Time Alignment in Car via Impulse Response - Page 3 - Home Theater Forum and Systems - HomeTheaterShack.com
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post #21 of 51 Old 07-05-15, 12:07 PM Thread Starter
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Re: Time Alignment in Car via Impulse Response

Posting some new measurements taken today. These are only the right side horn and midbass drivers.
No delays applied. Only crossovers have been set, and a tiny bit of EQ to take down some peaks.

I'll be interested to see if we can determine anything about the phase from these?

I was attempting for an acoustic crossover @ 1200Hz. Linkwitz 24 slopes.
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post #22 of 51 Old 07-05-15, 02:10 PM
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Re: Time Alignment in Car via Impulse Response

I reviewed the data.
As before, the IRs show very strong early reflections that make it impossible for me to adjust timing using the phase tracking method. If this were in a room situation I would question if both L+R Horns and L+R MR units were both operating during their measurements. The reflections are basically as strong or stronger than the direct sound.

I quickly checked your current timing for SPL support and found it be very good. There is support across the XO range and I did not improve it when I checked a few timing adjustments. Given this setup I would say the current timing is pretty well optimized. In looking at the IR locations the MB is leading the horn a little, but the distance is well within the range that is normal. I believed this alignment is as good as possible.
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post #23 of 51 Old 07-05-15, 04:25 PM Thread Starter
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Re: Time Alignment in Car via Impulse Response

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jtalden wrote: View Post
I reviewed the data.
As before, the IRs show very strong early reflections that make it impossible for me to adjust timing using the phase tracking method. If this were in a room situation I would question if both L+R Horns and L+R MR units were both operating during their measurements. The reflections are basically as strong or stronger than the direct sound.
Not surprising. The horns are mounted underneath the dash so there is almost do direct path to the LP. The sound is going to be reflecting quite a bit.

Quote:
I quickly checked your current timing for SPL support and found it be very good. There is support across the XO range and I did not improve it when I checked a few timing adjustments. Given this setup I would say the current timing is pretty well optimized. In looking at the IR locations the MB is leading the horn a little, but the distance is well within the range that is normal. I believed this alignment is as good as possible.
This was actually my exact thought, too. When I compared the overlays of each driver independently with the combined response, I saw the SPL support was good. Keep in mind that my house curve has quite a tilt to it because in a car environment we skew heavy on the bass.

This is a higher crossover point than I have traditionally attempted to use. My horns can play down to about 800Hz if I use 24 dB slopes. This time I was attempting a 1200Hz acoustic crossover point. However, it would appear that my measured crossover point was more like 1300Hz? Do you agree?

I was initially surprised that the SPL support was so good without any delays on the drivers. But when I think back to some of the threads about Linkwitz 4th order crossovers being 360 degrees out of phase, then it makes sense that a midbass driver which is closer to the LP might align well without any delay. Especially when the distance between the horn and the midbass is about 1 wavelength @ the crossover range. I think 1300Hz is about 10 inches, correct? That's about how much closer the midbass driver is to the LP vs. the horn.

Is my understanding of this on target?
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post #24 of 51 Old 07-05-15, 04:55 PM
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Re: Time Alignment in Car via Impulse Response

Have you ever considered performing the alignment using the phase trace?

Edit: oh , missed that part about early reflections making it impossible........
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post #25 of 51 Old 07-05-15, 04:57 PM
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Re: Time Alignment in Car via Impulse Response

but impossible? hmmm..........windowing?????
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post #26 of 51 Old 07-05-15, 05:01 PM Thread Starter
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Re: Time Alignment in Car via Impulse Response

I believe in my situation, since I am using horn-loaded compression drivers that are mounted under the dash, there really isn't much direct sound. Everything is reflected in some way. So I don't know if even windowing could clear the phase traces up enough to be helpful?
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post #27 of 51 Old 07-05-15, 05:07 PM
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No you're probably right,man that sounds very interesting. I'd love to get ahold of that project and throw my "rolly cart" on it..........I'm actually working on a really cool experiment right now, I'm at work, but is slow......
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post #28 of 51 Old 07-05-15, 05:16 PM Thread Starter
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Re: Time Alignment in Car via Impulse Response

What are people's opinions on whether or not I should be sitting in the driver seat during measurements?

These measurements thus far have been with me outside the car. I'm wondering if I should be in the car during measurements, however?
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post #29 of 51 Old 07-05-15, 05:24 PM
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Re: Time Alignment in Car via Impulse Response

Another plot which can be interesting when looking at time alignment is a wavelet spectrogram, I've been adding that to REW lately. Here is a normalised wavelet spectrogram of the combined right side data, with the peak energy arrival shown by the dashed line. Beta versions with the wavelet spectrogram are available for Windows and OS X.

Time Alignment in Car via Impulse Response-wavelet.png
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post #30 of 51 Old 07-05-15, 05:33 PM Thread Starter
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Re: Time Alignment in Car via Impulse Response

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JohnM wrote: View Post
Another plot which can be interesting when looking at time alignment is a wavelet spectrogram, I've been adding that to REW lately. Here is a normalised wavelet spectrogram of the combined right side data, with the peak energy arrival shown by the dashed line. Beta versions with the wavelet spectrogram are available for Windows and OS X.

Attachment 96241
Very cool, although I have no idea what I'm looking at. LOL

Is the goal to have the dashed line be smooth, with few of those vertical "jumps?"
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