Sunday, January 20, 2008

Drivers alignment

We are moving on the drivers alignment again. To make things a bit easier for me, I set up another XO with L Bressels 10th order filter and no parallel setting. In other words, each driver is only responsible for one section of the frequency.
Sub - up too 120Hz
woofer - 120 - 500Hz
mid 500 - 2000Hz
Tweeter - 2000Hz to 22000Hz

Note that these settings are arbitury and for alignment only. There is also a trick and that is drivers are delayed from the other one by 1000 taps. This is to ensure that the individual peaks can be seen later. Once this crossover is setup, it is then used in the colvolver engine and the logsweep is played for the following conditions
Sweep with all drivers
Sweep with no tweter
Sweep with no mid
Sweep with no woofer
Sweet with no sub

The following picture is the frequency and time domain of all the graphs.

I know, very difficult to see. Here is the blow up picture of the nomid and nowoofer
As you can see from the time domain graph, the pulse from each driver are seen clearly. Now we can than measure that exact location for each driver in terms of taps.
Left: 3125, 4010, 5005, 6000
Right: 3123, 4010, 5005, 6000

Now, we need to check the relative delay reference to the sub
Left:0, 885, 1880, 2875
Right:0, 887, 1882, 2887

Now, we need to compensate the 1000tap delay we set at the crossover
Left:0, -115, -120, -125
Right:0, -113, -118, -123

Negative means delay. The above number means the tweeter arrive to the mic first.
The delay is
Left:0, 115, 120, 125
Right:0, 113, 118, 123

Now align the tweeter:
Left:0, 115, 120, 125
Right:2, 115, 120, 125

Now, this can be used in the crossover setting and all the drivers become perfectly aligned. How do I know whether it make sense? lets look at the delay between the sub and the woofer for the left channel 115taps. 1/44.1K x 115taps = 0.0026sec. Sound travels at 300m/s so the delay is about 0.0026 x 300 = 0.782m which is exactly what I got physically!

There is one more thing I need to do - alignment between the left/right speaker. How? "you can generate a logsweep with Acourate: stereo L/R together. If you record it and convolve it with the inverse logsweep then the resulting pulse should have only 1 peak. Otherwise you have different distances."

Will post the results later


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