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Author Topic: Am I on the right track here? (time alignment)  (Read 8029 times)

Nils Erickson

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Re: Am I on the right track here? (time alignment)
« Reply #20 on: April 08, 2011, 03:34:00 am »

I think you have this backwards.  It would be 1.125 feet per millisecond which is equivalent to 0.889 milliseconds per foot.

If you want to be really picky, there are other factors that affect the speed of sound such as altitude and temperature but these numbers are good enough for estimating delay times.


   I thought that sound traveled at 1130 or so feet per second.  That speed is constant.  Humidity has an affect on the thickness of the medium "air" which has a big deal with how far the sound carries from the source.  Since sound will not travel in a vacuum then the thicker the air the better sound moves. 

This thread has struck me as one of the most interesting for me.  When there is plenty of stage bleed, I am gathering that a little delay will help.  I am going to play with my dr260 on this.  Should be easy to do at the next soundcheck.   I am loving this!

Sound travels at different speeds through air at differing humidities and temperatures.
In dry air at 20 C (68 F), the speed of sound is 343.2 metres per second (1,126 ft/s).

While I find this stuff really interesting to geek out on myself, I had to chuckle as I envisioned the BE adjusting the mains delay from 5 to 6 milliseconds as the humidity in the club raised due to more fans arriving and dancing.  ;D

Rather than doing those calculations then, I find it more productive to focus my brain on what is happening on the stage and making the music sound like what we are witnessing.  No sense in aligning the tops mid show if you have missed the fact that the keyboard player's solo is too quiet.

Not to discount that other crucial set up stuff, it really does help... Anyway, great info, thanks for some fun reading folks!

Cheers,
Nils
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luis Markson

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Re: Am I on the right track here? (time alignment)
« Reply #21 on: April 15, 2011, 07:37:51 pm »

I agree with Bennett. I start by sending a sine wave at the crossover frequency through the rig with the phase of the sub (or the tops) inverted then tweak the delay time of the subs back and forth till you get to the point of most cancellation and the apparent volume is at it's lowest point. Then flip the phase back to normal and season to taste by ear.

I am going to give this a go tomorrow. Can anyone direct me to a 150Hz.wav?
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Bennett Prescott

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Re: Am I on the right track here? (time alignment)
« Reply #22 on: April 15, 2011, 08:27:43 pm »

I am going to give this a go tomorrow. Can anyone direct me to a 150Hz.wav?

http://www.binkster.net/extras.shtml#cd
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-- Bennett Prescott
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"Give me 6dB and I shall move the world." -Archimedes

Dan Johnson

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Re: Am I on the right track here? (time alignment)
« Reply #23 on: April 15, 2011, 08:29:37 pm »

I am going to give this a go tomorrow. Can anyone direct me to a 150Hz.wav?
This link doesn't have exactly 150Hz but a lot of frequency tones as well as some other useful tools.  Scroll down to the test CD.

http://www.binkster.net/extras.shtml

Edit: Bennett beat me to it.
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luis Markson

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Re: Am I on the right track here? (time alignment)
« Reply #24 on: April 15, 2011, 08:33:57 pm »

This link doesn't have exactly 150Hz but a lot of frequency tones as well as some other useful tools.  Scroll down to the test CD.

http://www.binkster.net/extras.shtml

Edit: Bennett beat me to it.

Already got that one..... As you say, no 150Hz
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Bennett Prescott

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Re: Am I on the right track here? (time alignment)
« Reply #25 on: April 15, 2011, 08:55:03 pm »

Already got that one..... As you say, no 150Hz

In this case, close enough is close enough. I think I said earlier that you probably don't know what your actual crossover is anyway, so pick a frequency that matters to you and align it there.
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-- Bennett Prescott
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luis Markson

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Re: Am I on the right track here? (time alignment)
« Reply #26 on: April 15, 2011, 09:29:13 pm »

In this case, close enough is close enough. I think I said earlier that you probably don't know what your actual crossover is anyway, so pick a frequency that matters to you and align it there.

Sorry Bennet, but could you explain why (if 150Hz is chosen as the Xo in DSP) that the actual XO frequency is unknown?
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Brad Weber

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Re: Am I on the right track here? (time alignment)
« Reply #27 on: April 16, 2011, 08:08:59 am »

Sorry Bennet, but could you explain why (if 150Hz is chosen as the Xo in DSP) that the actual XO frequency is unknown?
That crossover frequency is defining the corner frequency for the crossover filters and not at what frequency the acoustic signal from the two drivers is equal.  However, difference in levels between the high frequency and low frequencies portions of the signal also affects the frequency at which the level of the two signals is equal and thus the effective crossover point.  A simple example is that if everything else is the same but your speaker has a HF driver with greater sensitivity, then the HF acoustic output would be greater relative to the LF output and thus where the HF output level equals the LF signal in sound pressure level will shift down in frequency.
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Dalton Brand

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Re: Am I on the right track here? (time alignment)
« Reply #28 on: April 17, 2011, 07:32:51 pm »

In the past I always added delay to compensate for the back line but recently I've run into issues with the increasing number of bands with IEMs. In a few of the brick lined rooms the drummer can end up in a weird zone of reflection from back of room back to the stage that would otherwise be less apparent were it not for the extra 10ft or so of delay plus digital board latency. Now I ask specifically during sound checks if there are issues. I can live without system delay if it means a happier rhythm section.
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Re: Am I on the right track here? (time alignment)
« Reply #28 on: April 17, 2011, 07:32:51 pm »


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