minimum distance to percieve a delay of sound for a event watched

Lightning flashes then you hear thunder, or for anything like this, because the speed of light through air is many times faster then sound though air the light will always reach us first. What is the minimum distance that humans will perceive the discrepancy?

It’s up to the individual. But conservatively, assuming most people can start to detect a delay at half a second, I would think that it would be at approximately 170 meters, ie the distance a sound wave can travel in half a second.

But, as most computer audio/midi people know, discrepancies as little has a few milliseconds can be detectable. Just use the speed of sound to determine the distance.

Sorry I have no answer to the OP, but it reminds me of when I was young…

For years a big warehouse/factory (Express Gifts) was being built on the other side of a valley I lived in (so you had a clear line of site to it, even though it was far away) They were using something to hammer walls of metal into the ground (pile-driver I think it’s called). It fascinated me that I could see the ‘hammer’ hit the metal, and then hear it about a second later. I am pretty sure I knew at the time why this happened, but it still fascinated me.

It’s definitely smaller than 100m. I remember timing a 100m sprint with a stopwatch when I was at school, and we were told to start our watches when we saw the smoke from the start gun, not when we heard the crack.

I estimate that people can detect a delay at much less than half a second. Our senses are pretty darn accurate.

I’d say about a 10th of a second.

:smack:, thought your second post was a double-post bensonGemini. sorry.

I’d guess about 50 metres. At cricket matches it is easy to percieve the difference from the boundary - you see the ball hit then hear the sound. This would be about 80 - 100 metres. Since the gap is quite perceptible I’d think you could pick it up even closer.

Sound travels 1 mile in about 5 seconds. That’s about 1 foot per millisecond.
A 100 msec difference between sound and vision is easily perceivable, at least for some types of events.
So, about 100 feet.

I´d like to crank the minimum delay to about an 18th or 20th of a second. Some years ago, while fiddling with electronic circuits I made an oscilator that operated both a speaker (blip!) and a led; I noticed that the minimum delay I could perceive both in the led and the speaker was the same (an interesting discovery by itself), at around 20 cycles per second. Of course YMMV :slight_smile:

It probably depends on the event a little. Lightning is a long event and may be harder to distinguish delay in the sound than if it was a single momentary event such as a brief flash of light, or a puff of smoke.

1920SDR wrote kind of what I wanted to say. It depends on the situation.

If you have an event with a very obvious visual cue, accompanied by a sound with a very sharp attack, like a cymbal crash, very small delays will be easily perceptible.

A movie is out of synch by only one frame (about 40 ms) with the soundtrack is noticeable. That would correspond to a distance of around 13 meters. IRL however, our brain expects sounds farther away to arrive with a certain delay, and those very short delays aren’t perceived as “out-of-synch” but as “sounding farther”.

I believe that most large music venues that have sets of speakers besides the main speakers at the stage have to put in slight delays in the eletric circuit so that the sound from the secondary speakers reaches an audience member at the same time as the sound from the main speakers.
Not sure exactly what distance it’s considered necessary for this.

Of course, human ears may detect two slightly out of sync sounds more easily than an out of sync sound and visual.

You can defintely demonstrate the diffence between the speed of sound and the speed of light to most people at a distnce of ~100 m.

I experimented with this as a teenager, and you can notice the delay at surprisingly close distances. I did it on a basketball court, watching somebody bouncing a ball. A delay was noticeable half a court away as I recall.