【 Weak current College 】 Studio sound reinforcement speaker power capacity is calculated

Studio sound reinforcement, and the other for any indoor sound reinforcement, there exists a sound reinforcement of sound pressure level determined with the speaker's power capacity commonly referred to as electric power. Although for a given room, designers can as a rule of thumb to determine their the familiar sound of power, but for a free room, a free speaker brands, however, only estimated empirically does not rely on the scientific computing is insufficient. Because power is too small, it will not reach the desired loudness, sharpness and distortion; while the power is too large, will cause unnecessary waste. After all, satisfied public places sound pressure level requirement not only of the power of the speaker and the speaker of the sensitivity and directional factor, directional coefficients and other parameters related to the reinforcement of sound field by a constant peak factor, room. Therefore, in establishing a new set of Studio sound reinforcement systems, you must carry out necessary calculations.
It should be noted that, following the sound power of calculation method is also suitable for outdoor sound reinforcement, but is no longer included in the room for constant.
1. a few basic concepts.
In concrete terms, let us first before doing the following:
1. Speaker of the nature of the factors, the nature of the coefficients and sensitivity level.
(1) the nature of the factor Q (d): it represents a point in space sound generated by the sound intensity than theoretically no links to speaker produce multiples of sound intensity increase. The actual calculation, it consists of speaker vertical radiation angle v and horizontal radiation angle h to characterization: Q (d) = 180O/sin-1 [sin (v/2) · sin (h/2)]-v and h in units are degrees (O), Q (d) dimensionless.
(2) the nature of the factor Q (θ): it is the speaker in deviation from their radiation angle θ axis of a point of acoustic pressure, than its axial with the distance points in multiples of sound pressure decay. Q (θ) consists of the following type of reference to point to the character pattern to the speaker (or links to sexually graphic) gives: 20lgQ (θ) = L (θ)-L (a), i.e.: Q (θ) = 100.05 [L (θ)-L (α)]-, L (θ) to deviate from the speaker axial θ angle measurement points of sound pressure level, L (a) for the axis up and the measuring points equal distance of sound pressure level.
(3) sensitivity level Ls: speaker at 1w baseline power driven (sound sources for pink noise), the axial 1m Department resulting sound pressure level. Units: dBspl. By this definition can be seen, if known-Ls, when you want the axes of the speaker (m) up r is the sound pressure level Lr 90dB, if evaluated at this time the speaker's power We, as long as the Lr equivalent to become axial 1m Department of sound pressure level Lr (when the only indoor direct sound energy, ignore mixed the sound energy, you can have: Lr = Lr + 20lgr), it can be used by Lr and Ls of sound pressure level difference, find out when We seek power and baseline power (lw) power level gap, then We reached. In other words, due to the difference between Lr and Ls is We produce sound pressure level with baseline power resulting sound pressure level difference, so the calculation (note not a physical concept) there are quantitative relationships: Lr-Ls = 10lg (We/lw) i.e. 10lgWe = Lr-Ls or: We = 100.1 (Lr-Ls) notes, because the actual listening to tempo is not possible to only one axis up, so We certainly have Q (d), Q (θ) and below that you want to talk about peak factor, room constant, on-just a simple case We in measure on an expression.
2. peak factor and room constants.
(1) peak factor Lp: peak sound pressure level and the valid values for the sound pressure level difference is defined as the peak factor, in dBspl. Typically, if not specified, the sound pressure level are valid values for the sound pressure level. Because without the reinforcement of sound source actually exist largely there are 8-18dB peak (human language signal peak sound pressure level is about more than RMS high 12dB, music signal peak than RMS high 10-18dB), because some in the valid values according to tempo sound pressure level determines the speaker's power, you must set the peak count in. However, the sound pressure level each 3dB, speaker power increase would have doubled earlier increases, 18dB peak mean power than RMS sound pressure level of design, 64 x expansion (for example, the original design of 100w power, this will expand to 6400w!), this allows the entire system without dynamic distortion of a sound reinforcement, but from a practical standpoint, these most of the time to use couldn't of excessive power reserve is a huge waste. So the actual design, usually based on usage, peak factor and dynamic limiting seek compromise between.
(2) room-constant R: a characterization of room sound absorption characteristics of the parameters: R = S · α/1-α, where α = (Σ α I · Si)/S-, S is the total surface area of the inner room, α is the room surface average absorption coefficient α I is the surface area, as the Si walls. sound absorption coefficient
3. sound pressure level Lr. Before the service and the room sound field distance speaker r at the sound pressure level Lr just Q (d), Q (θ), Ls, Lp, R functions, is a power We function. Therefore, We desire, you must first find anywhere on the indoor Lr expression. To describe the problem your convenience, if we put the sound field as the infinity of space, the speaker can be regarded as a point source, it emits a sound wave is no direction of spherical wave. Obviously, this time for sound power is Wa sound source, the ball surface area is 4 l r 2, distance of Wa r at that point I would sound intensity can be expressed as: I = l W a/4 r 2 because of the actual speaker of radiation is bound, so consider a Q (d) they are: I = Wa · Q (d)/4 l r 2 when you consider the point of departure from the speakers after the axial angle θ, have additional Q (θ): I = Wa · Q (d) · Q2 (θ)/4 l r 2 [note, because Q (θ) is a function of pressure, while the sound intensity and sound pressure is proportional to the square, and so on-Q (θ) in order to square form].
> Of course, the actual use of the room is not infinite, so the sound intensity in addition to these direct part of sound intensity, but also on the mixed sound superposition strong portion (4Wa/R), namely: I = Wa {[Q (d) · Q2 (θ)/4 l r 2] + 4/R} because of the sound pressure level and sound intensity level is equal to the number of relations (not a physical concept!), and the sound intensity level of the table type for LI: LI = 10lgI/1 × 10-12, last: Lr = Lw + 10lg {[Q (d) · Q2 (θ)/4 l r 2] + 4/R} where the sound power level Lw: Lw = 10lgWa + 120 above is only one speaker is indoors, when more than one index the same speakers, sound distance of a point inside the various speakers of r is not the same, not only that, the point of departure from each speaker axial angle θ will also vary, the resulting Q (θ) is different. At this point we have: Lr = Lwi + 10lg {[Q (d) Q2 (θ 1)/4 l r 12 + ... + Q (d) Q2 (θ n)/4 l r n 2] + 4/R} type, Lwi as one of the speakers of the sound power level, Q (θ n) to the point of departure from the nth speaker axial the directivity coefficient, rn to that point to the nth speaker distance. The type is a centralized speaker sound reinforcement, indoor anywhere an expression of the sound pressure level.
2. speaker power calculations.
As mentioned previously, speaker power calculation is subject to the following: first of all you must listen to the Studio uses to determine the tempo of the valid values for the sound pressure level and set an appropriate amount of peak factor (usually arts studio audience area of the sound pressure level for 85dB, peak factor extraction to 10dB); and then, depending on the size of the room sound reinforcement speakers selected vertical and horizontal directions of radiation angle, point to properties and sound sensitivity level; in these conditions, only after entering the actual speaker power calculations.
Since most of the Studio sound reinforcement applications centrally (such as the wings of the same place a power box), so the actual computing power is just prior to listening to tempo sound pressure level lower than the design value Lr 3dB, you finally find out that We are each side of the speaker of the respective power (because the sound pressure level to increase or decrease each 3dB, power is the doubling or halving).
In this way, the room sound field practical expression of the sound pressure level, you can approximate articulate: Lr = Lw + 10lg {[Q (d) · Q2 (θ)/4 l r 2] + 4/R} specific calculation step is this:
1. use type: Lr = Lw + 10lg {[Q (d) · Q2 (θ)/4 l r 2] + 4/R} r will distance speaker (m), from its axial θ point of space, a point on the design requirements of the sound pressure level Lr, converted into a distance to speakers, but also in 1m equal deviates from the angle of the sound pressure level L r ˊ: L r ˊ-Lr = 10lg {[Q (d) · Q2 (θ)/4 l] + 4/R}: 10lg {[Q (d) · Q2 (θ)/4 l r 2] + 4/R} type, Q2 (θ) by 20lgQ (θ) = 10lgQ2 (θ) = L (θ)-L (a), the reference to the characteristics of the pattern.
2. point to the character patterns, will seek out above L r ˊ converted to speaker axial 1m Department of sound pressure level Li: Li = L r ˊ + [-20lgQ (θ)]
3. included in the peak factor Lp, thereby seeking speakers axial 1m Department of peak sound level L I L I ˊ: ˊ = Li + Lp4. type: 10lgWe = L I ˊ-Ls, We seek.
Below we provide examples. An indoor one amplifying ready to place on the wings of the speakers. If the speaker vertical and horizontal radiation angle of coverage h, v-90O and sensitivity level for 85O, 86dB, room average sound absorption coefficient in the surface area of 0.2, as 800m2. Wishes to deviate from the speaker axial 30O, distance from the speaker Office make 3KHz 10m signal valid soundpressure level for 86dB (peak factor as a 10dB; speaker in the link to the characteristic pattern 3KHz figure, asks the speaker's power.
1. first of all find out room constants and speaker of the nature of the factor:
R = S · α/1-α = 800 × 0.2/(1-0.2) = 200 (m2) Q (d) = 180O/sin-1 [sin (v/2) · sin (h/2)] = 180O/sin-1 [(90O/2) · sin (85O/2)] ≈ 6.32. due to the demand side speakers produce sound pressure level is 86dB, single-side speakers produce the sound pressure level: Lr = 83dB. First θ = 30O, the distance from the speaker 10m Lr converted into an equal distance from speaker 1m, deviate from the angle of the sound pressure level L r ˊ: L r ˊ = 10lg {[Q (d) · Q2 (θ)/4 l] + 4/R}: 10lg {[Q (d) · Q2 (θ)/4 l r 2] + 4/R} + Lr = 10lg {[6.3 · Q2 (θ)/4 l] + 4/200} — 10lg {[6.3 · Q2 (θ)/4 l 102] + 4/200} + 83, Q2 (θ)-10lgQ2 (θ) = L (θ)-L (α) and point to properties of patterns available: 10lgQ2 (θ) = L (θ)-L (α) = 0-6 =-6 that Q2 (θ) = 0.25 thus available: L r ˊ ≈ 92dB3. then will deviate from the axial 30O L r ˊ become axial 1m Department of Li: we know by pointing to the pattern: Li = L r ˊ + 6 = 98dB4. included in the peak factor rear axle to the sound pressure level 1m Department: L I L I ˊ: ˊ = Li + Lp = 98 + 10 = 108dB5. finally find the speaker's power We: because: 10lgWE = L I ˊ-Ls = 108-86 = 22dB so: We ≈ 160 (w).