Today I shared an article from Wu Zongrong’s early article - "Hey! Sound people, let's talk about gain." As mentioned in the article, today's audio coils determine the number of speakers almost at the price, and the lesser rules are used to determine the number of speakers required at the site, or the gain of the amplifier. This problem has not been seriously discussed on the table in the past, this article is to understand the system's ability in a regular way. The following is the full text:
In the early days of the PA world, it was very hard to use the speakers and amplifiers to gain the sound. When the power level could be 100W or even 150W, after connecting the speakers, it was really the Tianba King! That is, how many watts are discussed by the mainstream, not the current sound pressure gain standard.
Today's 100-watt amplifier has become non-mainstream, and the high-tech speaker process has penetrated into the consumer circle, with an amplifier of 1000W or even higher wattage. In today's industrial technology, gaining this problem, as long as you have enough money, can be easily obtained. Only when the rules of the game are determined, people's conceptual identity is not updated synchronously, and knowledge faults often occur in this way. What's more, we are not a specification announcement unit, but the problem of language and text, then the ratio of "User Bug" is even more Taller.
Today in our audio circle, how many people use the rules of electrical physical logarithm to determine the number of speakers required at the scene, or the gain of the amplifier? Almost always about the number of speakers in the price, this problem has never been seriously talked on the table, now let us know how to manage our system in a regular way.
Foreword Architecture A set of sound enhancement/reinforcement systems that many people are not able to achieve. There is a big reason why you need support in sound transmission. Your face-to-face conversation is straightforward and clear, but what if we are 30 meters apart? When talking is easy and clear, then you need support, what is it? That's the electro-acoustic system, where electronic devices are used to extend the listening needs of a site, so some calculations of the combination of sound devices are required. (Next, we follow the example, to remove the mathematics as much as possible, the article is more interesting, the data to be imported here is the original physics and the rules of the human ear compared to the logarithmic property, rather than the new thing "array" algorithm. )
How much gain do we need?
A good Sound man can always establish a sound system that he wants to be on show. What is going on before and after the whole SPL, so that you can get the ups and downs of the music program during the period. If there is no such sound pressure value of the previous architecture operation, you You will find yourself always below or even exceed the specifications of the total gain requirement in the entire system. It is not uncommon to see such a situation in the circle.
It must be noted that the system with insufficient sound gain conditions should not be reluctant, not only the equipment but also its technical capabilities. In addition, when the total sound gain condition is higher than the rated demand on the spot, the sound man on the panel will enjoy the process with ease.
Let's assume the working situation: in an indoor medium-sized venue environment (which is often faced by people in this case), we want to have 95dB of normal music program sound pressure in the speaker-to-lister position, relative to its dynamic peak. That is 101dB, and then add our desired 10dB Head Room to meet the dynamic sound pressure requirements of the scene.
What we all know is that the emission of the horn sound is spherical-like scattering. The attenuation from the sound source point and the distance is proportional to the square of the distance. According to the measured value, the sound pressure level is doubled every time. It will consume 6dB (note that this conversion algorithm does not apply to vertical arrays).
It is also assumed that the sound console is mounted at 80 feet. The sensitivity of the speaker is based on the international AES (Audio Engineering Society) 1 meter 1W level, and the test standard value obtained by injecting the horn is used. ,which is:
Formula 1
Sound pressure distance loss = 20log (foot distance / 3.3)
Sound pressure distance loss = 20log (distance / meter)
The first line of Equation 1 is that if the distance is measured in feet, you can use it to convert to a meter, now substitute our assumed data (don't forget the engineering computer), using the 80-foot conversion of "Formula 1" The meter is about 24.242424.. It is 24 meters, then the log (log) of 24 meters, the value is 1.38475....... Multiply by 20, the final answer will be 27.6915...., rounding is 28dB.
So the story tells us that the listener's position and the 80-foot (24-meter) distance from the pronunciation point will have 28dB of sound pressure loss, okay! Add the dynamic peak 101dB set by the previous example plus the preset 10dB dynamic peak, plus 28dB distance loss, that is, 101dB+10dB+28dB=139dB. At this time, we know the position from the sound console to the speaker, its The maximum SPL needs to be 139dB. Of course, if there is a certain kind of speaker that still has 139dB after being pronounced at 80 feet from the original place, this is done with a single speaker. However, technology has not been so developed, so we must choose a rated peak sound pressure level that can meet the above AES standard of 1 meter @1W and can measure 139dB, and then increase the number of speakers of this specification, which is why the main speaker The number is so much, understand it.
The main speakers that everyone uses now are almost not monophonic (full-range), mostly three-way (3way), which is divided into high (HF), medium (MF), and low (LF) ranges.
The minimum power rating specifications declared by AES in each range are:
The range of the horn - HF - MF - LF
1W@1m value - 112dB - 109dB - 103dB
AES power rating - 200W - 400W - 1000W
The maximum SPL value obtained - 141dB - 141dB - 139dB
The maximum sound pressure of the speaker MAX.SPL:
Suppose there is a brand of horn, its sensitivity (1W@1m) is high (HF) 112dB, midrange (MF) 109dB, low (LF) 110dB, then we can use this formula to find its maximum sound pressure ( 1W@1m).
Equation 2:
Sound pressure maximum = speaker 1W@1m sensitivity + 10log (AES announced minimum power rating) + 6dB peak SPL = treble 112 + 10log (200W) + 6dB
SPL=112+23+6
SPL=141dB
According to the law of the engineering computer, you can write the total value all the way, and the general business computer can be first log (logarithm) from the treble 200W, and its value is multiplied by 10=23.010299.., plus 112dB=135.0102... Plus a 6dB crest factor. The treble component of this horn is required for 141dB greater than 139dB.
Here you can see that a very helpful mathematics is to know how many decibels (dBW) are converted to the back of any wattage, namely:
Equation 3:
10log (wattage)
The same midrange component is also imported into the sub-segment 2, but the SPL of the low-frequency component is lower than the standard, so the number of woofers that must double the same response frequency can meet the proposed sound pressure standard.
The second way is to reduce the energy of the middle/high range to match the sound pressure of the overall frequency band, and the opposite is to lower the previous sound pressure standard value.
If the sound pressure value from 141 dBSPL drops to the 139dBSPL position, this is not just a 3dB thing. As mentioned in the previous article, people increase or decrease the +3dB due to the size change of the sound, and this 3dB increase The reduction is a change of +-10 times the power of the post amplifier.
The above is an example of 8 ohms. In real investment applications, everyone is almost 4 ohms, which means that two speakers are connected to the side of the amplifier. Now let's see how they are. different. With a high pitch of 112dB, plus one is 115dB.
10log(10^(112/10)+10^(112/10))=115
In addition, when the 200W amplifier has a resistance of 4 ohms, it generally increases the energy by 75%. It cannot be 100% due to factors such as electric power, line loss, etc., so it becomes about 300 power to drive the two trebles.
Nested 2:
Sound pressure maximum = speaker 1W@1m sensitivity +10log (AES announces lowest power rating) +6dB peak MaxSPL=115dB+10log(300)+6dB
MaxSPL=115+24.7+6
MaxSPL=145.7=146dB
This result will meet the sound pressure standard we intend to set, and the sound pressure will increase without increasing the post amplifier. So what is different? That is, we have increased the number of speakers, and one more important is that each of the rear stages is doubling the current consumption at work. The most important thing is the temperature protection problem. Many of the latter stages are after the temperature is raised. It is often a problem to jump off or self-destruct to reduce the output power to make the circuit temperature drop quickly.
OK, go back to the previous 8 ohm content. In fact, people who know the insider know that they want to have a double sound pressure feeling, that is, you need to make a difference of nearly 10dB.
Therefore, we are still practical, here to explain, you see, we already know the maximum SPL value of each of the above-mentioned brand speakers, then we have to choose the appropriate power amplifier, use this formula to find each range Power rating, ie:
Equation 4:
dBW = Sound Pressure Peak - The sensitivity of the range component + the loss of the distance (the peak of the sound pressure) is the dynamic peak 101dB we previously predicted (95 listening + 6dB dynamic peak), and then add our desired 10dB dynamics He, (Head Room), so 101dB+10dB=111dB, the sensitivity of the range component is the 1W@1m value of each range component in the speaker, and the distance loss is the previous 80 s (24 meters). 28dB sound pressure loss value. ok, now import the value of each range to find its power amount, namely:
High frequency (111dB - 112dB) + 28dB = 27dBW.
Intermediate frequency (111dB-109dB) +28dB=30dBW.
Low frequency (111dB-103dB) +28dB=36dBW.
The power wattage in terms of dBW conversion can be seen in the attached table.
High frequency 27dBW=500W
IF 30dBW=1000W
Low frequency 36dBW=4000W
After finishing, we can see that some differences, that is, the bass part of the data, need to be enhanced a lot, we can use multiple sets of 1000W rear stage plus woofer, or the above-mentioned use of 4 ohms to achieve the proposed standard. After reading this article, I also got a few simple mathematical formulas, which can help us calculate the sound pressure for the previous planning, and the dynamic values ​​to be used, etc., you can look at the main user you are using. Speakers, what are their specifications, like my own MARTIN VRS-1000,
1m@1W=106dB, I use the rear stage of 1000W, so 106+30=136dB
In the 1m place, then I will get 109+31.5=140.5dB (1m position) with a general 4 ohm connection.
The purpose of this article is to let you know how much energy your rear-level and speaker equipment can have. This does not include the so-called good-sounding, this is only the post-stage and the horn. The forward-extending part is the pre-stage. Where are they adjusted? Where is the standard? This is a set of systems to be adjusted and understood after the establishment.
Mixing Console&Processors (mixer and processor)
The level of the mix's output level and the level of the processor under the chain, and finally when connected to the rear amplifier, you must be clear about the sound signals combined with the mixer, their signal level indication It is very important that your post-amplifier is fully loaded and how much level is indicated, that is, the amplifier reaches the maximum peak cut.
A typical mixer can handle output level levels between +18dBu and even +24dBu. Simply put, if you are in general +4dB, (1.23V) = 0VU; in addition, your digital processing device is -18dB (dBFS) or -20dB (dBFS) = +4dBu, relative if your amplifier is architecture When fully loaded at 0.775V. or 1.4V, you will know the scope of the overall amplifier operation, so you can understand the peak cut of the expander and the gain of the amplifier between the decibel value and the voltage. It is very important.
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