【 Weak current College 】 speaker power calculation

Speaker power calculation (1)

1. sound pressure level calculated-

The following is the sound field, at a distance r, a point of sound pressure level more convenient calculation formula:

SPL = 10log PWL + (Q/(4 * 3.14 * r * r) + 4/R), type, SPL: in point r distance, the unit of sound pressure level (dB), the sound pressure level benchmarks is 0dB = 20 a μ P. PWL: sound sources of sound power levels, units (dB), the sound power level benchmarks for 0dB = 10-12W. Sound power refers to the speaker's voice on output power amplifier output, not to the speaker's power. Sound power level expressed in DB of sound power. Therefore, sound power 1W is the sound power level 120dB. Q: acoustic sources point to a coefficient. ① When the sound source in the middle of the room, not at all, sound energy to spherical mode radiation, pointing to the coefficient is 1. ② sound sources on the ground to hemispherical mode radiation, pointing to the coefficient for 2. ③ placed two wall cross edge, to 1/4 coefficient the spherical radiation, point 4. ④ in room corner, to 1/8 spherical radiation, pointing to the coefficient is 8. R: the point is the distance from the sound source, units (m), R: room constants, units (m2), S: indoor surface area (m2), units, a average absorption: indoor, no units.

Room constant R represents the room on sound processing power, and the room's wall area and sound-absorbing capability, room the larger value. Average absorption rate, is a constant less than 1. Sound like a classroom that so-called relatively active room, about 0.25; but like the bedroom that lack the reverberation room, sound-absorbing ability is good, about 0.35. Type in parentheses to the left of the Q/4 π r 2 direct access to the sound of the sound pressure, it is inversely proportional to the square of the distance. Right 4/R is the room for reflective acoustic sound pressure. The second item of the sound source in the point of acoustic pressure, usually expressed in decibels. Because usually sound source position as 0dB, so other points are negative. As long as you know the type of content generation in this type of operation.
2. sound pressure level attenuation curve for

When A point is Q = 4, R = 100, the distance is the sound pressure level at 3m attenuation solution process: found in the links to the factor Q = 4 horizontal, right down to the intersection of the diagonals with 3m, then straight up find room constant R = 100 is the intersection of the curve. This is A point, and then level to the left along the vertical coordinates of the intersection, we will be able to read out the sound pressure level of attenuation as 11dB.

Cite a closer practical examples, with some later calculation and curves of two methods to solve. There is a long, wide 3.6m 5.4m, high 2.5m room walls average absorption rate = 0.3, if sound is placed in front of the room wall, with speaker-stand, close to the back wall, the audience seats left speaker 3m. Ask at this point the amount of attenuation of sound pressure level. First of all, no matter what kind of solution are you must first calculate the room constant R. Room six surface area:

First look at functional solution process: in the left one to Q/4 π r 2 = 2/4 π 32 = 0.0177, right another 4/R = 4/36 = 0.125. Therefore, the sound pressure level of attenuation as 10log (0.0177 + 0.125) =-8.5dB. Graphic process is as follows: from Q = 2 line → r = 3 wire, R = 20 ~ 50 space estimate where R = 36, playing a bit of "B", then to the left to read out the vertical coordinates of attenuation, is-8dB.

Speaker power calculation (2)

Third, the speaker output power estimation
Calculation of the amount of attenuation above would need to be combined with the tone of the power level you can get the PWL point of sound pressure level. So also must know how to calculate the sound power. Sound power output from the speakers is computed from the beginning, so it is first necessary to understand the clear sound of sensitivity or [output sound pressure level] concept. Speaker sensitivity 1W power input is defined as, 1 m, measured sound pressure level, expressed in dB/W/m. This is the natural characteristics of sound, when the value of 92dB/W/m, speaker of the electro-acoustic transformation efficiency of 1%. The amplifier 100W power you want output to exchange the sound power 1W. If the sensitivity to 92dB/W/m, 100W power rating also swap 1W of sound power, and the difference between a 3dB worse. For example, 89dB/W/m sensitivity of speaker, 200W power needed in order to get sound power 1W, 86dB/W/m of speakers that require up to 400W of power to get the sound power 1W.

With these relationships can take the power into sound power PWL, PWL = 10log (sound power output W/10-12W), sound power 1W = 120dB sound power level. For sensitivity 92dB/W/m speaker, 100W power driven at PWL as 120dB. In fact, when in actual use, there's no need to consider the concept of sound power, can be directly used to enter to the speaker's power and speaker sensitivity two to calculate out the PWL.

For example, a single tube 2A3 stereo amplifier, Mono, 7W 3.5W, speaker sensitivity to 92dB/W/m, PWL? 3 m distant sound pressure level? this time from the perspective of sound power, sensitivity 92 speakers, two speakers total sound power before 7/100 = 0.07W, DB represents the PWL is 120 + 10log0.07 = 120-11.55 = 108.45dB, or the direct use of power by extrapolating the simpler PWL = 10log (7/10-12) = 108.45dB, of course, this result is also on the sensitivity 92dB/W/m of a particular speaker. 3 in the room, at the hearing on the above have been worked out of the sound pressure level attenuation-8.5dB, you can get the actual sound pressure level SPL = 108.45-8.5 ≈ 100dB.BR>
If the speaker's sensitivity is not a 92dB/W/m, plus the actual sound sensitivity and 92dB/W/m of difference. Use multiples or actual level to be very troublesome, DBas long as the composers. For example, when the speaker sensitivity to 88dB/W/m, then the sound power level is 108.45 + (88-92) = 104.45dB, if sound sensitivity higher as 94dB/W/m, PWL = 108.45 + (94-92) = 110.45. 3m Department of sound pressure level corresponding to 96dB and 102dB. Sound pressure level can also be used noise or sound pressure meter to measure, but measured value is the average level of music than music peak to small 10 decibels. The meter indicates the level of the music for the actual music 88dB in peak with 98dB. In other words, you can hear in the music scene is a suitable sound, with instruments measured at 88dB, audio replay systems to the audience the sound pressure level with 98dB to design.

At this point, we know you have prescribed conditions, how to calculate the point sound pressure level. Some of those parameter is how to get or how to set it is not clear. In addition, audio and home theater enthusiasts, the more important how the sound pressure level as required to design power amplifier power, select speaker sensitivity, etc. is calculated.

S=2×(5.4×3.6+5.4×2.5+3.6×2.5)=83.88≈84m2，R=084×0.3/(1-0.3)=36。 As a speaker-stand, the speaker is not close to the ground wall edges, only one wall preferable Q = 2, if a speaker stand is very low or no speaker shelf in the middle of 2 ~ 4, from a value to 2. Panama