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Post by flyngfool on Sept 26, 2018 17:47:20 GMT
I am having a bit of a confused moment regarding speaker delay. Why is it, the further the speaker is from you, the more delay it gets? It seems counterintuitive. Wouldn’t you delay the speaker closest to you the most so the sound from the speaker further from you can catch up?
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Post by Michael Lawrence on Sept 26, 2018 17:59:12 GMT
Hi flyngfool-
Welcome. I'm not clear on what you've been reading to give you that idea. Electronic delay is used to time align arrivals from sources so they all arrive at a chosen point in space (usually the listening position) at the proper time. For home theater, the typical example is rear surrounds, which tend to end up placed physically closer to the listening position than the front speakers in many listening rooms. Left alone, they'd arrive earlier - because they're closer. So properly they should be delayed so their arrival matches that of the front speakers.
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Post by flyngfool on Sept 26, 2018 18:35:41 GMT
That’s what is confusing me. According to the delay chart, the further a speaker is from you the longer the delay is you input into your eq settings.
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Post by Michael Lawrence on Sept 26, 2018 18:51:51 GMT
My guess is that you're looking at a simple conversion chart that equates physical distance with the time required for a sound wave to travel that far. For example, 10 feet = 8.9 ms, etc.
Can you post a picture of the chart you're referencing?
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Post by flyngfool on Sept 26, 2018 20:03:17 GMT
My guess is that you're looking at a simple conversion chart that equates physical distance with the time required for a sound wave to travel that far. For example, 10 feet = 8.9 ms, etc. Can you post a picture of the chart you're referencing? Attachments:
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Post by Michael Lawrence on Sept 26, 2018 20:33:09 GMT
Yep, this is just a conversion table between distance and propagation delay. You can tell by the relatively large distances involved that this is more aimed at large-scale live audio systems rather than living rooms  In practice what you would do is measure the distances from the listening position to each speaker in your system (except for the subwoofer...different factors at play) and then delay the earlier ones by the amount of advantage they have. For example, if you have two speakers at 8 and 10 feet from the listening position, you would delay the closer one by 1.6 ms, or the amount of time it takes sound to travel the two feet difference. The chart just helps you convert between the distance and the time, but it's a lot more elegant to use a single-line formula instead of a whole table, plus you can find any value you like: d = vtd = distance v = velocity (speed of sound in this case) t = time You can use whatever units you like as long as you're consistent. Although I have to say that I work mostly in live sound reinforcement and we usually determine delay times with a dual channel audio analyzer rather than a physical measurement. The concept, however, is the same. EDIT: Fixed formula. Yikes! |
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Post by flyngfool on Sept 26, 2018 23:49:17 GMT
That makes sense now. Thanks!
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Post by Ethan Winer on Sept 28, 2018 16:27:43 GMT
Thanks Michael for chiming in. I suggested ff post here because you'd know. Also, I assume "the farther from the speakers, the longer the delay" means the farther the listeners are from the main front speakers?
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Post by Michael Lawrence on Sept 28, 2018 19:08:19 GMT
When thinking about delay times, you have to think from the POV of arrivals at the listener's position, not source locations.  We see that I did not go to art school. This is a crappy sketch of a typical situation in which we would be doing some delay alignment: this is a side view of a theater with a flown mono array above the stage (on the left) and seats on the floor level and also in the balcony, which you can see on the right. Depending on the room geometry, we would likely end up with under-balcony delay fills and sometimes also over-balcony delays. Following the McCarthy method, the time alignment points for the delay fills would be the lower off-axis edge of coverage. That is, measure the level on-axis to the speaker and move downward in the seating area until the HF level has dropped by 6 dB. I've indicated these points with yellow highlights. Put the reference mic there, and then we take measurements of both the mains and the delays independently, and we add delay to the underbalcs until the arrivals are sync'd. As we move backwards in the seating area, the delay fill becomes dominant in terms of level. As we move forward, the mains take over. It's not as simple as matching the arrival times, per say, because the single-box underbalcony fill will have a different phase response than the array so even if we compensated for propagation delay, the phase responses would likely still not be matched. This is why an analyzer is a superior solution to a tape measure. However, certainly we will be within a millisecond or so of the "time of flight" solution so that's a fine way of thinking of it. |
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