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TDA (Time-domain analysis) - Measurement Software - Review
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Re: TDA (Time-domain analysis) - Measurement Software - Review
All right, I promised I'd give a walkthrough how to setup a full system. The tape measure method isn't always accurate but can be used as a baseline to start from. There are many methods out there and people swear their method is superior...
This is what I find to be the optimal/easiest way of doing it, I ignore the difference between drivers on the same side to begin with. This is a combined "by ear"/measurement method.
1. First step is to make sure the left and right sides got an equal frequency response,
this is paramount, if L/R differs more than 3dB the entire procedure will fail.
If you use APL, the software automatically fixes the L/R balance. If you got a normal DSP you need to set it up manually with RoomEQ software or such.
We're interested in the first track, this is correlated pink noise (mono recording).
3. In your DSP mute all speakers except midbass drivers, keep both drivers on (left and right).
4. Now we need to determine the acoustic center, if you unsure where this is, it's usually slightly left of the physical center of the dash in most cars. Put a piece of tape there or something else to mark this place.
5. Play the correlated pink noise though both speakers (left/right), delay driver side until you hear the noise coming from the tape marker on dash.
6. Now mute midbass drivers and turn on both midrange drivers (in a 3-way). Repeat step 5.
7. Mute midrange drivers, turn on both tweeters. Repeat step 5.
8. Now all drivers are tuned to the acoustic center. Turn on all speakers + sub. Run TDA, place mic in the middle and about 6 inch in front of the headrest. Don't sit in the seat, it's ok to be in the back seat though.
9. Now we should have something to work with, all areas where the speakers don't overlap should be flat (a black straight line). What we want to look for is offsets and other discrepancies around the crossover of the drivers. This means that the speakers are misaligned to each other by some amount.
*** The tweeter crossover is usually place high in frequency, the wavelengths will be small and therefore a very small delay shift is required to bring them back in phase around the crossover. The lower in frequency we go the bigger delay is needed for a given phase shift. There are multiple way of lining up speakers to eachother within a channel, I believe the "magnitude summing method" is easiest but I don't wanna bring this channel off topic***
10. Now that we already set L/R coherency and just want to set the delay within a channel (the delays between all left OR right speakers), it's important that we don't change the L/R relation delay numbers, we only want to offset it.
Write down the actual delay between midbass drivers, between midrange drivers, between tweeters.
This number might be offset, but not changed.
In other words left midrange might have 1,5ms delay and right midrange 0ms delay. If you set 2ms delay on left and 0,5 on right, there is still 1,5ms delay between these two drivers and the center will not shift. This is what I refer to as an offset.
1. After running the sweep in TDA. It might look something this now;
Here we see that midranges are slightly delayed vs tweeters and the midbass is about 6ms away from midranges. DFR will show the numbers with precision. In this situation we want to delay midranges 6ms and tweeters 6,5ms.
2. Enter numbers + the relative delay between L/R in your DSP and do another sweep.
Should look something like this now. The shift at 50Hz are due to subwoofer group delay, that is a whole other topic...
In a time of universal deceit - telling the truth is a revolutionary act
# (George Orwell)
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