View Full Version : 9887 time correction confusion...

01-03-2008, 11:27 PM
So I was reading the manual for the CDA-9887 specifically about time correction. I understand the concept but having trouble figuring out what exactly to calculate. I understand that you can adjust each individual channel. I have a current 3-way setup, front stage, no rears. Following Example 1 in the manual for front left seat. You take the distance between the listener and the closest/farthest speaker. Take farthest - closest = difference and calculate that into the time correction formula. Take that value and input that as the front left channel. Here is where my questions come in. Do I need to input a time correction value for each channel including subwoofer? If so, how do I do the calculate for each channel? For example for the front right that is my farthest already, so I would come up with a negative value to input for the time correction calculation? *scratches head*

01-03-2008, 11:36 PM
#1. measure distance of all speakers.

#2. Pick the furthest speaker. This will be your reference point.

#3. Take the difference of each speaker from the furthest speaker.

The furthest speaker (usually subwoofer) will be 0.00ms on the t/a, so basically you do no time correction for the furthest speaker. The closest speaker to you should have the most t/a since that's the largest difference.

This is based on temperature since speed of sound is based on temperature, fyi. But, just assume some temperature for the sake of measurements.

For example, the subwoofer is 66 inches and is the furthest speaker. The following is from an excel sheet I made. 2nd number is distance in inches, and 3rd number is time correction in milliseconds (ms).
Subwoofer: 66 0
Drivers Tweeter: 35 2.295628013
Passengers Tweeter: 49 1.258892782
Drivers Midrange: 37.5 2.110496722
Passengers Midrange: 51 1.110787748
Drivers Midbass: 41.25 1.832799785
Passenger's Midbass: 55 0.814577682

So, you see that the driver's side tweeter (which is the closest speaker to you) has the most t/a @ 2.29ms. The subwoofer has 0 t/a.

One thing to keep in mind is reflection. If you have a speaker firing at the windshield you'll want to add some extra distance to account for that the best you can. Also, the excel sheet I use is just to give you an idea of where to start. You should play with the t/a a bit and listen to what you think sounds the best.

Also, I actually added about 8ms to every t/a value I calculated so that the sub has plenty of time to get "up front" and doesn't sound like it's coming from behind as much.

http://i18.photobucket.com/albums/b138/bikinpunk/th_timealignmentpicture.jpg (http://i18.photobucket.com/albums/b138/bikinpunk/timealignmentpicture.jpg)

If you want a copy of the excel file I'll be happy to e-mail you one.

01-03-2008, 11:45 PM
Thanks a bunch bikinipunk, that really cleared things up. So on step #3 wouldn't the farthest speaker always be the subwoofer?

01-03-2008, 11:47 PM

More than likely, but not necessarily.

I suppose you could say that if you have the sub under you or in your center console as I've seen, then it's closer than anything on the passenger's side.

01-04-2008, 12:59 AM
Each click of the dial (increment) is the same as a 1ms....

01-04-2008, 01:32 AM
Thanks guys, got things cleared up :)

01-04-2008, 04:08 PM
I found the easiest way to do it is to use the difference between the two front speakers and dial that time correction into your front left side, then just dial in the time correction for the sub while you're listening to it until it sounds like it's coming from the front.

01-04-2008, 05:31 PM
Thanks for the tip grampi.

01-05-2008, 08:54 PM
nevermind. :)

01-09-2008, 08:04 PM
Ok, getting a little confused now. On the 9887 unit, I see you can input #'s in distance cm or inches for each channel. So I'll just take the distance for each speaker to my head and input that?

01-09-2008, 08:14 PM
Yea. I was looking over the 9887 one day after I posted my response. A friend wanted it and I was doing the research for him and I noticed that they don't do t/a in ms like the other h/u's do, and rather you just input the distance. That makes things much simpler.

01-09-2008, 08:25 PM
Alright, that's what I figured. But here's the kicker. I think it wants you to input "L" which is the following equation, not the actual distance from listener to each speaker.
L = (distance of farthest speaker) - (distance of speaker you want to adjust)
Then you input L into the channels you want to adjust.

From how I understand is you adjust only the ones close to you and by playing around that's what sounded right to me. So I ended up adjusting my drivers tweet/mid/midbass, and leaving the rest at 0.

Because I tried inputing the numbers just by the distances alone and everything sounded way out of alignment. I got around 20cm for my tweet/mid and

01-09-2008, 08:32 PM
You will adjust EVERYTHING except the furthermost speaker.

Like I explained above, you will have a delta x (difference of distance) for every point based on the furthest driver as the reference driver.

01-09-2008, 08:48 PM
Ah I see, so I assume the only one I won't adjust is the subwoofer. Also, The distance I input for each driver is the distance from me to that speaker?

01-09-2008, 09:36 PM

Unless the manual states otherwise, I would assume this is true.

01-10-2008, 01:12 PM
i found that adjusting my time alignment was fairly easy to do just by listening to music. am i crazy for thinking i accomplished a proper setting this way?

01-10-2008, 02:06 PM
Yea with the time alignment you can't advance a speaker but you can delay the other speakers. So seeing as the farthest speaker away has the greatest distance to travel you have to "delay" all the other speakers in relation to that farthest speaker so that all the sound from the other speakers arrive at your ear at the same time. With that formula for L all you are doing is taking the distance from your ear to each speaker in relation to the furthest speaker.

Sounds like you are moving in the right direction, you will just have to make the measurements and then get the difference in distance between each speaker and your farthest away speaker.

01-10-2008, 03:30 PM
Ah ok so that's what I thought. When I tried to set the distance between me and all the speakers to be adjusted the image was going everywhere. Then I found a little paper note in the 9887 manuals which states that particular L formula. After adjusting by math, then by ear. Adjusting be ear is actually a good way. That's how I do my gains. But after the adjustments, the image sounded right.

01-11-2008, 12:07 PM
Nice glad to hear its working out good for ya. I'm currently mulling over the idea of swapping out my W205 for a carPC and a 9887. So hopefully I'll get to fiddle with all these features in the future, either that or just pick up a H701 and move on