14d (edited) • Audio 🎶
Delay Speakers 101
Let’s look at:
- Which Listening Environments Need Delays?
- What Problem Do Delay Speakers Solve?
- What Problem Do Delay Speakers Introduce?
- How Do We Solve These Problems?
Which Listening Environments Need Delays?
Delay Speakers are only necessary in very deep rooms, where in order for the people at the back of the room to hear just as well as the people at the front of the room, you (the sound tech) have to turn your Main Speakers up past their ideal volume until they’re unreasonably loud for the people in the front.
What Problem Do Delay Speakers Solve?
The main goal of sound reinforcement is to create a listening environment where sound is distributed evenly and with the same acoustic qualities, which ensures that every listener gets the same listening experience regardless of their listening position in the room.
So obviously, if the room is very deep and we only have one line of speakers in one depth position (our Mains), we’re going to run into the problem I just outlined where either it’s too loud for the people in the front or too quiet for the people in the back. This is the problem that delay speakers solve. By placing speakers in different depth positions in the room, we can have speakers that are placed closer to our listeners in the back, which allows us to maintain an ideal volume for all of our speakers and all of our listeners.
What Problem Do Delay Speakers Introduce?
However, delay speakers also introduce a problem that we didn’t have before. The problem is asynchronicity. In order to explain this problem, I’ve got an analogy for you.
Let’s say we’ve got 3 people in a racetrack and they’re going to have a race. Person 1 is 100 feet from the finish line, Person 2 is 50 feet from the finish, and Person 3 is 25 feet from the finish.
Assuming they all start at the same time and they all run at the same speed, will they cross the finish line at the same time? Of course not. Person 2 gets to start closer than Person 1 and Person 3 gets to start closer than both of them! Based on the current rules, Person 3 will finish 1st, Person 2 will finish 2nd, and Person 1 will finish last. Another way of saying this is that they will run asynchronously. They won’t move through the same space at the same time.
How Do We Solve These Problems?
If we want to get them in sync, what do we have to do? We have to delay Person 2 such that they can only start running when Person 1 arrives at their position, and we have to delay Person 3 such that they can only start running when both Person 1 and Person 2 arrive at their position. Based on these new rules, each person will move through the same space at the same time; they’ll run in sync.
We have this same problem when we introduce delay speakers to a room. Because electrical signals travel a lot faster than sound, if we don’t calculate and apply delay to our delay speakers, our sound sources are going to leave our speakers at the same time and be asynchronous with one another. This is going to sound unnatural and destroy intelligibility, which is especially critical for understanding speech. This is why we mute our effects on vocals when the performer stops singing and starts speaking.
In order to solve this problem, we need to calculate and apply delay to each of our delay lines.
Here is the formula:
Speed = Distance/Time
Speed of Sound = 1125ft/second or 343m/s
Therefore, if we reorder this formula to solve for delay time:
Delay Time = Distance/Speed of Sound
The only problem is seconds aren’t very useful as a unit of time. We want the answer in milliseconds, so we need to take the answer and multiply it by 1000 to get our delay time in ms.
Back to my analogy. If we use our Main Speakers (person 1) as a reference point, we see that our first line of Delay Speakers (person 2) is 50ft away from our Mains.
Therefore, the delay time for Delay Line 1 can be calculated as follows:
Delay Time = 50ft/(1125ft/s) =0.0444 s
In milliseconds = 0.0444 s x1000 = 44.4 ms
If we apply a delay of 44.4ms to Delay Line 1, now our Mains and Delay Line 1 are in sync but Delay Line 2 is still asynchronous.
Delay Line 2 (person 3) is 75ft away from our Mains (person 1), so we use the same formula:
Delay Time = 75ft/(1125ft/s) =0.0667 s
In milliseconds = 0.667 s x1000 = 66.7 ms
If we apply a delay of 66.7 ms to Delay Line 2, now all of our speakers are in sync.
There is a bit more complexity to this because of other factors that influence the speed of sound, such as elevation, temperature, and humidity, but this should be a good start for you to wrap your head around delay.
Let me know if you have questions or comments!
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Delay Speakers 101
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