## DDfusion (Apr 23, 2015)

You don't need to TA the sub. Just work the EQ till it blends and it will sit on the dash or hood if you're good.


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## SkizeR (Apr 19, 2011)

DDfusion said:


> You don't need to TA the sub. Just work the EQ till it blends and it will sit on the dash or hood if you're good.


that blending has a lot to do with timing. low frequencies are very phase sensitive


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## DDfusion (Apr 23, 2015)

You can't use basic measurements to align a sub, even more if it's in a trunk. 
Blending works.


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## Niick (Jun 3, 2015)

Sometimes, when I want to see which driver is arriving first in the crossover region I simply apply a bandpass filter to the incoming data and take a trace of the midbass ETC. Then, mute that one and look at the sub's filtered ETC. 

Sometimes, the sub is leading, sometimes the midbass is leading. (I'm talking about with different cars here) In almost all these cars though, the sub is physically farther away.


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## Niick (Jun 3, 2015)

DDfusion said:


> You don't need to TA the sub. Just work the EQ till it blends and it will sit on the dash or hood if you're good.


Now, when you say you don't need to "TA" the sub, do you mean that you don't need to adjust the relative timing between the midbass drivers and the sub? If so, I'm gonna have to disagree here. Almost ALWAYS, unless you DO adjust the relative timing between the two, you won't have good summation thru crossover, sometimes you have downright cancellation, unless you do adjust this timing relationship.........


Edit: but, using a tape measure is NOT the way to optimize this timing relationship. "Nulling" works good here


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## DDfusion (Apr 23, 2015)

Niick said:


> Now, when you say you don't need to "TA" the sub, do you mean that you don't need to adjust the relative timing between the midbass drivers and the sub? If so, I'm gonna have to disagree here. Almost ALWAYS, unless you DO adjust the relative timing between the two, you won't have good summation thru crossover, sometimes you have downright cancellation, unless you do adjust this timing relationship.........
> 
> 
> Edit: but, using a tape measure is NOT the way to optimize this timing relationship. "Nulling" works good here


Ask Andy how the MS-8 does it. My sub is on the hood with no TA. 
If I play around with the EQ close to the crossover point it starts pulling back. 

Op another important part is rattle elimination in the back of the car


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## Jepalan (Jun 27, 2013)

Seems like some terminology confusion going on here. I think everyone is saying the same thing. 

Niick gave a good description of why measuring distance does not work on the sub. I think this is the same thing DDfusion is saying when he says he doesn't time-align his sub. In other words, using bulk delay to align *arrival of the wavefront* with other drivers doesn't work for the sub. Mainly because the biggest issue we are dealing with for the sub is modal effects in the cabin and/or acoustic peaks/nulls in the crossover region.

To address the null/peak issues with the sub, one can use EQ, all-pass filters, or can use the TA adjustment on a processor to tune out the null/peak, but in all three cases you are not "timing aligning" the sub in the "optimizing arrival of the wavefront with bulk-delay" sense.

(Afterthought: I guess another way to deal with a peak in the sub-mid xover region is by leaving a gap between the sub LP and mid HP cutoff freqs)


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## SkizeR (Apr 19, 2011)

either way, there should be delay between the sub and midbass and NOT via distance. the phase response between the sub and midbass crossover is what your going after (remember, crossovers introduce a shift in phase which is what you want to try to correct here). if you have to delay your whole front stage, OR delay your sub to get that, so be it. heres a great article by our very own..

http://medleysmusings.com/subwoofers-and-time-alignment-in-the-car/


and a thread on here from a while back that i randomly remembered mic talking about adding sub delay. at the time, i didnt even understand it, but this thread somehow made me remember this thread

http://www.diymobileaudio.com/forum...ion/133580-time-alignment-sub-i-dont-get.html


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## Niick (Jun 3, 2015)

DDfusion said:


> Ask Andy how the MS-8 does it. My sub is on the hood with no TA.
> If I play around with the EQ close to the crossover point it starts pulling back.
> 
> Op another important part is rattle elimination in the back of the car


So, being that I have a relatively (potentially unique?) unique perspective of aligning/optimizing/tuning different systems in different cars on a regular basis, I definitely HAVE seen scenarios where good summation was achieved thru crossover at the listening position with out having to adjust any delay times between sub and midbass. That's SOME cars/systems/scenarios.

In others, there is a strong cancellation at crossover, as a result of phase induced negative summation, strong cancellation nulls like this CANNOT be addressed in the frequency domain (EQ), they are time (phase) domain problems, that need time domain solutions. 

Unless you happen to be running a HELIX DSP (the only car audio processor I've yet found that has adjustable AllPass filters), you're going to HAVE to address this problem with delay. 

The amount of delay, however, is NOT based on distance. Not at these low frequencies.

I hope that clears it up a little. I probably only made it more confusing for the OP!


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## Niick (Jun 3, 2015)

SkizeR said:


> either way, there should be delay between the sub and midbass and NOT via distance. the phase response between the sub and midbass crossover is what your going after (remember, crossovers introduce a shift in phase which is what you want to try to correct here). if you have to delay your whole front stage, OR delay your sub to get that, so be it. heres a great article by our very own..
> 
> http://medleysmusings.com/subwoofers-and-time-alignment-in-the-car/
> 
> ...


ErinH's method described in the link (Medley's Musings) is a common practice referred to in pro sound as "nulling"


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## SkizeR (Apr 19, 2011)

DDfusion said:


> Ask Andy how the MS-8 does it.



he already answered it




Andy Wehmeyer said:


> OMG.
> 
> First, phase only matters when there is more than one speaker playing the same frequencies. If your sub is 180 degrees out of phase with the rest of your system at 30 Hz and it's the only speaker playing that frequency (within 12dB or so), then it doesn't matter.
> 
> ...


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## sqnut (Dec 24, 2009)

Depending on how your dsp works, you can measure and input distances or delay in m/s to get matching arrival times from each driver. To integrate the sub and mids you need to get the timing right and need to tweak the response in the xover zone.

Lets say 2 way + sub and distances are: Sub 72, LW 38, RW 52, LT 42, RT 55

If you're setting TA in inches: 

Sub 72, LW 38, RW 52, LT 42, RT 55

If you're setting TA in m/s:

Sub 0, LW 2.52 m/s, RW 1.48 m/s, LT 2.22 m/s, RT 1.26 m/s

Both will give you same results. Delay is relative between two drivers. It makes no difference if you delay the sub or not as long as you delay the other drivers accordingly.


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## axipher (Oct 7, 2015)

Tons of great info here for me to read through tonight, just got really busy at work. But I can give some more details about my setup at least, just can't upload pictures.

For the MiniDSP 6x8, on the input side:
- 4 analog + 2 digital channels with mute, gain (+12 to -72db) and 6 PEQ/biquads
- channel routing/summing using a matrix of the input and output channels so you can map any output channel to any combination of the input channels

On the ouput:
- 8 channels RCA analog output
- independent 6 PEQ/biquad
- independent LPF and HPF, 6/12/18/24/30/36/48 dB/octave LR/BW or just Bessel
- invert
- mute
- gain (+12 to -72 dB)
- Time alignment up to 15 ms


So a good amount of options, only thing really missing would be better phase adjustments instead of just 0/180 degrees and each channel can have most of those settings linked to just one other channel so no real grouping for TA and other things.



As for my actual setup, I have Morel Ultra Tempo 6.5" in the door stock location, tweeters in the sails (little triangle panels on the door where the mirrors attach) and have them aimed towards the center of the car, and I plan to install some 3" drivers right in front of the door handles about 6 inches below the tweeters on the doors as well and they will have a slight angle on them towards the center of the car.

Then in the trunk I have a 12" sub-woofer in a sealed box facing the rear of the trunk, but moved all the way forward so I can still use the trunk. This is all being driven off a JL Slash 500/1v2 and 450/4 and JX360/4 to power the new 3" when they come in and maybe a second set of 6.5" Morel's in the front doors right beside the other ones with some custom fiberglass work.


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## Babs (Jul 6, 2007)

My sub delay and phase are both at zero.. I set the mains in phase with the subs, rather than subs in phase with the mains. So given the crossover phase shift, it thinks my sub is 130" away roughly, which of course it's not. But it's dialed in using "180-flip" method, I think pretty good.


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## TallTexan (Dec 14, 2007)

I thought all the kewl kids starting doing the alignment with noise track and ears technique from http://www.diymobileaudio.com/forum/how-articles-provided-our-members/96196-precision-time-alignment-using-only-noise-tracks-your-ears.html

The reader's digest version of this technique to leave the sub at 0 ms and do two drivers at a time with one out of phase, adjusting to where it sounds "worse" on each driver. Be sure to read the discussions at least on the first page.


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## mkvy (Jun 17, 2020)

What you do is measure Listening position (ear) to front of baffle (rear Facing Sub). Then measure Cone to tailgate distance and double it.
In my case it was 65 inches + (81/2 x2) = 82 inches... If you just leave it as the distance to the baffle plane you not be in phase...It will be off, with cancellation between the rear and front... quick beat music will not sound right.. off timing.
When wave travels it bounces off the tailgate... the bounce is the double distance that has to be added..

Upward facing enclosures dont need this addition, or forward facing obviously...

Also open deck hatchbacks with no blocking parcel shelf, quite often dont need this extra bounce distance as the air column is free to move and acts all as one chamber into the cabin

Enclosed trunk type setups with just a few holes in the deck... now these really do need this extra delay

When you get this sweet spot the bass will integrate so well it will appear to be coming from the front. You will be fully enveloped in bass. All the low frequencies will emanate even if you have a subsonic filter in the 30's. It will sound like you have no subsonic filter at all and you will have to double check the DSP just to believe it.. You will also be able to turn the bass up without distortion wheras before you had to limit the subwoofer level alot to get an ok sound

I have a 6th order enclosure. When i open one window to about the same size as the port ,the system its acting like an 8th order and gets even lower and louder


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## dumdum (Feb 27, 2007)

Please delete this as I was typing A reply while someone deleted the guys message


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## mkvy (Jun 17, 2020)

I am not adding delay to the subwoofer. I am adding delay to the front stage (DUHHHHH!) I am measuring the distance of the furthest speaker and adding delay to the front. Just because this thread is 5 years old does not mean the same mistakes cannot happen.
If low frequencies went everywhere at the same time you would not get a delay in thunder after the lightning bolt depending on how far away you are and topography


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## dumdum (Feb 27, 2007)

mkvy said:


> I am not adding delay to the subwoofer. I am adding delay to the front stage (DUHHHHH!) I am measuring the distance of the furthest speaker and adding delay to the front. Just because this thread is 5 years old does not mean the same mistakes cannot happen.
> If low frequencies went everywhere at the same time you would not get a delay in thunder after the lightning bolt depending on how far away you are and topography


The delay of thunder after lightening is due to the speed of sound vs the speed of light 🙈 you clearly don’t do science... at all... you’re previous reply got deleted as I expect this one too...

low frequencies are omni directional, they leave the cone and you get direct sound and also a little reflected sound, but mostly direct sound as bass frequencys will travel through metal easily... that’s why you can hear subs outside a car, but tweeters not so much

I am aware of needing to delay the closest speaker to match the arrival time of the closest, but also the phase of the arriving sound from neighbouring speakers

You stated you need to average the distance due to the sound being reflected from the tailgate... that’s not true... the end... and not how sound travels, read some books by Floyd toole and learn something 👍🏼


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## mkvy (Jun 17, 2020)

dumdum said:


> The delay of thunder after lightening is due to the speed of sound vs the speed of light 🙈 you clearly don’t do science... at all... you’re previous reply got deleted as I expect this one too...


DumDum for sure, you should get a job with the British government, as an advisor


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## dumdum (Feb 27, 2007)

mkvy said:


> DumDum for sure, you should get a job with the British government, as an advisor


Do enlighten me as to which part of the bit you quoted is inaccurate... I do work for the British government thanks as an electrical engineer 👍🏼


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## mkvy (Jun 17, 2020)

dumdum said:


> Do enlighten me as to which part of the bit you quoted is inaccurate... I do work for the British government thanks as an electrical engineer 👍🏼


 That explains things


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## mkvy (Jun 17, 2020)

Its ironic that he who claims inaccuracy puts no input into the thread


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## mkvy (Jun 17, 2020)

dumdum said:


> The delay of thunder after lightening is due to the speed of sound vs the speed of light 🙈 you clearly don’t do science... at all... you’re previous reply got deleted as I expect this one too...
> 
> low frequencies are omni directional, they leave the cone and you get direct sound and also a little reflected sound, but mostly direct sound as bass frequencys will travel through metal easily... that’s why you can hear subs outside a car, but tweeters not so much
> 
> ...


So explain why when i add the tailgate distance between cone and tailgate (x2) to the measurement the system is now timed as evidenced by FFT plot in REW


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## mkvy (Jun 17, 2020)

mkvy said:


> So explain why when i add the tailgate distance between cone and tailgate (x2) to the measurement the system is now timed as evidenced by FFT plot in REW



I am not averaging anything. Let me state again.
Measuring from Listening position to cone (front baffle of enclosure)
Then measuring from cone to tailgate
Then measuring Tailgate to cone (DUH!)
then adding, not averaging all 3 of these distances... wow, that was hard.


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## dumdum (Feb 27, 2007)

mkvy said:


> I am not averaging anything. Let me state again.
> Measuring from Listening position to cone (front baffle of enclosure)
> Then measuring from cone to tailgate
> Then measuring Tailgate to cone (DUH!)
> then adding, not averaging all 3 of these distances... wow, that was hard.


Still doesn’t understand how bass waves travel... can someone explain physics to this guy please... otherwise I will have to message andy and get him to tell floyd he’s got it all wrong all these years

I help plenty of people thanks mr ten post wonder, but if you’d been here a while you’d be aware of that 👍🏼


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## dumdum (Feb 27, 2007)

mkvy said:


> So explain why when i add the tailgate distance between cone and tailgate (x2) to the measurement the system is now timed as evidenced by FFT plot in REW


What’s an fft plot?? Fft is the complex maths that rew uses to calculate all sorts of graphs, it’s not an actual graph... but again you’d know that if you had a clue about what you were talking


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## dumdum (Feb 27, 2007)

mkvy said:


> That explains things


You’ve still not told me why I’m incorrect about lightening and thunder and one being light and one being sound? If you’re going to call someone out at least have the decency to back up what your saying is incorrect, I’m all ears 👍🏼


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## mkvy (Jun 17, 2020)

dumdum said:


> Still doesn’t understand how bass waves travel... can someone explain physics to this guy please... otherwise I will have to message andy and get him to tell floyd he’s got it all wrong all these years
> 
> I help plenty of people thanks mr ten post wonder, but if you’d been here a while you’d be aware of that 👍🏼



Ok, 
How do you yourself set timing to integrate rear firing subwoofers to front stage mids


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## mkvy (Jun 17, 2020)

I am very keen to hear your method, as this thread is the only one i can find about this subject. I explained my method right or wrong. Then you sent an explosive comment which was deleted, but saved in my phone alerts so i could read it. You have basically said that i do not know what i am doing. So, again explain your method so we can learn


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## dumdum (Feb 27, 2007)

It wasn’t an explosive comment... I pointed out it was a 5 year old post, and then I edited my comment to the one I left as yours got deleted

as for how I do it, I measure the phase of the midbass and subwoofer at the drivers seat right between my ears and match them and the arrival time As perfectly as I can to get a full 6db of summation through the crossover point, all errors due to crossovers, phase anomaly’s and time are taken out of the equation, basically there are three lines that all match up in the display using pink noise as a source and you can adjust phase live


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## mkvy (Jun 17, 2020)

dumdum said:


> It wasn’t an explosive comment... I pointed out it was a 5 year old post, and then I edited my comment to the one I left as yours got deleted
> 
> as for how I do it, I measure the phase of the midbass and subwoofer at the drivers seat right between my ears and match them and the arrival time As perfectly as I can to get a full 6db of summation through the crossover point, all errors due to crossovers, phase anomaly’s and time are taken out of the equation, basically there are three lines that all match up in the display using pink noise as a source and you can adjust phase live


What do you use to do that, REW?


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## dumdum (Feb 27, 2007)

mkvy said:


> What do you use to do that, REW?


No, smaart 7, rew is ok, but not as advanced as smaart which is designed to measure using pink noise and extract phase and time information from it as well as freq response also


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## mkvy (Jun 17, 2020)

dumdum said:


> No, smaart 7, rew is ok, but not as advanced as smaart which is designed to measure using pink noise and extract phase and time information from it as well as freq response also


Well, you are right about the right way of doing it. I've done some brain bashing today and learnt REW, i did look at it before but never grasped it... But now i have. The timing will be interesting, i'll run the tests tomorrow. Will be interesting to see how it compares to to the tape measure... 
Right now my system situation is sounding way better by measuring to cone, and cone to tailgate x2. But i still notice a slight timing issue with certain music. Very slight.. I'll post the results tomorrow


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## dumdum (Feb 27, 2007)

mkvy said:


> Well, you are right about the right way of doing it. I've done some brain bashing today and learnt REW, i did look at it before but never grasped it... But now i have. The timing will be interesting, i'll run the tests tomorrow. Will be interesting to see how it compares to to the tape measure...
> Right now my system situation is sounding way better by measuring to cone, and cone to tailgate x2. But i still notice a slight timing issue with certain music. Very slight.. I'll post the results tomorrow


If you’re in the U.K. when this crazy **** is done I’m in notts and love a tuning session

I didn’t get smaart anywhere near our Emma team spl cars last year... and one won every event it went to and came second overall in the season as it missed an event and a second car won every show bar one when it got second and won the overall entry unlimited championship

they will be next level with smaart to do timings of mids/midbass and subs and making them sound as one


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## mkvy (Jun 17, 2020)

dumdum said:


> No, smaart 7, rew is ok, but not as advanced as smaart which is designed to measure using pink noise and extract phase and time information from it as well as freq response also


REW first and then move to smart . I think i tried smart before and used the free trial. But probably can get it on another computer


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## dumdum (Feb 27, 2007)

I meant I’d have a tuning session with it, ie you could come visit 👍

New smaart is smaart 8, I have the older version, it needs a Dual input preamp and xlr mic so you can do transfer functions and phase live

a lot of people use a umik, but I found them a bit hit and miss with rew for timings perhaps due to varying latency for some reason, I think it’s due to the clock being in the usb mic or some such... and you can’t use a umik with smaart due to the combined sound card and mic...


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## mkvy (Jun 17, 2020)

mkvy said:


> REW first and then move to smart . I think i tried smart before and used the free trial. But probably can get it on another computer


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## mkvy (Jun 17, 2020)

dumdum said:


> I meant I’d have a tuning session with it, ie you could come visit 👍
> 
> New smaart is smaart 8, I have the older version, it needs a Dual input preamp and xlr mic so you can do transfer functions and phase live
> 
> a lot of people use a umik, but I found them a bit hit and miss with rew for timings perhaps due to varying latency for some reason, I think it’s due to the clock being in the usb mic or some such... and you can’t use a umik with smaart due to the combined sound card and mic...


Hope we get out of this mess soon, nice offer, we got to get this lockdown kicked soon


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## Mullings (Jan 31, 2016)

It’s good to see you 2 Brits smooth things out, if that were 2 Jamaican’s someone would’ve been dead already lol


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## mkvy (Jun 17, 2020)

OK i think i got it... Very nearly
The thing that was confusing the REW data and giving negative incorrect readings was a little blip to the left, out of this view in the impulse response.. REW was thinking this was the pulse..
Overlaying everything... It looks right..
I actually hooked up a small 3.5 inch full range to double check the timing in the trunk. The green curve is the actual sub.. you read the timing at the beginning of the wave.. unlike full range speakers where they create a definite big spike in the impulse... End result is that its 75 inches distance delay, not 104 that i mentioned before.. the front left is 27 inches distance delay difference to front right... 
So i think im correct to
set front left as about 48 inches distance delay
Front right 27 inches
Rear sub 75 inches..

Just one thing, i set the mic in the middle of the headrest for this test... Maybe i should set the mic left side of headrest for front left.. Right side of headrest for front right... im noticing image is slightly over to the left...

Another session tomorrow.... but ones things for sure... Timing is nearly spot on


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## mkvy (Jun 17, 2020)

edited


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## mkvy (Jun 17, 2020)

New update... I have Smaart 8 demo. My mic is a TRS type, not usb.. I have stereo to mono 3.5mm splitters so i can use my laptops mic in and speaker out as 2 in 2 out.. I have a 3.5mm splitter from the speaker (Headphone) out, one side goes to AUX in of headunit or dsp. The other split feeds into the reference side on mic in.
I have traces showing that in my current setup i needed to adjust a few things! I am now in phase around the crossover area between my rear subs and front mains


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## dumdum (Feb 27, 2007)

mkvy said:


> New update... I have Smaart 8 demo. My mic is a TRS type, not usb.. I have stereo to mono 3.5mm splitters so i can use my laptops mic in and speaker out as 2 in 2 out.. I have a 3.5mm splitter from the speaker (Headphone) out, one side goes to AUX in of headunit or dsp. The other split feeds into the reference side on mic in.
> I have traces showing that in my current setup i needed to adjust a few things! I am now in phase around the crossover area between my rear subs and front mains


Post some pics up, it really is easy when you can see phase and set time alignment also


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